Design Report
Team 17
Jonathan Gingrich
Lauren Grimley
Cassandra Miceli
Kerala Smith
Senior Design Project: Engineering 339/340
5/9/16
Copyright © 2015, Calvin College, Jonathan Gingrich,
Lauren Grimley, Cassandra Miceli, Kerala Smith
EXECUTIVE SUMMARY
Executive Summary
The objective of this project is design an odor-control system for the Wyoming Clean Water Plant
(CWP) that will reduce nuisance odors from the air. The proposed technology is a biofiltration unit
that will treat air emitted from the primary clarifiers and an uncovered splitter box (which splits the
effluent wastewater stream from the primary clarifiers into three aeration basins). The primary cause
of nuisance odors at the CWP is hydrogen sulfide, which is the contaminant targeted for removal by
the proposed odor-control system.
The CWP is currently using carbon adsorbers and chemical scrubbers for odor-control at various
locations throughout the plant, however these systems have proven difficult and costly to maintain.
As a result, the client is more inclined towards alternate odor control systems and has specifically
requested a biofiltration unit be designed for odor control at these sites. The team researched
multiple odor-reducing technologies to determine whether biofiltration is the best option for the CWP,
specifically comparing operating costs and maintenance needs. The feasibility of biofiltration was
confirmed with research, discussions with engineers and specialists, and successful case studies of
local wastewater treatment facilities.
During the fall of 2015, the team’s primary focus was on detailing biofiltration operation and design.
Pertinent information was obtained through extensive literary research, discussions with engineers
and specialists, and visits to operating biofilters in the area. During spring 2016, the team finalized
all design decisions and constructed design plans for the facility, including plan drawings and an
operation maintenance schedule.
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TABLE OF CONTENTS
Table of Contents
Executive Summary ______________________________________________________________________________________ 2
Table of Contents _________________________________________________________________________________________ 3
Table of Figures ___________________________________________________________________________________________ 8
Table of Tables ____________________________________________________________________________________________ 9
Table of Abbreviations __________________________________________________________________________________10
1
Introduction ________________________________________________________________________________________11
1.1
1.2
2
Calvin College Engineering Department__________________________________________________ 11
Senior Design _______________________________________________________________________________ 11
Team 17 __________________________________________________________________________________________ 11
Project Background ________________________________________________________________________ 13
Project Management _______________________________________________________________________________15
2.1
2.2
2.3
3
Senior Design Background ______________________________________________________________________ 11
Team Organization ______________________________________________________________________________ 15
Schedule __________________________________________________________________________________________ 15
Method of Approach _____________________________________________________________________________ 16
Research Techniques_______________________________________________________________________ 16
Team Communication______________________________________________________________________ 16
Project Overview ___________________________________________________________________________________17
3.1
Project Description ______________________________________________________________________________ 17
3.3
Scope & Objectives ______________________________________________________________________________ 18
3.2
3.4
3.5
3.6
Client _____________________________________________________________________________________________ 17
Design Constraints ______________________________________________________________________________ 19
Design Criteria ___________________________________________________________________________________ 19
Design Norms ____________________________________________________________________________________ 19
Transparency _______________________________________________________________________________ 20
Stewardship ________________________________________________________________________________ 20
4
Caring _______________________________________________________________________________________ 20
Odor-Control Background _________________________________________________________________________21
4.1
Overview _________________________________________________________________________________________ 21
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TABLE OF CONTENTS
Wastewater Treatment Facility Odor-Control ___________________________________________ 21
Public Concern _____________________________________________________________________________ 21
4.2
4.3
Government Regulations __________________________________________________________________ 21
Odor Source ______________________________________________________________________________________ 23
Overview ____________________________________________________________________________________ 23
Hydrogen Sulfide ___________________________________________________________________________ 23
Odor Treatment Alternatives ___________________________________________________________________ 24
Wet Air Scrubbing __________________________________________________________________________ 24
Carbon Adsorption _________________________________________________________________________ 25
5
Biofiltration _________________________________________________________________________________ 25
4.4
Odor-control Descision Matrix _________________________________________________________________ 25
5.1
Background ______________________________________________________________________________________ 27
Wyoming Clean Water Plant ______________________________________________________________________27
5.2
5.3
Plant Operations ___________________________________________________________________________ 27
Odor-Control _______________________________________________________________________________ 27
Exisiting Plant Operations ______________________________________________________________________ 27
Odor-control _____________________________________________________________________________________ 28
Headworks __________________________________________________________________________________ 28
Primary Clarifiers __________________________________________________________________________ 29
Biosolids Storage Tanks ___________________________________________________________________ 30
6
Splitter Box _________________________________________________________________________________ 32
Biofiltration Technology ___________________________________________________________________________34
6.1
6.2
Overall Process Description and Terminology ________________________________________________ 34
Mechanisms of Operations ______________________________________________________________________ 34
Biokinetics __________________________________________________________________________________ 35
Mass Loading Rate _________________________________________________________________________ 35
Biofilm Kinetics ____________________________________________________________________________ 35
Biodegradation _____________________________________________________________________________ 36
6.3
Microbiology________________________________________________________________________________ 37
Characterizing Biofilter Performance __________________________________________________________ 38
Removal Efficiency _________________________________________________________________________ 38
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TABLE OF CONTENTS
6.4
Elimination Capacity _______________________________________________________________________ 38
Factors Affecting Biofilter Performance _______________________________________________________ 39
Packing Media ______________________________________________________________________________ 39
Moisture Content ___________________________________________________________________________ 40
Nutrient Control ____________________________________________________________________________ 40
Temperature ________________________________________________________________________________ 40
pH Value ____________________________________________________________________________________ 40
Empty Bed Residence Time _______________________________________________________________ 41
Oxygen Content ____________________________________________________________________________ 41
Bed Depth ___________________________________________________________________________________ 41
Medium Diameter and Surface Area ______________________________________________________ 42
7
Pressure Drop ______________________________________________________________________________ 42
Alternative Design Considerations _______________________________________________________________43
7.1
Packing Media ___________________________________________________________________________________ 43
Natural vs. Synthetic Media _______________________________________________________________ 43
Layered Media ______________________________________________________________________________ 44
Inorganic Layer _____________________________________________________________________________ 44
7.2
Organic Layer _______________________________________________________________________________ 44
Moisture Control_________________________________________________________________________________ 44
Humidification Chamber __________________________________________________________________ 45
Irrigation ____________________________________________________________________________________ 45
7.3
Control Options ____________________________________________________________________________ 45
Air Distribution __________________________________________________________________________________ 46
Overview ____________________________________________________________________________________ 46
Air Flow _____________________________________________________________________________________ 47
Loading Rate ________________________________________________________________________________ 47
Pressure Loss _______________________________________________________________________________ 48
Channeling and Clogging __________________________________________________________________ 49
7.4
Effects of Configuration on Air Flow ______________________________________________________ 50
Ductwork & Equipment _________________________________________________________________________ 52
System Design ______________________________________________________________________________ 52
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TABLE OF CONTENTS
Sizing the Blower _____________________________________________________________________________________ 53
7.5
Configuration ____________________________________________________________________________________ 55
Flow Direction ______________________________________________________________________________ 55
Compartments______________________________________________________________________________ 56
Materials ____________________________________________________________________________________ 56
Cover and Insulation _______________________________________________________________________ 56
8
Condensation _______________________________________________________________________________ 57
Alternative Design Calculations & Results _______________________________________________________58
8.1
Media Selection __________________________________________________________________________________ 58
Media Selection Criteria ___________________________________________________________________ 58
Inorganic Layer Decision __________________________________________________________________ 59
8.2
Organic Layer Decision ____________________________________________________________________ 60
Sizing the Biofilter _______________________________________________________________________________ 61
Media Depth ________________________________________________________________________________ 61
Case Studies ________________________________________________________________________________ 61
8.3
Media Volume ______________________________________________________________________________ 62
System Recommendations ______________________________________________________________________ 62
Configuration _______________________________________________________________________________ 62
Empty Bed Residence Time _______________________________________________________________ 63
Media Particle Size _________________________________________________________________________ 63
9
Pressure Drop across Bed _________________________________________________________________ 64
8.4
Air Distribution System _________________________________________________________________________ 66
9.1
Scope of Design __________________________________________________________________________________ 69
Proposed Design Decisions _______________________________________________________________________69
9.2
Internal Design __________________________________________________________________________________ 70
Concrete Work______________________________________________________________________________ 70
Cover and End Plates ______________________________________________________________________ 70
Moisture Control ___________________________________________________________________________ 70
Media________________________________________________________________________________________ 71
9.3
Nutrient Addition __________________________________________________________________________ 71
External Design __________________________________________________________________________________ 72
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TABLE OF CONTENTS
Ductwork ___________________________________________________________________________________ 72
Blower Specifications ______________________________________________________________________ 73
9.4
Insulation ___________________________________________________________________________________ 74
Operation and Maintenance Requirements ___________________________________________________ 74
Start-Up _____________________________________________________________________________________ 74
Performance Evaluation ___________________________________________________________________ 74
Regular Maintenance Requirements______________________________________________________ 76
Long-Term Maintenance Requirements __________________________________________________ 76
10
Economic Analysis ______________________________________________________________________________77
12
References _______________________________________________________________________________________82
11
13
Acknowledgements _____________________________________________________________________________81
Appendices ______________________________________________________________________________________91
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TABLE OF FIGURES
Table of Figures
Figure 1. CWP Process Flow Diagram ........................................................................................................................... 13
Figure 2. Location of the CWP .......................................................................................................................................... 17
Figure 3. CWP Facility Layout ........................................................................................................................................... 18
Figure 4. Schematic view of a general scrubber system [15] .............................................................................. 24
Figure 5. Locations of Current and Proposed Odor-Control Units (Google Maps) ..................................... 28
Figure 6. Solids buildup on media of chemical scrubbers (Lauren Grimley)................................................ 31
Figure 7. Splitter Box at the Wyoming Clean Water Plant (Lauren Grimley) ................................................ 32
Figure 8. Splitter Box (Lauren Grimley) ....................................................................................................................... 33
Figure 9. Biofiltration Process Flow Diagram [18] .................................................................................................. 34
Figure 10. Schematic representation of the mechanisms in a biofiltration unit: (a) mass transport by
gas-phase and liquid-phase advection, and (b) mass transport by diffusion and biological reaction in
the biofilm [21]. ...................................................................................................................................................................... 36
Figure 11. Overview of Biodegradation Process for Biofiltration [19]............................................................ 37
Figure 12. Model-simulated sulfide elimination as a function of sulfide loading for various influent
H2S concentrations (straight line represents 100% elimination) [25]. .......................................................... 39
Figure 13.Removal Efficiency as a function of Sulfur Loading Rates [25] ...................................................... 48
Figure 14. Schematic of biofilm accumulation and Flow Channelization [45] ............................................. 50
Figure 15. Biofilter Inlet and Outlet Locations .......................................................................................................... 51
Figure 16. Hydrogen Sulfide Concentration as a function of the Distance from the Inlet [25] ............. 51
Figure 17. Hartzell Performance Curve for Backward Centrifugal Fan [50] ................................................. 54
Figure 18. Air Flow Profile in 100% Effective Duct Length [52] ........................................................................ 55
Figure 19. Required EBRT to Remove Various Concentrations of H2S [25] ................................................... 63
Figure 20. The Removal Capabilities of various Diameters of Lava Rock [25] ............................................. 64
Figure 21. Predicted Pressure Loss across the Lava Rock and Woodchip Layers ....................................... 65
Figure 22. Existing Hartzell Centrifugal Fan............................................................................................................... 66
Figure 23. Percent Contribution to Total Cost. .......................................................................................................... 79
Figure 24. Cost Comparison of Odor-Control Technology [62] .......................................................................... 80
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TABLE OF TABLES
Table of Tables
Table 1. Existing Odor-Control Systems at CWP _________________________________________________________ 14
Table 2. Odor-Control Technology Decision Matrix ______________________________________________________ 26
Table 3. Decision Matrix for the Inorganic Media Layer. ________________________________________________ 59
Table 4. Decision Matrix for the Organic Media Layer ___________________________________________________ 60
Table 5. Calculated Biofilter Volumes Using Various Models ____________________________________________ 61
Table 6. Parameters for a Biofilter Built in Jefferson County, Alabama by Biorem Technologies [5] _ 62
Table 7. Summary of the Biofilter Media Dimensions ___________________________________________________ 62
Table 8. Pressure Drop and Superficial Gas Velocity in a Biofilter [42] ________________________________ 64
Table 9. Recommended Parameters for Various Phases of the Biofilter Operation ___________________ 66
Table 10. Pressure Loss in the Air Distribution System _________________________________________________ 67
Table 11. Static Pressure of Blower _______________________________________________________________________ 67
Table 12. Blower Parameters during Phases of Operation ______________________________________________ 68
Table 13. Design Criteria for Proposed Biofiltration System ____________________________________________ 69
Table 14. Proposed Ductwork System ____________________________________________________________________ 73
Table 15. Blower Specifications ___________________________________________________________________________ 73
Table 16. Recommended Monitoring Operation [34, 61, 19] ___________________________________________ 75
Table 17. Biofilter Components Cost ______________________________________________________________________ 77
Table 18. Media Cost _______________________________________________________________________________________ 77
Table 19. Humidification and Irrigation Costs ___________________________________________________________ 77
Table 20. Splitter Box Covering Costs _____________________________________________________________________ 77
Table 21. Air Piping Costs __________________________________________________________________________________ 78
Table 22. Miscellaneous Costs _____________________________________________________________________________ 78
Table 23. Total Preliminary Cost for Biofilter ____________________________________________________________ 78
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TABLE OF ABBREVIATIONS
Table of Abbreviations
BioP
BOD
CL
CFM
CWP
DO
EAOC
EBRT
EC
EPA
FRP
gph
Gpm
H2S
HP
In. wg
ITSL
Ks
L
MDEQ
M-E
mgd
N/P/K
NS
O&M
OSHA
Ps
Pt
Pv
PAI
PBR
PLC
ppmv
ppbv
psi
PTI
PVC
Q
RE
RH
RPM
SCADA
SP
SRB
TAC
T-BACT
TDR
V
VFA
µ
biological phosphorous removal
biological oxygen demand
substrate concentration
cubic feet per minute (air flow)
Wyoming Clean Water Plant
dissolved oxygen
estimated annual operating costs
empty bed residence time
elimination capacity
Environmental Protection Agency
Fiberglass Reinforced Plastic
gallons per hour
gallons per minute
hydrogen sulfide gas
horsepower
Inches water gauge
initial threshold screening level
saturation constant
volumetric loading
Michigan Department of Environmental Quality
modified-Ergun equation
million gallons wastewater per day
nitrogen-phosphorus-potassium nutrient mixture
Navier-Stokes
operation and maintenance
Occupational Safety and Health Administration
static pressure
total pressure
velocity pressure
predicted maximum ambient impact
packed bed reactor
programmable logic controllers
part per million by volume
parts per billion by volume
pounds per square inch
Permit to Install
polyvinyl chloride
gas flow rate
removal efficiency
relative humidity
rotations per minute
Supervisory Control and Data Acquisition
static pressure
sulfate-reducing bacteria
Toxic Air Contaminant
Best Available Control Technology for Toxics
time domain reflectometry
volumetric loading
volatile fatty acids
cell growth rate
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INTRODUCTION
1 Introduction
1.1 SENIOR DESIGN BACKGROUND
Calvin College Engineering Department
Calvin College’s engineering program is an ABET accredited program that seeks to train engineering
students to apply their Christian faith in engineering. Provided with a liberal arts background, Calvin
engineering students are equipped to serve as well-rounded professionals in the engineering industry.
Senior Design
Calvin College’s Engineering Department requires senior engineering students to take an integrative
course that emphasizes design team formation, project identification, and production of a feasibility
study as an undergraduate capstone. The engineering students focus on developing task
specifications using design norms and basic analysis skills. Senior design teams develop and complete
a project that meets the needs of a client while working under the guidance of professors and
industrial consultants.
1.2 TEAM 17
The members of Team Bi0der (Senior Design Team 17) are civil/environmental and chemical
engineering seniors at Calvin College. This team was formed on the basis of a common interest for
environmental engineering shared among all four members. Working with local professionals and
Calvin College professors, Bi0dor has been given the opportunity to investigate the feasibility and
implementation of a biofiltration odor-control system for the Wyoming Clean Water Plant in
Wyoming, MI.
JONATHAN GINGRICH
CHEMICAL
Jonathan Gingrich is a Chemical Engineering and Biochemistry
double major from Columbus, Ohio. He has had an interest in water
purification for developing communities for some time now, which
has led to a research position at Calvin under Professor David
Wunder where he studied Bagasse Charcoal as a potential method
of water purification. He has also travelled abroad to Kenya to
study water systems and serve a local community in the region of
Samburu. After graduation, Jonathan will begin pursuit of a
doctorate degree in environmental engineering from the
University of Texas at Austin.
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INTRODUCTION
LAUREN GRIMLEY
CIVIL/ENVRIONMENTAL
CASSANDRA MICELI
CHEMICAL
KERALA SMITH
CIVIL/ENVIRONMENTAL
Lauren Grimley is a civil/environmental engineering senior from
Houston, Texas. Lauren is interested pursuing a career in the
scientific assessment of water-related challenges and the
development of innovative, sustainable solutions. This fall Lauren
will pursue a master’s degree in civil and environmental
engineering at the University of Iowa while working as a Graduate
Research Assistant at the IIHR-Hydroscience & Engineering
Research Center.
Cassandra Miceli is a Chemical Engineering and Biochemistry
double major from Montgomery, NY. She had the opportunity to
travel to Peru to learn about water purification. This opportunity
has confirmed her interest in water purification in developing
countries. She is interested in pursuing a career in environmental
engineering.
Kerala Smith was born and raised in southern Minnesota and has
since moved to the Grand Rapids areas for undergraduate studies.
She is majoring in civil/environmental engineering and has
developed a specific interest in water and wastewater treatment.
Internship and research experience has confirmed her interest in
this industry, and she is excited to be working in the Grand Rapids
area after graduation. She is grateful for her education at Calvin
College which has equipped her to enter into the professional
world.
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INTRODUCTION
Project Background
The purpose of this project is to determine the feasibility of designing an odor-reducing system using
biofiltration for the Wyoming Clean Water Plant 1 (CWP). This facility has a design capacity of 24
million gallons wastewater per day (mgd). The wastewater flows from the head works to the primary
clarifiers. The clarified water proceeds through the aeration basins and is sent to the secondary
clarifiers, while the solids are processed in the biosolids storage tanks located at the north end of the
facility. The treated wastewater is ultimately discharged to the Grand River. An overall process flow
diagram of the CWP is shown in Figure 1.
Figure 1. CWP Process Flow Diagram
1
2350 Ivanrest SW, Wyoming, Michigan
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INTRODUCTION
The treatment facility uses chemical scrubbers and carbon adsorption to control odors at different
locations throughout the plant, however the effectiveness and operating costs of these systems have
been unfavorable for the CWP. For this reason, the client has requested a study into the feasibility of
biofiltration as an alternative odor-control technology. The existing odor-control systems at the CWP
are shown in Table 1.
Table 1. Existing Odor-Control Systems at CWP
Odor Source
Odor-Control System
Headworks
Primary Clarifiers
Biosolids Storage
Tanks
Splitter Box
Chemical Scrubbers
Carbon Adsorber
Average H2S
Concentration
(𝐩𝐩𝐦𝐯 )
0
6.3
Uncontrolled
2.4
Chemical Scrubbers
12.3
Maximum H2S
Concentration
(𝐩𝐩𝐦𝐯 )
0
22
21.7
88
The CWP wishes to install an odor-control unit for odorous air emitted from the primary clarifiers
and the splitter box located just downstream. The target pollutant to be removed from the waste air
streams is hydrogen sulfide (H2S) and the contaminant removal goal for the design is to be below
detectable and nuisance levels; less than 2 parts per billion by volume (ppbv). This project includes
research into the feasibility of installing a biofiltration unit, design plans for the system, and
suggested operational specifications.
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PROJECT MANAGEMENT
2 Project Management
2.1 TEAM ORGANIZATION
The proposed design incorporates elements of both civil/environmental as well as chemical
engineering. The educational background of each member contributes well to the team dynamic. The
civil/environmental engineering students on Team Bi0dor contributed greatly to the operational
processes and layout of the biofiltration system, using their familiarity with the biological wastewater
treatment processes. With a background knowledge in reactor modeling, the chemical engineering
students focused primarily on the chemical and biological processes internal to the biofilter. All team
members were heavily involved in the research phase of the project, with each member focusing on
their area of education.
The team was advised by professor and professional civil engineer, Professor Robert Masselink, and
a chemical engineering professor, Professor Jeremy VanAntwerp. The team’s industrial consultant for
the project was Ben Whitehead, a civil engineer at Black and Veatch. Based on experiences and
specialty knowledge, each of these advisors has provided valuable insights and resources as the
project progressed.
2.2 SCHEDULE
The primary objectives for this project were divided between the fall and spring semesters. The main
goals for the fall semester included:






Clear and detailed communication with the client to fully understand the scope of the
project and the current operation of the CWP
Complete all preliminary research needed for biofilter design (media types, design
parameters and sizing, necessary components for operation, microbial activity, etc.)
Develop design criteria for optimal media selection and determine alternatives
(including organic and synthetic alternatives)
Visit wastewater treatment plant(s) in the area with operating biofilters
Connect with an odor-control design engineers and specialists
Complete base calculations of a biofilter sizing
The spring semester goals included:





Select and optimize media using a decision matrix
Perform all necessary design calculations
Select and optimize media using a decision matrix
Size the biofilter using a reactor model and kinetic analyses
Optimize operational components (irrigation, humidification, air distribution, etc.)
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PROJECT MANAGEMENT

Produce final report and a suggested operational schedule with design drawings
included
The team met regularly twice a week to discuss research, progress, and design decisions. At each
meetings, a plan of action was made and tasks for the week were distributed to each member.
Meetings with the faculty advisors occurred weekly on a rotating basis to address questions and
discuss progress.
2.3 METHOD OF APPROACH
The Method of Approach describes how the design process will be executed using research
techniques, team communication, and design methodology.
Research Techniques
To gain a background knowledge of biofiltration, the team conducted extensive research using
scholarly articles, research databases, informational websites, and industry professionals. Each team
member was given an area of research to focus on during each week.
Team Communication
The team used email corresponding and in-person conversations as a means for communication on
the project. Meeting regularly provided an opportunity for the team to discuss progress or potential
issues for the project.
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PROJECT OVERVIEW
3 Project Overview
3.1 PROJECT DESCRIPTION
The client for this project, Myron Erickson (Deputy Director of Public Works for the City of Wyoming),
requested the design of a biofiltration odor-control unit for nuisance odors emitted from the facility.
The primary objective of this project was to assess the feasibility of treating the odor emitted at the
splitter box and the primary clarifiers using biofiltration and to develop design and operational plans
for the system.
3.2 CLIENT
The city of Wyoming is located in Kent County, Michigan and is the second largest city in West
Michigan. The city is nearly 25 square miles with a population of 72,125 (according to the 2010
Census) [1]. Figure 2 shows the location of the wastewater treatment facility for Wyoming, named
the Wyoming Clean Water Plant (CWP). The facility treats wastewater from four nearby communities
and accommodates approximately 140,000 people [2]. The facility discharges its treated water to the
Grand River. To expand plant capacity to 24 million gallons of water per day, the CWP concluded a
$35 million expansion in 2006, which included the installment of new odor-control systems.
Project Location
Figure 2. Location of the CWP
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N
PROJECT OVERVIEW
3.3 SCOPE & OBJECTIVES
The primary objective of this project is to provide preliminary design plans for implementing
biofiltration technology at the CWP. The proposed system is designed to remove hydrogen sulfide
from the air emitted from the primary clarifiers and the splitter box located just downstream. This
project accomplishes the following objectives:





Provide research concerning possible design alternatives
Optimization design decisions and calculations
o Biofilter sizing
o Blower selection and air flow rate
o Moisture control system
o Media type
o Material selection
Preliminary design plans
Recommended operation and maintenance schedule
Preliminary cost estimate
The CWP currently has empty aeration basins onsite that are not in use. The client requested these
basins be retrofitted to house the proposed biofilter. This project investigated the feasibility of this
alternative and designed the biofilter based on the current infrastructure. Refer to Figure 3 for a
visual of the facility layout.
Figure 3. CWP Facility Layout
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PROJECT OVERVIEW
3.4 DESIGN CONSTRAINTS
There are a number of aspects of the design process that constrained how the final product was
developed. Establishing the location for the biofilter constrained the design to the existing
infrastructure of the empty aeration basins. Existing drainage and piping leading from the nearby
pipe gallery (located underground near the aeration basins) was used in the design. In addition to
incorporating the existing infrastructure into the design, the structural components of the biofilter
needed to accommodate maintenance needs, allowing for easy accessibility to the internal filter. The
location of the waste air streams dictated the amount of ductwork necessary to transport the air to
the biofilter site.
Furthermore, the CWP is using a 12,000 cubic feet per minute (cfm) fan for the existing carbon
adsorber currently being used to treat odor from the primary clarifiers and requested this fan be used
for the biofiltration unit. This airflow rate set the basis for design and constrained associated pressure
drop and sizing calculations for the filter.
Finally, safety was incorporated into the design of the biofilter in accordance with regulatory
standards and to ensure facility operators are not put at risk. Maintaining the safety of the design also
implies the biofilter is not to produce any pollutant byproducts.
3.5 DESIGN CRITERIA
The design criteria for the biofilter included the following:









The biofilter must be maintained at a minimum temperature of 59°F (15°C)
The unit must maintain an even water distribution in the filter with a moisture content of
approximately 60%
An even air distribution throughout the filter must be maintained
The pressure drop across the filter must be limited such that the desired removal efficiency
is maintained
Operation must be accomplished with the use of the 12,000cfm fan
The biofilter must maintain efficient operation for a range of H2S concentrations (up to 20
ppmv)
The selected media must minimize the need for maintenance and replacements
The structural design must be accommodating for maintenance repairs
The design is to have low energy requirements
3.6 DESIGN NORMS
Transparency, stewardship, and care were three design norms that helped to shape the motivation
and implementation of this project, with special consideration for the client and the environment.
The CWP currently uses chemical scrubbing and carbon adsorption at different locations throughout
the facility to reduce odorous air, however neither of these system are performing as they should and
have been very difficult and costly to maintain. The proposed biofiltration system has been designed
Page 19 of 91
PROJECT OVERVIEW
specifically to avoid similar issues by limiting operating costs and maintenance needs as much as
possible.
Transparency
To accomplish this goal, transparent communication between the team and the client was an
important component to the project. Transparency was maintained by communicating all design
alternatives, as well as disclosing any uncertainties the team has had with the design. Often a choice
needed to be made between cost and maintenance needs, thus discussing alternatives with the client
was an important part of the design process.
Stewardship
The second design norm of stewardship often helped with difficult design decisions. As an example,
one key component of the design was selecting the media. Synthetic media typically requires less
maintenance than does natural media, however natural media is the more economic and
environmentally-friendly alternative. Through discussions with the client and in light of our
dedication to environmental stewardship, natural media was selected. Furthermore, out of
consideration for the client and environmental conscientiousness, equipment currently on-site has
been repurposed and incorporated into the final design, thus lowering the initial cost of the project
and limiting the resources necessary for design. The biofilter is designed in empty aeration basins
on-site and the blower currently used for the carbon adsorber has been implemented into the design.
Caring
One of the most attractive aspects of a biofiltration system in comparison to alternative odor-control
technology is its relatively low maintenance needs. The operation of the system does not have the
safety concerns associated with systems that rely on chemicals for odor-reduction. This was an
important consideration in the design as the team sought to care for operators at the facility,
especially in light of the operational complications the plant is currently experiencing with their
odor-control systems.
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ODOR-CONTROL BACKGROUND
4 Odor-Control Background
4.1 OVERVIEW
Wastewater Treatment Facility Odor-Control
Odor-control technology can vary significantly and are selected depending on the unique
characteristics of the air. Common odor-control alternatives include chemical scrubbers, carbon
adsorbers, and various biological treatment options. At any location where wastewater is collected
or conveyed, there exists the potential to generate and release nuisance odors, usually resulting from
anaerobic conditions [3]. The microbes in the wastewater (a sulfate-reducing bacteria) have no
dissolved oxygen for respiration under these conditions. Instead, the microbes use the abundant
sulfate ion for respiration, producing the byproduct of hydrogen sulfide (refer to Sections 4.2.2 and
7.2.5 for the chemical reactions of this metabolism). Hydrogen sulfide (H2S) is the most common
pollutant detected in the air at wastewater facilities, and can be problematic due to its characteristic
rotten-egg odor and corrosive nature. Hydrogen sulfide has a low solubility in water, resulting in a
high likelihood it is released into the atmosphere, which is a particular concern in wet wells,
headworks, primary clarifiers, and biosolids storage tanks of wastewater treatment facilities.
Public Concern
As residential and commercial developments expand around wastewater treatment plants there is an
increasing need to reduce nuisance odors. Slow water movement through wastewater treatment
plants is required for the settling processes to effectively remove the solids and toxic materials in the
wastewater. Odor usually stems from stagnant water or water that has little to no oxygen transfer.
While in an enclosed space, these odorous chemicals can become health hazards, however in the open
air the purpose for odor control is primarily for nuisance reduction [3]. According to the Occupational
Safety and Health Administration (OSHA), hydrogen sulfide begins to produce its characteristic rotten
egg smell at a concentration of 0.1 to 1.5 ppmv and induces health risks at concentrations ranging
from of 2 to 5 ppmv, with fatal consequences at levels greater than ppmv [4].
Government Regulations
On the federal level, the United States government has directed the Environmental Protection Agency
(EPA) to complete studies involving composting, biosolids, agricultural wastes, septic solids, and
sewage sludge; however, the enforcement of nuisance odor-control is left to the States, local courts,
and referent executive agencies [5]. Regulation of odor proves to be challenging due to the subjectivity
of its measurements. No systematic “odor scale” exists due to the variability of the compounds and
individual reactions [5].
Odor-control in the state of Michigan is regulated by the emission of air pollutants, the parameters of
which are defined by Part 9 of the Air Pollution Control Rules. Odor at wastewater facilities is not
regulated according to quantitative standards [6]; however, the production of hydrogen sulfide
typically requires odor prevention due to nuisance odors. The production of any nuisance odor
Page 21 of 91
ODOR-CONTROL BACKGROUND
includes “any gas, vapor, fume, or mist, or combination thereof, from a well or its associated surface
facilities” [6], must be in compliance with R336.1901 from the Michigan Air Quality Division. The rule
is stated as follows.
“Notwithstanding the provisions of any other department rule, a person shall not cause or
permit the emission of an air contaminant or water vapor in quantities that cause, alone or in
reaction with other air contaminants, either of the following:
(a) Injurious effects to human health or safety, animal life, plant life of significant economic
value, or property.
(b) Unreasonable interference with the comfortable enjoyment of life and property.” [7]
Typically, odor-control is required due to consideration for the surrounding community, but is not
monitored unless produced at toxic levels. The Michigan Department of Environmental Quality
(MDEQ) regulates acceptable technology and corresponding emission standards on a case-to-case
basis. Hydrogen sulfide is included on the list of non-hazardous Toxic Air Contaminants (TACs)
regulated by the MDEQ, however emission standards vary based on the situation [8].
Michigan regulations for air are defined by Rules 224 - 232. The MDEQ defines Toxic Air Contaminant
(TAC) as
“Any air contaminant for which there is no national ambient air quality standard and which
is or may become harmful to public health or the environment when present in the outdoor
atmosphere in sufficient quantities and duration.”
Any odor-control unit must be granted a Permit to Install (PTI) according the Michigan Rule 201.
Furthermore, any PTI involving TAC emissions must satisfy analysis of the Best Available Control
Technology for Toxics (T-BACT), which is defined by Michigan Rules 224, 225, and 226.
According to the MDEQ Michigan Rule 224, the T-BACT must be used for emission control [9]. This
requires the applicant to complete an evaluation of alternatives for the T-BACT review, the extent of
which depends on the magnitude of emissions under consideration. The selected technology must
reduce TAC emissions to an achievable maximum amount as determined by the MDEQ.
Michigan Rule 225 requires any TAC to comply with health-based screening levels [10]. The predicted
maximum ambient impact (PAI) is not to exceed the initial threshold screening level (ITSL) for TAC
emissions. Compliance with these standards are demonstrated using the Allowable Emission Rate
Methodology of Rule 227(1) (a).
Michigan Rule 226 provides an exemption from the health-based screening level requirements [6].
This exemption applies if emissions do not violate Rule 901, which prohibits the emission of
contaminants that induce physical harm to life or property. Rule 226 is determined case by case.
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ODOR-CONTROL BACKGROUND
4.2 ODOR SOURCE
Overview
Many chemical compounds can be detected in the air as odors and their intensity varies with
concentration. The concentration at which an individual can first perceive an odor from a particular
substance is called the odor threshold, which is often used to establish regulatory standards. Inherent
difficulties exist with the regulation of odors because the perception of specific concentrations varies
based on the individual. Regulating odors involves monitoring the compounds that are being released
into the air as well as ensuring the effectiveness of odor-control units. Laws and regulations may
control the release of odors that are hazardous to the exposed parties by a technology called “off-side
receptor” controls, however a certain level of subjectivity is involved with these regulations.
Hydrogen Sulfide
Hydrogen Sulfide (H2S) is a colorless gas produced by wastewater solutions with multiple disruptive
side effects. Hydrogen sulfide occurs naturally through anaerobic decay of organic matter and
produces a distinct rotten egg odor. The concentrations of hydrogen sulfide found in wastewater
treatment facilities varies depending on the type of process involved and the characteristics of the
wastewater.
The production of hydrogen sulfide is stimulated with increasing levels of sulfate in the wastewater
influent, large organic loading rates, slow-moving water, and warm temperatures [11]. In wastewater,
sulfide exists in three forms: hydrogen sulfide gas, non-volatile ionic species hydrogen sulfide, and
sulfide. The abundance of these different forms is highly dependent on the pH of the wastewater [12].
Although hydrogen sulfide is present in the wastewater solution as either H2S aqueous (aq) or HS−
(depending on pH), only hydrogen sulfide as H2S has the ability to transfer between water and air and
contributes to the emission of H2S gas [13]. The breakdown of these two molecules into their ionic
forms are as follows [14]:
H2 S(aq) ↔ H + + HS − ,
HS − ↔ H + + S 2− ,
pK a1 ≈ 7.04
pK a2 ≈ 11.96
The main mechanism that results in the formation of sulfide is the microbial reduction of the sulfate
ion present in the wastewater. The dissolved oxygen (DO) concentration in the wastewater is
significantly reduced when the biological oxygen demand (BOD) is high, which causes sulfatereducing bacteria (SRB’s) to convert the sulfate ion to sulfide, as shown in the following reaction [12].
Anaerobic Microorganisms
SO2−
4 + Organic Matter →
H2 S + CO2
The rate of sulfide production depends on the concentrations of sulfate ions, dissolved oxygen, and
organic matter present in the water. Hydrogen sulfide is controlled by preventing the sulfide
formation or by removing sulfide after it has formed.
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ODOR-CONTROL BACKGROUND
4.3 ODOR TREATMENT ALTERNATIVES
Vapor-phase treatments use ventilation systems and are designed to maintain a negative pressure at
point sources of odor problems. The path of the odorous air is limited to a single discharge point
where the air is treated before it is released into the atmosphere. The intent is to reduce leaks of the
nuisance air at vents, hatches, or other open areas. Vapor-phase treatment technologies include liquid
redox technology, solids scavengers, wet air scrubbing, carbon adsorption, and biofiltration [3]. The
CWP currently uses wet air scrubbing and carbon adsorption for odor control, as described in the
following.
Wet Air Scrubbing
Wet chemical scrubbing is a proven and reliable odor-control treatment technology and can be used
for most water-soluble contaminants. In the wet air scrubber, the contaminants are solubilized from
the vapor phase into an aqueous chemical solution. These scrubbers use specific chemicals to strip
the pollutants from the air with a reactive chemical mechanism [3]. This is a common odor treatment
technology for removing hydrogen sulfide and most systems involve two chemicals to treat this
compound. Sodium hydroxide is used to dissolve hydrogen sulfide into the solution, then sodium
hypochlorite is employed to target the odor compounds for removal which is shown below.
H2 S + 4NaOCl + 2NaOH → Na2 SO4 + 4NaCl + 2H2 O
In wet air scrubbing units, a fan pushes the contaminated air through the media bed while spray
nozzles disperse the chemical over the incoming air and absorb the contaminants. After passing
through the system, the chemicals are often circulated through for reuse or are discarded. The treated
air is blown out of the system. A schematic of a general scrubber system is show in Figure 4.
Figure 4. Schematic view of a general scrubber system [15]
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ODOR-CONTROL BACKGROUND
Carbon Adsorption
Carbon adsorption passes the air stream over a bed of activated carbon and the contaminants adhere
to the surface of the carbon, thus removing them from the air stream. This is a relatively simple form
of odor-control and the primary operating cost comes from purchasing new activated carbon after
the carbon media has been exhausted, however the disposal and replacement costs associated with
carbon adsorption are high compared to alternative technologies. Moisture is a large limiting factor
for carbon adsorption. It is imperative that the carbon be kept dry, lest the adsorptive capacity is
greatly reduced. Activated carbon removes hydrogen sulfide and other odor-producing compounds
by catalyzing the oxidation of hydrogen sulfide, resulting in elemental sulfur and water according to
the following reaction.
1
2H2 S (g) + O2 (g) → S8 (s) + 2H2 O(g)
4
Most of the water produced from this process is lost to the air stream as it passes through the system,
while the sulfur is adsorbed into the porous surface of the activated carbon. The adsorption continues
until the pores can no longer take in sulfur. As the pores reach their capacity for sulfur uptake, the
odor compounds begin to break through the media, meaning noticeable odors are released from the
unit indicating the media needs to be replaced.
Biofiltration
Biofiltration odor-reducing technologies use microbial organisms to consume problematic odorproducing chemical compounds from waste air streams. The biological organisms are a constituent
of the biofilm attached to either organic or inorganic packing material. The microbial species used
are engineered for the specific target contaminant(s) found in the waste air stream. As the untreated
air is blown through the media bed, the microorganisms bio-chemically react with the contaminants
and act to break apart the compounds and release stabilized, treated air.
4.4 ODOR-CONTROL DESCISION MATRIX
A decision matrix consisting of six criteria was used to decide which odor-control technology to select
for this project. The criteria includes installation cost, maintenance and operations cost, popularity
of use for odor-control, projected life of the technology, satisfaction from users, and client preference.
Each criteria was ranked on a scale of 3 to 10. A high score indicated the importance of the criteria.


Client preference was highly ranked because our clients’ needs are of considerable
importance. The client is very interested in biofiltration technology making it a priority for
the team to investigate its feasibility. Client preference was ranked 10.
Operation and maintenance (O&M) costs includes the intensity and amount of labor involved
in maintaining the system as well as any chemical dosing requirements for the system. O&M
was ranked 8.
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ODOR-CONTROL BACKGROUND




Capital cost is an important consideration to avoid high upfront cost. However, capital cost
was ranked lower than O&M costs because it would contribute less to the overall cost during
the life of the project, assuming a robust design. Capital cost was ranked 7.
User satisfaction is important to from the stance of facility operators. Information concerning
various technologies used in the West Michigan area was gathered for this ranking. User
satisfaction was ranked 6.
The life of the system was considered to ensure a robust and sustainable design. Long lasting
systems received higher scores than technology with a shorter operating life. The life of the
filter was ranked 5.
Widely-used technology accounts for the history of the technology and whether time has
proven the practicality and effectiveness of its use. The extensive use of certain odor-control
technologies also validates the treatment’s existing customer support, manufacturing options,
and operator familiarity with the product. Widely-used technology was ranked 3.
Each odor-control technology was ranked according to the chosen criteria. Each was given a score
ranging from 1 to 6 based on how it performed in the given criteria. Multiply the score by the weight
of the criteria, the overall scores were tabulated for each technology. The decision matrix is shown in
Table 2. The odor-control technology that will be evaluated for installation at the CWP is biofiltration.
Table 2. Odor-Control Technology Decision Matrix
Criteria
%
Client Preference
O&M
Capital Cost
User Satisfaction
Filter Life
Widely-used
Score
10
8
7
6
5
3
Chemical
Scrubbing
Liquid
Redox
Biofiltration
Solid
Scavengers
Carbon
Adsorption
1
3
3
4
5
6
122
1
4
1
3
6
2
103
6
6
3
6
3
3
189
1
2
6
4
5
2
123
1
5
3
4
2
6
123
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Liquid
Phase
Treatment
1
2
6
3
5
2
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WYOMING CLEAN WATER PLANT
5 Wyoming Clean Water Plant
5.1 BACKGROUND
Plant Operations
The team obtained data concerning annual trends for influent wastewater flow rates, temperatures,
average BOD, and average DO concentrations from the CWP operators. This information helped to
provide a basis for determining trends of H2S production. A flow diagram of the wastewater through
the CWP is shown in Appendix A.
Odor-Control
The CWP currently uses odor-control systems at three locations throughout the plant. The odorcontrol systems remove a range of H2S levels, which would otherwise be released into the atmosphere
causing a nuisance odor. Other odor-producing compounds may be removed during the process of
H2S removal; however the plant does not monitor any other compounds because their effects are low
or insignificant. The facility has records of influent and effluent H 2S concentrations for each odorcontrol unit beginning in 2013. Operation personnel reported the production of H2S does not depend
on seasonal variations, which is supported by the data showing no recognizable pattern among
annual H2S readings. Rather, the influent wastewater composition and the amount of sludge present
in the system is directly responsible for the production of this compound.
The headworks building uses a chemical scrubber for odor-control; however, data from the past few
years has shown influent H2S concentrations remains at zero. The carbon adsorber has seen H2S
concentrations ranging from 0 to 22 ppmv and the chemicals scrubbers used for the biosolids tanks
obtain levels as high as 88 ppmv. Characterization of air effluent from each source at this facility are
in compliance with MDEQ regulations.
OSHA reports that prolonged exposure to H2S concentrations of greater than 2ppmv can induce health
hazards [16]. Because the H2S produced at the CWP would quickly become diluted into the
atmosphere if released, the facility treats H2S as merely a nuisance rather than a regulated health
hazard. Production of H2S contained within a building, such as at the headworks building, must be
treated due to health hazard concerns.
5.2 EXISITING PLANT OPERATIONS
The odor produced at each of the four sites under consideration varies slightly in composition.
Generally speaking, the odor is due to non-hazardous levels H2S compounds found in the air, which
produces a distinct “rotten egg” smell. The exact concentration of H2S in the air depends on the
composition of the wastewater at a specific site, which varies with conditions such as temperature,
humidity, flow rate, and upstream treatment. The temperature of the influent wastewater varies with
season, ranging from low 50’s in the spring to the low 70’s mid-summer (Fahrenheit). Average flow
rates in recent years was approximately 15.5 mgd, with approximately 11 to 12% supplied from
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WYOMING CLEAN WATER PLANT
industrial load. The average BOD per year is about 330 mg/L with maximum day load occasionally
exceeding 500 mg/L per year. Figure 5 shows locations of current odor-control systems at the CWP.
In the plant, one carbon adsorption unit is used to control odor from the primary clarifiers, and wet
chemical scrubbers are used for odor at the headworks building and the biosolids storage tank. The
splitter box currently has no form of odor-control.
5.3 ODOR-CONTROL
Chemical
Scrubbers
Carbon
Adsorbers
Splitter Box
Chemical
Scrubbers
Figure 5. Locations of Current and Proposed Odor-Control Units (Google Maps)
Headworks
A chemical scrubber was installed in 2000 in the headworks building to treat effluent air containing
hydrogen sulfide from the influent. The scrubber is comprised of two stages containing plastic media
through which contaminated air is processed. The air passes through the first chamber where it is
treated with a sodium hydroxide solution, followed by sodium hypochlorite treatment in the second
chamber.
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WYOMING CLEAN WATER PLANT
The components of the headworks process are enclosed within the building, so the air treatment
system is installed in the case of potentially hazardous H2S levels. Measurements taken within the
past year consistently show an influent H2S concentration of zero (Appendix B).
Primary Clarifiers
Carbon Media Specifications
The effluent air from the primary clarifiers and the head storage tanks is contained and directed to a
carbon adsorption odor-control unit. The system has dual flow operation, meaning incoming air
enters the middle of the chamber and is directed upward and downward to carbon beds. The top and
bottom beds are identical, each containing 1ft (or a volume of 266ft3) of high capacity activated
carbon and 2ft (a volume of 425ft3) of virgin activated carbon.
Since its installment in 2007, the carbon media has been replaced twice (three rounds of media
including the originally installed media). The carbon adsorption media is designed to be replaced
when the pressure difference across the top of carbon bed layer reaches a maximum of 5 to 6 psi. The
manufacturer claims this is to occur approximately once every 4 years. However, this maximum
pressure difference has not been reached since the installment of the unit and instead the plant uses
H2S emission as a basis for carbon media replacements. Under normal conditions, no H2S is released
from the carbon absorber so the media is replaced when the emitted H2S reading is greater than zero,
which is the reason the carbon media has been replaced more frequently than the manufacturer’s
recommendations.
Air samples are taken at six location in the filter (three at the top and three on bottom). One reading
is at the influent, one at mid-filter, and one at the exit for both the top and bottom layers. As the air
passes through these filter beds, the H2S concentration is depleted such that the effluent H2S
concentration is typically zero.
𝐇𝟐 𝐒 Readings
The greatest influent H2S concentration to the carbon adsorber within the past two years was 22ppmv,
with an average concentration of 6 ppmv. The unit began emitting a H2S concentration of 3 ppmv in
August, 2014 and the carbon was replaced shortly thereafter. Refer to Appendix C for H2S
concentration measurements from the previous two years.
Alteration to the Primary Clarifiers
The primary clarifiers were covered in 2009, which created a more anaerobic environment and
slightly altered settling characteristics of the sludge. Additionally, the fermentation process in the
primary clarifiers was recently altered. Fermentation applies to the sludge at the bottom of the
clarifier tanks, which was previously being pumped out of the tank at a rate of 4,000 to 5,000 gallons
per hour.
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WYOMING CLEAN WATER PLANT
In the summer of 2012, the plant experienced complications concerning biological phosphorous
removal (BioP) in the aeration basins. In order to solve the problem, it was determined more volatile
fatty acids (VFA) must be fed to aid the BioP process. To accomplish this, the fermentation time of the
primary sludge in the primary clarifiers (just upstream of the aeration basins) was extended. The
pump rate was slowed gradually over time and sampling for VFA occurred multiple times a week until
data showed that an adequate VFA concentration was produced. As of fall 2014, the plant discharges
1,000 to 2,000 gallons per hour of primary sludge. The rate is not adjusted unless septic conditions
occur in the clarifiers. In other words, the pump rate is slowed if sampling shows the VFA
concentration is too low.
Resulting Nuisance Odor
The carbon adsorption unit successfully treats the odor produced by hydrogen sulfide, but produces
a characteristic “fish tank” smell as a byproduct for unknown reasons. This effect has occurred since
the installation of the carbon adsorber and is seemingly unrelated to the primary clarifier alterations.
As a result, the unit requires media replacements far more frequently than what was recommended.
The CWP operators decided to replace the media the first time due to the extensive production of the
malodorous byproduct, which incurs within 2 months of replacement.
Biosolids Storage Tanks
Retired Carbon Adsorber
The odor-control building for the effluent air from the biosolids storage tank houses a retired carbon
adsorption unit. The system was installed in 2011, but was used for odor-control approximately 6
months before plant operators decided discontinue its use due to high costs. The air was rerouted to
the existing chemical scrubbers, which is the current configuration. During its use, however, the
system successfully removed H2S from the air completely, even when operating at a pressure
difference of 6 psi across the top of the carbon bed. The unit was manufactured by Siemens Water
Technologies and installed in 2007. The filter stack contains 2120 lbs. of Midas OCM Carbon Media
and is designed for an average H2S concentration of 10 ppmv with a peak concentration of 25 ppmv
and a maximum media saturation density of 0.73 g H2S /g carbon.
Chemical Scrubbers
Three wet chemical scrubbing units are used for odor originating from the biosolids storage tanks.
Refer to Figure 5 for their location. The chemical scrubbers at the biosolids storage tanks were
installed during plant improvements completed in 2005. The chemical scrubbers treat the
contaminated air stream using a two-stage system. Both stages use a plastic media of polypropylene
balls approximately 1.5 inches in diameter with a surface area of 48 square inches. The influent air is
passed through the media bed while the chemicals are sprayed from above. The contaminants in the
air are dissolved by the chemicals and removed with the liquid solution.
The first stage uses sulfuric acid at a concentration of 93% to remove ammonia from the air. This step
is not of great concern to plant operation and has no history of complications. The second step,
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WYOMING CLEAN WATER PLANT
however, is much more critical to the air treatment process. In this stage, a combination of sodium
hydroxide and sodium hypochlorite (bleach) at a concentration of 12% is used to target H2S for
removal.
As the air passes through this process, chemicals are extracted and deposited into the liquid stream.
Based on a liquid sample test taken in 2015, the composition of the liquid solution effluent from the
scrubber included 597 mg/kg Ca, 1010 mg/kg Na, and less than 230 mg/kg Si.
Solids Buildup
A white solid has been forming on the media of the chemical scrubber for unknown reasons (Figure
6). This has reduced the effectiveness of the chemical scrubber and increased operation and
maintenance costs due to frequent cleaning. The problem seemed to correlate with the alteration of
primary clarifiers (refer to Section 5.3.2 Alteration of Primary Clarifiers for further information)
however, it is unclear whether or not this is a direct cause of the solids buildup. The solid buildup was
tested and found to be a calcium-based compound. Attempts to solve this problem by installing a
water softener have proved unsuccessful. The only solution that has worked thus far is to halt the
filtration process to remove and replace the media; a solution that has proved costly in both time and
money.
Figure 6. Solids buildup on media of chemical scrubbers (Lauren Grimley)
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WYOMING CLEAN WATER PLANT
𝐇𝟐 𝐒 Readings
The highest documented influent H2S concentration the chemical scrubbers have seen in recent year
is 88 ppmv, which resulted in a H2S concentration at the outlet of 18 ppmv. The average influent H2S
concentration is 22 ppmv and typically there is a complete removal (refer to Appendix D).
Splitter Box
The splitter box at the CWP disperses a single effluent stream from the primary clarifiers into three
aeration basins (refer to Appendix E for a schematic diagram of the splitter box). Currently there is
no odor control for this site and the air is emitted into the atmosphere, as shown in Figures 7 and 8.
Beginning in November and ending in December of 2015, the hydrogen sulfide concentration and
temperature of the air have been recorded using an OdaLog gas data logger (refer to Appendix F). The
data shows that the H2S concentration fluctuates between zero and about 22ppm.
Figure 7. Splitter Box at the Wyoming Clean Water Plant (Lauren Grimley)
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WYOMING CLEAN WATER PLANT
Figure 8. Splitter Box (Lauren Grimley)
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BIOFILTRATION TECHNOLOGY
6 Biofiltration Technology
6.1 OVERALL PROCESS DESCRIPTION AND TERMINOLOGY
Within the past two decades, biotechnology has become a popular method for odor-control and VOC
reduction. Contaminated gases emitted from wastewater plants are often corrosive to infrastructure
or equipment and can have negative effects on human health and comfort. Biofiltration is an attractive
technology to treat the contaminated air because it requires no chemical addition and has a low
operational cost. In general, these systems require less maintenance and fewer media replacements
than competing odor-reducing technologies, which greatly relieves costs associated with upkeep.
Biofiltration functions effectively due to immobilized microorganisms found in the biofilm layer on
porous media. The contaminated vapor stream is passed through the media bed where the
contaminants are transferred from the vapor phase and deposited into the biological bilayer, where
they are then removed by metabolic processes [17]. The general process flow diagram of a typical
biofiltration system used for wastewater odor-control is shown in Figure 9.
Figure 9. Biofiltration Process Flow Diagram [18]
6.2 MECHANISMS OF OPERATIONS
Modeling a biofilter will include a mass balance of the contaminants, oxygen, pollutant degradation
byproducts, and biomass generation in all phases. Depending on the model, the resulting differential
equation is a combination of terms that describe the reactions and movements of pollutants in the
biofilter. These terms describe the following biofilter properties [19]:




Accumulation of reactive products
Dispersion effects in air
Mass transfer between the air and biofilm
Diffusional mass transfer in the biofilm
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BIOFILTRATION TECHNOLOGY




Consumption due to biological oxidation
Adsorption onto solid media
Biomass growth
Physiological state of the biomass
Assumptions that can be made to simplify the model include:







Biofilm and air interface is in a state of equilibrium
Ideal mixing in the liquid phase
Plug flow for the air phase
Constant biofilm thickness and biomass density (negligible biomass growth)
Steady-state conditions
Excess oxygen is available
Use of simple kinetics for biological oxidation
Biokinetics
The biofilter is modeled as a packed bed reactor (PBR) in order to size the biofilter according to the
desired removal efficiency of odorous components. A PBR is a reactor consisting of a long tube that
is filled with a porous media. The size of the biofilter chamber can be determined after the biofilter
media volume is calculated based on the residence time of the contaminant in the media. Usually the
incoming hydrogen sulfide reacts with the media and results in a chemical product (usually as SO2−
4 ).
To accurately determine the volume needed for the specified air flow, a rate law must be determined.
Multiple rate laws have been used to model the removal of hydrogen sulfide from air including:


Ottengraf and Ven Den Oover
o Assumes plug flow for the gas phase and a flat geometry for the biofilter
o Zero-order Diffusion or Reaction Limited
Michaelis-Menten
o Used to determine the rate of an enzymatic reaction
o Simplified depending on the concentration of the substrate
Mass Loading Rate
The mass loading rate is the mass of the contaminant entering the biofilter per unit area of volume of
filter per unit time. For hydrogen sulfide in particular, the mass loading rate is defined as the amount
of hydrogen sulfide that is introduced to the system per unit time/per unit volume of the packing
material (g H2 S⁄ft 3 hr) [20]. Modeling a biofilter can be done by defining boundary conditions and
developing a mass balance equation across the biofilm that is grown on the packing media.
Biofilm Kinetics
A key process in biofiltration is the transfer of pollutants from the air to the water phase via
adsorption into the moisturized packing media. Adsorption refers to the process in which pollutants
in the air interact with a solid surface of an adsorbent and bond via weak intermolecular forces [15].
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BIOFILTRATION TECHNOLOGY
After the contaminant has been adsorbed, biodegradation of the contaminants occurs within the
biofilm. Figure 10 shows the mass transport and kinetic mechanisms considered in a three-phase
model. This model incorporates advective flow mass transport in both the gas and liquid, mass
transfer at the gas-liquid and liquid-biofilm interfaces, internal diffusion in the biofilm, and active
biomass growth and decay reactions in the biofilm.
Figure 10. Schematic representation of the mechanisms in a biofiltration unit: (a) mass transport by gas-phase
and liquid-phase advection, and (b) mass transport by diffusion and biological reaction in the biofilm [21].
Alternatively, a two-phase model considers only the mass transfer in the two phases; the gas and the
biofilm. The mechanisms are the same as a three-phase model except liquid advective flow is not
included and only mass transport at the gas-biofilm interface is modeled, rather than mass transport
at both the gas-liquid and liquid-biofilm interfaces.
Biodegradation
The microorganisms in the biofilm carry out the metabolic activities that will transform the pollutants
into harmless products. The end products from complete bio-oxidation of the air contaminants are
CO2, water, mineral salts, and microbial biomass. Biofilms contain complex association of bacteria and
microbial communities making it challenging to maintain control of the biodegradation processes
occurring in air biofilters [19]. Refer to Figure 11 for a diagram depicting the process of
biodegradation.
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BIOFILTRATION TECHNOLOGY
Figure 11. Overview of Biodegradation Process for Biofiltration [19]
In order for biodegradation of the air pollutants to occur, the contaminants must be biologically
available to the degrading cells. The biodegradation rate of a contaminant depends on the rate of
uptake and the mass transfer by the microorganisms. Typically during operation, a contaminant
introduced into a bioreactor will shift the microbial populations towards a specific culture that will
appropriately metabolize the target pollutant [19].
Microbiology
Biological removal of hydrogen sulfide requires a bacteria that can accomplish the required redox
reaction. As a starting point for selecting a bacteria, the design must consider sulfur-oxidizing
bacteria, which catalyze the biological oxidation of hydrogen sulfide. Thiobacillus species are used
almost exclusively in biofiltration for hydrogen sulfide treatment because they most effectively
accomplish the above criteria [22, 23, 24].
Thiobacillus metabolize hydrogen sulfide using oxygen. The following equation shows the most
common form of removal.
H2 S + 2O2 → H2 SO4
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BIOFILTRATION TECHNOLOGY
The growth rates of the microbial species depends on the substrate concentration, environmental
conditions, pH, water activity, and available nutrients. The growth rate and substrate concentration
can be described by the Monod model shown directly below [19].
μ=
μmax CL
Ks +CL
In the case of a biofilter, the pollutant concentration is the substrate concentration (CL). When the
pollutant concentration is high, CL is far larger than the saturation constant (Ks) and a higher cell
growth (µ) is obtained. Pollutant degradation rate is more important than the growth rate because
an air treatment system is considered effective if it is able to maintain a high elimination capacity
(EC).
6.3 CHARACTERIZING BIOFILTER PERFORMANCE
Removal Efficiency
The percent removal of the pollutant, removal efficiency (RE), is often used to characterize
biofiltration performance. The equation to calculate RE is
RE(%) =
[H2 S]in −[H2 S]out
[H2 S]in
100%.
The influent hydrogen sulfide concentration determines the removal efficiency of the biofilter.
Elimination Capacity
A common method of characterizing a biofilter performance is to calculate the elimination capacity
(EC) as a function of the pollutant loading. Loading can be based on either bed volume or bed surface
area, but more commonly volumetric loading (L) is used [25]. These can be calculated using the
following equations.
L = [H2 S]in (Q⁄V)
EC = ([H2 S]in − [H2 S]out ) (Q⁄V)
Influent and effluent hydrogen sulfide concentration ([H2 S]in and [H2 S]out ) have units of
mass/volume, the volumetric gas flow rate (Q) has units of volume/time, and the volume (V) is the
volume of the empty biofilter bed.
The EC can only be less than or equal to the volumetric loading. As shown in Figure 12, a plot of EC
as a function of the volumetric loading that yields a straight line through the origin with a slope of
one would represent 100% contaminant elimination.
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BIOFILTRATION TECHNOLOGY
Figure 12. Model-simulated sulfide elimination as a function of sulfide loading for various influent H 2S
concentrations (straight line represents 100% elimination) [25].
At high loading, the EC approaches a maximum EC that is typically 0.28 to 8.5 g⁄ft 3 hr (10 to 300
g⁄m3 hr) for biofilters treating common pollutants such as VOCs and hydrogen sulfide. The maximum
critical loading of the pollutant is a function of the packing material and operating conditions. The
elimination capacity increases directly with an increase in loading, which may be a result of a high
biomass concentration in the biofilm under these conditions.
6.4 FACTORS AFFECTING BIOFILTER PERFORMANCE
Packing Media
Biofiltration relies on the microorganisms present in the packing material which degrade the
contaminants of concern. The microorganisms capable of degrading hydrogen sulfide are ubiquitous
such that the nature of the packing material is variable.
Successful filter media typically consider the following factors [26]:





Fine media or media with a high specific surface area can achieve higher levels of treatment
efficiency than larger media particles with a lower specific surface area
Media porosity, which impacts flow dynamics and mass transfer characteristics, affects
biofilter operation and performance
Organic matter in the media can affect the efficacy of the system
A greater absorptivity of the media can minimize effects of transient loading
Layering media types can help to distribute the gas flow evenly across the filter
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BIOFILTRATION TECHNOLOGY
The packing media must be regenerated after a length of time in order to maintain removal efficiency.
The need and frequency for regeneration depends on the media type, the moisture content of the
filter, and contaminants in the air stream.
Moisture Content
The microorganisms used in biofiltration require moisture to grow and sustain metabolic activities
at an optimum biodegradation rate. In a biofilter, moisture levels are often maintained by humidifying
the inlet airstream if the waste air does not already have a sufficient moisture content. In addition, an
inadequate water content can cause the media bed to dry out, causing cracks and channels to form in
the media bed. The required moisture content of the biofilter varies depending on water retention
characteristics of the media’s surface. In general, an optimal moisture content typically falls between
40 and 60% [19]. Conversely, excess water beyond this optimal range can inhibit oxygen transfer
between the biofilm and the contaminants in the air phase and can increase the pressure difference
across the media layer, rendering the biofilter ineffective.
Nutrient Control
Microorganisms consume pollutants for energy in order to maintain biological activity and growth
[19], but for biodegradation to be successful, the microorganisms must have access to additional
nutrients. Organic media beds may naturally contain sufficient nutrient levels, depending on the
media type, but nutrients must be added to synthetic packing media and some natural media
mixtures. However, the supply of nutrients must be limited in order to avoid clogging of the media as
a result of excessive biomass formation. This issue is more common when an inert packing media is
used because the nutrient supply must be closely monitored and adjusted accordingly.
Temperature
An important factor to consider with biological odor-control technology, compared to other physical
and chemical treatment alternatives, is operating at a specified temperature. Temperature control is
critical in these systems in order to prevent the risk of bacterial death due to thermal shock.
Temperatures of contaminated air originating from wastewater streams are relatively warm due to
the nature of the wastewater and typically range between 50 and 70 ᵒF (about 10 to 20 ᵒC). Most
biological activity operates under conditions of the mesophilic range 59 and 104 ᵒF (15 to 40 ᵒC),
which sets the recommended temperature range for biofiltration operation [19]. Heating or cooling
systems must be incorporated into the design of the biofilter to maintain this temperature range.
pH Value
An appropriate pH level must be maintained during biofilter operation. The oxidation of sulfur
compounds can lead to the formation of acid intermediates which lower the bed pH, subsequently
reducing the removal efficiency of the media [20].
Hydrogen sulfide is a highly soluble gas with a Henry’s constant of
2582 mL gas⁄L H2 O • atm at 68ᵒF (20ᵒC). The extent of odor caused by hydrogen sulfide depends
on the pH of the wastewater. If the pH is less than 5, sulfide is present predominantly in the form of
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BIOFILTRATION TECHNOLOGY
H2 S and is in a physical equilibrium with the gas phase. At a pH of 10, sulfide is dissolved as HS − . As
the pH approaches 7, both H2 S and HS − are present in the solution with approximately 50% of each
[15].
Microorganisms operate and grow in a specific pH range. Bacteria thrives in an environment that has
a pH of 5 to 9. Depending on the composition of the bed, the microorganisms will perform optimally
within a certain pH range and fluctuations of more than 2 to 3 pH units can cause harm to the
microorganisms. This can lead to the destruction of the microbial population [19].
Empty Bed Residence Time
An important parameter in biofiltration design is the Empty Bed Residence Time (EBRT). This term
refers to the ratio of medium volume to the volumetric air flow through the reactor bed. The EBRT is
used to determine the efficiency of the odor or VOC contaminant removal as well as the bioreactor
volume. The EBRT is based on statistically data, lab or pilot scale experiments, and predictive
modeling.
Low EBRT implies the required velocity and power consumption are high and there is a large
pressure drop across media. A high EBRT implies a large footprint and media volume as well as a high
capital cost. The following equation calculates EBRT where Vf is the filter bed volume (ft 3 ) and Q is
the airflow rate (ft 3 ⁄s) [25].
EBRT =
Vf
Q
Oxygen Content
Microorganisms involved in treating odorous air are predominantly aerobic, meaning they require
oxygen to perform metabolic functions. Biofilters typically operate between 5 to 15% oxygen [19]. It
is important to monitor oxygen in cases where there is a high contaminant-loading rate or a high
moisture content.
Bed Depth
The removal efficiency of hydrogen sulfide is also dependent on media bed depth. In order to
effectively remove H2S, a specific residence time is required for adequate contact between the
contaminant and the media. The required bed depth depends on residence time and determines the
required volume of the chamber. Most of the H2S is removed in the portion of the bed nearest to the
influent air flow.
The bed depth must also be optimized to provide adequate gas flow and rinse water distribution
throughout the bed. A deeper bed requires less space because it provides a larger bed volume per
unit area ratio. However, if the bed is too deep, the weight of the packing media causes structural
issues and poses a challenge for maintenance and media replacements. Common biofilter packing
depths range from 3 to 5 feet (0.9 to 1.5m) [25].
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Medium Diameter and Surface Area
The efficiency of hydrogen sulfide removal is dependent on the size of the media. Packing material
with a relatively small diameter can improve the performance of a biofilter with an insufficient
residence time. Smaller particles provide a greater total surface area, which increases the transfer
rate of the contaminant from the gas-phase to the biofilm, and thus improves removal efficiency [25].
However, the smaller the particle diameter, the larger the pressure drop, which results in a tradeoff
between removal efficiency and energy to push air through the filter.
Pressure Drop
The pressure drop increases linearly with packing height. The pressure drop across the biofilter bed
is often an issue when the packing material has a relatively small surface area. Larger media particles
reduce the pressure drop across the biofilter bed. Additionally, as air velocity through the filter is
increased, larger particles help to minimize the increase in pressure drop.
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7 Alternative Design Considerations
7.1 PACKING MEDIA
The size and overall cost of the biofilter largely depend on the characteristics of the packing media.
The media provides a suitable environment for microorganisms to grow and biodegrade pollutants
in the air stream.
The proposed media recommendations was selected based on its ability to lower operating costs and
reduce required maintenance while successfully removing pollutants from the air. The effectiveness
of packing media is based on size distribution, active surface area, porosity, adsorption properties,
and degree of compaction, water retention capabilities, and the physical properties of the media
under low pH conditions. Refer to Appendix G for research concerning a range of media types.
The performance of a media type largely depends on the following three parameters [27]:
1.
2.
3.
Specifications of the media material (i.e. temperature, void fraction, particle diameter,
water content, microbial characterization, and nutrients)
Characteristics of air flow through the media (i.e. superficial velocity, gas distribution, and
pressure at the inlet)
Substrate load conditions (i.e. solubility, microbial degradability, and applied loading
rate)
Natural vs. Synthetic Media
Organic media naturally contains bacteria within the structure itself and additional bacteria can
thrive on the surface after the formation of a biofilm. Both contribute to the overall bioactivity in the
system [19]. Natural media has a high overall removal efficiency at the beginning of the filtration
process which is likely due to a high sorptive surface area, however a large pressure drop can limit
the overall efficiency of the system. Natural media types include peat, compost, woodchips, lava rock,
and activated carbon. Mixtures of organic material can help to optimize several aspects of the biofilter
design to improve the overall contaminant removal efficiency.
An advantage of using synthetic media in biofiltration is that it can be engineered to have optimal
structural and surface area characteristics. Synthetic media types include polyurethane foam or
biosorbens. Synthetics do not experience compaction or degradation to the same extent that certain
types of natural media do, therefore they tend to have a longer media life [28]. Additionally, synthetic
media can reduce bed clogging caused by excessive biomass growth [29]. However, because it does
not contain a natural component, synthetic media must be inoculated with active bacteria.
Furthermore, synthetic media tends to be an expensive alternative to natural media and its eventual
disposal can cause environmental concern.
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Layered Media
Based on research, conversations with experts in biofiltration, and recent trends, a layered biofilter
bed is common for biofiltration. The biofilter bed often is layered with an inorganic media that is
covered by an organic polisher. With a single organic layer configuration, it is difficult and expensive
to control the pH of the media and media degradation occurs more rapidly. In contrast, an inert
inorganic base layer is more resistant to degradation and can extend the overall life of the media [30].
Inorganic Layer
Inorganic media used for biofiltration consists of some porous rock or mineral material. The more
porous the media is, the greater surface area is has and a greater removal efficiency it can achieve.
The inorganic media layer provides a strong and inert base that supports the organic layer and helps
to resist degradation resulting from acidic metabolic processes [30]. Due to its high removal efficiency
and resistance to degradation, the biofilter is designed such that the majority of the hydrogen sulfide
is removed in this layer. The main disadvantage of inorganic layer is its high costs in comparison to
synthetic or organic media. Additionally, the inorganic layer requires additional maintenance at startup because nutrients must be added to allow for microbial activity.
Organic Layer
The organic layer acts as a polisher, removing any additional odorous species that may be in the air.
Its organic nature and carbon content allows for a microbial activity and wider range of contaminant
removal. However, organic material is subject to degradation due to low pH. This degradation causes
compaction, resulting in high pressure drops and eventual clogging of the biofilter. When this
happens, the media needs to be completely replaced. If the air is initially treated through an inorganic
layer, any acid produced will not cause acidic degradation in the organic layer above, rather the acid
will be washed out to the bottom of the biofilter [30].
7.2 MOISTURE CONTROL
Moisture control is a critical component of biofiltration design and dictates the effectiveness of
pollutant removal. An insufficient moisture level limits or halts microbial growth and the rate of
decomposition. Excessive moisture, on the other hand, reduces the potential for mass transfer,
increases media pore clogging, increases pressure drop, reduces the space available for pollutant
transfer, and induces damage to the structure of the media bed. The required moisture content
fluctuates with the temperature of the influent air, the contaminant load in the air, and the
surrounding environmental conditions. Moisture is controlled using humidification of air prior to
entry, additional irrigation in and above the filter, periodically tilling the bed, and limiting the bed
height.
The optimal moisture content is determined by the physical properties of both the media and the
pollutant targeted for removal. Media that is more compact reduces the potential for moisture
retention in comparison to more porous media. Woodchips have the porosity necessary for proper
drainage, thus reducing the risk of overwatering and excessive saturation [31].
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The distribution of air must be considered in conjunction with the moisture content. Biofilters must
be designed to optimize even moisture distribution with adequate free air space. Methods must be
employed to avoid the “spiral effect”; air flows easier through drier areas, causing some areas of the
filter to become excessively dry while others become oversaturated [32]. Channeling of the media
bed occurs when pathways of high air flow develop through the media and reduce the moisture
content along the path. This is of particular concern at the inlet of the filter where the air stream
enters the filter, however these effects can be avoided with proper irrigation and air humidification.
The moisture content of the media must be evenly distributed, which requires periodic monitoring
at specific points throughout the media bed. Although essential, the moisture content can fluctuate
from the optimal amount as much as 30 L water/m3 media without any substantial harm to
performance [31].
Humidification Chamber
Humidifying the influent air is essential for biofiltration operation. The humidification process acts
to regulate temperature in the filter, to stabilize the unsteady influent air stream, remove particulates,
and prevent excessive drying of the media [33]. The humidification chamber must raise the moisture
content of the air to greater than 95%.
Humidification can be accomplished with a variety of methods including steam injection, spray
chambers, venuri scrubbers, and packed bed towers. Of these methods, packed bed towers are
particularly good for large biofilters with an airflow rate of greater than 5000cfm [34], however a
simple and inexpensive spray chamber can sufficiently saturate the incoming air [32, 33].
Irrigation
In addition to saturating the incoming air, an irrigation system is required to maintain an adequate
moisture content throughout the media bed.
Overhead sprinkler systems are commonly used for irrigation. The recommended water droplet size
should be less than 0.04 in (1mm) and the hydraulic loading rate lower than 1in/hr to reduce the risk
of structural damage to the media [35, 36, 37]. A high pressured misting system can be used to
encourage even water distribution. In general, the water application should be anywhere from 5 to
10 gallons per 100,000 cubic feet of off-gas [38]. The sprinkler system can be designed as multiple
zones that can be individually controlled so that irrigation is applied to various parts of the filter as
needed.
Additional drip irrigation installed at multiple levels and/or between layers of media can be used to
accommodate greater media bed depths. Irrigation hoses should be well perforated to encourage
even water distribution.
Control Options
To ensure adequate moisture content, it is advised that analysis of moisture content be performed
weekly [37]. Monitoring can be done with manual sampling or with an automated system.
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ALTERNATIVE DESIGN CONSIDERATIONS
Manual control requires sampling throughout the bed at a recommended distance of every 7000ft3
(200m3) of media [31] and at least 1 foot below the bed surface [37]. The moisture content should be
approximately 60% (by weight). Manual is recommended when the off-gas does not rapidly dry out
the media and when additional water is not needed for extended periods of time.
Fully automated monitoring can be accomplished using electric conductivity or capacity measuring
devices. This approach performs spot measurements throughout the media bed or uses load cells to
measure the moisture content by weighing all or portions of the media [31]. The weight will fluctuate
with water evaporation or irrigation application, thus the automated system is programmed to turn
on or turn off the irrigation system as needed. Programmable logic controllers (PLC) are commonly
installed in biofilter units to measure the moisture content, as well as a variety of other parameters.
Time domain reflectometry (TDR) devices can also be used in automated irrigation systems. The TDR
device measures the propagation speed of an electromagnetic pulse sent through the media bed to
determine the volumetric water content in the filter. TDR technology is advantageous because it can
read the distribution of water throughout the media bed, thus indicating the location where water is
needed most [33].
Automated sensor systems for moisture control run the risk of malfunction and misreading or
recalibration, therefore manual operator monitoring is typically advised to confirm moisture
requirements are being met. Consequently, semi-automated moisture control systems are commonly
used in biofiltration operation. The irrigation system in this form of control operates based on a timer
determined by the design. Manual or automatic moisture monitoring is performed periodically to
determine whether adjustments need to be made to the timer. If multiple irrigation zones are used in
the overhead sprinkler system, each zone can be set for a specific number of minutes and time of day
as needed.
As the filter media is installed into the biofilter structure, the material is recommended to be
thoroughly saturated so that the moisture content is adequate at startup and to ensure that fine
particles adhere to larger and more coarse particles [37]. Woodchip have a water holding capacity of
about 60 to 70% and the moisture content of the media bed should not fall below 60%.
7.3 AIR DISTRIBUTION
Overview
Proper air distribution throughout the system is important so that the entire media bed is used evenly
to remove contaminants. The distribution of air throughout the media can impact the biokinetics and
biofilm at different sections of the media bed. With different areas of the media bed providing
different levels of treatment, the system can become operationally difficult to maintain depending on
the varying requirements of nutrient or moisture of the various locations in the media bed.
Improved mixing and distribution of gaseous contaminants in biofilters can be achieved using a
packing media with a wide range of particles sizes and a high surface roughness rather than a smooth
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ALTERNATIVE DESIGN CONSIDERATIONS
material with uniform particle diameter. The inactive volume in the biofilter decreases with increased
gas flow velocity. This means that the most effective utilization of the biofilter volume is achieved
with higher gas flows. However, using a media with a wider particle size distribution along with a
high gas flow rate can increase the pressure drop across the bed and the operation costs. Optimal
operation conditions will hinge on the relationship between the pressure drop, particle size
distribution, and gas flow in the biofilter [39].
Air Flow
Modeling air distribution through the medium assumes it is homogenous, meaning it does not include
a horizontal component to the flow. Flow through porous media moves because of the pressure
difference across the media and is governed by Darcy’s law [40]. In biofilter operation, there is a single
Darcy region that is bound by two Navier-Stokes (NS) regions where the air flow is a result of the
pressure gradient, viscous forces, and inertial forces. Most of the air flow through the bed is strictly
caused by the pressure gradient and inertial forces are negligible [41].
Gas transport takes place in the mobile pore space of the media which is a function of total gas-filled
porosity, media pore size distribution, pore connectivity, and water content. Knowing the mobile pore
space is important to assess the fraction of the media that is participating in removing compounds
from the gas stream passing through the filter. Gas advective flow involves the transfer of gases
between mobile and immobile gas-filled pores via molecular gas diffusion. As the gas flow rate
increases, the gas is forced to flow also through the smaller pores thereby increasing the mobile gasfilled porosity [39].
Gas dispersivity increases as the particle size range increases. Greater dispersion results in increased
air distribution and increased mass transfer from the gas phase to the particles surface. This happens
because mass transport is directly proportional to the dispersion coefficient and the stagnant gas
boundary layer near the particle surfaces are thinner at higher mixing rates [39].
Loading Rate
Biofilter performance expressed as removal efficiency is evaluated as a function of sulfur loading
rates or residence times, as shown in Figure 13. The gas-loading rate is based on the mass of the
influent H2 S per volume of bed. At low influent H2 S concentrations of 20 ppmv, the removal efficiency
drops significantly more when the loading rate is increased [25].
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ALTERNATIVE DESIGN CONSIDERATIONS
Figure 13.Removal Efficiency as a function of Sulfur Loading Rates [25]
Air loading rates can be specified in many ways including ft 3 ⁄hr⁄ft 2 biofilter surface as well
as ft 3 air⁄hr⁄ft 2 biofilter. The EBRT requirements for a biofilter system generally fall within the
following categories: [25]



High Rate, Organic-based biofilter
o Design detention time is 15-45 seconds
o Surface loading rates typically 5-15 cfm⁄ft 2
o Requires detailed air distribution and moisture control
Lower Rate, Organic-based biofilter
o Design detention time is 45-60 seconds
o Surface loading rates typically 3-5 cfm⁄ft 2
o Usually open vessel designs
Soil-based media systems
o Design detention time is 60-120 seconds
o Surface loading rate of 1-3 cfm⁄ft 2
Pressure Loss
Energy consumption of a biofilter comes primarily from the electricity requirements needed to
operate the blower. The pressure drop across the bed is influenced by the superficial gas velocity,
packing medium, bed moisture content, and biomass growth. Controlling the pressure drop over the
biofilter bed will determine the filtration efficiency because the fluid flows through the system due to
a pressure differential across the bed. Additionally, the pressure drop across the media is a function
of airflow characteristics (flow rate, air density and viscosity) and the properties of the packing
medium (particle size, fractional void volume and porosity) [42].
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ALTERNATIVE DESIGN CONSIDERATIONS
Many models have been developed to characterize the relationship between pressure drop and
airflow velocity in a fixed packed column. At low velocities the viscous forces account for the pressure
drop, but kinetic effects become more important with higher velocities [40]. The constraints in
applying a theoretical flow model include the characterization of the geometry of the pore network,
the irregularity of the pore walls that creates fluid converging and diverging, and the interconnected
pore system being designated as a bundle of cylindrical tubes. Assumptions related to the shape and
geometry of the pore system is necessary to obtain analytical and numerical solutions.
The Ergun Equation relates pressure drop to gas flow in packed bed reactor. The equation shows that
there is a ratio of pressure drop to superficial velocity as a linear function of mass flow rate [43]. It
assumes that the total energy losses in a fixed bed are the sum of the viscous and kinetic energy losses.
The Modified-Ergun (M-E) equation was used to model the flow through the proposed biofilter where
the constants A and B are 150 and 1.75, respectively, as shown in the equation below. [44]
∆P =
AμL (1 − ε)2
BρL 1 − ε 2
υ𝑠 +
υ
2
3
ε
Dp ε 3 𝑠
Dp
𝜇
𝐿
𝐷𝑝
𝜀
𝜌
υ𝑠
Fluid viscosity
Depth of Bed
Particle diameter
Void Space of the bed
Density of the fluid
Superficial Velocity
Channeling and Clogging
Optimization of biofilter design requires an understanding of the mechanisms of biofilter clogging.
Biofilters are successful because the microorganisms use the contaminants in the air stream as a
substrate. Though warm temperatures and high moisture content is desired for biomass growth, it
must be controlled for each biofilter design. This is because rapid biomass formation can result in
clogging and channelization of flow through the media bed. Channelization is when the air passes
through the media bed without adequate contact time with the biofilm. Excess biomass can be
removed from the media surface by washing, chemical dissolution, or mechanical removal, but these
processes require additional operation and maintenance costs. Typically, the media is manually
removed and replaced.
Initially, biofilters operate as plug flow reactors, meaning the concentration of the contaminant
declines as the air continues to pass through the biofilter. Long-term operation of a biofilter results
in a limited network of smaller pores as biofilm continues to grow on the media’s inner surfaces. As
small pores are filled with biomass they isolate other connecting pores in the media from air flow so
that neither of the pores can contribute to air distribution or treatment. The remaining open pores
have a reduced surface area causing the pollutant removal efficiency to decrease while flow resistance
and pressure drop increase. Modeling the biomass growth is important to estimate the overall head
loss across the bed over time while predicting the effects of the changing surface area and biofilm
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ALTERNATIVE DESIGN CONSIDERATIONS
thickness on the biofilter treatment efficiency [45]. Biofilm thickness is determined as a function of
time from growth equations and clogging is determined as a function of biofilm thickness. The
changes in biomass growth and the resulting clogging can be determined with a pilot scale biofilter.
Clogging is most likely to occur first at the inlet of the biofilter where higher biomass densities are
formed. When the pore space of the media that allows for gas dispersion is limited, channelization
can occur through the media as shown in Figure 14.
Figure 14. Schematic of biofilm accumulation and Flow Channelization [45]
Additionally, anaerobic areas can form which will themselves produce foul odors. As channels in the
biofilter bed narrow as clogged regions expand, velocities through the open pores increase. The
higher velocities in these areas suppresses biofilm growth. After the air flows past the plugged
portions of the media, the air slowly spreads and connects the channels re-creating a plug flow regime.
The concentrations of biomass are highest in the surface layers of the biofilm and lower in deeper
layers. The amount of clogging occurring on the top layer is important because it causes head loss.
Biofilter models often assume that each layer in the biofilter will clog uniformly and that the upper
layer will clog simultaneously throughout. In reality, portions of the top layer will clog immediately
and channels will remain open and cause a gradual increase in headloss [45].
Effects of Configuration on Air Flow
In an actual system there is always a finite amount of variation in pressure in the x-direction and its
significance depends on the permeability of the medium. With higher permeable media,
heterogeneous flow (involving a horizontal component) is more likely to occur. Additional design
parameters must be considered to minimize this flow pattern with the most important being the
location of the inlet and outlet. There are a variety of locations for the inlet and outlet of a biofilter as
listed below and shown in Figure 15 [41].
●
●
●
●
●
Design 1 - the air enters the at the top left and exits the reactor at the bottom center
Design 2 - air enters the top center and exits at the bottom center
Design 3 - the air enters the top center and exits on the side wall below the medium
Design 4 - the air enters through the side wall above the medium and exits on the opposite
wall below the medium
Design 5 - air enters and exits on the same side wall
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ALTERNATIVE DESIGN CONSIDERATIONS
Figure 15. Biofilter Inlet and Outlet Locations
Most H2 S removal occurs in the part of the bed that is nearest the influent. At the Cedar Rapids Water
Pollution Control Facilities (WPCF), nearly 85% of H2 S is removed within the first 12 in (30cm) of the
bed nearest the influent and over 97% removal occurs within the first 18 in (46cm) of media depth.
Figure 16 shows the H2 S concentration profile through the depth of the lava rock bed at Cedar Rapids
WPCF.
Figure 16. Hydrogen Sulfide Concentration as a function of the Distance from the Inlet [25]
The location of the inlet to the biofilter impacts the areas of the bed that have high contaminant
removals as indicated by the graph above. The optimum biofilter design depends on the permeability
of the medium, the operational flow rate, and the design configuration of the air supply and air
discharging piping. With high velocities, the ideal system would include diffusers at the inlet and
outlet to evenly distribute the air and reduce the effects of flow heterogeneity. Multiple inlets and
outlets may also help to reduce the effects of flow heterogeneity [41].
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ALTERNATIVE DESIGN CONSIDERATIONS
7.4 DUCTWORK & EQUIPMENT
To overcome the back pressure caused by the filter bed, radial blowers are typical in a biofiltration
design. Vents for the off-gas are also commonly used to direct the air to the bottom of the filter bed
using distribution canals and air nozzles.
Common accessories included in a biofilter system are listed below [15]:





Pressure relief vacuum at the reactor cover
Foam separator tank to eliminate solid particles in the biogas
Sediment or water trap to eliminate high moisture content of biogas
Biogas flow metering device
Automated or manual back pressure regulator
System Design
Certain design parameters must be considered when sizing the ductwork for the biofilter. The biogas
flow rate is of primary concern when sizing the pipes and must be considered for minimum, average,
and maximum flow conditions. The necessary velocity of the gas must also be considered, which will
affect the configuration of pipe bends and the maximum allowable length of the pipe. Important
information that is needed to analyze a duct system for flow, pressures, and pipe sizes includes: [15]





Supply/Extract air quantities
Routing of the ductwork from fan to terminal
Sizing method and velocity limits
Ductwork dimensional criteria
Static and total pressure limit of the fan
The static pressure (Ps ) of a system is either positive or negative depending on whether or not the
pressure exerted by the air on the system is greater or less than the ambient atmospheric pressure.
The velocity pressure (Pv ) acts in the same direction as the air flow and is a measure of the kinetic
energy in the system. The total pressure (Pt ) in the system is the sum of the static pressure and the
velocity pressure. The pressure loss includes the duct frictional loss and the dynamic losses caused
by flow restrictions due to equipment in the system. The friction loss due to frictional drag of the air
moving along the surface of the duct can be calculated using the Darcy-Weisbach equation and the
friction factor. The dynamic losses due to fittings such as junctions, transitions, or elbows can be
calculated as an equivalent length of pipe for the system. This can be calculated by multiplying the
velocity head by friction loss coefficient for each piece of equipment [46]. The head loss calculated in
the system is used to properly size the fan.
Condensate drainage must be provided in the duct system because any excess water can cause
mechanical issues with the operation of the biofilter. Usually the excess condensate is discharge
through an indirect drain line path. Condensate drains can be incorporate throughout the piping
along with overflow drains. Additionally, fans are designed to have a drain pan that has a trap that
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ALTERNATIVE DESIGN CONSIDERATIONS
collects the condensate but prevents air from passing the indirect piping. The trap is sized based on
the negative or positive pressure of the fan. Typically, the trap is sized at 1.5 times the inlet or outlet
pressure of the fan, whichever is greater [47].
Sizing the Blower
Gas-moving machinery includes mechanical equipment that compresses and moves gas. Fans are
used for low pressures, blowers for intermediate pressures, and compressors for high pressures. Fans
are best for moving small volumes of gas at low pressures with discharge heads of about 3.9 to 59
inches of H2O (0.1 to 1.5 m H2O). In a centrifugal fan, a centrifugal force produced by the rotor causes
a compression of the gas which is called the static pressure head. Additionally, a velocity head is
produced because the velocity of the gas is increased. The increase in static pressure head and
velocity head are incorporated in the efficiency and power of the centrifugal fan which usually ranges
between 40-70%. When calculating the power of a fan, the gas is assumed to be incompressible. The
operating pressure or ‘duty point’ of the fan is the sum of the velocity head and static pressure of the
gas leaving the fan and is usually given in inches of water gage [48].
Fan selection requires knowledge of both design airflow rate and the pressure drop in the system.
The fan is required to have the ability to draw air from the sources and push it through the media bed.
Using the manufacturers supplied information, the fan can be selected [49].
The CWP uses a Backward Curve Centrifugal Fan manufactured by Hartzell Air Movement for the odor
control unit at the primary clarifiers which will be recycled and used for the biofilter in order to
reduce cost of equipment. Using the Hartzell-Flow calculator [50], the fan performance curves were
generated providing data of flow rate, static pressure, and power as shown in Figure 17.
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ALTERNATIVE DESIGN CONSIDERATIONS
Figure 17. Hartzell Performance Curve for Backward Centrifugal Fan [50]
The static pressure curve provides the basis for all flow and pressure calculations and can be used to
determine the fan’s pressure capability at any volume. The “duty point” or point of operation is the
intersection of the curves. The performance for the CWP’s fan is 12,000 CFM and 7.5” SP at 18.5 HP.
A fan must operate somewhere along its SP curve and if the fan speed is changed, the point of
operation must move up or down the system curve and SP curve. To obtain the performance of the
fan at lower speeds, the following fan laws can be used [51]:
1. CFM varies as RPM
2. SP varies as (RPM)2
3. HP varies as (RPM)3
An accurate HP rating is necessary to properly size the motor or to determine the operating efficiency
of the fan. If the system does not operate properly upon start-up, measurements can be taken and
compared against the available performance curve.
In order for a fan to achieve its rated performance, the airflow at the inlet must be fully developed,
symmetrical and free from swirl. The ducting on the outlet needs to be designed such that the
asymmetrical flow profile from the fan is allows to diffuse and approach fully developed flow as
shown in Figure 18. The effect on the fan performance when these conditions are not met is called
the System Effect [52].
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ALTERNATIVE DESIGN CONSIDERATIONS
Figure 18. Air Flow Profile in 100% Effective Duct Length [52]
The efficiency of the system is a combination of the efficiency of the components (fan, transmission,
motor, control system, system effect, and catalog fan efficiency). Overall fan efficiency is the primary
efficiency to consider when evaluating energy consumption rather than any single component. It is
critical to consider the effect of the system on the fan when attempting to reduce fan energy
consumption.
If a safety factor is included in the fan selection, it means that the fan will not operate at its best
efficiency point, but instead will operate at a point below. Operating below the efficiency point can
generate more noise and can be unstable. This could potentially be a problem for the CWP as the
biofilter does not require the fan to operate at its duty point [52].
If more than one fan is required to supply air to a biofilter, fan shutters may be needed to prevent
back drafting through the fans that are not running. Another option is to use only one fan to supply
each isolate biofilter unit. Dust accumulation on fans, guards, and shutters can significantly reduce
the fan performance. Therefore, duct design must provide access for fan maintenance and inspection.
Additionally, fans and motors should be able to operate in a corrosive environment [49].
7.5 CONFIGURATION
Space availability is a determining factor for the configuration of the biofilter. The bed can be open
with a single-bed, enclosed with multiple beds, a roof-top installation, etc. The filter volume is
designed around the removal efficiency, which depends on the rate and concentration of air
contaminant loading as well as the degradation rate of the media. It is important for designs regarding
cold weather environments to have a lid to shield from temperature changes as well as sunlight.
Flow Direction
Air may be directed through the biofilter either by up-flow or down-flow. In most enclosed biofilters,
down-flow is more advantageous because it improves moisture control in the bed. Because the
entrance point for the air experiences the greatest amount of drying in the filter, some suggest
downward airflow may be advantageous because irrigation can easily be applied at the top of the
filter. Additionally, concurrent air and water flow assists drainage [33, 53]. However, for contaminated
air containing acidifying compounds (such as reduced sulfur) it is recommended that upward airflow
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ALTERNATIVE DESIGN CONSIDERATIONS
is used so that the acidic products can be separated and flushed out from the effluent air using proper
drainage [31].
Compartments
Although biofilters can be designed with one bed chamber, it is beneficial to design two beds in order
to provide redundancy and operational flexibility [25]. The biofilters can be used in parallel which
allows for a bed to be isolated for maintenance without interrupting flow through the other bed.
Having an additional biofilter also provides the opportunity for expansion. Alternatively, the biofilters
can be constructed in series to treat different target pollutants in a single airstream, known as a twostage biofilter. This method is successful when more than one contaminant is being targeted for
removal (i.e. hydrogen sulfide and additional VOCs). Biofilters may also be designed with cycle
switching capabilities using two beds. This configuration designs two beds in series with the ability
to switch flow direction. This cycle switching operation allows for a greater biomass concentration
throughout the entire bed depth in both of the biofilters and helps to prevent clogging from excessive
biomass growth at the location of the influent stream. Additionally, this configuration continually
feeds a high contaminant concentration into both biofilters, which helps to prevent loading shock to
the microbial population [25].
Materials
The external design of the biofilter typically involves a steel or concrete structure designed to
accommodate environmental changes in the particular area. This involves insulation of the floor,
walls, and lid. The external structure must also be designed so the interior of the biofilter is easily
accessible [54].
The corrosive nature of hydrogen sulfide must be considered when selecting materials for the interior
of the biofilter. The storage space containing the packing media can be constructed or lined with a
non-corrosive material such as canvas, polyester cloth, or PVC-coated fabric [54]. Ideally, these
materials would be flexible and airtight as well. The material selected for the internal structure must
be based on characteristics of the unpurified gas.
Cover and Insulation
Biofilters can be constructed as open or covered bed systems. An open, single-bed system would be
constructed by excavating a hole approximately one meter deep that would be filled with sand or
compost that the contaminated air would filter through. [19] Today, biofilters are typically designed
as closed systems because they allow for more precision in controlling the biofilter operation and
provide a set footprint area for loading of the contaminant. Closed systems are easily engineered to
remain in compliance with odor regulations and can be more easily monitored than in-ground
systems.
The biofilter cover, air feed ducts, and rinse water feed pipes should be well insulated in cooler
climates [25]. The bed portion of the biofilter can be insulated by constructing it underground, by
adding an earth embankment, or by designing the walls with highly insulated material. The biofilter’s
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ALTERNATIVE DESIGN CONSIDERATIONS
performance is largely dependent on the temperature of the bed. In order to maintain the design
temperature in the biofilter the cover, air feed ducts, and rinse water feed pipes should all be insulated.
The bed portion of the biofilter will be located below ground and insulation can be added to reduce
heat loss in the system. Increasing the bed temperature can also be achieved by heating the feed air
or the rinse water.
Condensation
Condensation may occur as a result of adjusting the gas stream pressure while maintaining a constant
temperature. Gas stream pressure is typically adjusted in order to treat effluent streams consisting of
a condensable pollutant vapor and a non-condensable gas. Two types of condensers typically used
involve either surface or direct contact. Surface condensers can be shell and tube heat exchangers
where the coolant flows inside the tubes while the gas stream containing the pollutants flows around
the exterior of the tubes. Contact condensers operate by spraying a liquid directly into a gas stream,
which cools and condenses the pollutants [15].
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ALTERNATIVE DESIGN CALCULATIONS & RESULTS
8 Alternative Design Calculations & Results
8.1 MEDIA SELECTION
Based on client preference, natural media was selected for the proposed design largely due to the
addition cost and uncertainty of manufacturer availability associated with synthetic media. The team
performed due diligence and considered synthetic media in comparison to natural media (refer to
Appendix G).
A decision matrix based on research was used for the selection of the natural media type, both for the
organic and inorganic layer (refer to Table 3 and Table 4). The parameters considered in the decision
matrices were porosity, surface area, moisture content, retention time, and pH resistance. All
categories were weighted equally. The availability of the media was factored into the selection of the
media types used in the matrix, limiting the candidates to relatively common and easily-accessible
materials.
Media Selection Criteria
Media characteristics considered when evaluating suitable packing materials include porosity and
void fraction, media surface area, optimal moisture content, retention time, and pH and buffering
capacity.
Porosity and Void Fraction
The porosity and void fraction affects the development of microorganisms, gas flow distribution, and
clogging of the bed. A high porosity minimizes the pressure drop across the biofilter, reduces the head
loss, and increases the distribution of incoming waste gas. Additionally, a void volume between 40%
and 80% is desired because it keeps the operating pressure drop low and ensures easy gas flow.
Active Surface Area
Smaller particles provide a greater total surface area, which increases the external transfer rate of
pollutants, nutrients, and oxygen, and thus improves removal efficiency. The accumulation of
microorganisms is optimal in the presence of pores with sizes ranging between 1 to 10 micrometers.
Water Retention Capabilities
The media’s water-retention capabilities affects the water content of the media bed as a whole and
the microorganisms’ ability to carry out normal metabolic activities. Optimal water levels vary with
different filter media and are dependent on the media’s porosity, void fraction, and active surface area.
Low water content can cause the bed to dry with the development of fissures which result in
channeling and “short circuiting” of the media bed. Depriving the microorganisms of water can cause
a reduction in biodegradation. High water-holding capacity limits drainage from the bed and can
cause acid metabolites to accumulate on the packing material. Too much water inhibits the transfer
of oxygen to the biofilm creating anaerobic zones limiting the reaction rate. High water-holding
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ALTERNATIVE DESIGN CALCULATIONS & RESULTS
capacity is an advantage for the bacterial growth but often leads to void fraction reduction and bed
settlement. This results in an increased pressure drop across the bed, an increased residence time,
and preferential flow paths. The media’s water retention capabilities must be known because the
moisture control and monitoring is a critical aspect of the design and O&M.
pH-Level and Buffering Capacity
Microorganisms used in biofiltration are sensitive to pH changes, therefore the buffering capacity of
a media is important to neutralize the acidic byproducts of H2S oxidation and to help reduce the risk
of corrosion inside the filter chamber. Bacterial growth typically thrives at a neutral pH (a value
around 7). To increase the buffering capacity of a media and maintain a neutral pH, most suppliers of
biofilters add alkaline buffers, usually calcium carbonate or lime, to the filter material. A low pH can
cause acidic degradation of the media, specifically the organic layer, which decreases the lifetime of
the bed.
Compaction Resistance
With organic media, degradation and the subsequent compaction is a large issue and result in large
pressure drops over time as the media settles. This results in higher energy costs and the eventual
need to replace the filter as the biofilter becomes clogged. Therefore, compaction resistance was
considered when choosing the media for the organic layer.
Inorganic Layer Decision
Two commonly used and effective inorganic media types are lava rock and schist (a medium-grade
metamorphic rick), which were considered for the base layer in the biofilter bed. The media types
were ranked 1 and 2 for the inorganic layer, with 2 being advantageous. The results are shown in the
decision matrix below.
Table 3. Decision Matrix for the Inorganic Media Layer.
Media: Base
Layer
Porosity
Surface
Area
Schist
1
1
Volcanic
Rock
2
2
Optimal
Moisture
Content
2
2
Retention
time
pH
resistance
Total
1
1
6
2
2
10
As shown in Table 3, lava rock proved superior and is recommended for the proposed design. Lava
rock is porous with a high surface-area that will be effective in supporting biofilm growth and
allowing air flow, while providing structural support in the bed [30]. Lava rock was ranked higher
than schist in every category except moisture content. However, much of the moisture requirements
can be satisfied by the organic layer thus both inorganic media types received an equal score.
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ALTERNATIVE DESIGN CALCULATIONS & RESULTS
Research indicated that lava rock was an effective inorganic media which is supported by the success
of lava rock-based biofilters in operation in the West Michigan region (refer to Appendix H).
Organic Layer Decision
The organic media types evaluated for the CWP biofilter included mulch, woodchips, peat, soil and
compost. The ranking varied between 1 and 5, with higher values being advantageous. The decision
matrix is shown below in Table 4.
Table 4. Decision Matrix for the Organic Media Layer
Media:
Base Layer
Porosity
Surface
Area
Mulch
Woodchips
Peat
Soil
Compost
4
5
3
1
2
2
1
3
5
4
Optimal
Moisture
Content
4
5
3
1
2
Retention
time
pH
resistance
Compaction
Resistance
Total
5
2
5
3
1
2
4
5
1
3
4
5
3
1
2
21
22
22
12
14
Soil and compost had the lowest ranking and therefore are not recommended for use in the prosed
design. It is difficult to maintain a desired moisture content in soil and its capacity to remove odorous
contaminants drops quickly after becoming saturated [55]. Both soil and compost have a very low
porosity and resistance to compaction, resulting in more frequent replacements. Compost decays
over time more rapidly than its alternatives, which causes compaction, clogging, and head loss across
the bed, greatly limiting its lifespan [30]. Although compost is nutrient-rich, low-cost, and very
effective at contaminant adsorption, its overall ranking was much lower than competing alternatives
[30].
Woodchips, peat, and mulch have relatively large surface areas and are more resistant to compaction,
indicating these materials can effectively remove contaminants while retaining the media’s structural
integrity for a longer period of time. Mulch tends to have low porosity which causes higher airflow
resistance [56]. Peat and woodchips ranked equally because both have a good porosity, adsorption
capacity, and ability to support biofilm formation [55]. Although woodchips have a low surface area,
this characteristic provides a higher resistance to compaction and a longer lifetime. Additionally,
woodchips are more commonly used in industry, thus performance data is more widely available. The
availability of data was important for the proposed design so that sizing and pressure drop
calculations could be performed. Based on the matrix criteria, woodchips were selected as the organic
layer for the proposed system.
It is recommended the woodchips be supplied from manufacturer whose product is engineered to
have optimal properties with impurities and fine particles removed.
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ALTERNATIVE DESIGN CALCULATIONS & RESULTS
8.2 SIZING THE BIOFILTER
Optimizing the size of the biofilter includes changing the bed height to meet contact surface area
requirements, which are dependent on the selected media. The size of the biofilter depends on
achieving an adequate EBRT that ensures contaminant removal. As the bed height increases, the
pressure drop across the media will increase as well, resulting in higher electrical costs and a greater
potential for gas channeling through the media.
Other designed components of the biofilter are contingent on the size of the system. The volume and
dimensions of the biofilter determine the pressure drop, the size of the humidification, and the
amount of irrigation required. There are multiple ways to determine the size of a biofilter, but several
methods were screened from further consideration due to constraints in literature availability and
limitations in the ability to perform experimental research. The methods selected for comparison
were the rate law determination, EBRT optimization, elimination capacity, removal efficiency, and
mass transfer. Calculations for each model can be found in Appendix I and the final results are
presented in Table 5.
Table 5. Calculated Biofilter Volumes Using Various Models
Model
Volume Calculated (ft3)
EBRT Optimization
24,000
Elimination Capacity
750
Removal Efficiency
707
Mass Transfer
0.031
Media Depth
The height of the biofilter can be determined based on the estimated pressure drop. It was advised
by Marc Deshusses, a professor at Duke University, that the biofilter height should not exceed 5 feet
(1.5 meters). Wanting to conserve space in the aeration basin, it was decided that the pressure drop
calculations (section 8.3.4) were appropriate with the bed depth at a maximum height of 5 feet.
Case Studies
Based on calculations using various methodologies (calculations are presented in Appendix I), it was
determined that the size of the biofilter can range between 700 and 24,000 ft3. This is a large range
of volumes and does not provide much guidance as to choosing a sufficient size for complete removal
of hydrogen sulfide. As a result, to obtain a benchmark for the size of our biofilter, the proposed design
was compared to a biofilter case with a similar inlet concentration. The biofilter used for comparison
is located in Jefferson County, Alabama, and was installed by Biorem Technologies in 2002. The
information for the Biorem biofilter is shown below in Table 6.
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ALTERNATIVE DESIGN CALCULATIONS & RESULTS
Table 6. Parameters for a Biofilter Built in Jefferson County, Alabama by Biorem Technologies [5]
Flow rate capacity
51,000 cfm
Maximum hydrogen sulfide composition
25
ppmv
Average hydrogen sulfide composition
5
ppmv
Number of biofilters
6
each
Media volume
1,519
ft3
EBRT
20
sec
Height
8
ft
Length
39
ft
Width
8
ft
Media Depth
5
ft
The similarities in hydrogen sulfide concentration and the amount of air the Jefferson County
Biofilters treat indicates that the proposed biofilter for this project should be designed to be about
half of the size of the Jefferson County biofilters, thus the proposed system has a volume of 900 ft3.
Using an air flow rate of 2,000 cfm, the empty bed residence time is 46 seconds and the superficial
air velocity is 10 ft/s. Both are in the range of the desired operation for an industrial biofilter. However,
in keeping with the design of the biofilter cases that have been studied, the medium volume was
doubled in order to have two biofilters operating in parallel. The proposed configuration will both
lengthen the life of the media by reducing the load on a single biofilter, as well as allow for sufficient
operation in case maintenance needs to be performed on one of the biofilters. This volume will be
divided into 40% lava rock and 60% woodchips, according to our calculations in Appendix I.
Media Volume
A summary of the biofilter media dimensions are shown in Table 7. These characteristics can be
confirmed through pilot testing.
Table 7. Summary of the Biofilter Media Dimensions
Number of biofilters
2
each
Media Length per biofilter
14
ft
Media Width
12.7
ft
Media Height
5
ft
Media Area
178.5 Ft2
Media Volume
900
ft3
Volume lava rock needed
710
ft3
Volume woodchips needed
1,075 ft3
Total Media Volume required 1,800 ft3
8.3 SYSTEM RECOMMENDATIONS
Configuration
The proposed CWP biofilter will be located in the corner of an on-site empty aeration basin. The
benefit to retrofitting the aeration basin include a reduction in material and construction needs along
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ALTERNATIVE DESIGN CALCULATIONS & RESULTS
with the access to the existing pipe gallery and drainage. The biofilter will consist of two units (each
14’ x 12’-8” x 15’) that will operate in parallel with an up-flow air direction. The preliminary design
of the irrigation and humidification chamber for each unit is specified in Section 9.2 of this report and
design site plans (Appendix J).
Empty Bed Residence Time
The Cedar Rapids WPCFs recorded that the minimum residence time required to achieve a treatment
objective of 0.5 ppmv depends on the influent concentration. The effect is dramatic at an influent
concentration below 100 ppmv and at lower temperatures. This plot indicates that a facility with an
existing biofilter can accept higher influent concentrations (which would require a higher minimum
residence time) or an increase in flow rate which results in a decreased residence time [57].
Figure 19. Required EBRT to Remove Various Concentrations of H2S [25]
Because the maximum concentration of H2S emitted from either the splitter box or clarifiers is less
than 25 ppmv, the EBRT will be at a minimum of approximately 6 seconds. If additional waste air
streams are treated through the biofilter, additional hydrogen sulfide concentrations can be removed
with an increased EBRT.
Media Particle Size
Given the air properties and biofilter dimensions, the pressure drop across the bed and media layers
were calculated. The recommended size of lava rock for the CWP is 1 in (24mm) in order to provide
uniform airflow throughout the bed with adequate treatment. As shown in Figure 20, smaller packing
material achieves better H2S removal at low residence times.
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ALTERNATIVE DESIGN CALCULATIONS & RESULTS
Figure 20. The Removal Capabilities of various Diameters of Lava Rock [25]
Smaller particles increase the surface area available for gas-phase transfer to the biofilm therefore
increasing the removal of H2S. Though smaller lava rocks cause a larger pressure drop across the
biofilter bed, the pressure gradient over the layer is not prone to compression and helps to provide a
more uniform flow distribution throughout the bed over its life. The recommended size of woodchip
is one with a diameter no greater than 4 inches. The pressure drop across lava rocks and woodchips
with various diameters is shown in Appendix K.
Pressure Drop across Bed
When determining the gas flow rate, the pressure drop over the bed must be considered. Typical
pressure drops and superficial gas velocities in a biofilter are listed in Table 7 [42].
Table 8. Pressure Drop and Superficial Gas Velocity in a Biofilter [42]
Parameter
Average Maximum
Pressure Drop (in of H20)
0.08 to 0.4
4
Superficial Gas Velocities (𝐟𝐭⁄𝐬)
0.273
0.456
Using the Ergun Equation, the pressure drop across the biofilter bed was calculated using the clean
bed porosity. The lava rock modeled was 1 inch in diameter with a porosity of 0.50, and the woodchip
was 4 inches in diameter with a porosity of 0.52. In a single biofilter unit, the lava rock layer is 2 feet
deep and the woodchip layer is 3 feet deep. In order to predict the pressure drop over time as the
pores are filled with water or excess biomass growth, the porosity of the bed was decreased as
depicted in Figure 21.
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ALTERNATIVE DESIGN CALCULATIONS & RESULTS
0.35
0.30
Clean Bed Porosity
50% of Pores Filled
0.25
Pressure Drop [inH20]
75% of Pores Filled
0.20
0.15
Range of Operation
0.10
6,000 – 12,000 CFM
0.05
0.00
0.0
0.1
0.2
0.3
0.4
Superficial Velocity [ft/s]
0.5
0.6
Figure 21. Predicted Pressure Loss across the Lava Rock and Woodchip Layers
Studies have shown that the Ergun Equation produces a correlation that is a reasonable fit for
experimental data. Deviations from the trend line can occur with decreasing or increasing flow rate
which can be explained by the effect of the initial unsteady state flow where viscous forces dominate
[40]. The Cedar Rapids WPCF installed a lava rock biofilter (6 feet media depth) in 1998. By 2005, the
lava rock media had not been replaced and the pressure drop across the bed was only 0.2 to 0.5 in.
H20 [58]. Our model indicates a similar pressure drop across the proposed bed with a clean bed
porosity and as the pores are filled over time. A table of the recommended system parameters during
different phases of operation for a single biofilter unit are shown in Table 9. These will require
adjustment during operation since each biofilter runs differently.
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ALTERNATIVE DESIGN CALCULATIONS & RESULTS
Table 9. Recommended Parameters for Various Phases of the Biofilter Operation
Parameter
Avg. Bed Porosity (%)
Avg. EBRT (sec)
Bed Volume (ft3)
Flow Rate (cfm)
Loading Rate (ft/s)
Pressure Drop (in H20)
8.4 AIR DISTRIBUTION SYSTEM
Startup
Average
Operation Operation
(<1yr)
(1-5yrs)
51
18
1800
6000
0.278
0.001
26
14
1800
8000
0.370
0.016
Maximum
Operation
(>5yrs)
13
9
1800
12000
0.556
0.156
The biofilter system will be fed by a low velocity duct system where the air velocities are in the range
of 1200 to 2000 feet per minute (fpm). A low-velocity ductwork design requires larger duct sizes
which reduces friction losses and noise and vibration. Though these systems do occupy more space
and have a higher initial cost, they provide significant energy savings. The proposed system ductwork
was included reinstalling the existing centrifugal fan at the primary clarifiers odor control unit
(shown in Figure 22).
Figure 22. Existing Hartzell Centrifugal Fan
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ALTERNATIVE DESIGN CALCULATIONS & RESULTS
The static pressure is used to evaluate the amount of impact various ventilation system components
have on the airflow path. The fans create positive static pressure to move air through the system while
the components before the inlet contribute negative static pressure. The static pressure of one inch
of water is the suction needed to draw water up a straw one inch. For comparison, 1 psi is equal to
27.7 inches of static water pressure. The proposed design requires the blower to pull air from the
sources and push the stream the remaining distance to the biofilter as shown in the Site Plan. The
frictional losses from the ductwork and the dynamic losses from the fittings were measure in inches
of water gauge (in. wg) as shown in Table 10 (calculations in Appendix L).
Table 10. Pressure Loss in the Air Distribution System
Pipe Diameter (in)
Flow Rate (cfm)
Length (ft)
Velocity (fpm)
Frictional Losses (in. wg)
Dynamic Losses (in. wg)
Velocity Losses (in. wg)
Total Pressure Loss (in. wg)
Primary
Clarifiers
to Tee
18
3250
375
1783
0.52
1.21
0.20
1.73
Splitter
Box to
Tee
30
8750
250
1839
0.54
1.19
0.21
1.73
Tee to
Fan
Fan to
Biofilter
Biofilter
Internal
Biofilter
Outlet
36
12000
10
1698
0.01
0.21
0.18
0.22
36
12000
115
1698
0.09
0.30
0.18
0.39
30
12000
35
1222
0.22
0.34
0.19
0.56
42
12000
5
1247
0.00
0.10
0.10
0.10
The PVC pipe pressure ratings are approximately 120 psi which is significantly greater than the
pressure imposed on the proposed system. Cavitation of the pipe due to negative pressure will not
occur [59].
The required static pressure of the fan is the total pressure loss in the system added to the velocity
pressure at the outlet which is subtracted from the velocity pressure at the fan discharge point. The
performance for the CWP’s fan is 12,000 CFM and 7.5 inches of water SP at 18.5 HP (see performance
curve in Appendix M or Section 8.4.2). For the proposed ductwork, the required static pressure of fan
to provide a flow rate of 12,000 cfm to the biofilter is 4.8 inches of water. The Hartzell blower
proposed for the system is a suitable option for the distribution system as shown in Table 11.
Table 11. Static Pressure of Blower
Total Pressure Loss (in. wg)
Velocity Pressure at Fan Discharge (in. wg)
Velocity Pressure at Outlet (in.wg)
Static Pressure Required (in. wg)
Hartzell Blower Static Pressure (in. wg)
Page 67 of 91
4.72
0.18
0.10
4.80
7.5
ALTERNATIVE DESIGN CALCULATIONS & RESULTS
Using the fan laws, the static pressure, speed in revolutions per minute (RPM), and horse power (HP)
of the blower during different phases of operation can be calculated (see Appendix M). The
recommended blower operations are shown in Table 12.
Table 12. Blower Parameters during Phases of Operation
Parameter Start-Up Average Maximum
CFM
6000
8000
12000
RPM
878
1170
1755
SP
1.9
3.3
7.5
HP
2.5
5.9
20
As the pressure across the media bed increases, the controls and monitoring equipment will
recognize the pressure differential will increase the fan speed. This will be done using a variable
frequency drive motor.
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PROPOSED DESIGN DECISIONS
9 Proposed Design Decisions
9.1 SCOPE OF DESIGN
A complete built-in-place odor control system is recommended for the CWP to remove hydrogen
sulfide from air emitted from the primary clarifiers and the splitter box. The proposed design uses
biofiltration technology to treat the contaminated air and is to be constructed in retired aeration
basins located on site.
Based on facility data, the hydrogen sulfide concentration in the contaminated air averages at 6 ppmv
and reaches a maximum of 25 ppmv. A full chemical characterization is recommended to determine
the exact composition of the contaminated air.
The proposed biofiltration system includes the following components:







Media compartments
Unit cover
Humidification chambers
Irrigation system
Nutrient addition tank
Internal and external ductwork
Performance monitoring
The system is designed to allow for continuous operation (24 hrs/day for 365 days/yr). Two identical
biofilters each designed at full capacity are proposed to ensure continual operation when
maintenance is required.
Table 13 shows the criteria the proposed system was designed according to.
Table 13. Design Criteria for Proposed Biofiltration System
Parameter
Design Air Flow Capacity
Number of Biofilter Beds
Media Volume Per Bed
Woodchips
Lava Rock
Media Depth
Woodchips
Lava Rock
H2S Loading Rate
Average
Maximum
Removal Efficiency
Empty Bed Retention Time (range)
Design Inlet Air Relative Humidity (min)
Recorded Inlet Air Temperature (range)
Page 69 of 91
Value
12000
2
Units
scfm
each
3
2
ft
ft
535
355
6
25
99
9 to 35
10
50 to 70
ft 3
ft 3
ppmv
ppmv
%
sec
%
°F
PROPOSED DESIGN DECISIONS
9.2 INTERNAL DESIGN
Concrete Work
The proposed biofiltration system uses existing structures as a basis for design. Two walls of the filter
are retrofitted into the existing aeration basin. Construction includes two additional walls as well as
a concrete humidification chamber, which are to be cast-in-place concrete with reinforcing rebar (as
used in the existing structure). All exposed concrete must be installed with a protective epoxy coating.
The humidification chamber will be constructed as sloped grout. An air distribution plenum is
provided beneath the biofilter structure to provide an even distribution of air entering the biofilter
media. The plenum will be cast-in-place with a grout base poured with a slope of 0.042% (.5 inches
per horizontal foot). A preliminary design and layout of the system is provided, however detailed
construction plans are required prior to installation.
Cover and End Plates
The proposed biofilter is to be enclosed beneath a 4-foot fiberglass, weather-resistant cover. The
cover is domed shaped to ensure structural stability and for easy removal when maintenance is
required. The humidification chamber as well as the splitter box are to be enclosed with flat fiberglass
covers with hatch door access.
Moisture Control
Humidification Chamber
The humidification chamber was designed based on a worst case scenario with an inlet air
temperature of 95 degrees F and a relative humidity (RH) of 10%. The system was designed for an
effluent RH of 100%, which will require 0.787 gpm (178.74 kg/hr) of water (refer to Appendix N for
calculations and suggested model types).
The system will use two fine spray (hydraulic atomizing) stainless steel spray nozzles operating at
300 psi. The humidification system will be operated at a flow rate of 47 gallons per hour (gph),
although the nozzles have a flow rate capacity of 49 gph allowing for adjustable operation. Water lines
must be installed to the humidification chamber and any exposed water lines must be heat traced and
insulated. All drainage water lines will be installed underground.
Irrigation System
The irrigation system consists of an overhead sprinkler system. Based on the general rule of
biofiltration design of 5 to 10 gallons of irrigation water for every 100,000 cubic feet of air, the
irrigation system must provide 0.6 to 1.2 gpm of water. To avoid structural damage of the media bed,
the recommended hydraulic loading rate of woodchips is not to exceed 1 inch per hour, which allows
for a maximum flow rate of 1.84 gpm (to each bed) in the proposed system. The proposed overhead
sprinkler system consists of 32 stainless steel cone spray nozzles (16 for each bed) each with a flow
rate of 0.11 gpm located at a height of 3 feet above the media bed. The maximum flow rate capacity
of each nozzle is 0.14 gpm, allowing for adjustable irrigation if needed. The spray angle of each nozzle
Page 70 of 91
PROPOSED DESIGN DECISIONS
is 58℉, with a flow pressure of 20 psi. Each run of irrigation piping is equipped with an isolation valve
for operation and maintenance purposes (refer to proposed design plans, Appendix J).
System Design
The proposed biofilter is designed for upward airflow and downward irrigation so that acidic
products will be flushed from media bed.
The water source for both the humidification chamber and the irrigation system will be the facility’s
effluent water, which is available in the pipe gallery located near the proposed biofilter site. The
existing empty aeration basin structure has drainage installed that is directed to the influent wet well
of the plant, which will be used for water drainage of the biofilter.
Both the irrigation and humidification systems will be run continuously. Both lines will include flow
meters and isolation valves located in the pipe gallery for adjustable flow operation. The
humidification chamber is enclosed under a hatch cover for easy access and the irrigation system can
be accessed for maintenance by removing the dome cover of the biofilter.
Media
Installation
The lava rock media is to be installed as the base of the media bed. The wood chips should be added
in 1-foot layers on top of the lava rock layer, with each layer being raked and watered. Based on a
desired moisture content of 60%, about 5000 gallons of water must be applied to filter media during
installation to ensure adequate saturation. After media has been laid, biofilter operation should begin
within a 24 hour timeframe to avoid causing anaerobic conditions [34].
Media Compartments
The media is supported by a stainless steel grate located beneath the lava rock layer. The air flow will
be directed up through the grating and irrigation water will flow counter to air.
The system consists of complete pre-engineered enclosed concrete biofilters configured to eliminate
short-circuiting of the air stream and increase the contact between the media and the air. The
compartments are designed to have dual media layers of lava rock and wood chips. The flow from the
media compartment plenums will direct the air upward through the biofilter bed and exit the biofilter
cover through an exhaust stack.
Nutrient Addition
Biological Requirements
Thiobacillus bacteria is most commonly used in biofiltration systems to remove hydrogen sulfide. The
bacteria gains energy by degrading the H2S compound and produces sulfate or sulfuric acid as a result.
Thiobacillus is optimal for H2S removal because it requires a smaller amount of nutrients to oxidize
sulfide in comparison to other bacteria.
Page 71 of 91
PROPOSED DESIGN DECISIONS
The bacteria obtains energy from the degradation process and requires nutrients and carbon found
in organic material. The proposed design includes wood chips which will serve as a source of carbon
and mineral nutrients necessary for successful performance. However, over time nutrients deplete
from the media during operation and must be manually added to the system.
Nutrients are most commonly added through the irrigation system of the biofilter. Nutrients are
typically stored in tanks outside of the filter and pumped in using diaphragm pumps.
Nutrient Source
It is recommended that a generic commercial fertilizer mixtures such as 10/10/10 or 12/9/11
(N/P/K) be applied as needed to enhance biological growth. Because the biological life cycle in the
filter and biomass digestion internally recycle nutrients, however, nutrient levels are not strict and
can be lower than stoichiometric requirements without compromising biofilter performance [60].
The proposed design stores nutrients in a 55 gallon drum located in the pipe gallery. The tank will
feed directly into the irrigation line and will be operated as needed using a manual valve.
Because nutrient addition is not exact, it may be possible to use reclaimed wastewater as a nutrient
and moisture source. Although wastewater may not have a conventional or optimized composition, it
has been shown to successfully support nutrient levels. More investigation is needed to determine
whether this is a feasible alternative for the CWP.
9.3 EXTERNAL DESIGN
Ductwork
The splitter box air stream and clarifier air stream will be delivered to the biofilters through piping
located above ground. Placing the ducting system underground is possible but not feasible at the CWP
due to existing underground structures and utilities. All air distribution piping and ducts shall be
constructed of schedule 40 PVC pipe because of its low cost, durability, and resistance to corrosion.
The pressure loss calculations of the combined biofilter system and ductwork include a safety factor
such that the blow capabilities are not exceeded. Pipe insulation is proposed in order to reduce heat
loss from the air. Duct fittings and components should be installed according to the site plan.
The proposed system includes the ductwork from the splitter box and primary clarifiers to fan located
near the sources in order to primarily use the fan to push the air into the biofilter. The proposed layout
is shown in Appendix J and the site plan. The proposed quantities for the air distribution system are
shown in Table 14.
Page 72 of 91
PROPOSED DESIGN DECISIONS
Table 14. Proposed Ductwork System
Component
Isolation Valve/ Ball Valve
Damper Valve
18” PVC
30” PVC
36” PVC
42” PVC
Qty
4
2
280 ft
370 ft
120 ft
5 ft
Blower Specifications
The proposed odor control system is a single positive pressure system. Collection equipment will be
installed at the splitter box that will capture the air and direct it towards the biofilter. The existing
collection equipment at the primary clarifiers will be retrofitted such that the captured air is
redirected towards the biofilter. Recommendations for air handling equipment and controls are
provided.
The CWP operates a backward curve centrifugal fan at the primary clarifiers that will be reused for
the biofilter system. All components are to be compatible with the conditions and chemicals to which
they will be subjected to during normal operation (i.e. hydrogen sulfide, sulfuric acid). All surface
exposed to the contaminated air emissions are to be constructed of Polyvinyl Chloride (PVC),
Fiberglass Reinforced Plastic (FRP), stainless steel, or Epoxy-coated concrete. The blower
specifications are given in Table 15 and the manufacturer’s performance curve and fan configuration
are shown in Appendix M or Section 8.4.2.
Table 15. Blower Specifications
Manufacturer
Model No.
Fan Type
Material
Fan Size
Enclosure
Frame
Horsepower (HP)
Fan Speed (RPM)
Cycle/Phase
Voltage
Blade/Wheel
Service Factor
Flow Rate (CFM)
Static Pressure (SP)
Hartzell Air Movement
A41P0-272FA100FG-P3
Backward Curve Centrifugal Fan, Single Width
Fiberglass
27”
TEFC
256T
20
1755
60/3
230/460
FA 48.8
1.25
12000
7.5”
The blower is designed with an inlet and outlet pipe with a 36” diameter so there is no system effect.
Condensate drainage must be provided in the duct system because any excess water can cause
Page 73 of 91
PROPOSED DESIGN DECISIONS
mechanical issues with the operation of the biofilter. The trap seal is sized based on the negative or
positive pressure of the fan. Typically, the trap is sized at 1.5 times the inlet or outlet pressure of the
fan, whichever is greater. Additionally, plastic ducting condensation traps can be installed along the
piping layout with an overflow drain.
Insulation
The average temperature of the filter bed should remain above approximately 60 ℉, which can
typically be maintained as a result of biological activity in the filter if the incoming air is not too cool.
The temperature of the air emitted from the splitter box and primaries has an average value of 55℉,
which remains relatively constant throughout the year (refer to Appendix O for temperature data
from the facility). To maintain this air temperature as it travels to the filter, all air ducts are to be
insulated with 4 inches of foamed, weather-resistant insulation (thermal conductivity of 0.03 W/mK). Although insulation has a high capital cost, it is environmentally and economically sustainable in
comparison to energy-consuming alternatives (i.e. heat tracing or installation of a heating unit). Refer
to Appendix P for heat loss calculations. If the air temperature entering the filter is found to be below
45℉ during winter operation, a steam generator can be installed in the humidification chamber to
increase the temperature as well as humidify the incoming air.
9.4 OPERATION AND MAINTENANCE REQUIREMENTS
Start-Up
Inorganic media requires inoculation of the bacteria, and startup time can be reduced if organic
media is also inoculated. Activated sludge without excessive levels of pathogens can be used to
inoculate the media. Startup time for acclimation to occur can take anywhere from a few days to a few
months, and the timing will depend largely on the conditions of the surrounding environment with
colder conditions resulting in longer startup times. For this reason it is recommended the biofilter be
installed during warm months. To avoid causing exposure shock of the bacteria due to the loading of
the contaminant, the biofilter should not immediately be operated at full capacity and time is needed
to allow a thick biofilm layer to form on the media. Air flow should operate at 25 to 50% of the design
capacity for a timeframe of anywhere from 3 days to 2 weeks [34]. Because recorded H2S
concentrations are relatively low for the proposed system, exposure shock is not expected to be a
primary concern. It is recommended that 4 weeks are allowed for gradual acclimation to occur.
During this time, the blower fan speed is to be increased linearly from 6,000 cfm until average
capacity is reached at 8,000 cfm. The biofilter will need to be monitored during startup to ensure
successful operation and parameters to be monitored include airflow rate, relative humidity, and
temperature of the raw air at the inlet, as well as the H2S concentration at the inlet and outlet of the
biofilter.
Performance Evaluation
The frequency of cleaning depends on conditions of the biofilter, therefore several monitoring devices
are recommended for efficient operation. Parameters to be monitored include air flow rate, moisture
Page 74 of 91
PROPOSED DESIGN DECISIONS
content or relative humidity, temperature, pressure drop, and inlet/outlet contaminant
concentrations. All monitoring needs can be controlled by programmable logic controllers (PLC)
designed to communicate with the facility’s Supervisory Control and Data Acquisition (SCADA)
system. Table 16 shows a recommended monitoring schedule with possible measurement
instrumentation. Recommended instrumentation devices for the proposed design are highlighted.
Refer to the proposed Process Flow Diagram (Appendix J) for suggested placement of monitoring
devices.
Table 16. Recommended Monitoring Operation [34, 61, 19]
Operational
Parameter
Monitoring
Schedule
(recommended)
Reason for
Monitoring
Problematic
System
Response
Recommended
Measurement Device
-Input/output pressure
gages on blower
-Flow meters
-Difference manometer
-U-tube manometer to
measure static pressure
head
-Orifice plate (differential
pressure. Place
downstream of blower and
before tank)
-Pitot tube to spot check air
flow rate at inlet
-RH sensor
-Wet and dry thermometer
Pressure Drop
Weekly
Determine
pressure drop
across bed
Increase in media
compaction or
clogging
Air Flow
Weekly
Decline in blower
system speed
Increase in media
compaction or
clogging
Moisture
Content
Monthly
(unless prone
to drying)
Determine
effectiveness of
humidification
chamber
Determine
amount of
irrigation needed
(gal/h/ft2)
Determine
temperature to
help with heat
balance and
moisture control
Determine
acidification in
biofilter
Determine salt
content of
biofilter
Determine
removal efficiency
Relative Humidity
of air drops (input
and output %)
Temperature
Continual
Chemical
Composition
1 to 6 month
sampling
Emissions
As needed
Media bed drying
or over saturation
Changes in
input/output
temperature or
temperature
profile (℉)
Problematic
chemical
composition
Salt accumulation
Loss of removal
efficiency
Page 75 of 91
-Moisture probes
-Load cells
(Adjust flow rate and
duration)
-Thermometers
-Temperature probes at
multiple locations
-Thermocouples
-pH probe
-pH meter
-pH paper
-Conductivity probe
-OdaLogger at inlet and
outlet
PROPOSED DESIGN DECISIONS
Regular Maintenance Requirements
Regular maintenance needs includes monitoring the pH, moisture, temperature, and pressure drop
of the system. These measurements can be taken manually or using a using control and servicing
instruments. Additional nutrients will also be required and can be implemented at a set dosage
through the overhead irrigation system.
Long-Term Maintenance Requirements
Media will need to be replaced due to degradation and/or compaction, which is estimated to occur
once every 5 to 10 years. The replacement schedule will depend on the temperature and relative
humidity of the waste gas, the moisture content of the media bed, the stability of the media particles,
and the temperature, pH, and back pressure of the filter bed. Media replacement will be needed when
media crusting, salt accumulation, or a loss of porosity causes ineffective treatment.
High pressure drop (head loss) across the filter bed will typically be the primary indication that
maintenance is required. The operation speed of the blower will indicate the pressure drop across
the bed. However, a complete media replacement may not be necessary when the pressure drop
increases. Instead, periodically tiling the media can alleviate excessive back pressure due to
compaction. This may be needed at time intervals ranging anywhere from 6 months to 5 years. A till
or rotary can be used for this purpose and should be applied at least 15.75 in (400 mm) into the
media bed. The pH may need to be periodically adjusted as well (as a low pH will cause a decline in
microbial activity), which can be done by adding a caustic solution, such as oyster shells or dolomite
to the system, or by using rotary hoeing to add hydrated lime to the bed surface. [34]
Page 76 of 91
ECONOMIC ANALYSIS
10 Economic Analysis
The following preliminary cost estimate includes each component of the proposed design (Figures
17-23). The final cost incorporates contingency, engineering and surveying and general conditions
(Contractor’s overhead costs and miscellaneous expenses).
Table 17. Biofilter Components Cost
Concrete and Rebar
Grout
Fiberglass Cover
42” PVC Exhaust Pipe
8’x4’ Metal Grate
Concrete Coating
Appurtenances
Subtotal
$24,000
$6,000
$30,000
$1,250
$1,380
$13,740
$7,640
$84,020
Table 18. Media Cost
4 inch Woodchips
1 inch Lava Rock
Installation
Subtotal
$800
$10,400
$5,000
$16,193
Table 19. Humidification and Irrigation Costs
3/4-inch Copper Piping
3/4-inch valves
Spray Nozzles
Drainage Equipment
Appurtenances
Subtotal
$1,120
$9,000
$8,500
$2,000
$2,060
$22,680
Table 20. Splitter Box Covering Costs
Concrete Building
Concrete Coating
Appurtenances
Subtotal
Page 77 of 91
$13,000
$15,000
$2,800
$30,800
ECONOMIC ANALYSIS
Table 21. Air Piping Costs
18" PVC Pipe
27" PVC pipe
30" PVC Pipe
36" PVC Pipe
Reducer Coupling
Expander
Reducing Tee
Isolation Valve
Damper Valve
36" Elbow
24" Elbow
Insulation
Appurtenances
Subtotal
$15,960
$1,050
$44,400
$18,000
$750
$750
$3,400
$10,000
$6,000
$3,800
$1,870
$15,000
$21,200
$142,180
Table 22. Miscellaneous Costs
Monitoring and Controls (12% of
investment)
55 gallon Barrel for Nutrient Storage
Maintenance Access
Gas Detectors
Pressure Gages
Mobilization
Subtotal
$38,500
$1,000
$10,000
$2,000
$1,500
$10,000
$63,000
Table 23. Total Preliminary Cost for Biofilter
Total Biofilter Cost
Contingency
Engineering and Surveying
General Conditions
Total Estimated Construction Cost
$359,000
$107,700
$70,100
$18,000
$556,000
The resulting economic analysis for the proposed system is comparable to other case studies of
biofilters across the nation at similar sizes and media types [5]. A visual representation of the
distribution of costs is shown in Figure 23.
Page 78 of 91
ECONOMIC ANALYSIS
13%
15%
3%
19%
11%
6%
26%
Biofilter Components
Media
Contingency
Engineering and Surveying
Splitter Box
4%
Air Piping
Humidification and Irrigation system
Miscellaneous Items
Figure 23. Percent Contribution to Total Cost.
Operations Cost
Annual costs include the following, estimated to total to about $30,000 per year.



Electricity Demands
Nutrient Feed Supply
Maintenance Needs
Competing Technology
In comparison to competing odor-control technology, biofiltration is an economically sustainable
alternative (refer to Figure 24). While the capital cost is marginally higher for biofiltration technology,
the annual operating costs are significantly lower than competing alternatives.
Page 79 of 91
ECONOMIC ANALYSIS
Costs Comparsion of Odor-Control Technology
$3,500,000
$3,000,000
Biofilter
Cost
$2,500,000
Chemical
Scrubber
Cost
Cost
$2,000,000
$1,500,000
Carbon
Adsorption
$1,000,000
$500,000
$0
0
2
4
Year
6
8
10
Figure 24. Cost Comparison of Odor-Control Technology [62]
Conclusion
In conclusion, based on the preliminary design plan and costs analysis presented here, it is feasible
for the Wyoming Clean Water Plant to install the proposed biofiltration system. The proposed design
offers advantages in regard to operation and maintenance needs and is more environmentally
sustainable relative to alternative odor-control technology. The implementation of this system is
economically advantageous for the CWP as it would eliminate the use of the carbon adsorber and its
associated costs. Additionally, the repurposed infrastructure and equipment incorporated into the
proposed design make this solution particularly economically favorable.
Page 80 of 91
ACKNOWLEDGEMENTS
11 Acknowledgements
The Bi0der team would like to formally thank the following individuals for graciously offering their
time and knowledge to the success of this project:
Wyoming Clean Water Plant



Myron Erickson, City of Wyoming, for meeting with and advising the team.
Tom Wilson, Wyoming Clean Water Plant, for meeting with the team and providing
information, resources, and contacts throughout the design process.
Jon Burke, Wyoming Clean Water Plant, for giving the team a tour and providing operational
information about the plant.
Industrial Consultants





Ben Whitehead, Black & Veatch, for meeting with and advising the team as an industrial
consultant; providing resources and engineering design advice.
Chuck Kronk, Waterworks Systems and Equipment, Inc., for providing design information.
Mark Smith, Brown and Caldwell, for providing valuable biofilter design information.
Mark Prein, Prein and Newhoff, for example of biofilter designs
Marc Deshusses, Duke University, for providing information on biofilter volume sizing
Calvin Faculty



Dr. Jeremy Van Antwerp, Calvin College Chemical Advisor, for offering his insight and advice.
Bob Masselink, Calvin College Civil Advisor, for offering his insight and advice.
Dr. David Wunder, Calvin College, for offering his insight and advice.
Facility Operators



Larry Campbell, North Kent Sewer Authority, for information on the biofilter at PARCC Side
Clean Water Plant.
Scott Schoolcraft, PARCC Side Clean Water Plant, for information on the biofilters and for
giving us a tour of the plant.
Doug Humbert, Three Rivers Wastewater Treatment Plant, for providing information on the
biofilter at Three Rivers Wastewater Treatment Plant.
Page 81 of 91
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APPENDICES
13 Appendices
Appendix A – Wyoming CWP Flow Diagram
Appendix B – Headworks Hydrogen Sulfide Readings
Appendix C – Primary Clarifiers Hydrogen Sulfide Readings
Appendix D – Biosolids Storage Tanks Hydrogen Sulfide Readings
Appendix E – Splitter Box Diagram
Appendix F – Splitter Box Hydrogen Sulfide Readings
Appendix G – Media Type Research
Appendix H – Biofilter Case Studies
Appendix I – Biofilter Media Volume Calculations
Appendix J – Proposed System Design and Plans
Appendix K – Pressure Drop through Biofilter
Appendix L – Ductwork Friction Losses
Appendix M – Blower Performance Curve
Appendix N – Moisture Control Calculations
Appendix O – Wastewater Temperature Readings
Appendix P – Calculations for Heat Loss along Pipe
Page 91 of 91
Appendix A – CWP Flow Diagram (provided by Jon Burke)
Appendix B – Headworks H2S Readings
Headworks Building
Date
12/19/2014
1/28/2014
3/5/2014
5/15/2014
7/14/2014
8/4/2014
9/3/2014
10/30/2014
12/3/2014
1/15/2015
2/24/2015
3/24/2015
5/6/2015
6/16/2015
7/23/2015
8/24/2015
Air Inlet
(H2S
ppm)
Air Outlet
(H2S ppm)
System
Pressure
(psi)
0
0
4.7
0
0
4.8
0
0
4.8
0
0
4.6
0
0
4.9
0
0
4.9
0
0
5
0
0
5
0
0
5.1
0
0
5.2
0
0
5.2
Gas Detector out of service
0
0
4.8
0
0
4.6
0
0
4.6
0
0
4.6
Mist
Eliminator
Pressure
(psi)
Stage 1
Pump
Pressure
(psi)
Stage 2/3
Pump
Pressure
(psi)
Make
Up
Water
(gpm)
0.06
0.06
0.08
0.08
0.18
0.08
0.1
0.1
0.06
0.08
0
--0.08
0.08
0.07
0.08
17
16
17
15
15
17
15
15
15
17
17
--14
13.5
14
14
14
14.5
15
9
9.5
10
10
10.2
11.5
10.5
11
--10
10
11
11
1.5
1.5
1.5
1.5
1.5
1.5
1.5
1.5
4
1.5
1.5
--1.5
1.5
1.5
1.5
Appendix C – Primary Clarifiers H2S Readings
Upper Stack
UP
Upper Carbon Layer
UM
UL
Influent Air from
Primary Clarifiers
Lower Carbon Layer
LL
LM
LU
Lower Stack
Carbon Adsorber Schematic
Carbon Filter (Jb-2)
Date
2/5/13
2/27/13
4/1/13
4/29/13
6/3/13
7/10/13
7/24/13
9/12/813
10/3/13
11/27/13
12/16/13
1/7/14
3/5/14
8/5/14
9/3/14
10/30/14
12/10/14
1/15/15
2/26/15
3/24/15
5/6/15
6/16/15
7/23/15
8/25/15
H2S Air
Inlet
(ppm)
0
0
0
0
2
3
4
14
9
14
11
2
2
22
4
5
3
18
9
--3
7
3
9
H2S (ppm) Reading Location
UL
UM
UU
Upper Stack
Release H2S
(ppm)
0
0
0
0
0
2
2
9
7
12
7
0
0
8
3
0
0
0
0
--0
0
0
0
0
0
0
0
0
0
0
0
0
6
0
0
0
4
0
0
0
0
0
--0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
3
0
0
0
0
0
--0
0
0
0
------------0
0
0
--0
----2
0
0
0
0
0
--0
0
0
0
Pressure Diff.
Across Layer
(psi)
2.1
1.6
--2.5
2.8
2.8
2.8
3
3.4
2.2
2.5
--3.5
3.3
1.8
2.2
------2.7
3
3.4
3.4
Mist
Eliminator
------------------0
------2
2.3
2
0.6
------0.2
1.8
1.7
1.4
Appendix D – Biosolids Storage Tanks H2S Readings
Wet Well
Chemical Scrubber Layout
Zb-26
Zb-27
B Storage Tank
Not Used
Zb-28
West Storage
Tank
East Storage
Tank
Biosolids Storage Tanks Layout
Chemical Scrubbers for Bio Solids Storage (Z)
Date
Scrubber
12/19/2013
Zb-26
Zb-27
Zb-28
Zb-26
Zb-27
Zb-28
Zb-26
Zb-27
Zb-28
Zb-26
Zb-27
Zb-28
Zb-26
Zb-27
Zb-28
Zb-26
Zb-27
Zb-28
Zb-26
Zb-27
Zb-28
Zb-26
1/16/2014
3/5/2014
8/5/2014
9/3/2014
10/30/2014
12/10/2014
1/15/2015
West
Tank
H2S
(ppm)
2
0
East
tank
H2S
(ppm)
25
7
46
88
37
0
Inlet
Air
Flow
(CFM)
0
System
Pressure
for
Scrubber
(psi)
Mist
eliminator:
pressure up
to stack
Make Up
Water
Stage 1
(gpm? Or
gph?)
Make
Up
Water
Stage 2
0
5
0.07
2
1
2
6
0
2
1
2
5.2
0.07
2
1
34
5.8
0.8
2
2
5.8
0.7
2
1
Outlet
H2S
Reading
(ppm)
Outlet
LEL
Reading
(ppm)
17
18
0
0
0
7
35
O
Tanks
H2S
(ppm)
0
0
18
7
5.7
5.6
0.05
0.5
2
2
1
1
0
0
0
5.9
10.6
0.04
0
2
2
2
2
0
15
3500
2/24/2015
3/24/2015
5/6/2015
6/16/2015
7/23/2015
8/25/2015
Zb-27
Zb-28
Zb-26
Zb-27
Zb-28
Zb-26
Zb-27
Zb-28
Zb-26
Zb-27
Zb-28
Zb-26
Zb-27
Zb-28
Zb-26
Zb-27
Zb-28
Zb-26
Zb-27
Zb-28
0
0
9
9
5
5
0
0
21
21
9
9
4
4
35
35
35
9
9
9
6
0
0
0
0
12500
12000
0
10.4
0
2
2
0
0
10.6
6.5
0.1
0.35
2
2
4
5
0
0
0
6.2
8
7.8
6.4
0.27
0.27
0.35
0.25
2
2
2
2
5
5
6
5
0
0
6.4
8.4
0.25
0.25
2
2
1
1
Appendix E - Splitter Box Drawings
Appendix E - Splitter Box Drawings
Appendix F – Logger Data at Splitter Box
The following data was recorded using an OdaLog1 gas data logger which measured the effluent
hydrogen sulfide concentration form the air originating from the splitter box. The data was recorded
for a week beginning Nov. 24 and ending Dec. 30, 2015.
1
http://www.odalog.com/odalog/
The following photograph shows the location of the logger in the splitter box.
(photo credit: Kerala Smith)
Appendix G – Media Research
INTRODUCTION
Selecting the proper media is critical for biofiltration operations because it sets the basis for nearly
all other design parameters. Each media type is characterized by a specific residence time which
impacts the flow capacity, the necessary volume of the reactor, and the rate at which microorganisms
consume contaminants.
The media aids in contaminant removal by adsorbing the targeted pollutants as well as housing
bacteria that degrade the contaminants [43]. If properly selected, the media can accomplish
approximately 60% of the H2S removal without the presence of sulfur-reducing bacteria, meaning
less than half of the removal efficiency is due to biological metabolism [34]. Natural or synthetic
materials can be used in this application.
1.1 NATURAL MEDIA
Natural media is often easily-accessible and inexpensive in comparison to synthetic alternatives.
Natural media can be engineered to have specific desirable characteristics, such as a high sportive
surface area or enhance material strength. Natural media used for biofiltration is typically removed
of impurities or small particles prior to installation. Furthermore, natural media with organic content
contains nutrients needed for microbial growth bacteria, contributing to the overall bioactivity in the
system [29].
•
Peat (organic)
•
Aids in oxidization of hydrogen sulfide at a neutral pH level
•
Easily compacted, increasing the need for media replacements [53]
•
•
•
•
Highly porous and allows for adequate biofilm growth.
Regeneration of media is difficult after the deposition of fine sulfur particles are removed with
rinsing water [38]
Compost/Woodchips (organic)
•
•
•
•
Large surface area supports microbial growth in a naturally acidic environment
•
Compost can vary in degree of porosity, pH, water content, and chemical composition which
impacts the H2S loading capacity [17].
Particularly nutrient-rich material, aiding in microbial growth [50]
Relatively inexpensive [53]
Surface area and gas retention time decrease as a result of media compaction, drying, or
channeling, which prevents contaminated air from adequate contact with the media [27]
Activated Carbon (AC)
•
•
•
•
Acclimation can occur quickly in AC, reducing the start-up time [51]
Highly porous, providing a good environment for microbial growth [53]
Expensive material relative to alternative media types [53]
Experiences compaction over time, increasing clogging in the filter [51] [53]
•
Lava Rock
•
•
•
•
Primarily composed of hematite, titanohematite, and olivine
Typically inoculated with microorganisms prior to operation [52]
Highly porous material, providing a good environment for microbial growth [52] [53]
High resistance to bed compaction and has a low pressure drop across the layer [52]
1.2 SYNTHETIC MEDIA
An advantage of using synthetic media in biofiltration is that it can be engineered to have optimal
structural and surface area characteristics. Synthetics do not experience compaction or degradation
to the same extent that certain types of natural media do, therefore they tend to have a longer media
life [54]. Additionally, synthetic media is gaining popularity because it reduces bed clogging caused
by excessive biomass growth [55]. Because they do not contain a natural component, however,
synthetics must be inoculated with active bacteria. Furthermore, synthetic media tends to be an
expensive alternative and its eventual disposal raises some environmental concerns.
•
•
Polyurethane Foam (PU)
•
•
One of the best synthetic packing media for minimizing compaction and maximizing air flow
due to its low density and large porosity [55]
Relatively low commercial cost [55]
BiosorbensTM (manufactured by Biorem®)
•
•
•
First engineered, permanent biofilter media available on the market [56]
High specific surface area (40.9 m3/g of media), resulting in efficient adsorption and increases
rate of biological oxidation
Easily retains moisture while avoiding decomposition, degradation, and compaction (even in
strongly acidic environments)
Appendix H- Full Scale Case Studies
1.1 THREE RIVERS CLEAN WATER PLANT (TRCWP)
The Three Rivers Clean Water Plant is located on 409 Wolf Rd in Three Rivers. The facility currently
operates a biofilter to treat odorous air coming off of an Autothermal Thermopilic Aerobic Digestion
(ATAD) unit. The ATAD treats thickened material to produce a high-quality, pathogen-free product
[39]. Their first biofilter was designed and built by Thermal Process Systems in 2002. Due to the
plugging of the biofilter bed, the odor was not effectively removed from the influent air. This led to
complaints from surrounding community members. The biofilter was replaced and improved
between 2010 and 2013 because the original biofilter was not large enough to treat the inlet air. The
new biofilter and fan were designed to be three times their original design size. The TRCWP
supervisor, Doug Humbert, explained that the biofilter now only needs to be run between 20-25% of
its design capacity. Additionally, the first biofilter was rated at 2,300 CFM, while the new biofilter is
rated at 4,700 CFM with total system capacity of 7,000 CFM [40].
Figure 1. Completed Biofilter at Three Rivers Wastewater Treatment Plant [41]
The biofilter is installed in a concrete tank with a plenum to distribute air. The biofilter contains a
perforated fiber glass floor structure with a lava rock and a root stock media. There is a geo-textile
layer between each of these consecutive layers (Figure 2). The major odorous compound treated by
the biofilter is ammonia. The lack of hydrogen sulfide in the treated air is due to the ATAD aeration
system providing sufficient oxygen during the digestion cycle.
Figure 2. Installation of Porous Floor of Biofilter [41]
The biofilter is cleaned every 3-4 years, which is done when the media is changed. In order to avoid
the build-up of salts and organics, the biofilter can be flushed with water at the interface of the media,
which is done relatively often. To function properly, the temperature inside the biofilter needs to
remain between 65-95°F. The temperature is controlled by varying the amount of water in the air
humidifier. Humbert explained that insulation is not needed, since the temperature can be controlled
in this way. Additionally, the differing seasonal temperatures present in Michigan do not affect the
functional ability of the biofilter. Overall, the TRCWP is very happy with the biofilter. Humbert
mentioned that he would rather have another biofilter instead of the activated carbon unit that they
currently have to treat air at a different location in the plant.
1.2
NORTH KENT SEWER AUTHORITY
PARCC Side Clean Water Plant
North Kent Sewer Authority (NKSA) was founded to improve and repair the sanitary sewer collection
and transportation system for the City of Rockford, Plainfield Charter Township, and the Townships
of Alpine, Cannon, and Courtland. The PARCC Side Clean Water Plant (CWP) is located on 4775 Coit
Ave NE in Grand Rapids, MI. It was brought online in November of 2008. Designed by Prein & Newhof,
the plant’s design capacity is 6.6 million gallons per day (mgd), but it operates at an average daily
flow of 3.6 mgd. The main components of the plant are shown in Figure 3.
Biofilters
Biosolids
Headworks
Figure 3. PARCC Side CWP [63]
The influent plant water is primarily residential. The average water temperature throughout the plant
is approximately 50℉. The coldest the water gets is 40℉ during April and it is the warmest at 70℉
during August and September. The plant’s odor sources are treated using a lava-rock and cypress bark
biofilter that was incorporated with the plant’s design and construction. The biofilter is treating
hydrogen sulfide from air conveyed from the headworks building and the solids storage tanks.
Biofiltration System
The biofiltration configuration of the PARCC Side CWP includes two buried biofilters that operate in
parallel. Each biofilter is layered with lava-rock and cypress bark. Each has a packed bed depth
between 11-13 feet. The media sits in a fiberglass container which is encased in concrete as shown
in Figure 4.
Figure 4. PARCC Side CWP Biofilters (Lauren Grimley)
Air enters a humidifying chamber before it is forced through a foot deep opening at the bottom of the
biofilter. Once the air passes through this opening, it is forced up through a grate that holds up the
packing media. The headspace in the biofilter is approximately 4-5 feet and the ventilation pipe is
approximately 2 feet in diameter.
The headworks building is heated and has two variable frequency drive (VFD) blowers that operate
in parallel. These blowers move about 11,300 cfm of air directly off of the lift station, which is piped
to the biofilter underground. The average operation of the blowers is approximately 36.9 hertz and
the plant knows that the biofilter media needs to be replaced if the blowers reach 60 hertz. This
indicates that the media is clogged and the fans are working at maximum operation to push the air
through the biofilter bed. The two blowers alternate every 24 hours. At the solids handling unit, the
VFD blowers are sized at 2,600 cfm and send the air towards the biofilter through underground
piping.
Biofilters Configuration [42]
The plant uses three systems to ensure that the nutrient and moisture content of the biofilter is
adequate for bacterial growth. First, the plant continuously runs eight sprinklers in the
humidification chamber before the air enters the biofilter as shown in Figure 5.
Humidification
Sprinklers
Humidification
Chamber
Figure 5. PARCC Side CWP Biofilter Configuration (Lauren Grimley)
The plant also installed 16 sprinkler heads in the headspace of the biofilter that operate for 160
seconds every 20 minutes. Lastly, the plant uses a soaker hose (standard gardening hose) that is
located ⅓ of the media depth and it operates 140 seconds for every 20 minutes. The sprinklers and
hose use effluent water with liquid fertilizer 10-10-10 [43] added as a nutrient to the microorganism
growing in the biofilter media. This practice was recommended by the manufacturer. Prior to the
water being sprayed over the biofilter, it is put through a small filter that must be replaced when the
flow is less than 3 gpm. The optimum flow through the piping to the sprinklers is 11-12 gpm. The
filter is replaced approximately 3 times per year. The average temperature is approximately 50℉. The
past three month’s temperature and pH level of the air is shown in Table 1.
Table 1. Monthly PARCC Side CWP Temperature and pH Readings for Air Entering Biofilter
Date
September 2015
October 2015
November 2015
Temperature (℉) pH Value
72
57
55
7.38
7.65
7.59
The desirable pH level is 7, but the biofilter is expected to have operational problems if the pH level
is ever less than 2. The plant staff conducts quarterly inspections of the biofilter, recording
temperature, pH, and H2S levels in order to ensure the biofilter is operating properly. The annual
biofilter cost for is less than $5,000 in equipment (liquid fertilizer, sprinkler heads, filters, hose, etc.).
The plant purchases two 55 gallon drums of liquid fertilizer for approximately $1,000. The estimated
labor required for the biofilter maintenance and operation is 100 hours per year.
The plant is pleased with the little maintenance and effective performance of the biofilters. The
biofilters were sized to treat a higher loading rate of hydrogen sulfide that would occur when the
plant is operating at full capacity. The biofilters have responded well during irregular weather
conditions such as the flood of April 2013 when flow through the plant was operating over the
metered limit of 10 mgd. The plant does not backwash the packing media and the manufacturer rated
the media life at 10-years, but the due to the low flow rate of the VFD blowers, plant expects the
packing media to remain efficient much longer.
Appendix I – Biofilter Media Volume Calculations
1.1 RATE LAW AND KINETICS USE
If kinetic data is found, one can use the rate law and the flow rates or concentrations of the hydrogen
sulfide to be removed in order to determine the volume of the biofilter needed in order to remove the
hydrogen sulfide. The method for determining the volume size using two different models (the
Ottengraf and ven den Ooever model and Michaelis-Menten kinetics, along with the Monod equation)
are explained in Section 6.2.1). This was our initial choice for determining the biofilter volume, as it
provided the ability to consider the pressure drop across the biofilter, as well as to visualize the
removal of hydrogen sulfide across the entire length of the biofilter. However, as we started to solve
this model for the volume, we discovered that the experimental method of determining the rate law
would be too far out of our scope for this project. Taking experimental data requires a lot of time and
resources, both of which were highly limited for us. Also, working with gas and air is very hard to
control in the laboratory, so it was needed to look for data in the literature. This literature search
proved unsuccessful, as there was very limited data for the media types we had chosen for our
biofilter. After communicating with various biofilter experts, it was determined that this was not the
common way that a biofilter was sized, so other options were considered for the biofilter size.
1.2
EBRT OPTIMIZATION
According to Mark Smith, a biofilter designer for Brown and Caldwell, the rule of thumb for most
biofilter volume design was to assume that a square foot of a biofilter can remove the hydrogen sulfide
in 3 cfm of air. This was to be combined with an EBRT of 45-60 seconds. With this design, and
assuming a worst case scenario of 12000 cfm air coming in (the size of our blower), and an
assumption of 6 feet of media depth, the size of the biofilter would be 24000 ft3. This seems incredibly
large given our previous case studies at PARCC side. When using this rule of thumb at the PARCC side
plant, a treatment system that has been operating satisfactorily for almost 10 years now, would have
a volume of 28000 ft3, which is almost four times the volume of the actual system. This shows that
the model is very conservative in its estimate, as the volume is about 7000 ft3 and has worked fine
well past its perceived replacement time. So it is unlikely that this “rule of thumb” volume will be the
actual volume for our biofilter.
1.3
ELIMINATION CAPACITY
Another way to determine the volume of the biofilter is to use elimination capacity data. Elimination
capacity is the ability of a media to remove and process contaminants in the air. The values for media
volume are calculated by dividing the flow rate of hydrogen sulfide by the elimination capacity of the
media. In this case, the elimination capacity can be found from a literature search. It was found from
Ramirez-Saenz et al. that the elimination capacity of lava rock was 142 g/m3 h and the elimination
capacity of the wood chips was 130 g/m3 hr. The incoming air was assumed to have a concentration
of 25 ppm. 20 ppm was assumed to be removed from the air using the lava rock and the remaining 5
ppm was removed from the air using wood chips. Using equation 1,
EC =
(Cin − Cout )
∗Q
V
(Eq. 1)
Where EC is the elimination capacity, Cin is the inlet concentration, Cout is the concentration out of the
biofilter media layer, V is the volume of the media layer, and Q is the flow rate of air. With these two
sets of data and parameters and equation XXX, it was found that the total volume of the biofilter
should be about 750 ft2 (calculations shown in Appendix XXX). However, this resulted in an empty
bed residence time of 3 seconds. The target range for EBRT is 20 to 60 seconds, so having a small
EBRT is not ideal. If the flow rate is decreased though, then the EBRT increased. If we decrease the
flow rate to 2000 cfm, then the EBRT ended up being about 20 seconds, which is reasonable.
1.4
REMOVAL EFFICIENCY
The removal efficiency is another method in order to model the volume of the biofilter. In this method,
the data for removal efficiency was found from the literature as it depended on EBRT. Two different
academic journals reported Removal efficiency data against the Empty Bed Residence Time for the
media that we chose. These data are presented below. According to Marc Deshusses, Professor of Civil
Engineering at Duke University, this data could then be used in the form of
Removal = 1 − exp(−EBRT ∗ K)
(Eq. 2)
where removal is the percent of hydrogen sulfide removed, EBRT is the empty bed residence time,
and K is a constant. This equation was then linearized to form the new equation
− ln(1 − Removal) = EBRT ∗ K
(Eq. 3)
This linearized data is shown below in figure 2. The desired percent removal can then be used to
calculate the resulting EBRT which can then be used with a known volumetric flow rate of air to
determine the volume of the biofilter required using the equation,
EBRT =
V
Q
Where V is the volume of the biofilter and Q is the volumetric flow rate.
(Eq. 4)
The data for the removal efficiencies was found in academic journals. This data is presented below in
Figure 1.
% removal against EBRT lava rock
1
y = 0.009029ln(x) + 0.980479
R² = 0.918740
0.999
% Removal
0.998
0.997
0.996
0.995
0.994
0.993
0.992
0
1
2
3
4
5
6
7
8
9
8
9
EBRT (s)
Figure 1. Percent Removal Against EBRT for Lava Rock [25]
As was stated before, this data was linearized to the form of equation 3 above.
ln(1-%removal) against EBRT for lava rock
0
ln( 1- % removal)
-1
0
1
2
3
4
5
6
7
-2
-3
-4
y = -0.5119x - 2.7729
R² = 0.9829
-5
-6
-7
-8
EBRT (s)
Figure 2. Linearized data of Figure Removal Efficiency for Lava Rock
For our case, the air treated was assumed to have a concentration of 25 ppm H2S. The Removal
efficiency for both Lava Rock and Woodchips was 99.5% which meant that the concentration entering
the woodchips layer was 0.125 ppm and the concentration leaving the biofilter was .625 ppb, which
is the limit of detection. Using the data presented below, and the equations presented above, the
resulting volumes were 164 ft3 for lava rock, and 542 ft3 for woodchips for a total volume of 707 ft3.
There are some problems with this method. First, the EBRT is too short for an industrial sized
biofilter. The biofilters and media tested in the data taken from the academic journals were bench
scale or small pilot scale. This meant the EBRT may not be scalable to a full size biofilter, thus skewing
the resulting volume.
Another problem is that percent removal data for woodchips is hard to find, and the data that is
available is poor [65]. Because of this, the model gives a result that is not as reliable as the lava rock
data. Because of this, the %RE model is considered lightly, but only because it resulted in a volume
similar to the elimination capacity model.
120
y = 2.1921x + 80.194
R² = 0.1956
100
%RE
80
60
40
20
0
0
1
2
3
4
5
6
7
8
7
8
EBRT (s)
Figure 3. Woodchip Removal Efficiency against EBRT
0
-0.5
0
1
2
3
4
5
6
ln(1-%removal)
-1
-1.5
-2
-2.5
-3
y = -0.228x - 1.5879
R² = 0.2307
-3.5
-4
-4.5
EBRT (s)
Figure 4. Linearized version of Woodchip Removal Efficiency
The volume calculated using percent removal efficiency is still similar to the volume calculated using
the elimination capacity. However the ratio between the lava rock and woodchip media layers
changed dramatically. In the elimination capacity model, it was calculated that the ratio between the
lava rock and the woodchip layers would be about 1: 1.1. The ratio for the removal efficiency model
is however 1:3 in favor of woodchips. This is most likely due to the lower removal efficiencies and
elimination capacities, so more woodchips are needed to remove a similar amount of hydrogen
sulfide from the entering air. In both cases, more woodchips are needed than lava rock, an aspect that
should be seen in the final design of the biofilter.
1.5
MASS TRANSFER CALCULATIONS
For the degradation of hydrogen sulfide to H2SO4, as in all reactions, seven steps must take place.
These steps are shown in Figure 34.
Figure 5. Process of a reaction [66]
The seven steps are
1. Diffusion from the surrounding fluid (in our case, from the air into the water)
2. Diffusion into the catalyst (cell/bacteria)
3. Adsorption onto surface of the catalyst
4. Reaction (metabolic process)
5. Desorption
6. Diffusion out of cell
7. Diffusion out of fluid
In any case, one step could be slower than the rest of the steps, thus it is termed the limiting step. In
the other cases that we considered for the design of our biofilter, we assumed that the reaction was
the limiting step, and therefore could be used to size the biofilter. However, we also needed to consider
the mass transfer of the hydrogen sulfide (steps 1 and 7) to the cell in order to ensure that the biofilter
is designed to properly remove the hydrogen sulfide from the air. If the mass transfer is the limiting
step, then it will have a larger impact on the volume of the biofilter, which will result in a biofilter
volume that is greater than the one calculated by the rate limiting models. If the mass transfer rate is
faster than the rate of reaction, then the biofilter is sized properly. Using literature data, it was found
that the mass transfer coefficient for the transfer of hydrogen sulfide into water from the air is 9.567
x 10-4 m/s [48] . Using this and assuming an initial concentration of 25 ppm and an interface
concentration of 0 ppm, we can then put this into equation 5 below,
NA =
kc
∗ (cA − cAi )
(1 − yA )lm
(Eq. 5)
where NA is the flux of the hydrogen sulfide through the water interface, (1-yA)lm is the log mean
average of the mole fraction of hydrogen sulfide in the air, cA is the concentration in the bulk solution
of hydrogen sulfide and cAi is the concentration of hydrogen sulfide at the interface. Using the data
given, a flux was calculated to be .024 g/m2 s.
In order to determine the volume of the biofilter needed, the ratio of the surface area to the volume
of the biofilter was calculated. This was done by using equation 6
a=
6
∗ (1 − ϵ)
∅ ∗ Dp
(Eq. 6)
Where ∅ is the sphericity, DP is the particle diameter, and ϵ is the void fraction. Using the data in table
XXX for woodchips, the value for the ratio a, was determined to be 312.6 m -1. With a flow rate of
hydrogen sulfide assumed to be 0.006579 g/s, and the flux calculated above, it was determined that
the volume needed for the biofilter woodchips would be 0.031 ft3. This is incredibly small compared
to the rate of reaction calculation, meaning that the reaction rate calculations from before are the
limiting reactions. Therefore, it was decided that mass transfer was not needed to be considered for
our volume calculations as the rate calculations showed that the rate has more effect over the volume
than does the mass transfer.
Sphericity [67]
Void Fraction
Particle Diameter (m)
0.2
0.479
0.05
Appendix J
Proposed System Design and Site Plans
CALVIN COLLEGE ENGINEERING
TEAM BI0DOR
GRAND RAPIDS, MI
WYOMING CLEAN WATER PLANT
ODOR CONTROL
05/06/2016
Kent County
Project
Location
SHEET INDEX
Sheet No. Description
ONE-CALL NOTIFICATION SYSTEM
CALL BEFORE YOU DIG!!!
800-482-7171
Title
Title
1
General Site Plan
2
Process Flow Diagram
CODE USED : 2003 MICHIGAN BUILDING CODE
3
Existing Aeration Basin Plan Sections
GENERAL LIMITATIONS
USE GROUP = U (UTILITY AND MISCELLANEOUS)
OCCUPANCY = 26,955 MAIN FLOOR + 19,750 UPPER LEVEL © 500 SF
PER PERSON (SIMILAR TO WAREHOUSE) = 94 PERSONS
4
Proposed System Plan Views
5
Proposed Biofilter Cross Sections
6
Existing Fan Shop Drawings
CODE INFORMATION
CONSTRUCTION TYPE 3B - NOT SPRINKLED
GENERAL CONSTRUCTION NOTE
ALL UTILITIES SHOWN ARE APPROXIMATE LOCATIONS DERIVED FROM ACTUAL
MEASUREMENTS AND AVAILABLE RECORDS. THEY SHOULD NOT BE INTERPRETED
TO BE THE EXACT LOCATION NOR SHOULD IT BE ASSUMED THAT THEY ARE THE
ONLY UTILITIES IN THIS AREA.
All elevations labeled according to Wyoming Clean Water Plant Datum
Enlarged Plan (NTS)
Notes:
1. The splitter box will be enclosed by a concrete structure
designed for easy maintenance access.
2. All proposed concrete will be cast-in-place with
reinforcing rebar.
3. All exposed concrete will be installed with a protective
epoxy coating to prevent corrosion.
4. Ductwork will be installed a minimum of 15' above
ground for vehicle traffic.
5. Ductwork will be supported by structural columns where
necessary. All other ductwork can be supported by the
roof of existing buildings or installed along the side of
the buildings.
General Site Plan
(Not To Scale)
Wyoming Clean Water Plant Odor Control
Preliminary Biofilter Design
Reference Plans:
Black & Veatch
Clean Water Plant Stage 2 Improvements
General Site Plan
Project No. 69722
Plans Not For Construction
Date: 05/06/2016
3201 Burton SE Grand Rapids, MI 49546
Sheet No. 1 of 6
Process Flow Diagram
Wyoming Clean Water Plant Odor Control
Preliminary Biofilter Design
Plans Not For Construction
Date: 05/06/2016
3201 Burton SE Grand Rapids, MI 49546
Sheet No. 2 of 6
Concrete
Walkway
1E
3
Concrete
Walkway
Finished Grade
El. 608' - 0"
Concrete
Walkway
Finished Grade
El. 608' - 0"
2E
3
Column
Aeration Basin
Pipe Gallery
Existing Aeration Basin
(Proposed Biofilter)
El. 587' - 6"
A
EXISTING PLAN EL. 608' - 0"
1E
EXISTING SECTION
(refer to Plan View A, this sheet) SCALE: 1:100
El. 587' - 6"
2E
EXISTING SECTION
(refer to Plan View A, this sheet) SCALE: 1:100
SCALE: 1:100
Existing Aeration Basin Plan Sections
Wyoming Clean Water Plant Odor Control
Preliminary Biofilter Design
Plans Not For Construction
Date: 05/06/2016
3201 Burton SE Grand Rapids, MI 49546
Sheet No. 3 of 6
Irrigation Line:
Connect to Effluent
Water Source
in Pipe Gallery
Concrete
Walkway
Nutrient
Supply
Pipe Gallery
Humidification Line:
Connect to Effluent
Water Source
in Pipe Gallery
Connect to
Existing 16"Basin
Drain
Connect to
Existing 16"Basin
Drain
Pipe Gallery
Note:
Concrete
Walkway
Extension
not shown
for clarity
6" Condensation
Drainage
Reducing T-Connection
30" Air Flow Duct
Empty Aeration Basin
36" Air Flow Duct
30" Air Flow Duct
Empty Aeration Basin
Empty Aeration Basin
BIOFILTER No. 1
BIOFILTER No. 2
1
5
2
5
4
5
A
3
5
PLAN EL. 611' - 6"
SCALE: 1:100
Humidification Chamber
Hatch Cover
B
PLAN EL. 603' - 7"
SCALE: 1:100
Note:
Biofilter Cover
not shown for
clarity
C
PLAN EL. 595' - 4"
SCALE: 1:100
Proposed System Plan Views
Wyoming Clean Water Plant Odor Control
Preliminary Biofilter Design
Plans Not For Construction
Date: 05/06/2016
3201 Burton SE Grand Rapids, MI 49546
Sheet No. 4 of 6
Finished Grade
El. 608' - 0"
Pipe Gallery
El. 600' - 1"
Irrigation Line:
Connect to
Effluent Water
Source in Pipe
Gallery
Stainless Steel Grate
Spray Nozzles 3'
above media bed
El. 595' - 4"
Woodchip Media
Finished Grade
El. 608' - 0"
Concrete
Walkway
4" Insulation
El. 611' - 6"
El. 609' - 8"
36" Air Duct
Finished Grade
El. 608' - 0"
Existing Column
Lava Rock Media
Stainless Steel Grate
Air Distribution Plenum
El. 587' - 6"
42" Air Duct
El. 603' - 7"
2
SECTION
(See Sheet 4) SCALE: 1:100
El. 601' - 4"
El. 611' - 6"
El. 600' - 1"
Stainless Steel Grate
El. 609' - 8"
Finished Ground
El. 608' - 0"
El. 603' - 7"
Humidification Line:
Connect to Effluent Water
Source in Pipe Gallery
30" Air
Duct
Spray Nozzles 3'
above media bed
Pipe Gallery
El. 595' - 4"
3' - 0" Woodchip Media
2' - 0" Lava Rock Media
6" Condensation
Drainage
Connect to Existing
16"Basin Drain
Stainless Steel Grate
Air Distribution Plenum
Slight slope downward to
allow for drainage
3
SECTION
(See Sheet 4) SCALE: 1:100
Finished Grade
El. 608' - 0"
Elbow 1" above ground to
allow for drainage
El. 588' - 3"
Grout Slope 12" per foot
42" Air Duct
Outlet
Fiberglass Reinforced
Plastic Cover
1
El. 600' - 1"
6" Condensation Drainage
Connect to Existing
16"Basin Drain
SECTION
(See Sheet 4) SCALE: 1:50
Pipe Gallery
Proposed Biofilter Cross Sections
Fiberglass Access to Air
Distribution Plenum
Wyoming Clean Water Plant Odor Control
Preliminary Biofilter Design
El. 587' - 6"
Plans Not For Construction
4
Date: 05/06/2016
SECTION
(See Sheet 4) SCALE: 1:100
3201 Burton SE Grand Rapids, MI 49546
Sheet No. 5 of 6
8
6
7
5
4
24"
25 15/16"
1
DRAWING NOTES:
28"
D
2
3
21"
(INSIDE)
29"
(INSIDE)
29 7/16"
D
36"
28 1/2"
(OUTSIDE)
43"
28 1/2"
C
C
33 13/16"
ACCESSORY LIST (DISPLAYABLE)
14 5/16"
DESCRIPTION
28"
26 3/8"
2"
ACCESSORY LIST (NOT DISPLAYABLE)
SEE ORDER ACKNOWLEDGEMENT FOR DETAILS
QTY.
ACCESS DOOR
N/A
GUARD(S) IN AIRSTREAM
N/A
DAMPER
N/A
HEIGHT ADJUSTING SUB BASE
N/A
DAMPER ACCESSORIES
N/A
INLET FLANGE
N/A
DRAIN
WEATHER COVER
N/A
FRP COATING
N/A
FRP CONSTRUCTION
N/A
SPECIAL SHAFT SEAL
1
SPECIAL HARDWARE
1
B
14 13/16"
11/16" x 1 1/2" SLOT (QTY. 8)
29 5/8"
QTY.
DESCRIPTION
1
SPECIAL SHAFT
N/A
STARTERS & DISCONNECTS
N/A
VIBRATION ISOLATORS
N/A
B
14 13/16"
MODEL NUMBER:
A41P0-272FA100FGFCP3
UNLESS OTHERWISE SPECIFIED:
13 1/16"
DIMENSIONS ARE IN INCHES
25 3/8"
TOLERANCES:
FRACTIONAL 1/8"
ANGLES 1
A
PROPS & WHEELS ARE NOT
DRAWN AS BUILT AND ARE
FOR REPRESENTATION ONLY.
THE FAN MODELS AND
ACCESSORIES ARE
DIMENSIONALLY ACCURATE,
BUT ARE NOT VISUALLY
ACCURATE AS BUILT.
26 3/8"
34 3/8"
DRAWING SCALE:
BOTTOM VIEW
8
7
SCALED
6
5
4
FAN DESCRIPTION:
Series 41P - Fiberglass Backward
Curved Centrifugal Fan,
Packaged, Type FA
Hartzell Air Movement
Piqua, Ohio 45356
1-800-336-3267
www.hartzell.com
FAN TAG NUMBER:
PROPOSAL NUMBER:
Config-94617
00
HARTZELL SALES ORDER NUMBER:
MODEL REV: 01
3
A
REV
PROPRIETARY AND CONFIDENTIAL
ITEMS SHOWN ON THIS DRAWING ARE THE INTELLECTUAL
PROPERTY OF HARTZELL AIR MOVEMENT AND ARE PROVIDED
FOR INTERFACE DIMENSIONS ONLY. DRAWINGS AND
PERFORMANCE DATA SHALL NOT BE COPIED OR RELEASED
WITHOUT THE WRITTEN CONSENT OF HARTZELL AIR MOVEMENT
AND SHALL BE RETURNED ON REQUEST.
PAPER SIZE:
DATE: 4/21/2016
2
B
SHEET 1 OF 1
1
Appendix K
Ergun Equations
Ergun Equation
The Ergun Equation relates pressure drop to gas flow in packed bed reactor. The Modified-Ergun (M-E)
equation was used to model the flow through the proposed biofilter where the constants A and B are 150
and 1.75, respectively, as shown in the equation below. [36]
∆P =
AµL (1 − ε)2
BρL 1 − ε 2
υ𝑠𝑠 +
υ
2
3
ε
Dp ε3 𝑠𝑠
Dp
𝜇𝜇
𝐿𝐿
𝐷𝐷𝑝𝑝
𝜀𝜀
𝜌𝜌
υ𝑠𝑠
Fluid viscosity
Depth of Bed
Particle diameter
Void Space of the bed
Density of the fluid
Superficial Velocity
The density of the fluid was an average of the inlet air density and the outlet air density. The inlet and
outlet density were calculated using the ideal gas law (PV=nRT). The pressure at the inlet to the bed was
calculated using the following equation:
P1 = Patm − Plosses
P1 = pressure at the bottom of the bed
Plosses = friction and dynamic losses in ductwork and biofilter after fan outlet = 0.94 in. wg
= 0.034320926atm
Patm = 14.6960 atm
Inlet Air Properties
Dynamic Viscosity (lbf-s/ft^2)
Air Temperature (F)
Air Density (lbm/ft^3)
3.750E-07
60
0.07614
Outlet Air Properties
PV=nRT
Assume ΔP (PSI)
Atm Pressure (PSI)
P1 (PSI)
P2 (PSI)
Temp (Rankine)
R (ft-lbf/lbm-R)
Density Oulet (lbm/ft^3)
Solve for n/V
0.020
14.6960
14.6616
14.6417
519.7
53.4
0.07604
Used in Pressure Calculations
Average Air Density (lbm/ft^3)
0.0761
Media Properties
LAVA ROCK
Selected Properties Lava Rock Woodchip
Porosity
0.5
0.52
Diameter (in)
0.945
3.937
Lava Rock Diameter
48 1
mm
2
24
mm
3
12
mm
4
4.7
mm
55
mm
6
3.4
mm
Cedar Rapids WWTP Biofilter 7
Radius (cm)
1.2
Sphericity
0.5
Porosity
0.4
Hydrogen Sulfide Removal with Lava Rock 8
Particle Density
1.13
g/mL
Material Density
1.41
g/mL
Porosity
0.2
NA
Pore Size
5
mm
WOODCHIP
Type
2-in Oak 9
Natural medium 10
Porosity
0.559
---
Size
5
4750
1
Unit
cm
micro-m
Martin,Ronald W.,,Jr, James R. Mihelcic, and John C. Crittenden. "Design and Performance Characterization Strategy
using Modeling for Biofiltration Control of Odorous Hydrogen Sulfide." Journal of the Air & Waste Management
Association 54.7 (2004): 834-44. ProQuest. Web. 25 Oct. 2015.
2
Ibid.
3
Ibid.
4
Percolation Models and Channeling in Biofilter Clogging, Journal of the Air & Waste
Hydrogen Sulfide Removal with Lava Rock
6
Iowa Plant Case Study
5
7
8
Ibid.
Hydrogen Sulfide Removal with Lava Rock
9
Evaluation of Wood Chip-Based Biofilters to Reduce Odor
10
Sulfur Toxicity and Media Capacity for H2S Removal in Biofilters
Particle diameter
Porosity
Density
Specific Surface
Area
Pore Diameter
117.7
0.479
218
mm
NA
kg/m^3
5.37
7.86
m^2/g
micro-m
Void Fraction
0.565 11
0.67 12
0.05 13
0.441 14
Design Criteria 15
Source
Martin, Mihelcic, and
Crittenden
Chitwood and Devinny
Yang and Allen
Media
Type
Particle
Size (in)
Pressure Drop
(in H20/ft)
Superficial
Velocities (ft/s)
Lava Rock
Lava Rock
Lava Rock
Compost
0.047
0.472
0.315
0.315
0.024
42.828
0.040
2.447
0.066
0.262
2.165
0.919
Design Average Loading Rate Design Max Loading Rate
300
m/h
500
m/h
0.083
m/s
0.139
m/s
0.273
ft/s
0.456
ft/s
11
http://lib.dr.iastate.edu/cgi/viewcontent.cgi?article=1623&amp;context=abe_eng_pubs
http://www.tandfonline.com/doi/pdf/10.3155/1047-3289.59.5.520
13
http://onlinelibrary.wiley.com/doi/10.1002/cjce.5450830416/epdf
14
Ibid.
15
Martin,Ronald W.,,Jr, James R. Mihelcic, and John C. Crittenden. "Design and Performance Characterization
Strategy using Modeling for Biofiltration Control of Odorous Hydrogen Sulfide." Journal of the Air & Waste
Management Association 54.7 (2004): 834-44. ProQuest. Web. 25 Oct. 2015.
12
Biofilter Unit
Pressure Drop across Bed in a Biofilter Unit
900
40%
60%
360
540
14
13
5
2
180
Conversions
1 lbf to lbm-ft/s^2
1 in H20 to PSI
0.60
Void Fraction
Clean Bed Porosity (0 %)
50% Filled
75% Filled
Lava Rock
0.50
0.25
0.13
Woodchip
0.52
0.26
0.13
Bed Depth (ft)
Ratio, a
Specific Surface Area (ft^-1)
Particle Diameter (ft)
Particle Diameter (in)
Lava Rock
2
36.0
72.0
0.083
1
Woodchip
3
8.6
18.0
0.33
4
50% of Pores Filled
0.40
75% of Pores Filled
0.30
0.20
0.10
0.00
0.0
0.2
0.4
0.6
Superficial Velocity [ft/s]
Clean Bed Porosity
Air Flow Rate (cfm)
Superficial Velocity
(ft/s)
Lava RockPressure Drop
(inH20)
0
500
1,000
1,500
2,000
2,500
3,000
3,500
4,000
4,500
5,000
5,500
6,000
6,500
7,000
7,500
8,000
8,500
9,000
9,500
10,000
10,500
11,000
11,500
12,000
0.00000
0.04630
0.09259
0.13889
0.18519
0.23148
0.27778
0.32407
0.37037
0.41667
0.46296
0.50926
0.55556
0.60185
0.64815
0.69444
0.74074
0.78704
0.83333
0.87963
0.92593
0.97222
1.01852
1.06481
1.11111
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.001
0.001
0.001
0.001
0.001
0.001
0.001
0.002
0.002
0.002
0.002
0.003
0.003
0.003
0.003
0.004
0.8
1.0
1.2
0.00E+00
1.90E-05
5.37E-05
1.04E-04
1.70E-04
2.51E-04
3.48E-04
4.61E-04
5.89E-04
7.33E-04
8.93E-04
1.07E-03
1.26E-03
1.47E-03
1.69E-03
1.92E-03
2.18E-03
2.45E-03
2.73E-03
3.03E-03
3.35E-03
3.68E-03
4.03E-03
4.39E-03
4.77E-03
0.000
0.000
0.001
0.001
0.002
0.003
0.004
0.005
0.006
0.007
0.009
0.011
0.012
0.014
0.017
0.019
0.021
0.024
0.026
0.029
0.032
0.035
0.038
0.042
0.045
Wood Chip Pressure Drop
(inH20)3
0.000
0.000
0.000
0.000
0.000
0.001
0.001
0.001
0.002
0.002
0.002
0.003
0.004
0.004
0.005
0.005
0.006
0.007
0.008
0.009
0.010
0.011
0.012
0.013
0.014
Inlet Air Properties
Dynamic Viscosity (lbf-s/ft^2)
Air Temperature (F)
Air Density (lbm/ft^3)
3.750E-07
60
0.07614
Outlet Air Properties
PV=nRT
Assume ΔP (PSI)
Atm Pressure (PSI)
P1 (PSI)
P2 (PSI)
Temp (Rankine)
R (ft-lbf/lbm-R)
Density Oulet (lbm/ft^3)
Solve for n/V
0.020
14.6960
14.6616
14.6417
519.7
53.4
0.07604
Use in Calculations
Average Air Density (lbm/ft^3)
50% of Pores Filled
Wood Chip Pressure Drop Total Pressure Drop Lava RockPressure Drop
(inH20)
(inH20)
(inH20)2
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.001
0.001
0.001
0.001
0.001
0.001
0.001
0.001
32.174
0.0361
Clean Bed Porosity
0.50
Pressure Drop [inH20]
Volume of Bed (ft^3)
Percent of Lava Rock
Percent of Woodchip
V Lava Rock (ft^3)
V Wood Chip (ft^3)
Length (ft)
Width (ft)
Depth (ft)
Biofilter Units (EA)
Bed Area (ft^2)
0.0761
75% of Pores Filled
Total Pressure Drop Lava RockPressure Drop
Wood Chip Pressure Drop (inH20)6
(inH20)4
(inH20)5
0.000
0.000
0.001
0.001
0.002
0.003
0.005
0.006
0.008
0.009
0.011
0.014
0.016
0.019
0.021
0.024
0.027
0.031
0.034
0.038
0.042
0.046
0.050
0.055
0.05919
0.000
0.003
0.007
0.012
0.019
0.027
0.036
0.047
0.059
0.072
0.087
0.103
0.120
0.138
0.158
0.180
0.202
0.226
0.251
0.278
0.306
0.335
0.365
0.397
0.431
0.000
0.000
0.001
0.002
0.004
0.006
0.009
0.012
0.015
0.019
0.024
0.028
0.034
0.039
0.045
0.052
0.059
0.066
0.074
0.082
0.091
0.100
0.110
0.120
0.130
Total Pressure Drop
(inH20)7
0.000
0.003
0.008
0.015
0.023
0.033
0.045
0.059
0.074
0.091
0.110
0.131
0.154
0.178
0.204
0.232
0.261
0.292
0.326
0.360
0.397
0.435
0.475
0.517
0.5610
Pressure Drop of Lava Rocks with Various Particle
Diameters
1.6E-02
8mm
Pressure Drop (in H20)
1.4E-02
12mm
1.2E-02
24mm
1.0E-02
48mm
8.0E-03
6.0E-03
4.0E-03
2.0E-03
0.0E+00
0.0
0.2
0.4
0.6
Superficial Velocity (ft/s)
0.8
1.0
Pressure Drop (in H20)
Pressure Drop of Woodchips with Various Particle
Diameters
7.0E-03
6.0E-03
2cm
5.0E-03
10cm
5cm
15cm
4.0E-03
3.0E-03
2.0E-03
1.0E-03
0.0E+00
0.0
0.2
0.4
0.6
Superficial Velocity (ft/s)
0.8
1.0
Predicted Pressure Drop of 1-in Lava Rocks with Various
Porosities
0.12
0.50
Pressure Drop [inH20]
0.10
0.40
0.30
0.08
0.20
0.06
0.04
0.02
0.00
0.0
0.030
0.2
0.8
1.0
Predicted Pressure Drop of 4-in Woodchips with Various
Porosities
0.52
0.42
0.32
0.22
0.025
Pressure Drop [inH20]
0.4
0.6
Air Flow [cfm]
0.020
0.015
0.010
0.005
0.000
0.0
0.2
0.4
Air Flow [cfm]
0.6
0.8
1.0
Pressure Drop across the Bed of a Single Biofilter Unit with Various Media Diameters
Lava Rock
Bed Area (ft^2)
Air Density (lb/ft^3)
Dynamic Viscosity (lb-s/ft^2)
Air Temperature (F)
180
7.65E-02
3.75E-07
60
Air Flow Rate (cfm)
0
500
1,000
1,500
2,000
2,500
3,000
3,500
4,000
4,500
5,000
5,500
6,000
6,500
7,000
7,500
8,000
8,500
9,000
9,500
10,000
10,500
11,000
11,500
12,000
% Pore Space Available
Void Fraction
Bed Depth (ft)
Ratio, a
Specific Surface Area (ft^-1)
Particle Diameter (ft)
Particle Diameter (in)
100%
0.50
2.00
114.3
228.6
0.03
0.3
Superficial Velocity (ft/s)
0.00000
0.04630
0.09259
0.13889
0.18519
0.23148
0.27778
0.32407
0.37037
0.41667
0.46296
0.50926
0.55556
0.60185
0.64815
0.69444
0.74074
0.78704
0.83333
0.87963
0.92593
0.97222
1.01852
1.06481
1.11111
8mm
0.000
0.000
0.000
0.000
0.001
0.001
0.001
0.002
0.002
0.002
0.003
0.003
0.004
0.005
0.005
0.006
0.007
0.007
0.008
0.009
0.010
0.011
0.011
0.012
0.013
100%
0.50
2.0
114.3
228.6
0.04
0.5
100%
0.50
2.0
114.3
228.6
0.08
0.9
Lava Rock Particle Diameters
12mm
24mm
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.001
0.000
0.001
0.000
0.001
0.000
0.001
0.000
0.001
0.001
0.002
0.001
0.002
0.001
0.002
0.001
0.003
0.001
0.003
0.001
0.004
0.002
0.004
0.002
0.004
0.002
0.005
0.002
0.005
0.002
0.006
0.003
0.007
0.003
0.007
0.003
0.008
0.004
0.008
0.004
100%
0.50
2.0
114.3
228.6
0.16
2
100%
0.52
3.00
43.9
91.4
0.07
0.8
48mm
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.001
0.001
0.001
0.001
0.001
0.001
0.001
0.001
0.001
0.002
0.002
0.002
2cm
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.001
0.001
0.001
0.001
0.001
0.002
0.002
0.002
0.002
0.003
0.003
0.004
0.004
0.004
0.005
0.005
0.006
0.006
100%
0.52
3.00
43.9
91.4
0.16
2.0
Woodchip
100%
0.52
3.00
43.9
91.4
0.33
4
Woodchip Particle Diameters
5cm
10cm
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.001
0.000
0.001
0.000
0.001
0.000
0.001
0.000
0.001
0.000
0.001
0.001
0.001
0.001
0.001
0.001
0.001
0.001
0.002
0.001
0.002
0.001
0.002
0.001
0.002
0.001
0.002
0.001
100%
0.52
3.00
43.9
91.4
0.49
5.9
15cm
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.001
0.001
0.001
0.001
0.001
Pressure Drop across the Bed of a Single Biofilter Unit with Various Media Porosities
Bed Area (ft^2)
Air Density (lb/ft^3)
Dynamic Viscosity (lb-s/ft^2)
Air Temperature (F)
180
7.65E-02
3.75E-07
60
Air Flow Rate (cfm)
0
500
1,000
1,500
2,000
2,500
3,000
3,500
4,000
4,500
5,000
5,500
6,000
6,500
7,000
7,500
8,000
8,500
9,000
9,500
10,000
10,500
11,000
11,500
12,000
Void Fraction
Bed Depth (ft)
Ratio, a
Specific Surface Area (ft^-1)
Particle Diameter (ft)
Particle Diameter (in)
0.50
2.00
36.0
72.0
0.0833
1
Lava Rock
0.40
0.30
2.0
2.0
43.2
50.4
72.0
72.0
0.0833
0.0833
1
1
0.20
2.0
57.6
72.0
0.0833
1
0.52
3.00
8.6
18.0
0.333
4
0.42
3.00
8.6
18.0
0.333
4
Woodchip
0.32
3.00
8.6
18.0
0.333
4
Superficial Velocity (ft/s)
0.00000
0.04630
0.09259
0.13889
0.18519
0.23148
0.27778
0.32407
0.37037
0.41667
0.46296
0.50926
0.55556
0.60185
0.64815
0.69444
0.74074
0.78704
0.83333
0.87963
0.92593
0.97222
1.01852
1.06481
1.11111
0.50
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.001
0.001
0.001
0.001
0.001
0.001
0.001
0.002
0.002
0.002
0.002
0.003
0.003
0.003
0.003
0.004
Lava Rock Void Fraction
0.40
0.30
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.001
0.000
0.001
0.000
0.001
0.001
0.002
0.001
0.003
0.001
0.003
0.001
0.004
0.002
0.005
0.002
0.006
0.002
0.007
0.003
0.008
0.003
0.009
0.004
0.010
0.004
0.011
0.005
0.013
0.005
0.014
0.006
0.016
0.006
0.017
0.007
0.019
0.007
0.021
0.008
0.023
0.009
0.024
0.20
0.000
0.001
0.001
0.003
0.004
0.006
0.008
0.010
0.013
0.016
0.019
0.023
0.026
0.031
0.035
0.040
0.045
0.050
0.056
0.062
0.068
0.074
0.081
0.088
0.096
0.52
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.001
0.001
0.001
0.001
0.001
0.001
0.001
0.001
0.001
Woodchip Void Fraction
0.42
0.32
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.001
0.000
0.001
0.000
0.001
0.000
0.001
0.001
0.001
0.001
0.002
0.001
0.002
0.001
0.002
0.001
0.003
0.001
0.003
0.001
0.003
0.001
0.004
0.002
0.004
0.002
0.005
0.002
0.005
0.002
0.006
0.002
0.006
0.003
0.007
0.22
3.00
8.6
18.0
0.333
4
0.22
0.000
0.000
0.000
0.000
0.001
0.001
0.002
0.002
0.003
0.004
0.004
0.005
0.006
0.007
0.008
0.010
0.011
0.012
0.014
0.015
0.017
0.019
0.020
0.022
0.024
Appendix L
Ductwork Friction
Losses
Ductwork Pressure Loss
Splitter Box to Tee
Component
Isolation Valve
Damper
90 Deg Elbow
Flow Meter: Orifice Plate
Qty
1
1
4
1
K factor
0.04
0.3
0.45
3.5
Total
0.04
0.3
1.8
3.5
Qty
1
1
1
5
K factor
3.5
0.04
0.3
0.45
Total
3.5
0.04
0.3
2.25
Qty
1
1
K factor
1
0.19
Total
1
0.193
Qty
1
2
1
1
K factor
1
0.04
0.45
0.12
Total
1
0.08
0.45
0.12
Component
90 Deg Elbow
Expansion
Expansion
Contraction
Contraction
Contraction
Expansion
Location 1
NA
30" Pipe
Top of Media Bed
Humidication
Plenum
Headspace
42" Exhaust Pipe
Location 2
NA
Humid Chamber
Headspace
Plenum
Bottom of Bed
42" Exhaust Pipe
Atm
Qty
4
2
1
1
1
1
1
Component
Velocity (fpm)
Velocity Loss (in. wg)
Dynamic Loss (in. wg)
90 Deg Elbow
Expansion
Expansion
Contraction
Contraction
Contraction
Expansion
1222
1222
33
167
167
33
1247
9.31E-02
9.31E-02
6.93E-05
1.73E-03
1.73E-03
6.93E-05
9.69E-02
1.68E-01
1.68E-01
6.93E-05
7.62E-04
9.52E-04
2.49E-05
9.69E-02
Primary Clarifiers to Tee
Component
Flow Meter: Orifice Plate
Isolation Valve
Damper
90 Deg Elbow
Tee to Fan Inlet
Component
Tee
Reducer (36" to 29")
Fan Outlet to Biofilter
Component
Tee
Isolation Valve
90 Deg Elbow
Expander (29" to 36")
Biofilter
Sources
https://www.captiveaire.com/MANUALS/AIRSYSTEMDESIGN/DESIGNAIRSYSTEMS.HTM#Pressure_Losses_of_System
http://www.engineeringtoolbox.com/minor-loss-air-ducts-fittings-d_208.html
https://www.amca.org/UserFiles/file/Mark%20paper.pdf http://bepan.info/yahoo_site_admin/assets/docs/AES-Ductwork-SystemDesign.2134047.pdf
http://www.tsi.com/uploadedFiles/_Site_Root/Products/Literature/Application_Notes/TI-114A.pdf Kopolis
http://www.metropumps.com/ResourcesFrictionLossData.pdf http://en-co.wika.de/upload/DS_SP6904_en_co_11612.pdf
K factor
0.45
0.9
1.0
0.44
0.55
0.36
1
Total
1.8
1.8
1
0.44
0.55
0
1
Friction Losses in Expansion, Contration, and Pipe Fittings
Splitter Box to Tee
Frictional Losses (in. wg/ 100ft)
Frictional Losses (in. wg)
Dynamic Losses (in. wg)
Velocity Losses (in. wg)
Total Pressure Loss (in. wg)
1. Sudden Enlargement Losses
0.22
0.54
1.19
0.21
1.73
= 1 − 2. Sudden Contraction Losses
Primary Clarifiers to Tee
Frictional Losses (in. wg/ 100ft)
Frictional Losses (in. wg)
Dynamic Losses (in. wg)
Velocity Losses (in. wg)
Total Pressure Loss (in. wg)
0.14
0.52
1.21
0.20
1.73
= 0.55 1 − Tee to Fan Inlet
Frictional Losses 36" PVC (in. wg/ 100ft)
Frictional Losses 36" PVC (in. wg)
Dynamic Losses (in. wg)
Velocity Losses (in. wg)
Total Pressure Loss (in. wg)
Location 1
30" PVC Pipe
Humidifcation
Bottom
Top of Bed
Headspace
36" Line
Fan Outlet 29"
Expan
Cont
Cont
Expan
Cont
Cont
Expan
0.08
0.008
0.21
0.18
0.22
Location 2
Humidification
Plenum
Bed
Headspace
Atmosphere
Fan Inlet 29"
36"
A_1 (ft^2)
5
183
177
1
28
7
5
A_2 (ft^2)
183
36
1
177
10
5
7
Fan Outlet to Biofilter
Frictional Losses 36" PVC (in. wg/ 100ft)
Frictional Losses 36" PVC (in. wg)
Dynamic Losses (in. wg)
Velocity Losses (in. wg)
Total Pressure Loss (in. wg)
0.08
0.088
0.30
0.18
0.39
= !"#$
2
%&'( = )*+%% + -%.%)/+0)*) − -12%3'45
67#8 = velocitypressureatthefandischarge
6##$ ! = #K## ##$ !
= dynamic, component, andfrictionalpressurethroughtheairsystem
= !##
Biofilter
Frictional Losses 30" (in. wg/ 100ft)
Frictional Losses 30" PVC (in. wg)
Dynamic Losses (in. wg)
Velocity Losses (in. wg)
Pressure Drop Across Bed (in. wg)
Total Pressure Loss (in. wg)
Pressure Calculations
1. Write down or calculate all known variables
2. Write down or calculate all pressure losses in the section
List the component Losses/Gains
Occur through elbows, transitions, tees, or any other type of fitting.
Use the ASHRAE Fitting Diagrams to find Dynamic Loss Coefficients
for fittings.
0.06
0.021
0.34
0.19
0.20
0.56
Outlet
Frictional Losses 42" (in. wg/ 100ft)
Frictional Losses 42" PVC(in. wg)
Dynamic Losses (in. wg)
Velocity Losses (in. wg)
Total Pressure Loss (in. wg)
Total Pressure Loss (in. wg)
Velocity Pressure at Fan Discharge (in. wg)
Velocity Pressure at Outlet (in.wg)
Static Pressure Required (in. wg)
Hartzell Blower SP (in. wg)
Diameter (in)
Flow Rate (cfm)
Length (ft)
Velocity (fpm)
Frictional Losses (in. wg)
Dynamic Losses (in. wg)
Velocity Losses (in. wg)
Total Pressure Loss (in. wg)
Calculate the Dynamic Losses/Gains
∗ O
0.04
0.002
0.10
0.10
0.0990
O = 6!K## = Calculate the Frictional Losses/Gains
3. Sum up the component, dynamic, and fritional pressure for the section
4. Sum up the pressure losses for all of the sections
Correction for density is not need for tempeartures between 40-100 deg F.
Corretion for moisture is not needed for air temperature <100 deg F.
4.72
0.18
0.10
4.80
7.5
Primary Clarifier
18
3250
375
1783
0.52
1.21
0.20
1.73
4005
https://www.captiveaire.com/MANUALS/AIRSYSTEMDESIGN/DESIGNAIRSYSTEMS.HTM#Pressure_Losses
_of_System
Splitter Box
30
8750
250
1839
0.54
1.19
0.21
1.73
Tee to Fan
36
12000
10
1698
0.01
0.21
0.18
0.22
Fan to Biofilter
36
12000
115
1698
0.09
0.30
0.18
0.39
Biofilter Internal
30
12000
35
1222
0.22
0.34
0.19
0.56
Biofilter Outlet
42
12000
5
1247
0.00
0.10
0.10
0.10
K
0.95
0.44
0.55
0.99
0.36
0.19
0.12
Point
P (PSI)
Q (cfm)
D (in)
A (sf)
L (ft)
V (fpm)
Air Flow Characteristics at Various Locations in the System
1
2
3
4
5
6
7
14.7
14.7
12.973 12.751
14.7
14.31
13.76
3250
8750
36
36
12000
6000
12000
18
30
10
10
36
30
--1.77
4.91
7.07
7.07
7.07
4.91
72.00
250
375
12000
6000
110
35
--1839
1783
1698
849
1698
1222
167
8
13.66
12000
42
9.62
5
1247
Primary Clarifiers
2
3
5
4
6
Biofilter Unit 1
8
Fan
Biofilter Unit 2
7
1
Splitter Box
The friction loss per unit length of
pipe was calculated using both the
Darcy-Weisbach equation and the
Friction Chart (ASHRAE, 1997) as
shown to the right. The more
conservative of pressure losses was
given using the Friction Chart and
they were used to size the fan.
Appendix M
Fan Performance
Curve
FAN LAWS
CFM
RPM
SP
HP
NEW
8000
1170
3.3
5.9
NEW
6000
878
1.9
2.5
OLD
12000
1755
7.5
20
100% Effective Duct Length
Duct Diameter (in)
Effective Duct Length (ft)
Outlet Area
Blast Area
Ratio
No System Effect
36
7.5
4.59
4.45
1.0
0
On the fan’s inlet side, AMCA Publication 201 recommends that the elbows near the fan’s
inlet be located at least three duct diameters upstream of the fan. On the fan’s outlet side,
AMCA Publication 201 recommends that the effective duct length is 2.5 diameters when
duct velocities are 2,500 fpm or less, with one duct diameter added for each additional
1000 fpm. Additionally, a centrifugal fan needs 100% of an effective duct length on its
outlet to avoid System Effect.
Stevens, M. Fan Performance. Air Movement and Control Association International, Inc..
Appendix N – Moisture Control Calculations
Irrigation
Note: all calculations are for 1 biofilter bed
Volume of Water in Wood Chip Layer
Wood Chips
Size of Bed
15.1
Density of Dry Wood Chip
380000
Moisture Content
Calculated Amount of Water
Density of Water
Calculated Volume of Water
0.6
8586.8
1000.0
8.6
Calculated Volume of Water
2268.4
Lava Rock
Size of Bed
10.0
Density of Dry Wood Chip
520000
m3
g/ m3
g water/ g
water+media
kg water
kg/ m3
m3
gallons
m3
g/ m3
Moisture Content
Calculated Amount of Water
Density of Water
Calculated Volume of Water
0.155
958.0
1000.0
1.0
g water/ g
water+media
kg water
kg/ m3
m3
Total Volume of Water Needed
2521.5
gallons
Calculated Volume of Water
253.1
Irrigation Flow Rate Required
Hydraulic Loading Rate Approach
Length of Biofilter
Width of Biofilter
14.00
12.67
ft
ft
0.246
1.84
ft3/min
gpm
Hydraulic loading rate
0.001389
General Rule Approach
Air Flow Rate
12000
Flow Rate
Flow Rate
gal. water per 100,000 cu. ft air
5
6
7
8
9
10
gallons
Water Apply Rate
0.6
0.72
0.84
0.96
1.08
1.2
ft/min
cfm
gpm
gpm
gpm
gpm
gpm
gpm
Notes
*woodchips only
http://www.aquacalc.com/page/densitytable/substance/woodblank-chips-coma-and-blankdry
*derived from MC equation
*in wood chip layer at any
given time
*lava rock only
*from research RamirexSaenz et al., 2009
*from research Chitwood, et
al. 1999 AND Ramirex-Saenz
et al., 2009
*derived from MC equation
*in lava rock layer at any
given time
*from research Williams and
Miller (1992)
*HLR = flow rate / (L*W of
bed)
*maximum per biofilter
*5 to 10 gallons water per
100,000 cubic feet off gas
*from research Williams and
Miller (1992)
Humidification
Mollier Diagram Approach
Notes
Worst Case Scenario
Temperature of Incoming Air
35
Relative Humidity of Incoming Air
10%
Relative Humidity of Exiting Air
100%
Specific Humidity 1 (x_1)
0.0036
Specific Humidity 2 (x_2)
0.01125
Air Flow Rate (v)
5.6634
Density of Incoming Air (rho)
1.146
Water Flow Rate Required
Mollier Diagram:
*assumed worst case = 95 ᵒF
kg/kg
*from Mollier Diagram
kg/kg
m3/s
kg/ m3
m_w = v * rho (x_2 - x_1)
Mass Flow Rate of Water (m_w)
Volumetric Flow Rate of Water
Volumetric Flow Rate of
Water
ᵒC
0.049650193
0.787
gpm
4.96502E-05
kg/s
m3/s
*assumed worst case
*design for complete saturation
*from Mollier Diagram
*using a 12000cfm fan
*at incoming air temperautre
http://www.engineeringtoolbox.com/
steam-humidifying-air-d_697.html
Selecting Nozzle Type and
Number
Irrigation
Manufacturer:
Spraying Systems Co.
http://www.spray.com/cat75/hydraulic/files/31.html
Notes:
Spray diamter must be less than 1mm (0.04in)
Cumulative flow rate must be less than 1.85gpm
Minimuze flow pressure
Maximize spray radius
Need to cover an area of 12.667*14 =
Calculated Irrigation Flow Rate
177.3334
1.84
ft2
gpm
Nozzle Properties (based on selection criteria)
Manufacturer Category
Possible Nozzle Types
Capacity Size
Orifice Dia. Nom
Max Free Passage Dia
Pressure
Flow Rate Capacity
Spray Angle
Notes
Standard Angle Spray
G, GG, HH, GD, GGD
1
0.031
0.025
in
in
20
psi
58
degrees
0.14
gpm
*size of foreign particle that is
allows to pass
*entire angle of cone
Approach 1
Number of Nozzles Needed
Calculated Height of Nozzles
13.16
3.3
nozzles
ft
Approach 2
Choose Height of Nozzles
Calculated Coverage of Each Nozzle
Number of Nozzles Needed to Cover Total Area
Suggested Number of nozzles
Flow Rate of Each Nozzle
3
11.06
16.03
16
0.115
ft
ft2
nozzles
gpm
* based on flow rate capacity and
flow rate needed
Selecting Nozzle Type and
Number
Humidification
Total Cross Sectional Area
Calculated Humidification Flow
Rate
Manufacturer:
Spraying Systems Co.
http://www.spray.com/cat75/hydraulic/files/31.html
40.83
47.22
ft2
gph
Nozzle Properties (based on selection criteria)
Fine Spray Nozzle - Hydraulic
Manufacturer Category
Atomizing Nozzles
Possible Nozzle Types
Capacity Size
Orifice Dia Nom
Pressure
Flow Rate Capacity
Spray Angle
(small drops without compressed air)
LN, LNN, LND, LNND, N, NN, M
18
0.076
300
49
86
in
psi
gph
degrees
*entire angle of cone
nozzles
* based on flow rate capacity and flow rate needed
Approach 1
Number of Nozzles Needed
Calculated Height of Nozzles
0.549
4.624
ft
Approach 2
Choose Height of Nozzles
Calculated Coverage of Each
Nozzle
Number of Nozzles Needed to
Cover Total Area
Suggested Number of nozzles
Flow Rate of Each Nozzle
10
347.83
0.12
1
47.2184
ft
ft2
nozzles
gph
Appendix O – CWP Wastewater Temperature
Table 1. Hydrogen Sulfide Concentrations
Location
Splitter Box
Carbon Adsorber
Hydrogen Sulfide (ppmv)
Average
2.72
6.26
Maximum
21.7
22
Table 2.Water Temperature 2013-2015
Avg. Temp (F) 60
Max. Temp (F) 70
Min. Temp (F) 50
Table 3. Inlet Air Temp at Carbon Adsorber (11/19/15-1/4/16)
Avg. Temp (F) 48.0
Max. Temp (F) 59.7
Min. Temp (F) 26.9
Frequency
Histogram Water Temperature 2013-2015
120
100
80
60
40
20
0
50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70
Water Temperature (F)
Figure 1. Hydrogen Sulfide Readings 12/21/15-12/30/15
Appendix P – Ductwork Heat Loss Calculations
Using Longest Pipe Stretch
Notes
Calculate Surface Area of Pipe
Inner Pipe Diameter (Di)
Inner Perimeter of Pipe
Length of Pipe (longest distance)
Surface Area of Pipe
0.762
m
124.72
m
2.39
298.57
m
m2
Calculate Mass Flow Rate of Air
Air Flow Rate (v)
Density of Incoming Air (rho_air)
Mass Flow Rate of Air (m_dot_air)
5.66
m3/s
6.99
kg/s
1.2348
kg/m3
*using a 12000cfm fan, use flow rate at exit
*at incoming air temperature, assume
atmospheric pressure
Process of Calculating Heat Loss:
Calculate the Log Mean Temperature based on an assumed outlet temperature
Calculate Heat Loss based on convective heat transfer and the calculated Log Mean Temperature
Calculate Heat Loss based on the heat capacity of air using the assumed outlet temperature
Iterative Process - change the assume outlet temperature until the two values for Heat Loss match
Calculate Heat Loss based on
Convective Heat Transfer
* convective heat transfer
Initial Air Temperautre (T_air_in)
285.93
K
Surface Area of Pipe (A)
298.57
m2
Ambient Air Temperature (T_amb)
Convective Heat Transfer Coefficient
of Air (h)
Guess Outlet Temperautre (Inlet to
Biofilter) (T_air_out)
Calculated Log Mean Temperature
(T_LM)
Calculated Convective Heat Loss (Q)
Calculate Heat Loss based on Heat
Capacity of Air
Specifict Heat Capacity of Air
(C_p_air)
Mass Flow Rate of Air (m_dot_air)
Initial Air Temperautre (T_air_in)
Guess Outlet Temperautre (Inlet to
Biofilter) (T_air_out)
Calculated Heat Loss based on Heat
Capacity of Air (Q)
249.82
100
250.335
8.385917
250375.3
1005
6.993129
285.928
250.335
250151
K
W/( m2-K)
K
K
W
J/(kg-K)
kg/s
K
K
W
* 55 deg F
* -10 deg F
* forced convection, moderate speed flow of air
over surface
http://thermopedia.com/content/660/
* Q = m_dot_air * C_p_air * (T_air_in T_air_out)
* T_LM = ((T_in_air - T_amb) - (T_air_out T_amb)) / (ln((T_air_in - T_amb)/(T_air_out T_amb)))
* Q = h * A * T_LM
*at incoming air temperautre, assume
atmospheric pressure
* 55 deg F
* Q = m_dot_air * C_p_air *(T_air_in T_air_out)
Thickness of Insulation Needed
Thermal Conductivity of Insulation
(k)
Initial Air Temperautre (T_air_in)
Ambient Air Temperature (T_amb)
Surface Area of Pipe (A)
Specifict Heat Capacity of Air
(C_p_air)
0.03
285.928
249.817
298.5664
1005
Mass Flow Rate of Air (m_dot_air)
Acceptable Outlet Temperature
(T_acceptable_out)
6.993129
Thickness of Insulation Needed (t)
0.082773
Acceptable Heat Loss (Q_acceptable)
285.372
3907.62
3.258786
W/(m-K)
K
K
m2
J/(kg-K)
kg/s
K
W
m
inches
* plastics, foamed insulation materials
http://www.engineeringtoolbox.com/thermalconductivity-d_429.html
* 55 deg F
* -10 deg F
*at incoming air temperautre, assume
atmospheric pressure
* 54 deg F
* Q = m_dot_air * C_p_air *(T_air_in T_air_out)