Project Proposal and
Feasibility Study
Team 17
Jonathan Gingrich
Lauren Grimley
Cassandra Miceli
Kerala Smith
Senior Design Project: Engineering 339/340
12/11/15
Copyright © 2015, Calvin College, Jonathan Gingrich,
Lauren Grimley, Cassandra Miceli, Kerala Smith
EXECUTIVE SUMMARY
Executive Summary
The objective of this project is to design an odor-control system for the Wyoming Clean Water Plant
(CWP) that will minimize nuisance odors to tolerable levels. The proposed technology is a
biofiltration unit that will treat the air emitted from an uncovered splitter box. The splitter box directs
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 will be 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. These systems have proven to be challenging with respect to
maintenance and cost, causing the CWP to be more inclined towards using biofiltration. In order to
properly understand the advantages of biofiltration, the team researched multiple odor-reducing
technologies in order to verify that biofiltration was the best option for the CWP. Various design
criteria were considered to determine the optimal odor-reducing technology including; installation
and operation costs, the time required for maintenance, and the client’s preference. The feasibility of
biofiltration was confirmed through research, discussions with engineers and specialists, and the
success of biofiltration currently installed at plants in the area.
The majority of the design for the biofilter will be carried out during the spring of 2016. There are
multiple parameters that must be considered during the design process including packing media,
temperature, moisture content, oxidation reduction potential, pressure drop, pH, empty bed recovery
time, bed area, and medium depth. The biofilter will be modeled as a reactor in order to determine
the necessary volume. The media dictates many factors of the design and will be optimized in early
spring. The primary selection criteria for the packing media will depend on its upfront cost, the
anticipated maintenance and operation, the life of the media, and its environmental impact.
This Project Proposal and Feasibility Study details project goals and design alternatives, providing
the necessary parameters for design and affirming the feasibility of the project.
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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
1
Introduction ________________________________________________________________________________________10
1.1
Senior Design Background ______________________________________________________________________ 10
Calvin College Engineering Department__________________________________________________ 10
Senior Design _______________________________________________________________________________ 10
Team 17 _____________________________________________________________________________________ 10
Project Background ________________________________________________________________________ 12
2
Project Management _______________________________________________________________________________14
2.1
Team Organization ______________________________________________________________________________ 14
2.2
Schedule __________________________________________________________________________________________ 14
2.3
Budget ____________________________________________________________________________________________ 15
2.4
Method of Approach _____________________________________________________________________________ 15
Research Techniques_______________________________________________________________________ 15
Team Communication______________________________________________________________________ 15
Design Methodology _______________________________________________________________________ 16
3
Project Overview ___________________________________________________________________________________17
3.1
Project Description ______________________________________________________________________________ 17
3.2
Client _____________________________________________________________________________________________ 17
3.3
Objectives ________________________________________________________________________________________ 18
3.4
Design Constraints ______________________________________________________________________________ 18
3.5
Design Criteria ___________________________________________________________________________________ 19
3.6
Design Norms ____________________________________________________________________________________ 19
Transparency _______________________________________________________________________________ 19
Stewardship ________________________________________________________________________________ 20
Caring _______________________________________________________________________________________ 20
4
Odor-Control Background _________________________________________________________________________21
Page 3 of 84
TABLE OF CONTENTS
4.1
Overview _________________________________________________________________________________________ 21
Wastewater Treatment Facility Odor-Control ___________________________________________ 21
Public Concern _____________________________________________________________________________ 21
Government Regulations __________________________________________________________________ 21
4.2
Odor Source ______________________________________________________________________________________ 23
Overview ____________________________________________________________________________________ 23
Hydrogen Sulfide ___________________________________________________________________________ 23
4.3
Vapor-phase Treatment _________________________________________________________________________ 24
Wet Air Scrubbing __________________________________________________________________________ 24
Liquid Redox________________________________________________________________________________ 25
Biofiltration _________________________________________________________________________________ 25
Solid Scavengers____________________________________________________________________________ 25
Carbon Adsorption _________________________________________________________________________ 25
5
4.4
Liquid-phase Treatment ________________________________________________________________________ 26
4.5
Odor-control Descision Matrix _________________________________________________________________ 26
Wyoming Clean Water Plant ______________________________________________________________________28
5.1
Background ______________________________________________________________________________________ 28
Plant Operations ___________________________________________________________________________ 28
Odor-Control _______________________________________________________________________________ 28
5.2
Exisiting Plant Operations ______________________________________________________________________ 28
5.3
Odor-control _____________________________________________________________________________________ 29
Headworks __________________________________________________________________________________ 29
Primary Clarifiers __________________________________________________________________________ 30
Biosolids Storage Tanks ___________________________________________________________________ 31
Splitter Box _________________________________________________________________________________ 33
6
Biofiltration Technology ___________________________________________________________________________35
6.1
Overall Process Description and Terminology ________________________________________________ 35
6.2
Mechanisms of Operations ______________________________________________________________________ 36
Biokinetics __________________________________________________________________________________ 36
Mass Loading Rate _________________________________________________________________________ 36
Biofilm Kinetics ____________________________________________________________________________ 36
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TABLE OF CONTENTS
Biodegradation _____________________________________________________________________________ 38
Microbiology________________________________________________________________________________ 39
6.3
Characterizing Biofilter Performance __________________________________________________________ 40
Removal Efficiency _________________________________________________________________________ 40
Elimination Capacity _______________________________________________________________________ 40
6.4
Factors Affecting Biofilter Performance _______________________________________________________ 41
Packing Media ______________________________________________________________________________ 41
Moisture Content ___________________________________________________________________________ 42
Nutrient Control ____________________________________________________________________________ 42
Temperature ________________________________________________________________________________ 42
pH Value ____________________________________________________________________________________ 43
Empty Bed Residence Time _______________________________________________________________ 43
Oxygen Content ____________________________________________________________________________ 44
Pressure Drop ______________________________________________________________________________ 44
Medium Diameter and Surface Area ______________________________________________________ 44
Bed Depth ___________________________________________________________________________________ 44
6.5
Operation_________________________________________________________________________________________ 45
Materials ____________________________________________________________________________________ 45
Condensation _______________________________________________________________________________ 45
Cover and Insulation _______________________________________________________________________ 45
Air Distribution_____________________________________________________________________________ 46
Ductwork and Accessories ________________________________________________________________ 48
Configuration _______________________________________________________________________________ 48
7
Modeling ____________________________________________________________________________________________50
7.1
Introduction______________________________________________________________________________________ 50
7.2
Ottengraf and Ven Den Ooever Kinetics________________________________________________________ 50
Zero-Order Reaction-Limited _____________________________________________________________ 51
Zero-Order Diffusion-Limited _____________________________________________________________ 51
First Order __________________________________________________________________________________ 51
7.3
Michaelis-Menten Kinetics ______________________________________________________________________ 52
Zero-Order Kinetics in Concentration ____________________________________________________ 52
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TABLE OF CONTENTS
First-Order Kinetics ________________________________________________________________________ 52
Fractional Order Kinetics __________________________________________________________________ 53
7.4
Model Case Studies ______________________________________________________________________________ 53
Kinetics and Modeling of Hydrogen Sulfide Removal [42] ______________________________ 53
Michaelis Menten Kinetics _________________________________________________________________ 53
8
Biofilter Packing Media ____________________________________________________________________________55
8.1
Introduction______________________________________________________________________________________ 55
8.2
Natural Media ____________________________________________________________________________________ 55
Peat __________________________________________________________________________________________ 56
Woodchip and Compost ___________________________________________________________________ 56
Activated Carbon ___________________________________________________________________________ 58
Lava Rock ___________________________________________________________________________________ 59
Comparative Study _________________________________________________________________________ 60
8.3
Natural Mixtures_________________________________________________________________________________ 61
8.4
Synthetic _________________________________________________________________________________________ 61
Polyurethane Foam ________________________________________________________________________ 61
BiosorbensTM _______________________________________________________________________________ 62
9
Full-scale Biofilter Case Studies___________________________________________________________________63
9.1
Three Rivers Clean Water Plant (TRCWP) _____________________________________________________ 63
9.2
North Kent Sewer Authority ____________________________________________________________________ 64
PARCC Side Clean Water Plant ____________________________________________________________ 64
Biofiltration System ________________________________________________________________________ 65
Biofilters Configuration [61] ______________________________________________________________ 66
10
Basis of Design __________________________________________________________________________________69
10.1
Proposed Project Scope _________________________________________________________________________ 69
10.2
Design Criteria ___________________________________________________________________________________ 69
10.3
Conceptual Design _______________________________________________________________________________ 69
Biofilter Modeling __________________________________________________________________________ 70
Packing Media ______________________________________________________________________________ 71
Biofilter Size ________________________________________________________________________________ 71
System Configuration ______________________________________________________________________ 72
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TABLE OF CONTENTS
Air Distribution System ____________________________________________________________________ 72
Moisture Control System __________________________________________________________________ 72
Monitoring and Controls___________________________________________________________________ 73
Chemical and Nutrient Requirements ____________________________________________________ 73
Additional Equipment _____________________________________________________________________ 73
Economic Cost Analysis _________________________________________________________________ 74
10.4
Base Case Calculations __________________________________________________________________________ 74
10.5
Long-Term Odor-control Study _________________________________________________________________ 75
11
Acknowledgements _____________________________________________________________________________77
12
References _______________________________________________________________________________________78
13
Appendices ______________________________________________________________________________________84
Appendix A – Gantt Chart _______________________________________________________________________________ 84
Appendix B – Project Budget ___________________________________________________________________________ 84
Appendix C – CWP Flow Diagram ______________________________________________________________________ 84
Appendix D – Headworks H2S Data ____________________________________________________________________ 84
Appendix E – Primary Clarifier H2S Data ______________________________________________________________ 84
Appendix F – Biosolids Storage Tanks H2S Data ______________________________________________________ 84
Appendix G – Splitter Box Drawings ___________________________________________________________________ 84
Appendix H – Splitter Box H2S Data ____________________________________________________________________ 84
Appendix I – FIRM Map _________________________________________________________________________________ 84
Appendix J – Base Calculations _________________________________________________________________________ 84
Page 7 of 84
TABLE OF FIGURES
Table of Figures
Figure 1. CWP Process Flow Diagram ........................................................................................................................... 12
Figure 2. Location of the CWP .......................................................................................................................................... 17
Figure 3. CWP Splitter Box Location .............................................................................................................................. 18
Figure 4. Schematic view of a general scrubber system [16] .............................................................................. 24
Figure 5. Locations of Current and Proposed Odor-Control Units (Google Maps) ..................................... 29
Figure 6. Solids buildup on media of chemical scrubbers (Lauren Grimley)................................................ 32
Figure 7. Splitter Box at the Wyoming Clean Water Plant (Lauren Grimley) ................................................ 33
Figure 8. Splitter Box (Lauren Grimley) ....................................................................................................................... 34
Figure 9. Biofiltration Process Flow Diagram [27] .................................................................................................. 35
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 [30]. ...................................................................................................................................................................... 37
Figure 11. Overview of Biodegradation Process for Biofiltration [29]............................................................ 38
Figure 12. Model-simulated sulfide elimination as a function of sulfide loading for various influent
H2S concentrations (straight line represents 100% elimination) [35]. .......................................................... 41
Figure 13. Schematic of different designs of biofilter inlet and outlet locations [40] ............................... 47
Figure 14. Removal Efficiency of Activated Carbon Media [50] ......................................................................... 59
Figure 15. Completed Biofilter at Three Rivers Wastewater Treatment Plant [57] ................................... 63
Figure 16. Installation of Porous Floor of Biofilter [57] ........................................................................................ 64
Figure 17. PARCC Side CWP ............................................................................................................................................... 65
Figure 18. PARCC Side CWP Biofilters (Lauren Grimley) ...................................................................................... 66
Figure 19. PARCC Side CWP Biofilter Configuration (Lauren Grimley)........................................................... 67
Figure 20. Base Case Removal of Hydrogen Sulfide across a Peat Filled Packed Bed Reactor .............. 75
Page 8 of 84
TABLE OF TABLES
Table of Tables
Table 1. Existing Odor-Control Systems at CWP _________________________________________________________ 13
Table 2. Odor-Control Technology Decision Matrix ______________________________________________________ 27
Table 3. Characteristics of Two Types of Wood Chip Media Types for Biofiltration [49] _____________ 57
Table 4. Properties of Biosorbens media [56] ____________________________________________________________ 62
Table 5. Monthly PARCC Side CWP Temperature and pH Readings for Air Entering Biofilter ________ 67
Page 9 of 84
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 better prepared 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 are composed of 3-5
engineering seniors who develop a project that meets the needs of a client while working under the
guidance of industrial consultants.
Team 17
The members of Team Bi0der (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 design
alternatives for an odor-control system for the CWP as their senior design project.
JONATHAN GINGRICH
CHEMICAL
Jonathan Gingrich is a Chemical Engineering and
Biochemistry double major from Columbus, Ohio. He has an
interest in water purification for developing communities,
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. His current
plans post-graduation involve attending graduate school to
obtain a PhD in environmental engineering.
Page 10 of 84
INTRODUCTION
LAUREN GRIMLEY
CIVIL/ENVRIONMENTAL
Lauren Grimley is a civil/environmental engineering senior
from Houston, Texas. Lauren is passionate about waterrelated challenges and is interested in pursuing a career
working on projects within the water-energy nexus.
Through engineering projects in Peru and coursework in
Europe, she has developed a well-rounded perspective of
water resources and water quality issues. Lauren is
interested in the scientific assessment of environmental
challenges and the development of innovative, sustainable
solutions.
CASSANDRA MICELI
CHEMICAL
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
CIVIL/ENVIRONMENTAL
Kerala Smith was born and raised in southern Minnesota
and is majoring in civil/environmental engineering.
Internship and research experience has confirmed her
interest in water/wastewater treatment processes as well
as environmental remediation and assessments. She has
had the opportunity to travel abroad to Germany for study
and to Peru for water resourcing engineering experience,
equipping her with a unique global perspective on the field
of engineering.
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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 CWP at 2350 Ivanrest, SW, Wyoming, Michigan. The CWP is a wastewater
treatment facility with a design capacity of 24 million gallons per day (mgd) of flow. The wastewater
enters the plant where grit and floatables are removed at the headworks building. The wastewater
then flows to the primary clarifies where settlement of large particles and sediment occurs before the
flow proceeds through the aeration basins where biological growth and particle flocculation is
stimulated. The solids formed are processed at the biosolids storage tanks at the north end of the
plant while the wastewater is sent through the secondary clarifiers prior to chlorination and
discharge into the Grand River. An overall process flow diagram of the CWP is shown in Figure 1.
Figure 1. CWP Process Flow Diagram
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INTRODUCTION
The CWP desires to install an odor-control unit over a splitter box of primary clarifier effluent. The
target pollutant to be removed from the waste air streams is hydrogen sulfide (H2S). Bi0dor aims to
reduce the concentration to below detectable and nuisance levels (less than 2 ppbv ). The existing
odor-control systems at the CWP are shown in Table 1. The treatment facility uses chemical scrubbers
and carbon adsorption to control odors at locations throughout the plant. However, the effectiveness
and associated operating costs of these systems has been unfavorable for the CWP.
Table 1. Existing Odor-Control Systems at CWP
Chemical Scrubbers
Carbon Adsorber
Average H2S
Concentration
(𝐩𝐩𝐦𝐯 )
0
6.3
Maximum H2S
Concentration
(𝐩𝐩𝐦𝐯 )
0
22
Chemical Scrubbers
12.3
88
Uncontrolled
2.4
21.7
Odor Source
Odor-Control System
Headworks
Primary Clarifiers
Biosolids Storage
Tanks
Splitter Box
The current odor-reducing processes produce an undesirable byproduct. The chemical scrubber is
experiencing excessive solids buildup for unknown reasons and the carbon filtration unit produces a
nuisance odor, a “fish tank” smell, which the manufacturer cannot identify. Given the issues with their
existing odor-control systems, a new approach using biofiltration is the proposed odor treatment
method for the splitter box. This project will also include a general evaluation of the current operating
odor-control systems at the CWP and provide a conceptual design for a biofiltration system to treat
all odor sources at the CWP.
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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 expertise of each member contributes well to the team dynamic. The
civil/environmental engineering students on Team Bi0dor will be able to contribute greatly to the
physical processes, construction, and layout of the biofiltration system using their familiarity with
the biological wastewater treatment processes. The chemical engineering students will be
knowledgeable in modeling the biofilter as a reactor using specific chemical reactions necessary for
the success of the treatment process. All team members are heavily involved in the research phase of
the project, with each member focusing on their area of education.
The team is advised by professional civil engineer, Robert Masselink, and Professor Jeremy Van
Antwerp, a chemical engineering professor at Calvin College. The team’s industrial consultant is Ben
Whitehead, a civil engineer at Black and Veatch. Based on experiences and specialty knowledge, each
of these advisors provide valuable insights and are able to refer the team to resources that aid to the
progress of the project.
2.2 SCHEDULE
The primary objectives for this project are divided between the fall and spring semesters. The main
goals for the fall semester include:






Communicate with our client to fully understand the current operation of the CWP
Complete all preliminary research needed for design of the project (media, design parameters,
environmental parameters, microbial abilities, etc.)
Narrow down the media selection to a few optimal alternatives (including organic and
synthetic)
Visit wastewater treatment plant(s) that currently have operating biofilters
Connect with an odor-control design engineer
Complete base calculations of a biofilter
The spring semester goals include:






Select media using a decision matrix
Model the biofilter as a reactor by performing kinetic analyses
Optimize the biofilter design based on design parameters
Prepare design specification and design drawings
Recommend equipment and biofilter location
Produce final report
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PROJECT MANAGEMENT
The team meets regularly twice a week to discuss research and progress. At each of these meetings,
a plan of action is made and tasks for the week are distributed to each member. Meetings with each
of the two professors occur weekly on a rotating basis to address questions and discuss progress.
Each team member also tracks their hours working on the project on a spreadsheet located in the
shared google drive. A complete schedule is outlined in the Work Breakdown Schedule located in
Appendix A.
2.3 BUDGET
Bi0dor has determined that it is not within the scope of our project to build a pilot-scale biofilter at
the CWP during the spring semester. Through the advice of practicing engineers, the team and client
has decided that a characterization of the air emitted from the splitter box is not required. The
biofilter will be designed to remove the hydrogen sulfide assuming the biofilter will effectively
remove any other pollutants. However, any testing or project expenses will be funded with $500
budget from Calvin College’s Engineering Department.
If a characterization study was to be completed on the air, the majority of the cost will be used to
contract out the services. The team would need to purchase equipment including Tedlar Bags and a
Vac-U-Chamber which would cost approximately $3945 [1]. Additionally, the VOC analysis of the gas
is $125 per sample [2]. Assuming that samples would be taken weekly for 1 month, the cost for the
sampling at 5 locations in the plant is estimated at $6645 [3]. Obtaining the characterization of the
effluent is $6145 over budget, therefore the sampling and analysis will likely not take place without
aid from the CWP.
2.4 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 acquire knowledge on biofiltration, the team has used a combination of scholarly articles,
informational websites, industry standards, research databases, and books. Each team member is
given an area of research to focus on during weekly meetings. In general, the chemical team members
focused on finding information concerning the kinetics of biofilters while the civil team members
focused on the types of media alternatives and construction of the system.
Team Communication
The team uses a combination of emails and face-to-face conversations to communicate with each
other. Meeting regularly provides an opportunity for the team to discuss progress or developing
issues that may hinder forward movement. Goals for each week are set during these meeting and
tasks are distributed among the team members.
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PROJECT MANAGEMENT
Design Methodology
The weighted functional analysis is a good method to when there are many conflicting, inter-relating
factors that must be rationalized and considered [4]. There are number of variables that affect the
efficiency of biofilters, therefore this approach will be useful during the design process. It will provide
a method to rank each unit process with respect to odor-potential based on trends determined by
research. The approach is as follows:
1.
2.
3.
4.
5.
6.
Identify all of the odor sources at the plant that have a potential to contribute to the
perception of the odors
Establish a set of parameters regarding odors and odor-potential
Assign weights to each parameter
Establish objective scoring
Calculate total weighted average
Rank unit processes accordingly
This method allows for the project to be approached with a methodology of research, model
development, and biofilter design. It is important that each aspect of the design be thoroughly
researched before it is recommended for the final design.
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PROJECT OVERVIEW
3 Project Overview
3.1 PROJECT DESCRIPTION
Our client Myron Erickson, Deputy Director of Public Works for the City of Wyoming, requested the
design of a biofilter odor-control unit at the splitter box as an alternative to other odor-reducing
technologies. The primary objective of this project is to assess the feasibility of treating the odor
released at the splitter box using biofiltration. Another goal is to develop a long-term odor-control
plan to assess the feasibility of treating all odor sources at the CWP with a single biofilter.
3.2 CLIENT
The City of Wyoming is in Kent County, Michigan, and it is the second largest city in West Michigan,
located on the southeast corner of Grand Rapids. The city is nearly 25 square miles and has a
population of 72,125 according to the 2010 Census [5]. The wastewater treatment facility for the City
of Wyoming is called the Wyoming Clean Water Plant (CWP) and it is located on 2350 Ivanrest Ave
SW in Grandville, MI as shown in Figure 2. The facility treats wastewater from four nearby
communities and accommodates approximately 140,000 people [6]. The facility discharges its water
to the Grand River after treatment. 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 odorcontrol systems detailed in the following sections.
Project Location
N
Figure 2. Location of the CWP
Page 17 of 84
PROJECT OVERVIEW
3.3 OBJECTIVES
The primary objective of this project is to design a biofilter that removes hydrogen sulfide from the
air emitted from the splitter box just downstream of the primary clarifiers as shown in Figure 3.
Splitter Box
Figure 3. CWP Splitter Box Location
Biofilters are gaining popularity in the United Stated due to their low-cost and low-maintenance
requirements. The CWP is currently using other odor-reducing technologies that have proven to be
challenging in regards to maintenance and cost. The CWP is interested in investigating the feasibility
of converting their plant’s odor treatment system to biofiltration. Team Bi0dor intends to produce a
preliminary design of a biofilter for the splitter box that meet the specified constraints and design
criteria. Additionally, the team will assess the feasibility of biofiltration as a method of odor-control
for the entire plant.
3.4 DESIGN CONSTRAINTS
There are a number of aspects of the design process that will constrain how the final product is
developed. One constraint is to exclude the use of chemicals from the final design. The CWP currently
has odor-control technology that requires the use of chemicals but the plant operators would prefer
Page 18 of 84
PROJECT OVERVIEW
to move away from this method due to complications they are currently experiencing, as described
in the following sections of this report. In general, biofilters require less maintenance than competing
odor-reducing technologies, decreasing the labor required to maintain them.
Additionally, safety must be incorporated into the design of the biofilter in such a way that complies
with regulatory standards and is accommodating to plant staff during daily maintenance and repairs.
Safety also implies that the biofilter will not produce any pollutant byproducts that will cause harm
to any persons. The final design will comply with all government regulations.
3.5 DESIGN CRITERIA
The design criteria for the design of the biofilter includes, but is not limited to, the following:







The biofilter must be maintained at optimum operating temperatures.
The biofilter media must be moisturized continuously and uniformly.
The loading conditions for air flow rate must be maintained at a constant rate.
The biofilter should be able to operate efficiently with variability in gas flow or spikes in H2 S.
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
Our team has chosen three design norms to consider for our project. These are transparency,
stewardship, and caring.
Transparency
The basis of the design norm transparency comes down to communication. As a team, we want to
ensure that we are making our deliverables clear to our client. Although our time and budget
constraints may not allow for the installment of a full-scale biofiltration system, we will make certain
to provide the CWP with a preliminary design under full disclosure. We want to communicate with
the plant while recognizing the limitations of our knowledge so that we might be entirely transparent
with them in areas where our experience may fall short.
Additionally, as a team, we are dedicated to remaining transparent with one another. Our differing
schedules require that each member clearly communicates with the other members in an effective
and timely manner. Because the team combines two engineering concentrations, we have an
opportunity to benefit from multiple perspectives with our design approach. However, this diversity
also requires us to focus on communicating clearly with one another. Being transparent with our
client and with our team members will allow Bi0dor to be far more effective in working as a team to
complete this project.
Page 19 of 84
PROJECT OVERVIEW
Stewardship
One of the most attractive aspects of a biofilter is that it normally requires little maintenance to run
effectively. This is a very important aspect in our design process, especially in light of the operational
complications the plant currently has with their existing odor-control system. Our design will
minimize maintenance requirements for the plant operators, reduce the frequency of media
replacements, and eliminate the use of chemicals. Our team intends to evaluate the packing media
selections in light of their carbon footprint, including the energy consumed to produce, deliver, and
dispose of the media. Additionally, to be better stewards towards the client, surrounding community,
and biosphere the biofilter will be optimized in order to reduce energy consumption and carbon
emissions wherever possible.
Caring
Our final design norm is caring, which applies not only to our client but extends also to the
surrounding community and neighborhoods. The CWP is located across the river from Millennium
Park in Grand Rapids. Members of the community have detected nuisance odors in the park and in
their backyards. Bi0dor intends to care for our client and for the surrounding community by
developing a biofiltration design that will reduce unpleasant odors. Furthermore, hydrogen sulfide
emitted from a wastewater plant can be highly toxic at high concentrations. The plant is currently
producing hydrogen sulfide at levels that may induce physical harm if exposed to the gas for an
extended period of time. Currently, the hydrogen sulfide dissipates into the air and is primarily a
nuisance instead of a hazard. In light of our Christian values, we wish to practice engineering in order
to benefit the public and our client.
Page 20 of 84
ODOR-CONTROL BACKGROUND
4 Odor-Control Background
4.1 OVERVIEW
Wastewater Treatment Facility Odor-Control
Wastewater treatment facilities use a number of odor-control technologies to reduce nuisance odors
to tolerable levels, and they are selected depending on the unique characteristics of the air. Common
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 [7]. 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 Section 6 for the chemical reactions of this metabolism).
Hydrogen sulfide has a rotten-egg odor and can cause severe corrosion. Hydrogen sulfide is released
to the atmosphere easily because of its low solubility in wastewater, and this most often occurs at wet
wells, headworks, primary clarifiers, and biosolids storage tanks. Hydrogen sulfide is the most
common pollutant detected in the air at wastewater facilities, though additional pollutants may be
present.
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 harmful to the body. In the open air,
the reason to control theses pollutants stems only from a nuisance concern [7]. 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 100ppmv
[8].
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 [9]. 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 [9].
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
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ODOR-CONTROL BACKGROUND
regulated according to quantitative standards [10]; however, the production of hydrogen sulfide
typically requires odor prevention due to nuisance odors. The production of any nuisance odor
includes “any gas, vapor, fume, or mist, or combination thereof, from a well or its associated surface
facilities” [10], 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.” [11]
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 [12].
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 Best Available Control Technology for Toxics (T-BACT)
must be used for emission control [13]. 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 [14]. 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 [10].
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 are 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. Inherent difficulties exist with the regulation of odors because
the concentration of compounds and the reaction of the individual varies. 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 (H2 S) 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 gas begins to produce its characteristic rotten egg smells 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 100 ppmv. [15]. The concentrations of hydrogen
sulfide found in treatment plants varies depending on the type of process involved and the
characteristics of the wastewater. For municipal treatment, hydrogen sulfide concentrations are
between 45 and 537 ppmv and up to 1000 ppmv in the biogas from anaerobic sludge digester. Others
have reported the concentration of hydrogen sulfide to be 0.1 to 10 ppmv [16].
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 [17]. 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 [18].
Although hydrogen sulfide is present in the wastewater solution as either H2 S (aq) or HS − (depending
on pH) only hydrogen sulfide as H2 S has the ability to transfer between water and air and contributes
to the emission of H2 S gas [19]. The breakdown of these two molecules into their ionic forms are as
follows [20]:
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 [18].
Anaerobic Microorganisms
SO2−
4 + Organic Matter →
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H2 S + CO2
ODOR-CONTROL BACKGROUND
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.
4.3 VAPOR-PHASE TREATMENT
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 wet
air scrubbing, liquid redox technology, biofiltration, solids scavengers, and carbon adsorption [7].
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 [7]. This is the most 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 [16]
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ODOR-CONTROL BACKGROUND
The greatest problem to overcome with this technology is to minimize interaction with potentially
hazardous chemicals, while maintaining adequate treatment of the odor-producing compounds [21].
Liquid Redox
Liquid redox odor-control units use a chelated metal (usually iron) to remove gaseous hydrogen
sulfide and convert it to elemental sulfur. This treatment source is best used in digester gas (biogas)
applications, where the concentration of hydrogen sulfide is relatively high (>200lbs⁄day). If the
concentration is lower than this, then chemical scrubbers are a better choice since they have a much
lower capital cost [7].
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.
Solid Scavengers
Solid scavengers are chemicals or other substances that, when injected into the contaminated stream,
react with the hydrogen sulfide, removing it from the stream. This technology results in very little
corrosion, which means the capital cost is low; however, the chemicals required to scavenge cost quite
a bit, making operating costs comparably high [22].
Carbon Adsorption
In a carbon adsorber unit, the air stream passes over a bed of activated carbon and the contaminants
adhere to the surface of the carbon, thus removed from the air stream. This is a relatively simple form
of odor-control and the only real cost comes from purchasing new activated carbon after the old
carbon has been spent. 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. The disposal and replacement
costs associated with carbon adsorption are also high compared to alternative technologies.
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.
2H2 S (g) + O2 (g) →
1
S (s) + 2H2 O (g)
4 8
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
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ODOR-CONTROL BACKGROUND
odor compounds begin to break through the media, meaning noticeable odors are released from the
unit indicating the media needs to be replaced.
4.4 LIQUID-PHASE TREATMENT
Liquid-phase technologies involve the treatment of the wastewater stream using chemicals to control
or inhibit the formation of odorous compounds. This technology prevents hydrogen sulfide from
escaping the liquid phase and entering into the vapor phase, thus eliminating the release of this
odorous and corrosive gas pollutant. Liquid-phase technologies often involve the use of iron salts or
a nitrate solution which is applied to water to dissolve or precipitate sulfide [7]. Another way that
this method is utilized is through the use of bioxide to treat the hydrogen sulfide in the water as it
enters through the pipes of the treatment plant. Bioxide is Ammonium Calcium Nitrate that is used in
many wastewater treatment plants to remove hydrogen sulfide before it reaches the plant [23]. Like
solid scavengers, this chemical has a very low capital costs, but a high operations cost, as the chemical
must be constantly purchased.
4.5 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. Our client is very interested in biofiltration technology making it a priority for
our 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.
Capital cost is another important consideration because some odor treatment technology can
be ruled out due to high upfront cost. However, capital cost was ranked lower than
maintenance and operation 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 consider because it validates the advantages and
disadvantages of different odor-control technologies from the viewpoint of plant supervisors
around the West Michigan area. For some of the treatment technologies, we were unable to
gather information on the level of satisfaction with that particular method, so they were given
an average score. User satisfaction was ranked 6.
The life of the filter was considered because Bi0dor wanted to choose a filter that would
effectively serve the client for a long time without the need to invest in a new system. Longlasting systems received higher scores than technology with a shorter operating life. The life
of the filter was ranked 5.
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ODOR-CONTROL BACKGROUND

Widely-used technology is an important consideration because some odor-control
technology has existed and been used for a longer amount of time, thus proving themselves
effective technology. The extensive use of certain odor-control technologies also validates the
treatment’s existing customer support, manufacturing options, and operator familiarity with
the product. Plant operators will likely prefer the installation of a technology they are familiar
with or one that has been proven. 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
117
WYOMING CLEAN WATER PLANT
5 Wyoming Clean Water Plant
5.1 BACKGROUND
Plant Operations
The team is in contact with the CWP operators to receive information concerning annual trends for
influent wastewater flow rates, temperatures, average biochemical oxygen demand (BOD), and
average dissolved oxygen (DO) concentrations. This information will help to provide a basis for
determining trends of H2 S production. A flow diagram of the wastewater through the CWP is shown
in Appendix C.
Odor-Control
The CWP currently uses odor-control systems at three locations throughout the plant. The odorcontrol systems target a range of H2 S levels, which would otherwise be released into the atmosphere
causing a nuisance odor. Other odor-producing compounds may be removed during the process of
H2 S 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 H2 S concentrations for each odorcontrol unit beginning in 2013. Operation personnel reported the production of H2 S does not depend
on seasonal variations, which is supported by the data showing no recognizable pattern among
annual H2 S 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 H2 S concentrations remains at zero. The carbon adsorber has seen H2 S
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 H2 S concentrations of greater than 2ppmv can induce
health hazards [24]. Because the H2 S produced at the CWP would quickly become diluted into the
atmosphere if released, the facility treats H2 S as merely a nuisance rather than a regulated health
hazard. Production of H2 S 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 H2 S compounds found in the air, which
produces a distinct “rotten egg” smell. The exact concentration of H2 S 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
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WYOMING CLEAN WATER PLANT
rates in recent years was approximately 15.5 million gallons per day (mgd), with approximately 11
to 12% supplied from industrial load. The average BOD per year is about 330 mg/L; however,
maximum day load can exceed 500mg/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; therefore, the air
treatment system is installed in the case of potentially hazardous H2 S levels. However, measurements
taken within the past year consistently show an influent H2 S concentration of zero (Appendix D).
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 266ft 3 ) of high capacity activated
carbon and 2ft (a volume of 425ft 3 ) of virgin activated carbon.
At the current time, 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 H2 S emission as a basis for carbon media replacements. Under normal conditions, no H2 S
is released from the carbon absorber so the media is replaced when the emitted H2 S reading is
greater than zero, which is the reason the carbon media has been replaced more frequently than the
manufacturers 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 H2 S concentration is depleted such that the effluent H2 S
concentration is typically zero.
𝐇𝟐 𝐒 Readings
The greatest influent H2 S concentration to the carbon adsorber within the past two years was
22ppmv, with an average concentration of 6ppmv. The unit began emitting a H2 S concentration of
3ppmv in August, 2014 and the carbon was replaced shortly thereafter. Refer to Appendix E for H2 S
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 H2 S 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 H2 S concentration of 10 ppmv with a peak concentration of 25 ppmv
and a maximum media saturation density of 0.73 g H2 S /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.
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WYOMING CLEAN WATER PLANT
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,
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 H2 S 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 H2 S concentration the chemical scrubbers have seen in recent years
is 88 ppmv , which resulted in a H2 S concentration at the outlet of 18ppmv. The average influent H2 S
concentration is 22 ppmv and typically there is a complete removal (Appendix F).
Splitter Box
The proposed biofiltration unit will treat the air originating from the wastewater passing through the
splitter box, which disperses a single effluent stream from the primary clarifiers into three aeration
basins. Refer to Appendix G for a schematic diagram of the splitter box. As shown in Figures 7 and 8,
the splitter box is currently open to the atmosphere. Beginning in November of 2015, the hydrogen
sulfide concentration and temperature of the air produced have been recorded using an OdaLog gas
data logger (refer to Appendix H). 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.
Biofiltration is gaining popularity due to its relatively recent success in full-scale application. It is a
practical and relatively inexpensive method for treating large volumes of moist air containing low
levels of odor-producing biodegradable compounds. Biofiltration is commonly used to treat hydrogen
sulfide, a compound that typically originates from anaerobic fermentation processes [25]. In general,
these systems require less maintenance and fewer media replacements than competing odorreducing 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, typically by being
pushed upward. As the air moves through the bed, the contaminants are transferred from the vapor
phase and deposited into the biological bilayer, where they are then removed by metabolic processes
[26]. The general process flow diagram of a typical biofiltration system used for wastewater odorcontrol is shown in Figure 9.
Figure 9. Biofiltration Process Flow Diagram [27]
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BIOFILTRATION TECHNOLOGY
6.2 MECHANISMS OF OPERATIONS
A steady-state model is needed to describe the mass transport and attenuation of odor-causing air
emissions in a biofiltration unit. Mechanisms that have been evaluated include advective flow, mass
transfer from the bulk phase to the biofilm, biofilm internal diffusion, and biological reaction in the
biofilm.
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 stream reacts with the media and results in a chemical product. In the case of a biofilter
designed as a PBR, the reactant is the hydrogen sulfide in the air and the product is the oxidized
hydrogen sulfide (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 which are discussed in detail in Section 7.
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⁄m3 hr) [28]. The mass loading along the length of the bed declines as a contaminant
is removed when a biofilter is operating under constant flow conditions [29]. The overall mass
loading rate for the system is based on the concentration of the contaminant at the inlet. 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 step 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 [16].
After the contaminant has been adsorbed, biodegradation of the contaminants occurs within the
biofilm. Often it is assumed that the gas and liquid are at equilibrium, as described by Henry’s law.
Furthermore, the gas-phase concentration of the contaminant can be expressed as a dimensionless
air-water partition coefficient [29]. This can be modeled by experimentally determining the
equilibrium between the gas and liquid in response to temperature, and using the linear relationship
between these two parameters to determine the partition coefficient.
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-
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BIOFILTRATION TECHNOLOGY
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 [30].
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. Important assumptions include:










Transport of the target compound is in the axial direction is by plug flow
There is no dispersion or channeling
The gas and liquid pressure drops across the bed are so small that the gas and liquid
volumetric flow rates can be assumed constant along the column
The packing material consists of solid particles of certain average radius and sphericity
The mass flux at the gas-liquid and liquid-biofilm interface for the two-phase model are
described by the linear concentration driving force approximation
The biofilm internal mass flux can be determined using Fick’s law
The thickness of the biofilm is small relative to the curvature of the solid particles
The biofilm consists of active biomass that is responsible for substrate removal and inactive
biomass that plays no role in substrate removal such that the active biomass concentration is
a function of time, axial position, and radial position
The pH change across the column does not influence the reaction rates
The biological reaction is single-substrate limited (only hydrogen sulfide)
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



The total biomass accumulation within the biofilm is described by a Monod kinetic expression
and substrate use is related to the total biomass accumulation by the yield coefficient
The biomass decay rate is directly proportional to the active biomass concentration
Intrinsic inhibitors in the biofilm hinder the active biomass concentration from growing
beyond a maximum value
A minimum concentration of living bacteria necessary for the system to allow the biofilm to
develop is always present and does not die out but is not capable of substrate removal
Biodegradation
The key element of the biofilter design is the biofilm where the contaminants are consumed by
masses of organisms growing on the medium. These microorganisms 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 on the biodegradation processes occurring in air biofilters [29]. Refer to Figure 11 for a
diagram depicting the process of biodegradation.
Figure 11. Overview of Biodegradation Process for Biofiltration [29]
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. It is important to analyze the microbial
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community structure and how it changes during the biodegradation processes. The differences in the
community must be characterized from the inlet to the outlet of the biofilter because the
concentration of dissolved oxygen and contaminants will decline over the depth of the biofilter matrix.
Ways to characterize the community include culture-dependent and culture-independent methods.
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 [29].
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. Several other factors that
contribute to the selection of bacteria include, but are not limited to, the following [25]:




Cost of the bacteria
Ability to reduce sulfates without undesirable byproducts (i.e. secondary pollutants) under a
variety of environmental conditions
Thermodynamic and kinetic parameters of the reaction(s)
Other bacteria present in the anaerobic fermentation process and potential interactions that
may occur between them
Bacteria that has been identified as sulfur-reducing include Xanthomonas, Hyphomicrobium,
Pseudomonas, and Thiobacillus [31]. However, Thiobacillus species are used almost exclusively in
biofiltration for hydrogen sulfide treatment because they most effectively accomplish the above
criteria [32, 31, 33].
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 [29].
μ=
μmax CL
Ks +CL
In the case of a biofilter, the pollutant concentration is the substrate concentration (C L). When the
pollutant concentration is high, CL is far larger than the saturation constant (Ks) and a higher cell
growth (µ) is obtained. At lower concentrations, growth is a first-order reaction. 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).
It has been hypothesized that sulfate accumulation is the inhibiting factor for microorganism
oxidation capacity, and thus the performance of the filtering media [34]. If sulfate accumulates in
large amounts, the pH lowers to a toxic level for bacterial growth (which typically thrive at a neutral
pH) [31]. The removal of H2 S is not inhibited by the transfer of sulfate from the moisture phase into
the biofilm phase, however it is affected by sulfate precipitation caused by high H2S loading instead.
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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
The elimination capacity (EC) decreases when the Henry’s constant increases because there is a
partition located away from the biofilm phase where degradation occurs. Compounds with a high airwater partition coefficients tend to have lower removal rates [29].
A common method of characterizing a biofilter performance is to calculate the 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 [35]. These can be calculated using the following equations.
L = [H2 S]in (Q⁄V)
Q
EC = ([H2 S]in − [H2 S]out ) ( ⁄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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Figure 12. Model-simulated sulfide elimination as a function of sulfide loading for various influent H 2S
concentrations (straight line represents 100% elimination) [35].
Actual elimination will approach 100% during low loading operations. At high loading, the EC
approaches a maximum EC that is typically 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. The concentration of biomass is limited by space constraints in the biofilm
and is further limited by an increasing influent hydrogen sulfide concentration.
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 [36]:




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
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
Layering media types can help to distribute the gas flow evenly across the filter
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. Adsorbent regeneration is achieved by volatilization of the
adsorbed compounds which is accomplished by increasing temperature using steam or by lowering
the pressure across the media bed [16].
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% [29]. 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
[29], 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 (15 to 40 ᵒC), which sets the
recommended temperature range for biofiltration operation [29]. The temperature of the
contaminated air stream must be adjusted prior to coming into contact with the microbial population.
Heating or cooling systems must be incorporated into the design of the biofilter to maintain this
temperature range.
A sufficient bed temperature may be achieved by heating the feed air, however this requires
additional equipment in the biofilter and increases the amount of energy used. Additionally, heating
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the air will decrease its relative humidity and may cause the bed to quickly dry out [35]. For this
reason, steam is often used to satisfy both the heating and humidity requirements.
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 [28].
Hydrogen sulfide is a highly soluble gas with a Henry’s constant of 2582 mL gas⁄L H2 O • atm at 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 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 [16].
Sulfide is a product of bacterial degradation that is able to auto-oxidize, meaning it can react with
oxygen when the system is at normal temperatures [37]. This is a rapid biological reaction that is
highly dependent on the pH, the concentration of the reactants, and the presence of heavy metals at
catalytic concentrations. At acidic pH levels (less than 7), elemental sulfur is the major oxidation
product, but basic pH values (greater than 7) cause thiosulfate and sulfite to be the major oxidation
products.
Microorganisms operate and grow in a specific pH range. Bacteria thrives in an environment that has
a pH of 5 to 9 while fungi prefers a pH ranging from 2 to 7. 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 [29]. If the pH falls below 3.2, the biological population will be rendered
inactive and the removal efficiency of the biofilter will suffer significantly.
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 (m3 ) and Q is
the airflow rate (m3 ⁄s) [35].
EBRT =
Vf
Q
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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 [29]. It
is important to monitor oxygen in cases where there is a high contaminant-loading rate or a high
moisture content.
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. The pressure drop through
a compost biofilter ranges from 20 to 35,000 Pa/m•bed-depth for particle sizes ranging from less
than 1.2 mm to greater than 12 mm and air velocities ranging from 0.02 to 0.28 m/sec [35]. The
following equation calculates the pressure drop across the biofilter bed where 𝜇 is the fluid viscosity,
𝜌′ is the density of the particle, ɸ𝑠 is the shape factor of the particles, 𝐷𝑝 is the particle diameter, 𝜀 is
the void space of the bed, 𝜌 is the density of the fluid, and 𝑣 ′ is the fluid velocity [38].
Δp 150μρ′ (1 − ε)2 1.75ρ(v ′ )2 1 − ε
= 2 2
+
L
ε2
ɸs Dp
ε2
ɸs Dp
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 [35].
However, as stated in 6.4.8, 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.
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 0.91 to 1.5m [35].
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6.5 OPERATION
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.
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 [39].
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 [39]. 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.
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 [16].
Cover and Insulation
Biofilters can be constructed as open or covered bed systems [29]. 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. 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 [35]. 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.
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Air Distribution
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]:
𝑘 𝛿𝑃
𝑘 𝛿𝑃
𝑢𝐷 = − 𝜇 ( 𝛿𝑥𝐷 ) AND 𝑣𝐷 = − 𝜇 ( 𝛿𝑦𝐷 ).
The horizontal air velocity is represented by 𝑢𝐷 and the vertical air velocity by 𝑣𝐷 . The permeability
of the media is 𝑘 (m2 ), the absolute viscosity is , and the pressure 𝑃𝐷 . In an actual biofilter, there is a
single Darcy region that is bound by two Navier-Stokes (NS) regions. The air flow in the NS region is
a result of the pressure gradient, viscous forces, and inertial forces, whereas in Darcy regions flow is
strictly caused by the pressure gradient. Inertial forces are negligible and the fluid is assumed to be
incompressible in both regions [40]. Conventional biofilter media have a low permeability ranging
from 5.4 × 10−10 m2 and 1.1 × 10−9 m2 , however low permeability typically results in higher
operating costs [26].
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, 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 13 [40].





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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Figure 13. Schematic of different designs of biofilter inlet and outlet locations [40]
Heterogeneity as a function of flow rate through the biofilter:
For simulations with Design 1, a low Reynolds Number (Re) causes a slightly greater flow through
the left side of the biofilter medium than the right side because the air takes the shortest path
between the inlet and outlet of the biofilter. At high Re, the inertial forces are greater. The momentum
of the air tends to carry it across the medium to the other side of the biofilter. This results in a lower
medium pH near the wall opposite of the inlet than the medium towards the center of the tank. The
lower pH indicates that more hydrogen sulfide is oxidized to sulfuric acid in that region. The
concentration of hydrogen sulfide in the air is modeled as uniform, indicating a greater mass of air
passes through regions that result in a lower pH. The biofilter experienced relatively low vertical
velocity near the central upper region of the media [40].
Flow heterogeneity as a result of permeability:
Flow heterogeneity increases as permeability increases when a constant Re is maintained. At low
permeability, the flow in the reactor has only a minor horizontal tendency and curvature. Flow
through the medium is divided between the left and right side of the biofilter, and as permeability
increases the effect of a moderate momentum with an Re equal to 1,500 causes the majority of air to
pass through the media on the right side of the chamber.
The configuration in Design 5 has the lowest flow heterogeneity over a wide range of Re. For all
designs described here, at low Re and low permeability removal efficiency is approximately 95% [40].
With an increase in Re and the dimensionless permeability coefficient F, the removal efficiency
declines. The coefficient F is calculated using the permeability of the media (𝑘) and the width of the
reactor (𝑊) according to the following equation.
F=
k
W2
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BIOFILTRATION TECHNOLOGY
The design with the greatest removal efficiency depends on the operation air flow rate. At lower Re
the inertial effects are small, but at high permeability the flow path is determined by the location of
the inlet and outlet. All the designs have a higher removal efficiency when the medium has a very low
permeability (𝐹 ≅ 6.5 × 10−7 ) [40]. The pressure loss across the medium is much greater than the
horizontal pressure differences caused by inertial forces.
The optimum biofilter design depends on the permeability of the medium, the operational flow rate,
and the design. With high Re and permeability, 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 [40].
Ductwork and Accessories
Certain design parameters must be considered when sizing the ductwork for the biofilter [16]. 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.
Additional design components of a biofilter are needed for practical operation [41]. If the air stream
needs to be cooled to meet temperature constraints in the biofilter, heat exchangers are often used to
cool hot off-gases. Spray nozzles are commonly used to provide the humidity in the chamber required
for continual bioactivity. Spray nozzles may also be used to distribute steam for both heating and
humidity purposes. Alternatively, automatic irrigation dispersed from the top of the chamber may be
used to maintain the required moisture content in the filter material. 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 [16]:





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
Configuration
Although biofilters can be designed with one bed chamber, it is beneficial to design two beds in order
to provide redundancy and operational flexibility [35]. 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
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BIOFILTRATION TECHNOLOGY
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 [35].
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MODELING
7 Modeling
7.1 INTRODUCTION
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 [29]:








Accumulation of reactive products
Dispersion effects in air
Mass transfer between the air and biofilm
Diffusional mass transfer in the biofilm
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
Modeling is an appropriate alternative to building a full-scale biofilter. Odor measurements and
analysis are expensive and are based on grab samples, which do not take into account environmental
fluctuating conditions throughout the course of a year. Designing a biofilter without taking into
account condition variations could result in an inadequate design and the inability to expand the
design in the future. Predictive models validated by pilot scale test data are a valuable tool to ensure
that the biofilter is not over or under designed.
7.2 OTTENGRAF AND VEN DEN OOEVER KINETICS
The Ottengraf and ven den Ooever models are often used by engineers and researchers to aid in the
construction of biofilters. This is a simple model that assumes plug flow for the gas phase and flat
geometry for the biofilm. There are three variations of this model: first-order reaction modeling,
zero-order reaction modeling, and zero-order diffusion models. All cases are due to two different
processes occurring in the biofilter: diffusion and reaction. In a biofilter, the gas must first diffuse into
the biofilm before it can react with the biofilm. In the case of a zero-order reaction, it is assumed that
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MODELING
one of the two actions is much slower than the other. If the rate of diffusion is much slower than the
rate of reaction, then it is said that the reaction is diffusion limited. Conversely, if the rate of reaction
is the slower of the two actions, then the rate is reaction limited. If both have equal importance in the
rate determination, then the rate is first order.
Zero-Order Reaction-Limited
The zero order Ottengraf and ven den Ooever reaction-limited case assumes that the reactant diffuses
completely into the biofilm before the reaction is completed. The mathematical model used is
Cout = Cin − k 0 ⦁ (EBRT)
where Cin is inlet concentration (kg/m3), Cout is the outlet concentration (kg/m3), k0 is zero order
reaction rate constant (kg/m3s) and EBRT is the Empty Bed Residence Time. ko is calculated using
the following equation
k0 =
u∗ (XV)As δ
Y
where u* is the specific growth rate (s-1), XV is the biofilm density (kg/m3), As is the biofilm surface
area per unit volume of biofilter (m-1), δ is biofilm depth (m), and Y is the yield coefficient which is
equal to the amount of biomass produced/substrate consumed. Equation (1) in a previous section of
this report can be used to calculate EBRT.
Zero-Order Diffusion-Limited
The zero order Ottengraf and ven den Ooever reaction-limited case assumes that the reaction occurs
completely before the molecule can completely reach the end of the biofilm. When this happens, it is
assumed that the biofilm is not fully active. Therefore, if this model is the best fit for biofilters, then
optimization should occur to ensure complete use of the biofilter. The rate law for this reaction is
Cout = Cin (1 − β1
where β1 = As √
EBRT
√Cin
2
)
k0 ∙f(Xv )∙H2−S,W
2m
and f(XV) is the ratio of diffusivity of a compound in the biofilm to water, DH-2 S,W is the diffusivity of
H2S in water (m2/s), and m is the dimensionless Henry’s constant of the pollutant.
First Order
The steady state first order reaction is modeled by the following rate law:
Cout = Cin e−k1 ∙EBRT
where k1 is the first order rate constant. This rate constant can be estimated using
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MODELING
𝑘1 =
𝐴𝑠 𝑋𝑣 ∙ 𝜇∗ ∙ 𝑓(𝑋𝑉 ) ∙ 𝐷𝐻2 𝑆,𝑊
√
tanh(𝛽2 )
𝑚
𝐾∙𝑌
X ∙μ∗
where β2 = δ√K∙Y∙f(X V)∙D
V
H2 S,W
and K is the monod kinetics constant.
7.3 MICHAELIS-MENTEN KINETICS
For general biochemistry, Michaelis-Menten is widely used to determine the rate of an enzymatic
reaction. Due to the fact that the process outlined is a biological process, it is important to consider
this model as a possible model for our design.
The rate law is given as
−r =
Vmax ∙ C ∙ B
Km + C
where C is the substrate concentration, B is the population density, Vmax is the maximum reaction rate,
Km is the Michaelis constant, and t is the reaction time. If the reaction is allowed to proceed under
steady state, which is assumed in the case of a biofilter, the equation can be simplified based on three
different scenarios.
Zero-Order Kinetics in Concentration
The zero-order kinetics case occurs when the substrate concentration is very high. If the system is
flooded with the substrate (in this case, H2S), then the resulting Michaelis- Menten equation simplifies
to
−r = Vmax B = k o
where ko is the rate coefficient.
This dramatically simplifies the equation needed to develop the size of the biofilter to be used.
However the assumption that C is very large is a poor one as it means that the air would be saturated
with hydrogen sulfide. Because the H2S levels rarely go above 20 ppm (30 mg/m3), the concentration
of hydrogen sulfide is very dilute which means that zero-order kinetics are not a good model for this
reaction.
First-Order Kinetics
If the substrate is dilute, then the rate can be taken to be first order. The equation for this is
−r = k1 C
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MODELING
where k1 is the first order rate constant. This equation initially seems to hold true for our system as
the concentration of hydrogen sulfide in the air is assumed to be dilute. However, this should be still
be compared to the final model.
Fractional Order Kinetics
In this situation, Km and C are considered comparable to one another. In this case, the MichaelisMenten equation cannot be simplified. It is not known what the half saturation constant is in this
reaction so this model must be considered in order to determine if it is the correct fit for our reaction.
7.4 MODEL CASE STUDIES
Kinetics and Modeling of Hydrogen Sulfide Removal [42]
In a journal article by Shareefdeen, Ahmed and Aidan, the degradation of H2S in a biofilter was
measured using the Ottengraf models described above. These models were used for data collected in
a modular bench scale biofilter. The biofilter used contained a packing material made of hollow
cylindrical particles that were coated with nutrients to encourage biological growth. Data was taken
at multiple different EBRTs that ranged from 20 to 60 seconds. For each of the three situations of the
Ottengraf models, the ratio of inlet and outlet concentrations were changed. For zero order, reaction
limiting Cout/Cin was plotted against EBRT/Cin. This resulted in very scattered data and a poor R value,
indicating it is a poor model for the reaction. For zero-order, diffusion limited reaction, (Cout/Cin) 0.5
was plotted against EBRT/Cin. This resulted in a more linear graph, with an R value of -0.935,
indicating near linearity. However, when the first order model was graphed (ln Cout/Cin against EBRT),
the R value was 0.967, which is the most linear option. This means that first-order kinetics is the best
choice for this reaction
Michaelis Menten Kinetics
Yang and Allen (1994) used a biofilter with a compost media and a gas flow rate of 68 lpm and an
EBRT of 16 seconds with a total packing volume of 0.018 m3 [26]. It was found that each of the models
were a good fit for the biofilter based on the concentrations of H2S entering the filter. For
concentrations above 400 ppmv, the zero-order model held true. It was found that the rate law
became
C = Co − 26.1t
meaning that k0 is 26.1 ppmv/s. This is the maximum H2S concentration that can be removed from
the air by the biofilter at a time, which sets a maximum elimination capacity for this biofilter at 130
g S/m3hr.
For inlet concentrations below 200 ppmv, the reaction was first order. This reaction took the linear
regression form of
C
ln (C ) = −0.54t,
o
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MODELING
resulting in a first order rate coefficient, k1, of 0.54 s-1.
When the inlet concentration of hydrogen sulfide was between 200 and 400 ppmv, the reaction rate
law required fractional order kinetics. To find a model to represent this case, the Ottengraf diffusion
limiting model was used. This model has the form of
2
C
H
k o De a 0.5
= [1 − ( ) (
) ]
Co
Ug 2mCo δ
where C is the outlet gas concentration, Co is the inlet gas concentration, H is the height of the filter
bed, Ug is the gas velocity, a is the interfacial area per unit volume, De is the effective diffusion
coefficient, m is the distribution coefficient of the component and δ is the bio-layer thickness. In order
to solve the above equation the fractional order reaction coefficient needs to be defined. This can be
calculated by
kf = (
k o De a 0.5
)
2mCo δ
Since all of the above variables defining kf are operating conditions under steady state operation, kf
can be considered constant. For this reason, the Ottengraf diffusion limiting model can be rewritten
as
C
= (1 − k f t)2
Co
where t is the reaction time determined by the height of column, H, and the mass velocity of air Ug.
If 1-(C/Co)0.5 is plotted against t, then the result is a straight line with a slope of kf. The experimental
biofilter in the Yang and Allen study had a hydrogen sulfide loading of 309 ppmv, resulting in a kf,
which is equal to the slope, of 0.064 s-1.
So, for any concentration of H2S entering a biofilter, a rate law can be determined. If the concentration
of H2S is below 200 ppmv, then the rate law is first order. If the concentration is above 400 ppmv, then
the rate law is zero order. If the concentration is between zero and first order, then the rate law is a
fractional order and the Ottengraf diffusion model is used to describe the oxidation of hydrogen
sulfide.
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8 Biofilter Packing Media
8.1 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. Media is chosen based on a variety of factors including the classification of
the target contaminant, the preferences of the microbial community, and the surrounding
environmental conditions.
Media used in biofilter beds consist of relatively inert materials with large surface areas, which can
more easily adsorb contaminants, as well as a microbial population and the nutrients necessary to
sustain their life [43]. Studies have shown that these parameters can be satisfied with either organic
or synthetic materials, depending on the conditions unique to each biofilter. If properly selected, the
biofilter media can accomplish approximately 60% of the H2S removal without the presence of sulfurreducing bacteria, meaning less than half of the removal efficiency is due to biological metabolism
[34].
8.2 NATURAL 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 [29].
Adsorption [qad(C)] of contaminants onto the media’s porous surface dominates at low contaminant
concentrations. Sorption [qp(C)] continues as a result of hydrophobic partitioning from the liquid
phase, which allows the media to hold the contaminant after it has been solubilized from the gaseous
air phase. The combination of adsorption and sorption provides the total sorption [q(C)] of the
contaminant as shown in the following equation [29].
q(C) = qp (C) + qad (C)
Adsorption on organic media acts according to standard adsorption reactions (i.e. Polanyi adsorption
potential for gas-phase adsorption), as shown in the equation below [29].
εd = RT ln (
P0
)
P
In this equation, ε𝑑 is the differential work of adsorption, 𝑃 is the total pressure, 𝑃0 is the partial
pressure, 𝑇 is the temperature, and 𝑅 is the ideal gas constant.
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Peat
Fibrous peat has often been used in biofilters to remove or reduce sulfur compounds, and is proven
to aid in successful oxidization of hydrogen sulfide at a neutral pH level. Peat has a large specific
surface area to support microbial growth in a naturally acidic environment. A study was completed
on the removal of hydrogen sulfide and CS2 with an acid peat biofilter used at a wastewater pumping
plant and an industrial site [44]. The peat mixture was comprised of 50% coarse horticultural peat
and 50% peat fibers and was found to have high removal efficiencies. The mixture was naturally acidic,
with a pH of 4, and had a low nutrient content (0.32 mg/kg P, 0.53 mg/kg Mg, 0.25 mg/kg K, 8.8
mg/kg N, and 1.1 mg/kg S).
Peat is a suitable material for biofiltration because it is highly porous and allows for adequate biofilm
growth. The study determined that SO42- accumulates on the surface of the biofilm, which allows it to
be easily removed from the liquid layer [44]. However, excess of SO42- causes the organic filter
material to overload and if the concentration is more than 100 mg/g S, the need for media
replacements is more frequent. The regeneration of peat is difficult after the deposition of fine sulfur
particles are removed with rinsing water [45].
The sulfur removal capacity was higher for neutralized peat than for natural peat. The operating
temperature for this experiment ranged from 25 to 35ᵒC during summer months, which is the
optimum temperature range for bacteria growth, and 10 to 20ᵒC during the winter. The volume of the
filter material in this experiment decreased by 15% due to compression of the decomposed material
in a highly acidic environment. It was concluded that biofilters can be successfully employed for low
hydrogen sulfide concentrations ranging from 0.1 to 20 mg/m3 and their removal efficiency is
improved by neutralizing the peat. The maximum elimination capacity of natural peat was found to
be 144 g H2S m-3 day−1. This result is poor in comparison to inoculated peat biofilters observed over
the long-term, having a capacity of 360 to 575 g H2 S m−3 day −1 [46, 47], or of compost with a
capacity 3300 g H2 S m−3 day −1 [26]. However, the elimination capacity of aged and acidic compost
can only be approximately 10% of the maximum capacity of new filter media [26]. This indicates that
evaluation of long-term experiments is needed to accurately determine the elimination capacity of
peat biofilters [44].
Woodchip and Compost
The performance of a compost-based biofiltration largely depends on the following three parameters
[48]:
1.
2.
3.
Specifications of the media material (i.e. temperature, void fraction, particle diameter,
water content, microbial characterization, and nutrients)
Characteristics of the ability for the gas to flow through the biofilter (i.e. superficial
velocity, gas distribution, and pressure at the inlet)
Substrate load conditions (i.e. solubility, microbial degradability, and applied loading
rate)
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Depending on the composition of the media, compost can vary in degree of porosity, pH, water
content, and chemical composition – each of which impact the H2S loading capacity and affect the
selection of the material [26].
The suggested operating conditions of a biofilter that targets H2 S (using compost media in particular)
are as follows [26]:





Temperature: 25 to 50°C
Compost pH: >3.0
Compost water content: 50±15 %
Compost sulfate content: <25 mg/g S
Pollutant retention time: >15 sec
Typically, removal efficiency begins to decline due to a reduced available surface area on the biofilm
resulting from accumulated biomass. However, in compost-based systems, 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 [48]. If these issues are identified soon after
they begin, they can typically be remedied by mixing the media.
One laboratory study investigated the results of a biofilter with a 2-ft bed height using a natural media
comprised of a compost and woodchip mixture with a weight ratio of 50/50 [49]. This media resulted
in removal efficiencies of 90%, 96%, and 89% for H2S influent concentrations of 20, 50, and 100 ppmv,
respectively. In comparison to synthetic media, the pressure drop of natural media was nearly double.
The authors of this experiment reported the natural media had a high overall removal efficiency at
the beginning of the filtration process, likely due to a high sorptive surface area, but the large pressure
drop limited the overall efficiency of the system.
Another study observed the effects of two woodchip types; shredded western cedar (WC) and 2-inch
hardwood (HW) [50]. The characteristics of the two media types are shown in Table 3.
Table 3. Characteristics of Two Types of Wood Chip Media Types for Biofiltration [50]
This experiment provides an example of the use of nutrient-rich organic media. Three biofilters were
tested with varying EBRTs, which impacted the removal efficiency as well as the moisture content.
Both WC and HW showed highly successful results for odor-reduction when the moisture content
was at 60% and the EBRT was minimized.
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Activated Carbon
One case study completed a bench-scale horizontal biotrickling filter (HPF) using three 15 x 15 x 10
cm segments of dark activated charcoal and using Acidithiobacills thiooxidans as the sulfur-reducing
bacteria [51]. Fifteen days were allowed for acclimation onto the column before hydrogen sulfide was
introduced. The inlet concentration ranged from 20 to 100 ppmv and the retention time ranged from
4 to 16 seconds. Water was circulated through the biofilter at a rate of 2.4 L/min to maintain moisture
levels. Results were determined both in the startup and over the long-term.
In the startup portion of the test, it was determined that the activated carbon was able to remove
100% of the hydrogen sulfide while allowing the biofilm time to acclimate, indicating that little
acclimation time is needed for a biofilter that uses activated carbon as the media. In the long term,
the removal efficiency increased with time and decreased with influent concentration. Complete
removal was achieved at a retention time of 11 seconds and removal efficiency remained above 80%
for the duration of the entire test.
The activated carbon, horizontal biofilter performed on par with a normal biofilter at low inlet
concentrations as well as reduced sulfur accumulation within the bed. However, the horizontal design
and biotrickling meant that the residence time had to be increased in order to improve efficiency. It
is hypothesized that the increased retention time was due to the water layer, which added an extra
barrier between the contaminated air and the biofilm [51].
As with most granulated particles, activated carbon is subject to settling, as shown around day 100
in Figure 14. The granulated nature of the carbon particles leave it susceptible to gravitational effects,
therefore the bed became clogged resulting in a sudden decrease in removal efficiency. Over time,
small particles begin filling the holes between larger particles, causing air flow through the column
to be constricted. This results in more energy required to push the air through the column, and
ultimately decreased efficiency, as shown in Figure 14. So, while activated carbon is beneficial for its
adsorptive properties, especially during the startup phase, it comes with the risk of settling later on.
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BIOFILTER PACKING MEDIA
Figure 14. Removal Efficiency of Activated Carbon Media [51]
Lava Rock
Lava rock is primarily composed of hematite, titanohematite, and olivine and has a particle density
of 1.13 g/mL, a material density of 1.41 g/mL, and a porosity ratio of 0.20.1 Usually lava rock-based
biofilters are inoculated with microorganisms prior to operation which can be done using
recirculation water containing sulfur-oxidizing microorganisms. In 2005, a study was done with lava
rock media in biofilters at Cedar Rapids Water Pollution Control Facilities in Iowa to treat hydrogen
sulfide [52]. To provide moisture and nutrients needed for microbial growth, secondary effluent
containing 30 mg/L of CBOD and 50 mg/L TSS was sprayed on the top of two parallel lava rock beds
for 5 minutes every hour. The facility had an inlet hydrogen sulfide concentration ranging from 50 to
300 ppmv and the treatment objective was 0.5 ppmv at the outlet.
The largest pore size in lava rock are approximately 5 mm. The results of this laboratory study
indicated that water has difficulty penetrating the rock to reach the pores located far away from the
surface, thus the pores at the surface hold the water creating an ideal environment for microbial
Particle density is the ratio of the weight of the dry rock to the total volume of the particle, including
the pore volume. Material density is the ratio of the weight of the dry rock to the total volume of
material only. The porosity ratio is the pore volume compared to the total volume of the particle.
1
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BIOFILTER PACKING MEDIA
growth. The porous structure of the lava rock includes a specific surface area for microbial
attachment that does not include the largely inaccessible inner pores. Unlike organic packing media,
lava rock demonstrated the ability to resist bed compaction, and the full-scale biofilters at the Cedar
Rapids Water Pollution Control Facilities did not have to be replaced after a minimum of 7 years. The
pressure drop across the bed was also relatively low.
Relatively low pH values of approximately 2 to 3 in biofilters can contribute to an active lava-rock
surface chemistry where Fe3- and/or Fe2- is released. These ions are believed to be recyclable in the
biofilter serving as a mechanism creating synergy between the iron ions and the hydrogen sulfide. It
is likely that the release of iron ions from the lava rock could enhance the removal rate of hydrogen
sulfide
Comparative Study
One study compared the effectiveness of 11 different packing materials in biofiltration [53]. The
packing materials that were considered included coconut fiber, fibrous peat, heather, granulated peat,
a mixture of peat and heather, wood chips, bark, mulch, activated carbon, schist and volcanic rock.
The pilot-scale biofilter was 0.85 meters in diameter and 1.25 meters tall. The EBRT used was 47
seconds, which was kept constant throughout the experiment. The moisture of the filter ranged from
6 to 20 L/day and was maintained using an overhead sprinkler system. Gravel was used as support
for the packing material.
Compaction is an undesirable characteristic in biofiltration media because it causes the pressure drop
across the filter to increase. In this study, this effect was particularly significant with peat, heather,
coconut fiber, and bark. The required residence time of the filter was relatively low when these
materials were used.
Compaction must be balanced with surface area, which increases the space available for adsorption
of the contaminants onto the media surface. Schist and volcanic rock contained the highest surface
area. Activated carbon also had a high specific surface area, however it was shown to compact easily,
resulting in a lower residence time.
Economic evaluation was also evaluated in this study. The calculation was based on estimations of
the life of the media, the cost of media replacement, and the cost of disposal (which was done for a
10-year running cost for each media type). It was determined that fibrous materials (coconut fibers,
and fibrous peat) were more likely to settle, requiring more of the material to be added over time. In
addition, coconut fibers and fibrous peat had the highest material cost out of the organic material
considered. Activated carbon, though possessing one of the highest specific surface areas, also had a
high material cost.
Due to low cost and a high chance for bacterial colonization, wood mulch was determined to be one
of the best choices for biofiltration. Although more expensive, schist was an attractive alternative
because of its high surface area. According to this study, peat and heather (combined), wood mulch,
pine bark, and schist were considered the best alternatives of those studied and suggested for further
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BIOFILTER PACKING MEDIA
study. The authors of this experiment concluded that wood mulch, pine bark and schist are the
optimal packing media due to their low cost, high surface area, and minimal compaction. Wood mulch
was the most efficient of the three with respect to cost and operation.
8.3 NATURAL MIXTURES
Mixtures of organic material can help to optimize several aspects of the biofilter design. Each material
provides a specific desirable result, thus improving overall contaminant removal efficiency.
A pilot scale biofilter was used to perform laboratory and field experiments using a media bed
consisting of air-dried compost (consisting of 50% digested sewage sludge and 50% forest products),
perlite, and crushed oyster shell [53]. For optimal results, the compost made up approximately half
of the entire organic mixture. About 50% by volume of perlite was added, which helped to decrease
the pressure drop across the filter bed by increasing the porosity of the mixed media. Crushed oyster
shells, added at 1mEq/g of media, provided the mixture with a source of calcium carbonate, which
acted as a buffering agent to stabilize pH levels.
For the field experiment, the water content was significantly less than 50%, resulting in low removal
efficiencies initially [53]. The removal rate of hydrogen sulfide immediately improved after the water
content was raised. Further humidification was not required for the field test because the inlet gases
were saturated with water vapor from the wastewater stream. The inlet H2 S varied between 1 and
80 ppmv , which was reduced to an outlet concentration of 0.1 to 8 ppmv . The field test showed that
the pH of the drainage water from the biofilter fell from 6.5 to 1.5 over a period of 2 months, however
the filter media remained at a pH of approximately 7. This result indicated that the oyster shells,
containing calcium carbonate, successfully buffered the media by preventing drastic pH variability.
Microorganisms used in biofiltration are sensitive to pH changes, therefore buffering agents are
required to neutralize the acidic byproducts of H2 S oxidation. Additionally, system buffering helps to
reduce the risk of corrosion inside the filter chamber.
8.4 SYNTHETIC
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
Polyurethane (PU) foam is regarded as one of the best synthetic packing media for minimizing
clogging, maintaining high hydrogen sulfide removal efficiency, and maintaining low pressure drops
along the bed. PU is an inert material with low density, large porosity, and a relatively low commercial
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BIOFILTER PACKING MEDIA
cost [55]. The high porosity permits uniform gas flow distribution, allowing maximum contact
between the odorous air stream and the biofilm biomass. Additionally, the low density minimizes
problems associated with compaction of the packing material.
A study was conducted using a laboratory-sized biofilter packed with PU foam materials with
Thiobacillus thioparus bacteria [55]. To determine the maximum biofilter efficiency, three EBRTs
were used (100, 70 and 30 seconds) with an initial hydrogen sulfide concentration ranging between
25 to 750 ppmv. The packing material was PU foam cubes with a 1 cm 3 volume and a density of 20
kg/m3. The biofilter operated continuously for 118 days to study three EBRTs with varying
concentrations. The results of this experiment showed that the hydrogen sulfide removal capacity
was greater than 95% for the medium concentrations of 300, 150 and 100 ppmv with empty bed
residence times of 100, 70 and 30 seconds, respectively. The experiment showed that PU is a very
effective packing media for removing hydrogen sulfide.
BiosorbensTM
BiosorbensTM is manufactured by Biorem® and were the first engineered, permanent biofilter media
available on the market [56]. The media particles consist of water-soluble cores coated with waterinsoluble adsorbing material, allowing for a high specific surface area (40.9 m3/g of media). This
results in more effective and efficient adsorption, increasing the rate of biological oxidation and
improving the efficiency of hydrogen sulfide removal. Additionally, BiosorbensTM are able to retain
moisture while avoiding decomposition, degradation, and compaction even in strongly acidic
environments. Theoretically, these qualities allow BiosorbensTM to be permanent in biofiltration of
hydrogen sulfide. Table 4 lists some properties of BiosorbensTM media.
Table 4. Properties of Biosorbens media [57]
A study was conducted in which two identical pilot scale biofilters made of PVC columns, 8 inches in
diameter with 4 feet of BiosorbensTM media, were operated under differing conditions. Pure hydrogen
sulfide was supplied to the humidified air stream. For each trial, the air flow rate, media pH, leachate
pH, moisture content, total sulfur and SO42-, SO32-, S2- were measured. The results showed that the
biofilter effectively removed more than 99% of the hydrogen sulfide throughout the 118 days that the
biofilter was operating. Additionally, this efficiency was constant regardless of the varying inlet
hydrogen sulfide load and the empty bed resistance time [57].
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FULL-SCALE BIOFILTER CASE STUDIES
9 Full-scale Biofilter Case Studies
9.1 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
[58]. 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 [59].
Figure 15. Completed Biofilter at Three Rivers Wastewater Treatment Plant [60]
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 16). 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.
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FULL-SCALE BIOFILTER CASE STUDIES
Figure 16. Installation of Porous Floor of Biofilter [60]
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.
9.2 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,
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FULL-SCALE BIOFILTER CASE STUDIES
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 17.
Biofilters
Biosolids
Headworks
Figure 17. PARCC Side CWP
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 18.
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FULL-SCALE BIOFILTER CASE STUDIES
Figure 18. 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 [61]
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 19.
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FULL-SCALE BIOFILTER CASE STUDIES
Humidification
Sprinklers
Humidification
Chamber
Figure 19. 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 [62] 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 5.
Table 5. Monthly PARCC Side CWP Temperature and pH Readings for Air Entering Biofilter
Date
Temperature (℉) pH Value
September 2015
72
7.38
October 2015
57
7.65
November 2015
55
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.).
Page 67 of 84
FULL-SCALE BIOFILTER CASE STUDIES
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.
Page 68 of 84
BASIS OF DESIGN
10 Basis of Design
10.1 PROPOSED PROJECT SCOPE
The project proposal is to design an odor-control system for the CWP using biofiltration technology.
The scope of the project includes:
1) Provide a preliminary design of a biofilter for the splitter box while meeting regulatory
standards.
a. Design Specifications
i. Biofilter(s) size, configuration, location
ii. Biofilter materials and construction
iii. Piping accessories and additional equipment
iv. Blower selection and sizing
b. Detailed cost estimates
c. Operation and maintenance plan
d. Life cycle analysis of the biofilter
2) Provide a conceptual design of a single biofiltration system to treat all odor sources at the
CWP.
The team will select a media for the biofilter appropriate for the CWP with a decision matrix. Sizing
and modeling the biofilter will be done after the media is selected.
10.2 DESIGN CRITERIA
A successful designed odor-control unit will be easy to operate and maintain, will have a low energy
input, and will effectively remove hydrogen sulfide from the air. Our biofilter design for the splitter
box will meet the following requirements:





Less than 2 ppbv of H2S exiting the biofilter
Less than 150-200 hours of labor per year required for Operation and Maintenance (O&M)
Common media (i.e. multiple suppliers)
Reduce chemical and nutrient additions
Reuse plant effluent water
10.3 CONCEPTUAL DESIGN
The proposed project to design a biofilter for the CWP is a feasible alternative to other odor-control
technologies. Through research and advice from engineering professionals, Bi0dor has developed a
conceptual design process that will include making engineering decisions to optimize important
components of the biofilter in order to develop a preliminary design. Multiple approaches and
alternatives will be considered when evaluating the biofiltration system.
Page 69 of 84
BASIS OF DESIGN
Biofilter Modeling
Bi0dor proposes modeling the biofilter as a Packed Bed Reactor (PBR), a decision that is based on
research of existing models. This assumes that the biofilter and the reaction remain isothermal, the
flow rate of air is constant, the initial concentration of hydrogen sulfide is constant, and that all of the
odorous compounds in the air are represented by the concentration of hydrogen sulfide. For our
initial base calculation, pressure drop and mass transfer were not taken into account. However, these
variables will be included for the final calculations.
In reaction engineering, the volume of a PBR is determined by the rate of the reaction and the flow
rate of the influent. The general design equation for this reactor is
dFa
= −ra
dV
Where dFa is the change in concentration of the chemical species (in this case, hydrogen sulfide), dV
is the change in volume of the reactor, and ra is the rate of the reaction. The integrated form of the
equation is
Fa
dFa
Fao −ra
V=∫
The rate is determined experimentally. As we do not have the time nor the resources to dedicate
towards the development of this rate law, we will depend on research from others to determine what
rate law best suits the reaction that is occurring in the biofilter.
As shown above, the first order model best fits this reaction. This means that the rate equation takes
the form of
−ra = k ∙ Ca
Where k is the rate constant, and Ca is the concentration of H2S in the air. When isothermal, Ca can be
simplified to
Ca = Cto ∙
Fa Po
∙
Ft P
Where CTo is the total concentration entering the reactor, Ft is the total flow rate of all components in
the system, Po is the initial pressure, and P is the final pressure. Plugging all of this into the PBR
equation, one gets the equation
Fa
dFa
F P
Fao k ∙ C ∙ a ∙ o
to F
t P
V=∫
The three variables in this equation are the initial flow rate (Fao), the initial concentration (Cto), and
the rate constant (k). The rate constant is dependent on the material type and has some dependence
on the temperature of the system. Because we are assuming the system is isothermal, this should be
Page 70 of 84
BASIS OF DESIGN
taken as a constant. However, the rate constant, like the rate law, can only be experimentally
determined. To properly size the biofilter, data is needed to determine this rate constant. Therefore,
our group needs to find kinetics data specific to the media that is chosen in order to design the
correctly sized filter for the odor removal process.
Packing Media
Choosing the biofilter packing media is vital to the sustainability and cost of the system. The media
provides an environment for the microorganisms used to biodegrade pollutants in the air to grow.
The media selection will largely determine the cost and size of the biofilter. The variable weather
conditions in West Michigan are not expected to be an issue based on research and discussions with
local plants that use biofiltration. This is because the air coming off the wastewater remains at an
average temperature of 50℉ (Appendix H). In depth research on natural media, along with the option
of mixing or layering various media types, alternatives will be provided for the CWP biofilter. A media
recommendation will be 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 capacities, and the physical
properties of the media under low pH conditions. Key parameters considered when selecting the
media include the mass transfer between the air and biofilm, the solubility of the pollutants, nutrient
control, and elimination capacity. These will all be taken into account when making the decision about
the media type and consequently, the size of the reactor.
Biofilter Size
The packing media for the biofilter determines the size of the biofilter. Specifically, the bed height and
cross sectional area are needed for adequate residence time so that pollutants are effectively removed
at the full range of potential concentrations. Based on preliminary hydrogen sulfide readings from
the splitter box, the range of H2S concentrations is zero to 22 ppmv (Appendix H). Additional data is
being gathered to better understand the range of concentrations of hydrogen sulfide emitted off the
splitter box. Based on hydrogen sulfide readings gathered from the splitter box and the experimental
results of other successful case studies, the biofilter dimensions will be designed to meet the lowest
required retention time while obtaining acceptable removal levels of hydrogen sulfide under
maximum pollutant loading conditions.
Optimizing the size of the biofilter includes changing the bed height to meet contact surface area
requirements, which are dependent on the media selected. 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.
Page 71 of 84
BASIS OF DESIGN
System Configuration
Biofilters can either be open to the atmosphere or enclosed. Bi0dor will be designing a covered
biofilter to maintain the environment needed in the biofilter for the microorganisms to remain alive
and functioning. Another advantage to covering the biofilter is to prevent operational and
maintenance issues with the varying climate conditions in West Michigan.
With engineering design, redundancy in a system is important to ensure the process can continue
running during maintenance or operational obstacles. The North Kent Clean Water Plant operates
two biofilters in parallel. Biofilters are operated in series if the air has multiple contaminants that are
best removed in multiple stages. Bi0dor intends to consider the splitter box layout and surrounding
plant area to determine the best location for the facility that is easy for operators to access while
remaining out of flood danger from large storm events that have impacted the CWP in the past. The
biofiltration system will be optimized so that the design footprint is minimized. Reusing and
retrofitting existing equipment at the CWP will be evaluated, or more specifically, the potential of
installing the biofilter in the unused aeration basins.
Air Distribution System
Air distribution throughout the system is important so that the entire media bed is used evenly to
remove contaminants. Refer to Section 6.5.4 for the effects of undistributed air throughout the media
bed. Factors to consider when designing the biofilter include the locations of the influent and effluent
air. The distribution of air throughout the biofilter can impact the biokinetics and biofilm at different
sections of the media bed. With varying 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.
Alternatives for the blower and piping necessary for the distribution of the air in the biofilter will be
analyzed. The blower size and speed depend on the duct size, system pressure loss, and airflow rates
through the biofilter. There are opportunities to install piping through existing tunnels at the plant.
The advantages of various piping options will be evaluated for the conveyance of air in the network.
Alternatives include the use of perforated pipes buried in gravel or prefabricated, interlocking blocks.
Necessary valves will also be incorporated into the final design of the system. A sustainable approach
will be taken when sizing the blowers and pumps in order to minimize electrical costs.
Moisture Control System
Maintaining the appropriate moisture content in the biofilter is necessary for the media to sustain
microbial activity. The moisture content required is a function of the ambient temperature, relative
humidity, and flow rate of the feed gas. Humidity in the biofilter is maintained by humidifying the feed
air or by direct irrigation using a sprinkler system. Often there is a humidification chamber that
increases the moisture content of the incoming air with sprinklers using the plant’s effluent water.
Bi0dor intends to evaluate the use of a watering controls system for the sprinklers and hoses in order
to provide moisture to the biofilter.
Page 72 of 84
BASIS OF DESIGN
The amount of water required to maintain the media will be determined based on the climate and
existing moisture content of the foul air emitted from the splitter box. The collection and disposal of
excess water will be considered in the design. Other potential issues the design will address include
channeling of the media bed as well as flooding or foaming due to the flow of excess water. A
sustainable approach will be taken when designing the moisture control system such that water is
conserved and re-used efficiently at the CWP.
Monitoring and Controls
The control of pH will be incorporated in the design of the biofilter and installation of a pH recording
system will be performed based on previous case studies. Fluctuations of the pH in the system can
negatively affect the removal efficiency of the biofilter by disrupting microbial activity and
characteristics of the media itself. A range of operable pH conditions will be recommended so that
the life of the media will be extended and maintenance is minimized. The proposed biofilter will
include a range of pH, temperature, and humidity for acceptable operation. This will depend on the
media selected.
Based on the level of automation desired by the CWP, instrumentation and control requirements will
vary. The necessary components include volumetric flow meters measuring the airflow from the
blowers and control valves to maintain appropriate water levels in the humidifiers. Additionally, a
flow meter can be installed to monitor the total effluent plant water used for irrigation and a
differential pressure manometer to monitor the pressure drop across the biofilter.
Chemical and Nutrient Requirements
Often fertilizers and other liquid nutrients are fed to the biofilter, which depends on the operation of
the biofilter and the media selected. Bi0dor intends to minimize the chemicals or nutrients added to
the biofilter in order to reduce annual operating costs and labor. However, if these nutrients are
needed to ensure robustness of the system, then careful consideration of the type of nutrient and the
dosing needed will be performed in order to efficiently utilize the maintenance budget of the plant.
Additional Equipment
The location of the biofilter will be determined by the filter size required by the design. Options that
will be evaluated for the design the biofilter include locating the system over the splitter box structure
or locating it elsewhere on the plant site. Furthermore, the location of the biofilter will consider the
history of average rain events for this geographical region. However, the group will also consider
unique cases and potential flooding events as we decide the optimal location for the biofilter. The
storm event in 2013 resulted in flooding in the CWP headworks as a result of excess flow in the system
and inadequate on-site drainage because the plant is located in the FEMA floodplain (Appendix I).
Stormwater management will be taken into account when designing the biofilter so that the system
will not be negatively impacted either structurally or operationally by substantial rain events.
Page 73 of 84
BASIS OF DESIGN
Economic Cost Analysis
Estimates of the annualized cost of operation of the proposed biofiltration system will be developed,
including a total annualized cost after design specifications have been determined. Estimates will be
based on vendor information, cost data found in literature, and general engineering principles
accepted in the industrial practice. Because this technology is relatively new, average project life of a
biofilter is unknown and costs will be based on conservative and best-case medium life estimates. For
cost estimates, we will assume the biofilter life is 30 years. To be conservative with our estimates a
contingency of 30% will be used.
Bi0dor’s design will include an estimated cost estimate for the following:
1. Initial Cost
 Packing media
 Biofilter chamber
 Equipment (i.e. piping, ducts, sprinklers, accessories, valves, etc.)
 Construction Equipment
 Blowers
2. Annual Cost
 O&M (hours of labor)
 Operating costs ($/kWh)
 Equipment repairs
3. Media Replacement (10-15 years)
 Media cost
 Media disposal (i.e. landfill, incineration, land apply, etc.)
 Equipment replacement
A life cycle inventory will be completed on the odor footprint and carbon footprint of our
recommended biofilter.
10.4 BASE CASE CALCULATIONS
The initial calculations to size the biofilter used the rate law data taken from Dumont and Andres [63].
The packing material peat was selected for the base calculations because of its successful
performance in the case study. The Michaelis-Menten kinetics values for Vm and Ks published in the
report were used (refer to 7.3 for a review of Michaelis-Menten kinetics). The concentration of H2S in
the system was considered dilute, and the rate law took the form of
−ra =
Vm ∙ Ca
.
Ks
Using the program Polymath, the biofilter volume was calculated using the reactor design equation
for a plug flow reactor
Page 74 of 84
BASIS OF DESIGN
dFa
= ra.
dV
Polymath is a differential equations solving program. Imputing a system of differential equations,
polymath will run a series of iterations to solve the equations simultaneously. A base case of 2,000
cfm of air with an initial H2S concentration of 22 ppmv was assumed for these base calculations. The
calculated reactor (i.e. biofilter) volume needed to reduce the H2S below nuisance levels (20
mol/hour or a conversion of 0.99) was 28 m3. Detailed calculations can be found in Appendix J. A
graph of the flow rate of hydrogen sulfide as a function of reactor volume is shown in figure 20.
Flow rate of hydrogen sulfide
(mol/hr)
2500
2000
1500
1000
500
0
0
5000
10000
15000
20000
25000
30000
Volume of reactor (L3)
Figure 20. Base Case Removal of Hydrogen Sulfide across a Peat Filled Packed Bed Reactor
The PARCC Side Clean Water Plant (capacity of 6.6 mgd) currently uses two biofilters operating in
parallel, each having a volume of approximately 30 m3. Our base calculations indicate that the biofilter
volume is feasible. Additional optimization will be completed for the preliminary design using air
flow rate data, H2S concentrations in the air flow, and media characteristics.
10.5 LONG-TERM ODOR-CONTROL STUDY
The primary scope of the project is to propose an odor-control technology to treat the nuisance air
emitted from the wastewater in the splitter box. The CWP invests in high quality designs for the long
term. A preliminary study will be completed to answer the question, “What would it take to treat all
odor emitted from the CWP with a single biofiltration system?” The future of the plant influent may
include additional industrial connections who seek to be serviced by the CWP. The composition of the
wastewater and resulting odor may need to be reevaluated depending on the characterization of the
industrial wastewater. Under the guidance of Ben Whitehead and his colleagues at Black & Veatch, it
will be assumed that the primary contaminant is hydrogen sulfide because additional pollutants are
Page 75 of 84
BASIS OF DESIGN
effectively removed by the biofilter when designed based on only the H2S concentration. The long
term sustainability study will include a proposal for the dimensions and configuration of the
biofilter(s). Retrofitting the existing unused aeration basins will be evaluated as an alternative to
constructing a full biofilter. It will be assumed that the CWP intends to convert all current odorcontrol technologies to biofiltration by the year 2020. A cost estimate for this large biofilter will be
completed assuming the project life is 30 years. These will be the factors that go into the feasibility of
a biofilter for the entire plant.
Page 76 of 84
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:
Myron Erickson, City of Wyoming, for meeting with and advising the team.
Ben Whitehead, Black & Veatch, for meeting with and advising the team as an industrial consultant;
providing resources and engineering design advice.
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.
Chuck Kronk, Waterworks Systems and Equipment, Inc., for providing valuable biofilter design
information,
David Wunder, Calvin College, for offering his insight and advice.
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.
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[52] H. Li, D. R. Lueking, J. R. Mihelcic and K. Peterson, "Biogeochemical analysis of hydrogen sulfide removal
by a lava-rock packed biofilter," Water Environment Research, vol. 77, no. 2, pp. 179-186, 2005.
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selection of packing materials for biofiltration of rendering odourous emissions," Water, Air, & Soil
Pollution, vol. 224, no. 7, pp. 1-13, 2013.
[54] R. Govind and S. Narayan, "Selection of bioreactor media for odor control," Biotechnology for Odor and
Air Pollution Control, pp. 65-100, 2005.
[55] J. J. Goncalves and R. Govind, "Analysis of Biofilters Using Synthetic Macroporous Foam Media," Journal
of the Air & Waste Management Association , vol. 59, no. 7, pp. 834-844, 2009.
[56] I. BioRem Technologies, "Leading the Evolution of Biofiltration: Biosorbens - Permanant Biofilter Media,"
BioRem
Technologies,
Inc,
[Online].
Available:
http://www.edaenv.ca/_mndata/edaltd/uploaded_files/BIOREMs%20Brochure%202005.pdf.
[Accessed 2015].
[57] Z. Shareefdeen, B. Herner, D. Webb and S. Wilson, "Hydrogen sulfide (H2S) removal in synthetic media
biofilters," Environmental progress, vol. 22, no. 3, pp. 207-213, 2003.
[58] J. P. Scisson, "ATAD, The next generation: design, construction, start-up and operation of the first
municipal 2nd generation ATAD," Proceedings of the Water Environment Federation, no. 6, pp. 205-222,
2003.
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Michigan, 2013. [Online]. Available: http://www.threeriversmi.org/city-departments/clean-waterplant/. [Accessed 2015].
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12 2015].
[61] S. Schoolcraft, "Assistant Superintendant," North Kent Sewer Authority, PARCC Side CWP.
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comparitive study," Journal of Chemical Technology and Biotechnology, vol. 85, pp. 429-434, 2009.
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4, pp. 34-40, 1992.
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Available: http://www.michigan.gov/deq/0,4561,7-135-3311_4231-9162--,00.html.
[67] A. E. Quality, "Overview of Michigan's Air Toxic Rules," Department of Environmental Quality, [Online].
Available: http://www.michigan.gov/deq/0,4561,7-135-3310_70310_70487_4105-11749--,00.html.
[68] T. ". P. M. Newsletter, "Scrubber/Biofilter Wastewater Odor Control Market to Reach $800 Million in
2015," Gold Dust, Dec 2010.
[69] E. H. M. B. Dirkse, "Odour Control on Waste Water Treatment Plants and Pumping Stations using DMT
Biotrickling Filtration," DMT Environmental Technology, 2009.
[70] H. Bohn, "Consider biofiltration for decontaminating gases," Chemical Engineering Progress, 88(4), pp.
34-40, 1992.
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Page 83 of 84
APPENDICES
13 Appendices
APPENDIX A – GANTT CHART
APPENDIX B – PROJECT BUDGET
APPENDIX C – CWP FLOW DIAGRAM
APPENDIX D – HEADWORKS H2 S DATA
APPENDIX E – PRIMARY CLARIFIER H2 S DATA
APPENDIX F – BIOSOLIDS STORAGE TANKS H2 S DATA
APPENDIX G – SPLITTER BOX DRAWINGS
APPENDIX H – SPLITTER BOX H2S DATA
APPENDIX I – FIRM MAP
APPENDIX J – BASE CALCULATIONS
Page 84 of 84
ID
Task
Mode
1
2
3
4
5
6
7
8
9
10
11
12
Task Name
Hours
Website
Select Webmaster
Create Website
Final Website Posted
Miscellaneous
Team Photos
Project Brief
Project Poster
Presentations
Oral Presentation 1
Oral Presentation 2
Business Final
Presentation
13
Presentation to
Wyoming
14
Business Plan
Work Break Down
Structure
15
16
1
10
20
2
2
5
4
8
8
4
5
Deadline
Duration
Thu 10/15...
Fri 10/16/15 1 day?
Tue 10/27/... 9 days
Wed 10/28... 7 days
Mon 10/2...
Sun 10/25/... 1 day
Mon 10/19... 4 days
Fri 11/6/15 5 days
Wed 12/9...
Mon 10/26... 9 days
Wed 12/2/... 34 days
Tue
37 days
12/15/15
Wed
12/9/15
33 days
Start
Finish
Thu 10/15/15Thu 10/15/15
Fri 10/16/15 Wed 10/28/15
Tue 10/20/15Wed 10/28/15
Tue 10/20/15Tue 10/20/15
Wed 10/14/15Mon 10/19/15
Tue 10/20/15Mon 10/26/15
Wed 10/14/15Mon 10/26/15
Mon 10/26/15Thu 12/10/15
Mon
Tue
10/26/15
12/15/15
Mon
10/26/15
Wed
12/9/15
Fri 12/11/15
Tue
5 days
10/20/15
Wed
10/14/15
Tue
10/20/15
Executive Summary
Vision and Mission
Statement
1
1
Sun 11/15/... 24 days
Sun
24 days
11/15/15
Wed 10/14/15Sun 11/15/15
Wed
Sun
10/14/15
11/15/15
18
Industry Profile and
Overview
3
Sun
11/15/15
Wed
10/14/15
19
Business Strategy
6
Company Produts and 2
Services
Sun 11/15/... 24 days
Sun
24 days
11/15/15
Wed 10/14/15Sun 11/15/15
Wed
Sun
10/14/15
11/15/15
Marketing Strategy
4
Competitive Analysis 3
Description of
1
Management Team
Sun 11/15/... 24 days
Fri 12/11/15 28 days?
Fri 12/11/15 28 days?
Wed 10/14/15Sun 11/15/15
Wed 11/4/15Fri 12/11/15
Wed
Fri 12/11/15
11/4/15
Operations
Financial Forecasts
Loan or Investment
Proposal
2
3
2
Fri 12/11/15 28 days?
Fri 12/11/15 28 days?
Fri 12/11/15 28 days?
Wed 11/4/15Fri 12/11/15
Wed 11/4/15Fri 12/11/15
Wed
Fri 12/11/15
11/4/15
15
Fri 12/11/15 28 days
Fri 12/11/15
Wed 10/7/... 33 days
Fri 12/11/15 5 days
Mon 11/16... 24 days
Fri 12/11/15 20 days?
Mon 11/3...
Sun 11/15/... 5 days
Mon 11/30... 12 days
Fri 4/15/16
Sat 1/2/16 26 days
Sun 1/3/16 2 days
Fri 4/15/16 71 days
Wed 11/4/15Fri 12/11/15
17
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
Appendices
PPFS
Research
Outline
Draft
Final
Air Testing
Collect Samples
Analyze Samples
Biofilter Prototype
Project Planning
Order Equipment
Pilot Biofilter
Construction
Final Report
Research
Outline
Draft
Final
Final Poster
Outline
Draft
Final
Senior Design Night
Presentation
Project: WBS_Senior Design.mpp
Date: Sat 11/14/15
8
40
45
30
2
10
15
2
45
30
3
40
10
2
14
4
4
Fri 5/6/16
Fri 4/15/16
Tue 3/15/16
Fri 4/15/16
Fri 5/6/16
Fri 5/6/16
Wed 4/20/...
Fri 4/29/16
Fri 5/6/16
Fri 5/6/16
Fri 5/6/16
24 days
Appendix A - Gantt Chart
Sep 27, '15
Oct 4, '15Oct 11, '15
Oct 18, '15
Oct 25, '15
Nov 1, '15Nov 8, '15Nov 15, '15
Nov 22, '15
Nov 29, '15
Dec 6, '15Dec 13, '15
Dec 20, '15
Dec 27, '15
Jan 3, '16Jan 10, '16
Jan 17, '16
Jan 24, '16
Jan 31, '16
Feb 7, '16Feb 14, '16
Feb 21, '16
Feb 28, '16
Mar 6, '16Mar 13, '16
Mar 20, '16
Mar 27, '16
Apr 3, '16Apr 10, '16
Apr 17, '16
Apr 24, '16
May 1, '16
May
T T S MW F S T T S MW F S T T S MW F S T T S MW F S T T S MW F S T T S MW F S T T S MW F S T T S MW F S T T S MW F S T T S MW F S T T S MW F S T T S MW F S T T S MW F S T T S MW F S T T S MW F S T T S MW F S T
Sun
11/15/15
Thu 10/1/15 Mon 11/16/15
Thu 10/1/15 Wed 10/7/15
Wed 10/14/15Mon 11/16/15
Mon 11/16/15Fri 12/11/15
Tue 11/10/15Sun 11/15/15
Sun 11/15/15Mon 11/30/15
Mon 11/30/15Sat 1/2/16
Sat 1/2/16 Sun 1/3/16
Sun 1/10/16 Fri 4/15/16
11 days
11 days
24 days
16 days
Tue 1/5/16
Tue 3/1/16
Tue 3/15/16
Fri 4/15/16
Tue 1/19/16
Tue 3/15/16
Fri 4/15/16
Fri 5/6/16
8 days
10 days
6 days
Thu 4/7/16 Mon 4/18/16
Mon 4/18/16Fri 4/29/16
Fri 4/29/16 Fri 5/6/16
46 days
Fri 3/4/16
Fri 5/6/16
Task
Summary
External Milestone
Inactive Summary
Manual Summary Rollup
Finish-only
Split
Project Summary
Inactive Task
Manual Task
Manual Summary
Deadline
Milestone
External Tasks
Inactive Milestone
Duration-only
Start-only
Progress
Page 1
Manual Progress
Appendix B – Project Budget
Explanation of Costs
According to Test America and GSA advantage, the cost for a VOC analysis of gas is around 125 dollars
a sample1. 200 dollars is assumed for shipping and labor costs. To collect these samples, Tedlar bags
are needed (as well as a lung pump to collect the air). 1L bags cost 102 dollars apiece from Sigma
Aldrich2 and the Vac-U-Chamber (10 sample bags included) is $1425 from SKC inc.3 Assuming
samples will be taken weekly for 1 month, the cost for this sampling at 5 spots in the plant is $6445.
For the Pilot Plant, hydrogen sulfide will be used as that is the primary gas in the effluent. A 29 L
canister can be purchased from Norlab gasses for $1654. Materials of construction were estimated at
$500. This results in a total cost of $665 for the entire pilot plant.
These two projects are therefore estimated to cost $7110. With our available funds from Calvin, we
would need $6610 from the Wyoming Water treatment plant.
https://www.gsaadvantage.gov/ref_text/GS07F5687P/0P0KH5.389P2D_GS-07F5687P_GSAPRICELIST15SEPT2015.PDF
2 http://www.sigmaaldrich.com/analytical-chromatography/analytical-products.html?TablePage=16369234
3 http://www.skcinc.com/catalog/index.php?cPath=200000000_202000000_202000550_202000551
4 http://www.norlab-gas.com/15m7/gases-cylinders/hydrogen-sulfide-h2s.html
1
Appendix C – CWP Flow Diagram (provided by Jon Burke)
Appendix D – 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 E – Primary Clarifiers H2S Readings
Upper Stack
UP
Upper Carbon Layer
UM
UL
Influent Air from
Primary Clarifiers
LL
Lower Carbon Layer
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 F – 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 G - Splitter Box Drawings
Appendix G - Splitter Box Drawings
Appendix H – 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. 1, 2015. At this time, the logger is still installed and
taking data.
The following photograph shows the location of the logger in the splitter box.
(photo credit: Kerala Smith)
1
http://www.odalog.com/odalog/
Project Location
Appendix H - FIRM Map
Appendix J – Base Case Calculations