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wastewater > Biological Treatments > Flashcards

Biological Treatments Flashcards

1
Q

how to treat biodegradable const. and nutrients?

A
  1. Transform into acceptable end products (transforming to CO2)
  2. Incorporate into flocs or biofilm to separate from WW
  3. Conventional Activated Sludge
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2
Q

Biomass Growth in Batch Mode Phases

A
  1. Lag Phase
  2. Exp. Growth Phase
  3. Stationary Phase
  4. Decay Phase
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3
Q

Microorganism Metabolism reactions

A

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)

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4
Q

Biomass Yield

A

Y=Biomass produced/Substrate consumed

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5
Q

Stoichiometric in biochemical biomass yield if substrate is 1

A

substrate: 1
from 1 substrate y become biomass and 1-y is O2 used to oxidized into CO2+H2O

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6
Q

Substrate and biomass are usually measured as?

A

Substrate: COD
Biomass: COD, VSS, TSS

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7
Q

COD Glucose

A

1.07 g COD or O2/g Glucose

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8
Q

COD of Biomass

A

1.42 gCOD/gVSS

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9
Q

What are true yield, biological yield, and observed yield

A

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

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10
Q

Types of Energy Source and Carbon Source

A

Energy Source: Redox (Chemotrophs) and Light (Phototrophs)

Carbon Source: Autotrophs (inorganic carbon e.g CO2) and Heterotrophs (org. Carbon)

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11
Q

Other name for Chemo Autotrophs and Chemo Heterotrophs

A

Chemo litotrophs and chemo organotrophs

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12
Q

What are chemoautotrophs and chemo heterotrophs?

A

chemo autotrophs: Nitrifying bacteria, methanogens

chemoheterotrophs: Animals, Fungi, Bacteria

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13
Q

What is e- donor and e- acceptor?

A

e-donor: Oxidized substance or SUBSTRATE (e.g org. compound, ammonia, acetate)

e-acceptor: Reduced Substance (Oxygen, nitrate, CO2)

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14
Q

What is Aerobic, Anaerobic, and Anoxic?

A

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

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15
Q

What are Obligate Anaerobic and Obligate Aerobic?

A

Obligate Anaerobic: Org. only survive in absence of O2

Obligate Aerobic: Org. that only meet their energy needs with O2

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16
Q

What are Facultative Anaerobic and Facultative Aerobic?

A

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

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17
Q

What are obligate anaerobes and obligate aerobes

A

obligate anaerobes: Org. that only survive in the absence of O2

obligate aerobes: org. that can only meet their energy needs with O2

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18
Q

What is e-acceptor and e-donor of below process
1. Aerobic Respiration
2. Aerobic Nitrification
3. Anaerobic Respiration
4. Fermentation
5. Methanogenesis

A

e-donor | e-acceptor

  1. Organic compound | O2
  2. Ammonia | O2
  3. Organic Compound | Nitrate inorganic
  4. Organic Compound | Organic Compound
  5. Acetate | CO2
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19
Q

Aerobic Heterotrophs

A

Org removal in CAS (include PAOs)

e-donor: Org Compound
e-acceptor: O2
C-Source: Org Compound
Result: New cells, CO2+H2O

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20
Q

Nitrifiers, Aerobic lithoautotroph

A

Ammonia Oxidation
e-donor: Ammonia (NH4+)
e-acceptor: O2
C-Source: CO2
Result: New cells, NO2- or NO3-

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21
Q

Denitrifiers, Anoxic Heterotrophic

A

N removal after ammonia oxidation
e-donor: Org Compound
e-acceptor: NO2- or NO3-
C-Source: Org Compound
Result: New cells, CO2+H2O
N2

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22
Q

Anaerobic heterotrophic

A

Anaerobic process for org removal
e-donor: Org Compound
e-acceptor: Org Compounds
C-Source: Org Compound
Result: New cells, CH4 and CO2

23
Q

What is miu, miumax, and K

A

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

24
Q

Death Regeneration Model

A

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

25
Q

coefficient values that are used to predict rate of substrate utilization and biomass growth

A

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)

26
Q

S=Xs+Ss conversion into biomass (VSS) how?

A

yield factor (mg VSS/mgCODd)

27
Q

What consist in activated sludge mass balance

A

Substrate to be removed: Biodegradable organics (ss and Xs)

Sludge (XB and XI)

Effluent: Unbiodegradable soluble organics (Si)

Oxygen

28
Q

What are the 3 unbiodegradable particle

A

XI,0 VSS: Organics inert in influent
XI,0 FSS: Inorganic inert in influent
XE-VSS or XE-TSS: Endogenous residue

29
Q

What is the difference between with and without recycling?

A

without recycling SRT=HRT

30
Q

What is MLVSS and MLSS

A

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

31
Q

Effect of longer SRT to sludge production

A

lower sludge production

32
Q

Typical value of MLSS and MLVSS

A

MLVSS= 2.5g/l
MLSS=3g/l

33
Q

Conversion from VSS to TSS

A

TSS = VSS/0.85

34
Q

Return Flow Rate Mass Balance

A

QrXr - (Q+Qr)X = 0

R=Qr/Q

35
Q

Typical Xr concentration

A

6000-12000 mg/L

36
Q

Why is F/M ratio should be constant?

A

to ensure uniform substrate removal

37
Q

What is F/M Ratio

A

Rate of substrate (BOD) provided to M/O per unit volume of MLVSS

F/M=QSo/VX

38
Q

What does F/M Ratio influences

A
  1. Process performance
  2. Oxygen Requirements
  3. Sludge Age & Production
  4. Type of M/O in AS
39
Q

Higher F/M Ratio Meaning

A

lower %BOD Removed, lower O2 requirement, lower HRT, lower SRT, higher wasting sludge

40
Q

How to control F/M Ratio when it’s too high

A

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

41
Q

What is Sludge Volume Index

A

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

42
Q

How to calculate SVI?

A

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

43
Q

What is good Activated sludge?

A

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

44
Q

what does floc structure contain in activated sludge?

A
  1. Biological components (bact, fungi, protozoa): balanced growth of floc forming and filamentous bacteria
  2. Non Biological Components
    organic, inorganic, exocellular polymers) help m/o to stick to each other)
45
Q

Reasons for poor settling sludge

A

configuration of treatment plant, organic loading (F/M ratio), Environmental condition (DO conc), Presence of particular ww constituents

46
Q

Ideal sludge structure

A
  1. Balanced growth of floc forming and filamentous organisms
  2. Strong large flocs
  3. Low SVI
  4. Clear supernatant
47
Q

Problem of:
1. Dispersed growth,
2. Pinpoint floc

A
  1. 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

48
Q

Filamentous bulking

A

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

49
Q
  1. Rising sludge
  2. Foaming
A
  1. 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

  1. 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

50
Q

What is Selector

A

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

51
Q

Kinetics based selector

A

High substrate –> High F/M Ratio

Floc forming specific growth rate (miu) is more than filamentous

52
Q

Metabolic Based Selector

A

Anoxic/Anaerobic condition favour floc formers because filamentous cannot use nitrate/nitrite and also cannot store polyphosphate

53
Q

Viscous Bulking

A

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

wastewater (4 decks)

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