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![Page 1: Oxygen supply - Major investment (1 M$/y per treatment plant) Fine bubble diffusers Nitrogen Removal How? : Aerobic Nitrification NH3 + O2 NO3 Anaerobic.](https://reader030.fdocuments.in/reader030/viewer/2022032802/56649e0d5503460f94af6c85/html5/thumbnails/1.jpg)
Oxygen supply -Major investment (1 M$/y per treatment plant)Fine bubble diffusers
Nitrogen Removal How? : Aerobic Nitrification NH3 + O2 NO3Anaerobic Denitrification NO3 + organics N2
Problems Nitrifiers grow slow and are sensitive and need oxygenDenitrifiers need organics but no oxygen
Nitrification can be either sequential or simultaneous:
Waste Water Treatment Technology
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List Pollutants to be removed
• Suspended material (inorganic, bacteria, organic)• Dissolved organics (COD,BOD)
– COD = chemical oxygen demand (mg/L of O2)– dichromate as the oxidant– BOD5 = biochemical oxygen demand(mg/Lof O2 in 5 days– microbial O2 consumption over 5 days
• N• P• pathogens• odor, colour• ultimate aim: recycle of water for re-use•
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Why organic pollutant removal?
Organic pollutants represent an oxygen demand (COD or
BOD)
Bacteria in the environment will degrade the pollutants and
use oxygen.
If oxgygen uptake > oxygen transfer
oxygen depletion .
Collapse of ecosystem
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Why nutrient removal?Simplified Sequence of events of
eutrophication
Pristine aquatic ecosystems are typically limited by
nutrients.
Supply of nutrients (N or P)
photosynthetic biomass (primary and secondary).
More oxygen production and consumption
Sedimentation and decay of dead biomass
Depletion of oxygen in sediment/water column
Collapse of ecosystem
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Why nutrient removal?comprehensive Sequence of events of eutrophication (needs understanding of
anaerobic respirations)Pristine aquatic ecosystems are typically limited by nutrients.Supply of nutrients (N or P) photosynthetic biomass (primary and secondary). More oxygen production and consumption Sedimentation and decay of dead biomass Depletion of oxygen in sediment/water column Oversupply of e- donors Use of other electron acceptors (anaerobic respirations) Ferric iron reduction to ferrous iron (Fe3+ --> Fe2+) Sulfate reduction to sulfide (H2S) (poison, oxygen scavengerSolubilisation of iron and phosphate (ferric phosphate poorly soluble)Further supply of nutrients cycle back to beginningO2 depletion, sulfide and ammonia buildupUpwards shift of chemocline --> Killing of aerobic organismsFurther sedimentationCollapse of ecosystem
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Simplified Principle of of Activated Sludge
•After primary treatment (gravity separation of insoluble solids)
•Secondary treatment: Oxidation of organic pollutants, (COD and BOD removal, partial N removal
•Needed: NH4+ conversion to N2 ? How?
Activated Sludge (O2 + X)
Clarifyer
100:1
Biomass Recycle (Return Activated Sludge)
COD,NH4+, phosphate
to ocean
Excess sludge
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What is Nitrification?Microbial oxidation of reduced nitrogen compounds (generally NH4
+).
Autotrophic ammonium oxidising bacteria (AOB) (Nitrosomonas, Nitrosospira etc.):
NH4+ + 1.5 O2 NO2
- + H2O + 2 H+
Autotrophic nitrite oxidisers (Nitrobacter, Nitrospira etc.)
NO2- + 0.5 O2 NO3
-
Aerobic conversion of NH4+ to NO3 + removes some of the oxygen demand (COD)+ removes NH4+ toxicity ot fish and odor from wastewater- does not accomplish nutrient removal
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What is denitrification?•Microbial reduction of oxidised nitrogen compounds (generally NO3
-).
•Anoxic process using nitrate as an alternative electron acceptor to oxygen (anaerobic respiration)
•Catalysed by non- specialised factultative aerobic heterotrophic bacteria.
•A series of reduction steps leading to potential accumulation of intermediates
•Electron donor: organic substances (BOD, COD)
NO3- + 2 H+ + 2 e- NO2- + H2O (nitrate reductase)
NO2- + 2 H+ + e- NO + H2O (nitrite reductase)
2 NO + 2 H+ + 2 e- N2O + H2O (nitric oxide reductase)
N2O + 2 H+ + 2 e- N2 + H2O (nitrous oxide reductase)
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Review of Terms
•Metabolic processes can be differentiated between:
•Processes that make use of exergonic redox reactions, conserve the energy of the reaction as ATP
Catabolism or Dissimilation or Respiration
typically oxidative process (degradation or organics to CO2)
•Processes that drive endergonic reactions by using the ATP generated from Dissimilation
Anabolism or Assimilation or Biomass Synthesis
typically reductive processes (synthesis of complex organics from small building blocks
If the building block is CO2 autotrophic
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Energy source Photo Chemo
Electrondonor
Organo Litho
C-source Hetero Auto
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The Nitrogen cycleOxState
-3 CNH2 NH4+ -2-10 N2+1+2 NO+3 NO2-+4+5 NO3-
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The Nitrogen cycleOxState
-3 CNH2 NH4+ -2-10 N2+1+2 NO+3 NO2-+4+5 NO3-
Dotted lines are assimiliative paths
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The Nitrogen cycleOxState
-3 CNH2 NH4+ -2-10 N2+1+2 NO+3 NO2-+4+5 NO3-
Nitrogen fixation:Atmospheric N2 reduction to ammonium and amino acids.
Syntrophic Rhizobia types, free living bacteria and cyanobacteria.
Reactions serves assimilation.
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The Nitrogen cycleOxState
-3 CNH2 NH4+ -2-10 N2+1+2 NO+3 NO2-+4+5 NO3-
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The Nitrogen cycleOxState
-3 CNH2 NH4+ -2-10 N2+1+2 NO+3 NO2-+4+5 NO3-
Nitrification step 1 Nitritification:
Ammonium as the electron donor for aerobic respiration.
Chemo-litho-autrophic.
Nitrosomonas type species.
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The Nitrogen cycleOxState
-3 CNH2 NH4+ -2-10 N2+1+2 NO+3 NO2-+4+5 NO3-
Nitrification step 2 Nitratification:
Nitrite as electron donor for aerobic oxidation to nitrate
Chemo-litho-autrophic
Nitrobacter type species.
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The Nitrogen cycleOxState
-3 CNH2 NH4+ -2-10 N2+1+2 NO+3 NO2-+4+5 NO3-
Denitrificationusing either nitrate (NO3-) or nitrite (NO2-) as the electron eacceptor for anaerobic respiration.
Most COD can serve as electron donor.
Non-specific bacteria replacing O2 with Nitrate as e- acceptor when oxygen is depleted.
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How to accomplish overall N-removal?
Recycled sludge
AerobicTreatment
Anaerobic Treatment
Clarifier
Effluent
Nitrification typically occurs during the aerobic treatment of wastewater:
COD + O2 CO2Ammonium + O2 Nitrate
In addition to the aerobic activated sludge treatment an anaerobic treatment step is included aiming at N-removal (tertiary treatment)
Insufficient N removal is typically achieved. why?
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How to accomplish overall N-removal?
Recycled biomass(sludge)
AerobicTreatment
Anaerobic Treatment
Clarifier
Effluent
•N removal by the anaerobic step requires an electron donor to reduce NO3- to N2.
•This electron donor is organic material.
•Solution A: Add organic material to the anaerobic treatment step.
•Example: Methanol
•Problems: costs, contamination
•Alternative solutions?
NH4+COD
NO3-CO2
N2CO2
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How to accomplish overall N-removal?
Recycled biomass(sludge)
AerobicTreatment
Anaerobic Treatment
Clarifier
Effluent
•The obvious solution to successful N removal:
•Use the COD as electron donor for nitrification and denitrification
•How to allow anaerobic denitrification to occur in the presence of oxygen?
NH4+COD
NO3-CO2
N2CO2
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How to accomplish overall N-removal?
Recycled biomass(sludge)
AerobicTreatment
Anaerobic Treatment
Clarifier
Effluent
•Observations in the laboratory have shown that aerobic nitrification and anerobic denitrification can sometimes occur at the same time.
•This simultaneous nitrification and denitrification (SND) has been the focus of many R&D projects for improved N-removal.
NH4+COD
NO3-CO2
N2CO2
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Idea for SND • Q: How to allow anaerobic denitrification at the same time
as aerobic nitrification?
• A: Intelligent oxygen control, not straightforward:
• Aerobic: COD + O2 CO2
• Ammonium + O2 Nitrate
• Anaerobic: COD + Nitrate N2 + CO2
• COD should be e-donor for nitrate reduction, not oxygen reduction.
• Oxygen supply will burn COD faster than ammonium
• No COD No denitrification NO3- pollution
• Goal for improved N removal: Slow down aerobic COD oxidation, to leave electron donor for denitrif.
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Ideas for SND
• 1: Alternating aeration
• 2: Limiting aeration
• 3: SBR technology: Slowing down COD oxidation by conversion to PHB
• Intelligent aeration control
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Return Activated SludgeAir Line
Influent
Effluent
Waste Sludge
Clarifier
Plug flow allows alternating aerobic / anaerobic conditions without time schedule
Biomass Retention in WWTP
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Alternating Aeration in Batch Systems • Aerobic: COD + NH4+ + O2 NO3- + residual COD
• Anoxic: Residual COD + NO3- N2
• There is always substantial COD + O2 CO2 wastage. Effective N removal is limited
Which phase is anaerorobic, which lines are COD, NO3- and NH4+ ?
![Page 26: Oxygen supply - Major investment (1 M$/y per treatment plant) Fine bubble diffusers Nitrogen Removal How? : Aerobic Nitrification NH3 + O2 NO3 Anaerobic.](https://reader030.fdocuments.in/reader030/viewer/2022032802/56649e0d5503460f94af6c85/html5/thumbnails/26.jpg)
Alternating Aeration in Batch Systems • Aerobic: COD + NH4+ + O2 NO3- + residual COD
• Anoxic: Residual COD + NO3- N2
• There is always substantial COD + O2 CO2 wastage. Effective N removal is limited
COD
NH3
NO3-
aerobicanoxic
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Alternating Aeration in Batch Systems • Aerobic: COD + NH4+ + O2 NO3- + residual COD
• Anoxic: Residual COD + NO3- N2
• There is always substantial COD + O2 CO2 wastage. Effective N removal is limited
COD
NH3
NO3-
aerobicCODand NH3oxidation
anoxicCOD oxidationwith NO3-
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•Compromise with DO to go so low that ammonium oxidation is still working and denitrification is enabled.
•Basically: Run nitrification and denitrification at same speed sophisticated control needed.
What is SND (Simultaneous Nitrification and Denitrification) ?
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Oxygen dependency of Nitrification
Nitrification is not only limitedby the substrate concentration (nitrate) but also by the oxygen concentrationdouble limitation\
Nitrif.
DO (mg/L)
Rat
e
3
33
3
33max NH
OO
O
NHNH
NHNHNH X
kS
S
kS
SSURSUR
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Oxygen dependency of Denitrification
DO (mg/L)
Rat
e
Denitri.
Oxygen inhibition constant (ki)can be measured and used for modeling
Similar to half saturation constant
half inhibition constant
3
33
3
33max NO
OO
O
NONO
NONONH X
kiS
ki
kS
SSURSUR
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Oxygen dependency of SND
Underoxidation: NH3 build- up
Over-oxidation: NO3- build-up
To match Nitrif. and Denitri.:
Flux of reducing power (NH3, COD) should match flux of oxidation power. But how?
What is the magical DO level that enables max SND?
How does the SND curve change with different loading rates, biomass levels and N:C levels?
Over-oxidation
Under-oxidation
Nitrif.
DO (mg/L)
Rat
e
Denitri.
SND
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•Minimise aeration costs by running at low DO
•Avoid external COD addition to
(a) lower costs
(b) encourage (AOB) rather than heterotrophs
adapt high N-removal performance sludge
•Avoid pH fluctuations (costs, performance loss)
•Save further O2 and COD by SND via nitrite
•Simplified operation
Why Simulaltaneous nitrification and denitrification(SND) ?
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•Minimise aeration costs by running at low DO
•Avoid external COD addition to
(a) lower costs
(b) encourage (AOB) rather than heterotrophs
adapt high N-removal performance sludge
•Avoid costs for pH corrections (nitrification uses acid while denitrification produces acid (can you show this with stoichiometric
equations?)
•Save further O2 and COD by SND via nitrite
•Simplified operation
Why Simulaltaneous nitrification and denitrification(SND) ?
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SND pathway
If nitrification and denitrification can occur simultaneously there is a possibility of by-passing nitrate formation and nitrate reduction
SND via nitrite.
Has the advantage of oxygen savings and COD savings.
NO2-NO2
-
NO3-
N2
NH3
COD
O2
NH2OH
N2O
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Nitrification
DO Effect on Nitrification and Denitrification
DO (mg/L)
Rat
e
NO2- reduction
NO3-
SND via NO2- can operate more easily than SND via NO3- as oxygen has a stronger inhibition effect on nitrate reduction than nitrite reduction
If SND proceeds via nitrite,then: how much savings are generated?
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Nitrif.
DO (mg/L)
Rat
e
Denitri.
Over-oxidation
Under-oxidation
Nitrif.
DO (mg/L)
Denitri.
NH3
[N]
in o
utflo
w
Conclusion: For best N-removal in the outflow of the treatment process, a low DO should be chosen
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Laboratory Sequencing Batch Reactor
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Tenix / Murdoch UniversitySND SBRpilot plant(Woodman Pt.03-12-24)
Labview control
Bioselector,
Online OURmonitoring,
N2O emission,
O2 minimisation
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Return activated sludge ready to be contacted with incoming feed to allow “feast time” and enhance floc formation
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Idea: Making use of bacteria’s behaviour of taking up organic substances for storage as PHB.
Denitrification needs organic reducing power: • Either sufficient COD or PHB storage• Problem with COD: degrades quicker than NH3• no COD left for denitrification
Advantages of bacterial Storage of COD as PHB as PHB:
1. Oxidises slower lasts longer important for SBR
2. Reducing power inside the floc rather than outside
3. Reducing power can be settled and build up.
Why Storage Driven Denitrification?
PHB
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Denitrification needs organic reducing power: • Either sufficient COD or PHB storage• Problem with COD: degrades quicker than NH3• no COD left for denitrification
Advantages of bacterial Storage of COD as PHB as PHB:
1. Oxidises slower lasts longer important for SBR
2. Reducing power inside the floc rather than outside
3. Reducing power can be settled and build up.
Why Storage Driven Denitrification?
PHB
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BOD storage as PHB needs ATP
2 Acetate
TCA cycle
2 Acetyl-CoA (16 e-)
2 CoA
8 NADH (16 e-)
Bio-mass
PHB (18 e-)
ETC
2 CoA 4 ATP
24 ATP
2 CO2O2
H2O
1 NADH (2 e-)
Mechanisms for ATP generation:•O2 respiration•Nitrate respiration•Glycogen fermentation•Poly-P hydrolysis
Our results:Storage
under some O2 supplyGlycogen, P
complicated NO3- too low.Aerobic
bioselector?
PHB
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• PHB physically separated from O2
• Selective availability of O2 to AOB.
• PHB may be more readily oxidised by nitrate or nitrite being formed by the aerobic reaction
COD
NH3
O2
NO2- PHB
anoxic
N2
aerobic
Expected Benefit of Storing Reducing Power Inside the Floc
CO2PHB
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A B
C D
Increasing PHB (dark) buildup in bacterial biomass (red) during early
phase of SBRPHB
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Three phases could be observed•1st : COD PHB•2nd : PHB driven SND (60%)•OUR indicates NH3 depletion•3rd : wastage of reducing power
0
1
2
3
4
Nitr
og-c
omp.
(m
M)
0
2
4
6
8
10
Car
b. c
omp.
(C
mM
)
AnoxicAerobic
NO3-
0 50 100 250 300 350Time (min)
00 50 150 200
Time (min)
10
20
30
40
50
SO
UR
(m
gO2/
g/h)
NH3
OUR
PHB
•69 % N-removal, no reducing power left
•Needed: Automatic stopping of aeration when ammonia is oxidised to prevent PHB oxidation with oxygen
•Could be detected from OUR monitoring
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Aim: Avoid wastage of reducing powerby: auto-aeration cut-off
Outcomes:•More PHB preserved•N-rem 6986%•Less air•Shorter treatment
Effect of auto-aeration cut-off onPHB levels and N-removal
0
1
2
3
4
Nitr
og-c
omp.
(m
M)
0
2
4
6
8
10
Car
b. c
omp.
(C
mM
)
AnoxicAerobic
0
1
2
3
4
0 50 100 150 200 250 300 350
Time (mins)
Nitr
og. c
om
p. (
mM
)
0
2
4
6
8
10
Car
b. c
omp.
(mM
)
Aerobic Anoxic Settle
PHB
NO3-
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0
1
2
3
4
0 50 100 150 200 250 300 350
Time (mins)
Nitr
og. c
om
p. (
mM
)
0
2
4
6
8
10
Car
b. c
omp.
(mM
)
Aerobic Anoxic Settle
Special features of PHB hydrolysis kinetics
PHB degradation kinetics is ~ first order:dependent on PHB, but independent of biomass
However, ammonium oxidation is proportional to biomass:higher sludge concentrations should favour autotrophic over heterotrophic activity helps SND.
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0
1
2
50 100 150 200
Time (mins)
-d(S
OU
R)/
dt (
mg
/g/h
2 )
Ammonium
depletion
Use of negative derivative of OUR to detect ammonium depletion
Effect of aeration cut-offon next cycle?
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Longer term effects of PHB buildup (not examinable)
0
10
20
30
40
50
60
70
0 50 150Time (min)
SO
UR
(m
g/L
)
NH3 –OUR
Cycle 1
5
8
Cycle 12
PHB analysis and SPOUR monitoring show:
PHB can be build up over several cycles
improved SND
explains biomass “adaptation”
no need for emptying cells
one over-aerated cycle can
loose all “savings”
from prev. cycl.
review end of aeration DO high?
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0
1
2
3
4
5
0 1 2 3 4 5 6 7 8 9 10 1112 13cycle
PH
B (
mM
)PHB build-up over 12 cycles
PHB analysis and SPOUR monitoring show:
PHB can be build up over several cycles
enabling more reducing power and better denitrification
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PHB driven SND performance after 12 cycles of controlled PHB build-up
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
0 50 100 150 200 Time (min)
Co
nc
(m
M)
NO3-NO2-
NH4+
With close to complete N-removal:no point for front denitrification phase DO required for COD storage
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Below this point for 2007 only
• Nitrogen removal by separating nitrifiers from denitrifiers
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BIO301 - Leonie Hughes
Biological nutrient removal
• As the main influent N species of wastewater is ammonia, nitrification must precede denitrification
• BUT if oxygen and organic carbon are present, heterotrophic organisms will consume the carbon
• This is a waste of both oxygen ($$) and carbon ($$) causing the cost of operation to increase
• If the influent COD can instead be stored internally by the heterotrophs for later use in denitrification, this would save on both oxygen and carbon
![Page 55: Oxygen supply - Major investment (1 M$/y per treatment plant) Fine bubble diffusers Nitrogen Removal How? : Aerobic Nitrification NH3 + O2 NO3 Anaerobic.](https://reader030.fdocuments.in/reader030/viewer/2022032802/56649e0d5503460f94af6c85/html5/thumbnails/55.jpg)
BIO301 - Leonie Hughes
Multiple sludge approach to WWT
Stage 1 - storage of influent COD
BIOFILM Heterotrophic denitrifiers
Influent wastewater
Acetate and Ammonia
Effluent wastewater
Ammonia
Acetate PHB
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BIO301 - Leonie Hughes
Multiple sludge approach to WWT
Stage 2 - oxidation of ammonia
BIOFILM Heterotrophic
denitrifiers
Influent wastewater
Ammonia
Ammonia Nitrate
BIOFILM or SBR
Autotrophic nitrifiers
Effluent wastewater
Nitrate
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BIO301 - Leonie Hughes
Multiple sludge approach to WWT
Stage 3 - reduction of nitrate
BIOFILM Heterotrophic
denitrifiers
Effluent wastewater
Nitrogen gas PHB + Nitrate
BIOFILM or SBR
Autotrophic nitrifiers
Influent wastewater
Nitrate
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BIO301 - Leonie Hughes
Commercialisation of PHB
• Enhanced bacterial food source for use in aquaculture
• Biopol - biological alternative to petrochemical plastics
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BIO301 - Leonie Hughes
The need for biodegradable plastics
• 6 billion plastic bags are used every year in Australia
• All plastic products make up 4% of all waste going to landfill
• Reduction in plastic going to landfill will make landfill lifespans longer
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BIO301 - Leonie Hughes
History of Biopol• ICI/Zenica published the first patents in the 1980s for
a complete production pathway of PHB with minimal cost extraction
• Biological fermentation method
• Shampoo bottle for Wella was highest profile product
• In 1996 Monsanto purchased the patents and shifted the focus to PHB production in genetically modified crops
• Continued public perception affecting commercialisation of GM crops contributed to the selling of the PHB patents to Metabolix
• Metabolix now have exclusive rights to manufacture, sell and use PHA related products regardless of origin
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BIO301 - Leonie Hughes
Wastewater - free source of PHB?
• One of the limitations of PHB production is the high cost compared to petrochemical based thermoplastics
• If we know that
• Activated sludge can make it and
• Wastewater can be used as the substrate
• Surely this may change the economics?
• Much research is focused on pursuing this
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BIO301 - Leonie Hughes
Wastewater - free source of PHB?
Question:
• Consider that wastewater is a waste product that people are currently paid to remove
• If it becomes a resource, what would stop governments charging those who want it
• What if this counteracts the previous economic statement?
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Phosphorous Removal• Called “phosphorous accumulating organisms” (PAO’s)
• Require fluctuating conditions of aerobic and anaerobic conditions à SBR can provide perfect environment.
• The PAO’s have a pool of poly-inorganic phosphate (poly-Pi) inside the cell.
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Phosphorous Removal
Anaerobic conditions• hydrolyse a phosphate bond to produce energy in order
to import substrate (typically acetate) into the cell.
• Hydrolysed Pi released into the medium and PHA is produced
• Called the “P release phase”.
Aerobic conditions
• the bacteria take up phosphorous to regenerate poly-Pi pool
• PHA as the energy source• Called the “P uptake phase”
Overall net reduction of phosphorus in the wastewater.
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Nitrous Oxide (N2O) Production During SND
The Environmental Impact of N2O
• Nitrous oxide is a greenhouse gas
• global warming potential 250 times greater than CO2
• Estimated N2O responsible for 6% of global warming
• involved in the destruction of the ozone layer
• leading to an increase in the incidence of skin cancer and related health problems
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Nitrous Oxide (N2O) Production During SND
• N2O is an intermediate of denitrification
• Produced from the reduction of NO2- (nitrite reductase)
• N2O is reduced to N2 (nitrous oxide reductase)
• Nitrous oxide reductase is highly oxygen sensitive
• Oxygen, even at very low levels (0.02 mg O2/L), will stop the enzyme working and cause N2O to be emitted
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Nitrous Oxide (N2O) Production During SND
• N2O also produced by Autotrophic ammonium oxidising (nitrifying) bacteria, if the oxygen concentration is very low.
• In an SBR operated for SND both nitrifiers and denitrifiers in the flocs will be exposed to low dissolved oxygen concentrations
Result: • SBR's operated for SND have a greater tendency to
emit N2O than traditionally wastewater treatment plants
• could be of environmental concern.
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In a nutshell• Nutrient rich wastewater released into waterways can
lead to eutrophication.• During nutrient removal of wastewater, aerobic and
anaerobic processes need not be separated as traditionally thought.
• Under oxygen limitation, simultaneous nitrification (aerobic) and denitrification (anaerobic) can be achieved, due to anoxic zones inside the floc.
• Effective denitrification requires a carbon source.• Control of aeration to DO < 1 can help conserve carbon
for heterotrophic denitrification, improving denitrification.• SND via nitrite provides savings in reduced oxygen and
BOD consumption.
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Surface aeration of activated sludge
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Bulking sludge due to Filamentous Bacteria (S. natans)
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Foaming sludge due to Nocardia
Anaerobic Ammonium Oxidation (Anammox)The oxidation of ammonium to dinitrogen gas (N2) with nitrite as the electron acceptor by autotrophic bacteria.
Discovered at the Kluyver Laboratory, Delft, The Netherlands in 1995.For the first time, ammonium was discovered to be oxidised in the absence of oxygen by a rare species of bacteria Planctomycetes, Candidatus Brocadia anammoxidans.
NH4+ + NO 2- N2 + 2 H2O (Go’ = -357 kJ mol-1)Ammonium can be oxidised directly to dinitrogen gas, without the need for the multi-step process of aerobic nitrification and heterotrophic denitrification.
Anaerobic Ammonium Oxidation (Anammox)The oxidation of ammonium to dinitrogen gas (N2) with nitrite as the electron acceptor by autotrophic bacteria.
Discovered at the Kluyver Laboratory, Delft, The Netherlands in 1995.For the first time, ammonium was discovered to be oxidised in the absence of oxygen by a rare species of bacteria Planctomycetes, Candidatus Brocadia anammoxidans.
NH4+ + NO 2- N2 + 2 H2O (Go’ = -357 kJ mol-1)Ammonium can be oxidised directly to dinitrogen gas, without the need for the multi-step process of aerobic nitrification and heterotrophic denitrification.
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