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Wastewater > Nitro, Denitro, P Removal > Flashcards

Nitro, Denitro, P Removal Flashcards

1
Q

What is Eutrophication?

A

Unnatural enrichment of P& N in lake which causes algal bloom

Plants die and sink thus decomposed by bacterias and fungi, O2 is comsumed by the bact to decompose and release N and CO2 and energy. O2 depletion causes anoxic environment which kill fish. Additionally, ammonia and H2s can also be released due to anoxia which is poisonous

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2
Q

Limit for Total P and Total N

A

Total P <1-2 mg/L
Total N < 10-15 mg/L

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3
Q

Nitrogen present in WW as

A

Ammonia: 50-80% of Total N in WW

Organic Nitrogen: proteins, DNA, etc will be hydrolysed to ammonia

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4
Q

Nitrogen cycle how to reach from NH3 to N2

A

Annamox: directly
Nitrification: NH3 -> NO2- -> NO3-
Denitrification: NO3- -> N2

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5
Q

How does nitrification occur?

A
  1. Oxidation process
  2. by nitrifying bacteria (Aerobic Chmolithoautotrophs)

C-Source: CO2
e-donor: NH4+
e-acceptor: O2

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6
Q

Two step bio-oxidation process and bacteria involved

A

Nitritation: NH4->NO2- (Nitrosomonas)
Nitratation: NO2- -> NO3-
(Nitrobacter)

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7
Q

what are the effect of nitration in terms of pH, Oxygen consumption, and alakalinity?

A
  1. pH decrease
  2. requires O2
    ammonia ox: 3.43 gO2/gN-NH4+
    Nitrite ox: 1.14 gO2/gN-NH4+
  3. Consume alkalinity: 7.14 g CaCO3/gN
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8
Q

Nitrification Microbiology Facts

A
  1. Growth rate of nitrifying bact is slower than those for organic matter, so SRT should be long enough so that F/M is low to enable development of nitrifiers.
  2. Nitrite doesn’t usually accumulate in system because the rate to oxidize ammonia to produce NO2 is slower than consuming NO2, So so Ammonia oxidation to NO2 is Rate Limiting reaction.
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9
Q

Yield

A

Y=Produced biomass/consumed substrate (N) or oxidized N
(g COD/gN) or (g VSS/gN)

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10
Q

What are the environmental factors affecting nitrification?

A

Temperature
pH: sensitive to pH usually occur at almost neutral pH (6-9)
Alkalinity: consumes alkalinity 2 eq so 2x50/14=7.14 gCaCO3/gNoxidized
DO: <0.5 mg/l greatly inhibit, ideally 1.5-2 mg/l

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11
Q

Alkalinity details for nitrification:
how much consumed, how to maintain pH-7

A

alkalinity consumed: 7.14 g CaCO3/gNoxidized

To maintain pH=7 Alk>70 mgCaCO3/L

Alk goals = Alk in - alk consumed + alk to be added

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12
Q

What is primary settler effect on Nitrogen

A

Primary setller increases TKN/COD ratio as it remove 30-40% of COD influent and only remove 10-20% TKN

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13
Q

What is minimum sludge age

A

results of growth and decay, below minimum SRT, biomass is washed out. Minimum SRT should be computed at worst condition. Usually 5 day.

if nitrification and COD removal in one tank, SRTm depends on nitrifiers growth rate

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14
Q

Mass Balance Nitrogen oxidation

Nitrification

A

Nitrogen oxidized (QSNO3)=Nitrogen influent (QTKNin) - Nitrogen Effluent (QNe) - Nitrogen in cell mass (0.12 Pxbio)

Cell formula C5H7NO2 biomass contains 0.12 gN/gVSS)

px bio = PxH + PxE + PxA

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15
Q

Increasing TSS what will happen

A

smaller reactor volume (due to reaction rate)
but cannot be increased above reasonable values because aeration limitation, separation capacity in secondary settling tank

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16
Q

What is denitrification

A

Biological REDUCTION of nitrate to nitric oxide and nitrogen gas (remove excess nitrogen)

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17
Q

Which microrganism involved in denitrification?

A

Heterotrophs, facultative aerobic organisms where under anoxic nitrate is final e- acceptor

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18
Q

What is strong inhibitor for denitrification?

A

O2

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19
Q

What is the difference between anaerobic and aerobic respiration in terms of COD or organic compounds

A

growth is lower in anoxic condition rate is slightlt lower due to lower energy

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20
Q

What are the conditions required for denitrification?

A

Availability of organic carbon (COD)
Anoxic Condition (Nitrate Presence, DO absence)

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21
Q

What does denitrification produced?

A

Alkalinity & N2

22
Q

How much Alkalinity produced from denitrification?

A

1 mol alk produced per 1 mol N denitrified

3.57 g CaCO3/gN-NO3

23
Q

What are advantage of denitrification in terms of Alkalinity

A
  1. Reduced 50% alkalinity requirements
  2. Enhanced operation of secondary sedimentation. Control Filamentous bacteria growth, improve settling characteristics.
  3. Control Nutrients
24
Q

O2 Equivalent of nitrate

A

2.86 gO2/gN

which mean N has much higher capacity to remove COD. 1 g of Nitrate can save 2.86 g o2 for aerobic respiration process

25
Q

Difference between heterotrophs in aerobic and in anaerobic

A

Reduced growth yield factor and growth rate.
Nitrate is e-acceptor instead of O2 and might influence kinetics so there’s a correction factor (0.7-0.9) for anoxic growth

26
Q

What are the two flow diagrams of activated sludge denitrification?

A
  1. Pre-Anoxic (substrate driven) Most common
  2. Post Anoxic (endogenous driven)
27
Q

Advantages of Pre Anoxic

A
  1. Saves energy because COD is removed before aerobic zone
  2. Alkalinity produced before nitrification
  3. Already includes selector (avoid filamentous growth and sludge bulking)
  4. No need for additional COD addition
  5. For high risk of eutrohication risk, primary settler not used because increase TKN/COD Ratio
28
Q

Maximum N Removal is related to

A
  1. COD availability in WW
  2. Enough Nitrification rate
  3. Maximum internal recycle Rate (up to 400%Qin)

Related to ratio of flow across tank
C/Cin = Qin/(Qin+Qr+Qn)

29
Q

COD removed by aerobic and anaerobic?

A

aerobic: 3.03 g cod/gO2
anaerobic: 8.6 g COD/gN

30
Q

O2 consumption in nitrification and denitrification

A

nitrification consume 4.57 gO2/gN

Denitrification saves/recover 2.86 gO2/gN

So in denitrification 2.86/4.57 = 0.63 of O2 is saved

31
Q

What is SDNR?

A

Specific Denitrification Rate is rate of how much nitrate is consumed or reduced per day relative to amount of VSS in denitrification tank.

Pre-Anox has higher SDNR than post anox

32
Q

SDNR related to

A

organic load to anoxic tank (F/M Ratio)
%of rbcod relative to bcod in influent
temperature
Internal recycle

33
Q

HRT for denitrification typically

A

2-10h

34
Q

How to remove phosphorus?

A

Biological Process: EBPR
Chemical Process: Alum or iron salts
Hybrid: Phostrip

35
Q

What is the advantage of EBPR

A

Reduced chemical costs, less sludge production, recovery more easy

36
Q

How does Biological Phosphorus Removal works?

A

By selection of biomass capable to accumulate P inside cell above its P requirement for growth

by PAOs (Phosphorus Accumulating Organisms)

and removed with excess sludge

37
Q

Explain PAO in Anaerobic conditions

A
  1. PAO used energy stored in polyphosphates and assimilate acetate or VFA
  2. PAO then produce PHB
  3. Soluble orthophospahe (PO43-)
  4. PHB content in PAO increase, Polyphosphate decrease

No Growth

38
Q

Aerobic or Anoxic Condition of PAO (O2 or NO3-)

A
  1. Store PHB is metabolized, providing energy from oxidation and carbon from new cell growth
  2. Energy is used to form polyphosphate in cell storage so soluble ortophosphate is removed from water and stored in cell
  3. Cell growth occur due to PHB utilization
  4. New biomass with high polyphosphate storage accounts for phosphorus removal
39
Q

Sludge P Content

A

Without PAOs: Approx. 0.02 mg P/mg VSS
or 0.015 mg P/mg TSS

With PAOs: 0.06-0.15 mg P/mg VSS
or 0.05 / 0.10 mg P/mg TSS

40
Q

PAO can accumulate how much P, how about heteretrophs?

A

PAOs 0.4 g P/ gVSS
Heterotrophs: 0.02 gP/gVSS

41
Q

What are PAOs two requisites?

A
  1. Alternating anaerobic/aerobic operating conditions (by recirculation)
  2. Presence of VFAs (can gain from hydrolysis)
42
Q

Why O2 and Nitrate recycle in anaerobic tank decrease EBPR effectiveness?

A

Heterotrophic will consume VFAs instead of PAO when O2 and NO3 not available thus competing with PAOs

43
Q

Explain about PHB production and what it used

A

Related to fermentable materials (VFA, acetic acid, etc) that is represented as fraction of Ss (rbcod).

In Anaerobic, fraction of Ss is transformed into VFAs

where PAOs assimilate and produce PHB

44
Q

rbCOD/bCOD ratio meaning in P removal

A

higher rbCOD/bCOD meaning higher Ss meaning higher formation of VFAs thus greater %P content of Activated sludge, the greater the EBPR

45
Q

What is phoredox

A
  1. Anaerobic tank for P release and the aerobic tank for P assimilation
  2. Short SRT (2-4d)
  3. Pros: simple, low BOD/P ratio, good P removal and settling sludge
  4. Cons: P removal is affected when nitrification occur which might at high T (20c)
46
Q

in phoredox how is the products like in Anaerobic tank and aerobic tank?

A

in Anaerobic tank: VFA decrease due to assimilation by PHB, so PHB increase, and Poly-P decrease as it release PO43- to produce energy for PHB to assimilate VFA

in Aerobic tank: PHB use O2 for oxidation and release CO2+H2O and produce energy which poly-P used to uptake PO43-. So, PHB decrease, Poly-P increase, PO43- in water decrease

47
Q

3-stage modifdied bardenpho is what

A

A2O
Amaerobic for P release
Anoxic for Denetrification
Aerobic for Nitrification and P Assimilation

Internal recycle from aerobic to anoxic for nitrate

48
Q

effect of higher anaerobic volume in P removal

A

Higher anaerobic volume –> higher biomass in sludge anaerobic –> higher VFA –> higher PAO substrate –> higher EBPR

48
Q

Environmental factors in P removal (SRT and conc of o2 or NO3-)

A

SRT
SRT < 3d: High P removal due to higher heterotrophic mass & bCOD fermented to VFA
SRT >3d: P removal lower due to extended endogenous phase, lower PAO mass is wasted per day

higher O2 and NO3- presence in recycle, lower P removal due to competition

49
Q

How to manage sludge EBPR

A

if sludge undergo another anaerobic condition P will be released again so it the digested sludge/thickened sludge will contain high P concentration.

To prevent: thickening with DAF, gravity belt thickener, stabilization (composting)

50
Q

for chemical phosphorus removal where to insert the lime or alumunium or ferric iron

A

Pre-precipitation: before biological treatment line, P removed with primary sludge (lime not used) improve separation in primary settler

Co-precipitation: Just before secondary sedimentation (AS tank) or after it to improve sludge separation. Aeration is used to oxidize Fe(II) to Fe(III)

Post-precipitation: After secondary settler have special tank, will be high efficiency because special for P but expensive. can be combined with other tech like filtration

51
Q

What are pros and cons of chemical P removal

A

pros:
1. increased settling characteristics of WW and AS
2. Simple reactors, simple operations
3. Less sensitive to inhibition than biological process
4. rapid interactions, small tank

Cons
1. Very high increase of sludge production
2. Production of chemical sludge (disposal issue)
3. increased water salinity
4. pH neutralization may be required after
5. Cost of chemicals

Wastewater (4 decks)

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