Biological Treatments Flashcards
how to treat biodegradable const. and nutrients?
- Transform into acceptable end products (transforming to CO2)
- Incorporate into flocs or biofilm to separate from WW
- Conventional Activated Sludge
Biomass Growth in Batch Mode Phases
- Lag Phase
- Exp. Growth Phase
- Stationary Phase
- Decay Phase
Microorganism Metabolism reactions
Catabolism: Decompose complex organics to simpler products and produce energy through redox storing in form of ATP
Anabolism: simple product and energy used to create new complex molecules (cells)
Biomass Yield
Y=Biomass produced/Substrate consumed
Stoichiometric in biochemical biomass yield if substrate is 1
substrate: 1
from 1 substrate y become biomass and 1-y is O2 used to oxidized into CO2+H2O
Substrate and biomass are usually measured as?
Substrate: COD
Biomass: COD, VSS, TSS
COD Glucose
1.07 g COD or O2/g Glucose
COD of Biomass
1.42 gCOD/gVSS
What are true yield, biological yield, and observed yield
True yield (Y): Amount of biomass produced from alive M/O per consumed substrate when decay and maintenance doesn’t occur
Biological Yield (Ybio): include net biomass generation (decay)
Observed Yield (Yobs): What we observed meaning including all
YObs = VSS generation/substrate consumtpion
Can be use to estimate sludge production
Types of Energy Source and Carbon Source
Energy Source: Redox (Chemotrophs) and Light (Phototrophs)
Carbon Source: Autotrophs (inorganic carbon e.g CO2) and Heterotrophs (org. Carbon)
Other name for Chemo Autotrophs and Chemo Heterotrophs
Chemo litotrophs and chemo organotrophs
What are chemoautotrophs and chemo heterotrophs?
chemo autotrophs: Nitrifying bacteria, methanogens
chemoheterotrophs: Animals, Fungi, Bacteria
What is e- donor and e- acceptor?
e-donor: Oxidized substance or SUBSTRATE (e.g org. compound, ammonia, acetate)
e-acceptor: Reduced Substance (Oxygen, nitrate, CO2)
What is Aerobic, Anaerobic, and Anoxic?
Aerobic: O2 is present and available as e-acceptor
Anaerobic: No free O2 is present, SO2-, NO3-, CO2 as e-acceptor
Anoxic: O2 is not available, Nitrate & Nitrite as e-acceptor
What are Obligate Anaerobic and Obligate Aerobic?
Obligate Anaerobic: Org. only survive in absence of O2
Obligate Aerobic: Org. that only meet their energy needs with O2
What are Facultative Anaerobic and Facultative Aerobic?
Facultative Anaerobic: Org. can grow either in presence or absence of O2
Facultative Aerobic:
Org. that can use nitrate/nitrite as e-acceptor when O2 not available
What are obligate anaerobes and obligate aerobes
obligate anaerobes: Org. that only survive in the absence of O2
obligate aerobes: org. that can only meet their energy needs with O2
What is e-acceptor and e-donor of below process
1. Aerobic Respiration
2. Aerobic Nitrification
3. Anaerobic Respiration
4. Fermentation
5. Methanogenesis
e-donor | e-acceptor
- Organic compound | O2
- Ammonia | O2
- Organic Compound | Nitrate inorganic
- Organic Compound | Organic Compound
- Acetate | CO2
Aerobic Heterotrophs
Org removal in CAS (include PAOs)
e-donor: Org Compound
e-acceptor: O2
C-Source: Org Compound
Result: New cells, CO2+H2O
Nitrifiers, Aerobic lithoautotroph
Ammonia Oxidation
e-donor: Ammonia (NH4+)
e-acceptor: O2
C-Source: CO2
Result: New cells, NO2- or NO3-
Denitrifiers, Anoxic Heterotrophic
N removal after ammonia oxidation
e-donor: Org Compound
e-acceptor: NO2- or NO3-
C-Source: Org Compound
Result: New cells, CO2+H2O
N2
Anaerobic heterotrophic
Anaerobic process for org removal
e-donor: Org Compound
e-acceptor: Org Compounds
C-Source: Org Compound
Result: New cells, CH4 and CO2
What is miu, miumax, and K
specific growth rate (gvssnew/gvss.d)
maximum specific growth rate (g new cells/gcellsd)
K is maximum specific substrate utilization rate (g substrate/g microorg. d)
K=miumax/yield
Death Regeneration Model
Slowly Biodegradable material (Xs) Hydrolyze into Easily Biodegradable Material (Ss)
and then it grow and oxidized by e-acceptor creating new cell or biomass (XB) and then the new cell will eventually dies or decay (fd) and become inert material (Xi or XE) and Xe can be recycled become Xs and undergo same process
coefficient values that are used to predict rate of substrate utilization and biomass growth
K: Maximum specific substrate utilization rate (g substrate/g microorganism)
Ks; Half saturation constant (g/m3) when 1/2 miumax
Y: Yield (mgVss/mgBOD5)
b: Specific endogenous decay (d-1)
S=Xs+Ss conversion into biomass (VSS) how?
yield factor (mg VSS/mgCODd)
What consist in activated sludge mass balance
Substrate to be removed: Biodegradable organics (ss and Xs)
Sludge (XB and XI)
Effluent: Unbiodegradable soluble organics (Si)
Oxygen
What are the 3 unbiodegradable particle
XI,0 VSS: Organics inert in influent
XI,0 FSS: Inorganic inert in influent
XE-VSS or XE-TSS: Endogenous residue
What is the difference between with and without recycling?
without recycling SRT=HRT
What is MLVSS and MLSS
MLVSS in terms of VSS
XT-VSS = XB-VSS + XE-VSS + XI-VSS
MLSS in terms of TSS
XT-TSS = XB-TSS + XE-TSS + XI-VSS + XI-FSS
Effect of longer SRT to sludge production
lower sludge production
Typical value of MLSS and MLVSS
MLVSS= 2.5g/l
MLSS=3g/l
Conversion from VSS to TSS
TSS = VSS/0.85
Return Flow Rate Mass Balance
QrXr - (Q+Qr)X = 0
R=Qr/Q
Typical Xr concentration
6000-12000 mg/L
Why is F/M ratio should be constant?
to ensure uniform substrate removal
What is F/M Ratio
Rate of substrate (BOD) provided to M/O per unit volume of MLVSS
F/M=QSo/VX
What does F/M Ratio influences
- Process performance
- Oxygen Requirements
- Sludge Age & Production
- Type of M/O in AS
Higher F/M Ratio Meaning
lower %BOD Removed, lower O2 requirement, lower HRT, lower SRT, higher wasting sludge
How to control F/M Ratio when it’s too high
Reduce Influent BOD Load: equalization or pre-treatment to reduce BOD spikes.
Increase Biomass Concentration: Reduce sludge wasting or increase the return activated sludge (RAS) rate
What is Sludge Volume Index
Used to monitor changes in settling characteristics of the Mixed liquor solids due to any operation, influent, or T changes.
Must be considered in the design of secondary sedimentation
How to calculate SVI?
SVI= settled volume of sludge (ml/l)/ Suspended Solids (g/L)
100 ml/g: good settling sludge
>150 ml/g: filamentous growth
1L sample - imhoffcone 30 mins
What is good Activated sludge?
1.Sludge flocs settle and compact well in settler
2. Clear effluent
3. Good SRT control
4. Good compaction thus reducing dewatering cost and waste disposal cost
what does floc structure contain in activated sludge?
- Biological components (bact, fungi, protozoa): balanced growth of floc forming and filamentous bacteria
- Non Biological Components
organic, inorganic, exocellular polymers) help m/o to stick to each other)
Reasons for poor settling sludge
configuration of treatment plant, organic loading (F/M ratio), Environmental condition (DO conc), Presence of particular ww constituents
Ideal sludge structure
- Balanced growth of floc forming and filamentous organisms
- Strong large flocs
- Low SVI
- Clear supernatant
Problem of:
1. Dispersed growth,
2. Pinpoint floc
- Lack of EPS thus lack of bioflocculation, individual cells or small clumps leads to high SVI and turbid effluent due to short SRT and high hydraulic turbulence so should adjust SRT, F/M and aeration
2.
Flocs break down due to low filamentous bacteria, high SVI and **
cloudy effluent** due to long SRT and low F/M and** excessive aeration**. should adjust SRT, F/M, aeration and add cationic poly electrolytes
Filamentous bulking
Excessive filamentous bacteria, interfere with settling and compaction, overflow of sludge blanket.
Overabundance of filamentous bact due to:
1. T&pH variations
2. Low DO due to poor mixing
3. Long SRT (low F/M)
4. Limited nutrients
5. Presence of sulfides.
Solution:
1. Add disinfectants that can kill filamentous (cholorination or H2O2)
2. Equalization for pH& T, improve aeration to keep DO>2 mg/L, SRT and F/M adjustment),
3. Add selector
- Rising sludge
- Foaming
- Rising Sludge
Problem: denitrification in settler release N2 gas which attach to flocs and float them creating turbid effluent
Solutions:
1. Stop nitrification by shortening SRT (if nitrification not required)
2. Include denitrification before secondary settling
3. Increase recycling to reduce SRT in clarifier
- Foaming
Problem: presence of surfactants, and certain bacteria which makes foam on surface and solids overflow
Solutions: remove oil and grease, using chloride spray on surface of foam, surface wasting of AS thus reduce SRT
What is Selector
small tank or series of tanks where incoming WW is mixed with return sludge to select floc forming bacteria and surpress filamentous.
HRT=30-60 min
short enough to avoid BOD oxidation, long enough that sBOD are taken by floc forming and stored as PHB so when in aeration floc forming gradually oxidize their storage while filamentous starve
Kinetics based selector
High substrate –> High F/M Ratio
Floc forming specific growth rate (miu) is more than filamentous
Metabolic Based Selector
Anoxic/Anaerobic condition favour floc formers because filamentous cannot use nitrate/nitrite and also cannot store polyphosphate
Viscous Bulking
Excessive production of EPS by floc forming, jelly like sludge
Effects: high SVI, poor settling,
Causes: high F/M short SRT, too much floc forming, Biological phosphorus removal causing excessive growth of acinetobacter that produce excessive polymer
Solutions: adjust F/M by adjusting SRT, Addition of Nutrients, bypass WW around selector, dosage of poly electrolytes
