ERT 319
Industrial Waste
Treatment
Biological Treatment
Processes of Industrial
Wastes
“Ability to calculate and compare
the treatment methods for
particular wastes.
&
Ability to design and evaluate
various unit operations
for waste treatments.”
Biological treatment / Unit operation
INTRODUCTION
Objectives of Biological Treatment:
a) Transform (i.e., oxidize) dissolved and particulate
biodegradable constituent s by microorganisms into
acceptable end products,
b) Capture and incorporate suspended and non-settleable
colloidal solids into a biological floc or biofilm,
c) Transform and remove nutrients, such as nitrogen and
phosphorus.. why???
d) In some cases, remove specific trace organic constituents and
compounds.
For industrial wastewater:
- To remove or reduce the concentration of organic
and inorganic compounds.
 because some of the constituents and
compounds are toxic to microorganism,
pretreatment may be required before discharging to
municipal collection.
Biological Processes for wastewater treatment
Activated sludge process
Aerated lagoons
Trickling filters
Rotating biological contractors
Trickling filter
Aerobic biological oxidation of organic matters
Nutrients for microbes to
Converts organic matters to
CO2 and H2O
vi = stoichiometric coefficient
Biomass produced
Composition & Classification of
Microorganisms
** Revise the cell components, compositions,
structure, DNA, RNA, microbial Growth &
metabolism, C & N sources …
Refer Chapter 7, page 555-563
COMMON TERMINOLOGY IN BIOLOGICAL TREATMENT PROCESS
Bacteria metabolism
Aerobic, autotrophic
Aerobic, heterotrophic
Anaerobic, heterotrophic
Do you understand:
Aerobic?
Anaerobic?
Heterotrophic?
Autotrophic?
Phototroph?
Chemotroph?
Bacterial reproduction:
In 30 min of generation time (time required bacteria to divide into 2 organisms)
1 bacterium would yield ~ 17 x 106 bacteria in 12 h and the mass ~ 8.4 µg
Biomass yield Y = g (biomass produced) / g (substrate consumed)
VSS- common method to measure biomass growth
Microbial Growth Kinetics
Growth kinetics govern the substrate oxidation and biomass
production
TSS conc. in biological reactor
- Organic compounds mostly defined as biodegradable COD
(bCOD) or ultimate carbonaceous BOD (UBOD). bCOD and UBOD
comprise of soluble (dissolved), colloidal and particulate
biodegradable components.
- Biomass solids in bioreactor = TSS & VSS
- The mixture of solids resulting from combining recycled sludge
with influent wastewater in bioreactor = mixed liquor suspended
solids (MLSS) and mixed liquor volatile suspended solids
(MLVSS)
- Solid = biomass, nonbiodegradable volatile suspended solid
(nbVSS) and inert inorganic total suspended solid (iTSS)
1) Rate of utilization of soluble substrates
(-ve : substrate decreases with time)
rsu = rate substrate conc. change due to utilization, g/m3.d
k = max specific substrate utilization rate, g substrate/ g microbe . D
Ks = substrate conc. at one-half max substrate utilization rate g/m3
X= biomass concentration, S= limiting substrate concentration g/m3
2) Rate of Biomass Growth with soluble substrate
Specific biomass growth rate, μ= rg/X
3) Rate of oxygen uptake
4) Effects of temperature
5) Total volatile suspended solids & Active biomass
Example 7-5 Determine Biomass and Solids Yields
For an industrial wastewater activated sludge process, the
amount of bsCOD in the influent wastewater is 300 g/m3 and
the influent nbVSS concentration is 50 g/m3 . The influent
flowrate is 1000 m3 /d, the biomass concentration is 2000
g/m3 , the reactor bsCOD concentration is 15 g/m3 , and the
reactor volume is 105 m3. If the cell debris fraction fd is 0.10,
determine:
a) The net biomass yield
b) The observed solids yield
c) The biomass fraction in the MLVSS
d) Specific biomass growth rate, µ
Solution:
?
?
Aerobic Biological Oxidation
Wide range of microorganisms used:
Ex: Aerobic heterotrophic bacteria able to
produce extracellular biopolymers that
result in the formation of biological flocs,
then separated by gravity settling.
- Protozoa: consume free bacteria and colloidal
particulates – aid effluent clarification.
Stoichiometry:
Electron donor
Electron acceptor
Biological Nitrification
Nitrification:
2-step biological processes;
• Ammonia (NH4-N) is oxidized to nitrite (NO2-N)
• Nitrite is oxidized to nitrate (NO3-N)
Why??
1) Ammonia & nitrite– associate DO conc. & fish toxicity
2) Need for nitrogen removal:
– control eutrophication & water-reuse application
Total conc. of organic and ammonia nitrogen in municipal wastewater: 25-45
mg/L
Stoichiometry:
Two step oxidation of ammonia to nitrate
Nitroso-bacteria (Nitrosococcus, Nitrosospira, etc):
2NH4+ + 3O2
2NO2- + 4H+ + 2H2O
(Nitrobacter, Nitrococcus, Nitrospina, etc):
Nitrate:
Safer form to
aquatic lives
Biological Denitrification
Denitrification:
The biological reduction of nitrate to (nitrite) then to nitric oxide,
nitrous oxide, and nitrogen gas.
Biological nitrogen removal is used in wastewater treatment :
- where there are concerns for eutrophication,
- and where groundwater must be protected against elevated NO3-N
concentration.
2 modes of nitrate removal:
1) Assimilating nitrate reduction (ANR)
2) Dissimilating nitrate reduction (DNR)
• ANR involves the reduction of nitrate to ammonia for use in cell
synthesis (Fig 7-20)
Assimilation occurs when NH4-N is not available and is
independent of DO concentration.
• DNR is coupled to the respiratory electron transport chain, and
nitrate or nitrite is used as an electron acceptor for the oxidation of
a variety of organic or inorganic electron donors (Fig 7-20).
• Microorganism for denitrification: both heterotrophic and
autotrophic ( most are facultative aerobic organisms with the
ability to use oxygen as well as nitrate or nitrite).
- Example: Achromobacter, Acinetobacter, Bacillus,
Chromobacterium, Pseudomonas, Rhizobium, etc.
Biological Denitrification
Types of denitrification process
a) Substrate driven
b) Endogenous driven
In the first flow, nitrate produced in the aeration tank is recycled
back to the anoxic tank (anaerobic). Because the organic
substrate in the influent wastewater provides the e- donor for
oxidation-reduction reactions using nitrate, the process is termed
substrate denitrification. Or because the anoxic process precedes
the aeration tank, the process is known as a preanoxic
denitrification.
In the second process, denitrification occurs after nitrification and
the e- donor source is from endogenous decay. BOD removal has
occurred first, and is not available to drive the nitrate reduction
reaction, and called postanoxic denitrification.
It has much slower rate of reaction than preanoxic denitrification.
Often, an exogenous carbon source such as methanol or acetate
is added to postanoxic processes to provide sufficient BOD for
nitrate reduction and to increase rate of denitrification.
Nitrogen cycle
Anaerobic Fermentation & Oxidation
• Used primarily for treatment of waste sludge and
high-strength organic wastes.
• As a pretreatment step due to low quality effluent.
• Advantages:
Lower biomass yield
Energy (methane) can be recovered from
biological conversion of organic substrate
Cost-effective; savings in energy, nutrient addition
and reactor volume.
Three basic steps in anaerobic
oxidation of wastes:
1) Hydrolysis:
•
particulate material is converted to soluble compounds that can then
be hydrolyzed further to simple monomers that are used by bacteria
that perform fermentation.
2) Fermentation (or acidogenesis):
•
•
•
Amino acids, sugars, and some fatty acids are degraded further.
The principle products are acetate, H2, CO2, and propionate and
butyrate.
Acetate, H2, CO2  precursors of methane formation
(Methanogenesis)
3) Methanogenesis:
Carried out by 2 groups of microorganisms (or Methanogens):
a) Aceticlastic methanogens
– split acetate into methane and CO2
CH3COOH
CH4 + CO2
b) Hydrogen-utilizing methanogens
- use H2 as electron donor and CO2 as the
electron acceptor to produce methane
Nuisance organisms in anaerobic fermentation
- When the wastewater contains significant concentrations of
sulfate
- Sulfate-reducing bacteria can reduce sulfate to sulfide (toxic to
methanogenic bacteria)
- Then, how to solve??
How??
Environmental factors:
- Anaerobic processes are sensitive to pH & inhibitory
substances (ex: NH3, H2S, etc.)
- pH near neutral  preferred ;
- pH below 6.8  methanogenic activity is inhibited
- Due to about 30-35 % CO2 (high) produced in anaerobic
process, high alkalinity is needed to neutralize pH
- Range of alkalinity, i.e., 3000-5000 mg/L as CaCO3 is often
found.
In industrial wastewater
applications which mainly contain
carbohydrates, it is necessary to
add alkalinity for pH control.
Types of Biological Process for
Wastewater Treatment
Suspended
Growth
Process
Attached
Growth Process
(Biofilm)
SUSPENDED GROWTH
BIOLOGICAL TREATMENT
PROCESS
Suspended Growth Processes (SGP)
 Microbes are maintained in liquid suspension by mixing
methods
 Most common SGP: Activated-sludge process (ASP)
- ASP uses activated mass of microbes capable of
stabilizing a waste under aerobic conditions
- mix wastewater with microbial suspension at certain
contact time, mechanically 
• MLSS
• MLVSS
 MLSS flows to clarifier (where microbial suspension is settled
and thickened)
“Activated sludge (AS)”
AS is returned to aeration tank to continue
biodegradation of organic material
1
Reactor- microbes are
kept in suspension and
aerated
Activated
Sludge
Process
3
2
Recycle system –
returning solids from
clarifier to reactor
Liquid-solids
separation – ex:
clarifier
Plug-flow ASP
Complete mix ASP
Selection & Design of
Physical Facilities for
ASP
Aeration
Systems
Aeration
Tanks
Solids
Separation
Solid
Separation
Facilities
Page 816 (textbook)
Selection & Design for Activated
Sludge Processes
1) Aeration System
Aeration system must be adequate to:
a) Satisfy the bCOD of the wastes
b) Satisfy the endogenous respiration by the biomass
c) Satisfy the O2 demand for nitrification
d) Provide adequate mixing
e) Maintain minimum dissolved O2 conc. throughout the tank
 If the O2 transfer efficiency of aeration system is known, we can
design /estimate the actual air requirements for diffused air
aeration or installed power of mechanical surface aerators.
• Aeration-achieved via diffused air (diffuser) or
surface aerator.
• Aeration equipment must be designed with
enough flexibility to:
– Meet minimum dan max O2 demand
– Prevent excessive aeration and save energy
2) Aeration Tanks and Appurtenances (support
facilities)
a) Aeration Tanks
- Usually constructed of reinforced concrete and left open to
atmosphere
- Capacity if aerated with diffused air:
• capacity range of 0.22 to 0.44 m3 /s  at least 2 tanks needed
• capacity range of 0.44 to 2.2 m3 /s  at least 4 tanks needed
• capacity range over 2.2 m3 /s  at least 6 tanks or more
-
Depth of wastewater in the tanks: between 4.5 and 7.5 m
Freeboard: 0.3 – 0.6 m above waterline
-
Width-to-depth ratio of the tanks (spiral-flow mixing): 1:1, 2.2:1 or
1.5:1 (most common)
Tank with diffusers on both sides, greater width are permissible.
Triangular baffles or fillet may be placed longitudinally in the
channel to eliminate dead spot
-
Refer Table 8-28 for typical aeration tank dimension for
mechanical surface aerators.
b) Flow distribution
- for multiple units of primary sedimentation tanks &
aeration tanks
- methods of splitting or controlling the flow rate, for
ex: splitter boxes equipped with weirs or control
valves or aeration tanks influent control gates.
- Hydraulic balancing of flow by equalizing the
headloss from the primary sedimentation basins to
the individual aeration tank.
c) Froth control systems
- Foaming- when the aerated wastewater which
contains soap, detergents & other surfactants
- Foaming action produces froth that contains sludge
solids, grease, and wastewater bacteria.
- Wind may lift & blow the froth  contaminate
whatever it touches, slippery, and difficult to remove
once it has dried.
- solutions: remove froth by spraying clear water or
screened effluent through nozzles or,
adding antifoaming chemical additives in spray water
d) Nocardia Foam Control
- Nocardia foam is a thick layer of brown biological foams that
forms on the top of aeration tanks and clarifiers.
- Nocardia organisms grows, tend to trap air bubbles  float
to the surface and accumulate as scum (dirty foam)
- Controlled by:
i) Spraying chlorine solution directly into foam layer
 in some cases, spray nozzles installed within a hood
located across the width of plug flow aeration tanks
 may not be effective, because it can cause floc
breakup & inhibit BOD removal and nitrification
ii) Addition of cationic polymer
3) Solids Separation Facilities
• to provide well-clarified effluent and concentrated solid
a) AS settling tank types
- circular or rectangular
• Circular tank:
Diameter = 2 – 60 m (or 10 -40 m)
tank radius –not more than 5 X sidewater depth
• Sludge collector
• Rectangular tank
– Max length:<10 x depth, commonly 90 m
– Width=6 m, use multiple sludge collection if 6m <width <24m
• Sludge collectors (rectangular):
a) Chain and flight
b) Traveling bridge
• Other type of settling tank :stacked clarifiers, tube
and plate settlers and intrachannel clarifiers
Suspended Growth Aerated Lagoons
• Suspended growth aerated lagoons (SGAL) are relatively shallow
earthen basins varying in depth from 2 – 5 m, provided with
mechanical aerators on floats or fixed platforms.
• Mechanical aerators:
- to provide oxygen for biological treatment of wastewater ,
- to keep the biological solids in suspension.
• SGAL are operated on a flow-through basis or with solids recycle.
• Types of SGAL:
1. Facultative partially mixed
2. Aerobic flow through with partial mixing
3. Aerobic with solids recycle and nominal complete mixing
Process Design Considerations for flow-through
lagoons:
1) BOD Removal
- the basis of design is SRT=hydraulic RT
- BOD conc: S/S0=1/1+kt
2) Effluent characteristics
- TSS and BOD conc.
3)
4)
5)
6)
Temperature effects
Oxygen requirement
Energy requirement for mixing
Solids separation.
Example 8-14 Design of a Flow-through Aerated Lagoon (Page 846)
Design a flow-through aerated lagoon to treat a wastewater flow of 3800 m3/d,
including the number of surface aerators and their kilowatt rating. The treated
liquid is to be held in a settling basin (lagoon) with a 2-d detention time before
being discharged. Assume that the following conditions and requirements apply:
1.
2.
3.
4.
5.
6.
7.
Influent TSS = 200 g/m3 (influent TSS are not degraded biologically)
Influent sBOD = 200 g/m3
Effluent sBOD = 30 g/m3
Effluent suspended solids after settling = 20 g/m3
Kinetic coefficients: Y = 0.65 g/g, Ks = 100 g/m3, k = 6.0 g/g.d, kd = 0.07 g/g.d for
T = 20 to 25 ⁰C
Total solids produced are equal to computed volatile suspended solids divided
by 0.85
First-order observed soluble BOD removal-rate constant k20 = 2.5 d-1 at 20 ⁰C.
8. Summer air temperature = 30 ⁰C
9. Winter air temperature during coldest month = 6 ⁰C
10. Wastewater temperature during winter = 16 ⁰C
11. Wastewater temperature during summer = 22 ⁰C
12. Temperature coefficient, θ = 1.06
13. Aeration constants: α = 0.85, β = 1.0
14. Aerator oxygen transfer rate = 1.8 kg O2/kWh
15. Elevation = 500 m
16. Oxygen concentration to be maintained in liquid = 1.5 g/m3
17. Lagoon depth = 3.3 m
18. Design SRT = 5d
19. Power required for mixing = 8 kW/103/m3
ATTACHED GROWTH
BIOLOGICAL TREATMENT
PROCESS
Attached Growth Processes (AGP)
- Microorganisms are attached to an inert packing
material
- The organic material and nutrients are removed from
wastewater flowing past the attached growth (or
Biofilm)
- Ex. packing material : rock, gravel, slag, sand,
redwood, plastics, etc.
- The packing can be submerged completely in liquid
or not submerged, with air or gas space above
biofilm liquid layer
- Most common:
Trickling filter – wastewater is distributed over the top area of
a vessel containing non-submerged packing material
Fig 7.3 Attached growth biological
treatment process
Trickling filter (TF)
Process flow in Trickling Filter
The wastewater is applied over the bed of supporting media (rocks, stones,
ceramic pieces, slag, etc) by rotating arms.
The effluent is collected in the secondary clarifier, to separate washed out
biomass solids before final disposal.
 As the wastewater trickles through the filter media, growth of
microorganism takes place on the surface of packing material known as
bio-film or slime layer.
 When the wastewater passes over this film, contact between
substrates or food (waste) and microorganism is established, thus, the
waste is decomposed aerobically by the attached biomass.
(Facultative bacteria –attach in trickling filters, decompose the organic
material in the wastewater along with aerobic and anaerobic bacteria).
 Then, a stage comes when anaerobic conditions are developed nearer
to the media surface and the microorganisms cannot remain attached
or fixed to the media.
 the slime layer then eventually peels off (or washed out) and removed
from the filter along with (next) flow.
- the washed out of slime layer is called sloughing.
Typical trickling filter process flow diagram
Single stage
Two stage
Design Criteria of Trickling Filter
a) Dosing rate
• Dosing rate in Trickling Filter (TF) is the depth of
liquid discharged on top of packing for each pass of
the distributor.
• For higher distributor rotational speeds, the dosing
rate is lower.
• With 2 or 4 arms, TF is dosed every 10 – 60s.
• Investigations show that reducing distributor speed
results in better filter performance  improve BOD
removal, reduce Psychoda & Anisopus fly population,
biofilm thickness, and odors.
Higher Dosing Rate
Larger water volume
applied / revolution
Greater agitation –
causes more solids
to flush out
Greater wetting
efficiency
Wash away
fly eggs
Thinner biofilm – increase
surface area & more aerobic
biofilm
b) Loading criteria
 Quantifying biomass / biological & hydrodynamic properties in
TF are not possible. Why ??




Attached growth is not uniformly distributed in TF
The biofilm thickness can vary
Biofilm solids concentration may range from 40 to 100 g/L
The liquid does not uniformly flow over the entire packing
surface area.
 Hence, use broader parameters such as: volumetric organic
loading, unit area loadings, and hydraulic application rates 
used as design / operating parameters to relate treatment
efficiency
ROTATING BIOLOGICAL CONTACTORS
(RBC)
• RBC consists of series of closely spaced circular disks
(polystyrene or polyvinyl chloride) submerged (typically
40%) in wastewater and rotated through it.
• The dicks are attached to a horizontal shaft.
 The assembly of shaft, disks and rotating equipments is called
one module. Normally in industrial waste treatment, more than
3 modules arranged in series or parallel.
Removal Mechanism of RBC
• As the shaft rotates, the surfaces of rotating disks alternately come in
contact with the microorganisms and organic content of wastewater
and atmosphere.
• During the rotation, the microbes get attached to the disks, and O2
from atmosphere is transferred to the wastewater to maintain aerobic
condition.
• The microbes attached to the disks surface grow in the form of
biological film and consume organic content in the wastes.
• After some times, as the bio-films thicken,s,
an anaerobic condition develops nearer to
the disks surface , then the slime layer gets
washed out (sloughing) by incoming waste
water flow.
 the sloughed bio-films is ultimately
removed in the secondary clarifier before
final disposal of treated effluent.
………>> Similar mechanism to Trickling filter <<…………
Process Design Consideration for
RBC
• Staging of RBC unit- why?
• Loading criteria
– Assume first stage 12-20g sBOD/m2d
– Total BOD loading 24-30g BOD/m2d
• Effluent characteristics
- Refer Table 9-8
• Secondary clarifier design
– Similar with those used in trickling filter
Example 9-7 Design of staged RBC for BOD Removal
Given the following design conditions, develop a process
design for a staged RBC system
Parameter
Unit
Primary Effluent Target Effluent
Flowrate
m3/d
4000
BOD
g/m3
140
20
sBOD
g/m3
90
10
TSS
g/m3
70
20
• Solution: Page 938
Follow step in page 937
1. Determine influent and effluent sBOD conc. and
WW flowrate
2. Determine RBC disk area for the first stage based
on max SBOD of 12-15 g sBOD/m3d
3. Determine number of RBC shaft using standard disk
density 9300 m2/shaft
4. Select number of trains, flow,number of stages,disk
area/shaft
5. Based on assumption in Step 4, calculate the sBOD
in each stage. If the effluent sBOD is met, calculate
the organic and hydraulic loading.