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8/12/2019 Aerated Anoxic Principles
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Page 1 Water Technologies
Aerated Anoxic Principles
Arkansas Water Environment Associations2012 Waters Worth It Specialty Conference
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Page 2 Water Technologies
Getting Started
Define: Aerated Anoxic
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Page 3 Water Technologies
The terms can be very confusing and aconsiderable number of definitions arrived at
Aerated-anoxic Anoxic-aeration Anaerobic-aeration Anammox bacteria
what in the world am I talkingabout!
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Page 4 Water Technologies
Aerated-Anoxic is not limited to Siemensaeration systems but can be included inany activated sludge aeration processes,such as:
Multichannel Oxidation Ditch
Aeration tanks in series
Multi-pass plug flow systems
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Page 5 Water Technologies
Aerobic
Reactor
Secondary
Clarifier
Internal Recycle
RAS
Influent
WAS
Effluent
Conventional plantdesigns use dedicatedanoxic and aerobic biological reactors
Anoxic
Reactor
No air added to the anoxic reactor
Nitrification achieved in the aerobic reactor
Nitrates brought back through internal recycle at 4Q
4Q
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Page 6 Water Technologies
Aerated anoxicprocesses operate at constantoxygen deficit in the first part of the process
Aerobic Reactor Secondary
Clarifier
Internal Recycle
RAS
Influent
WAS
EffluentAerated
Anoxic
Reactor
Aerated
Anoxic
Reactor
O2suppl ied to aerated anoxic reactors is less than O2demand
No internal recycle required for total nitrogen removal
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A conventional oxidation ditch with aerobic and anoxic
zones is not the same as aerated anoxic reactors in series
Conventional Oxidation Ditch
O2supply must exceed demand for complete treatment
It is diffi cult to control aerobic and anoxic zones in a single reactor
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Complete Mix
Plug Flow
Aeration Tanks
Complete Mix vs. Plug Flow
Influent
Influent
Effluent
Effluent
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Aeration Tanks
Typical Oxidation Ditch
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Aeration Tanks
Converting Plug flow to Complete Mix
Option 1: Add some pipes
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Orris Albertson
Control of Sludge Bulking
Discussed the history of activatedsludge innovations used over 70years ago
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Early Innovators
Wellington Donaldson 70 years ago
decided to compartmentalize plug flow
tanks
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Orris Albertson
Control of Sludge Bulking
Phoenix 91st Avenue WWTP:Aerated-anoxic system
Established that anoxic tank could be mixed with
course bubble air instead of conventional mixers
Anoxic tank equaled 25% of total volume
Air did not hurt denitrification.
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Aerated Anoxic
Nitrification
Nitrification Requirements:
Adequate oxygen
Alkalinity
Adequate sludge age
Adequate ammonia
Advantages of Nitrification inAerated Anoxic Reactor:
Air did not hurt denitrification.
Immediate source of nitrates fordenitrification
Simultaneous nitrification-denitrification takes place
A short-cut nitrification/
denitrification pathway isavailable
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Ive got a problem with what
youre saying
thats not the way I learned it!
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Where does the nitrification occur?
Q: Does all the nitrificationoccur in the high DO zone?Y or N
A: Not in aerated anoxic systems the low DO reactors arethe BEST environment for thenitrifiers
0 0.5
2
Orbal DO profile in mg/l
The nitrification occurs wherethe majority of O2is delivered.
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Page 19 Water Technologies
Carey, OH WWTP Case Study
Overview
Challenge: Five rectangular tanksoperating in parallel with nitrificationproblems. Ammonia level was notmeeting requirements
Solution: Switch operation from parallelto series.
Results:
Before (Two in parallel): eff. Ammonia
1.7 mg/l After (Three in Series): eff. Ammonia
0.03 mg/l
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Page 20 Water Technologies
Reactors in series improve nitr ification
Carey, OH WWTP case study
Challenge: 5 tanks in parallelwith nitrification problems
Ammonia not meeting limits
Solution: Switch parallel to series
Parallel Series
Results:
Before (parallel):eff. NH3 1.7 mg/l
After (series):
eff. NH3 0.03 mg/l
Explanation:
Switch to series eliminatedshort circuiting
Reactors in series created
aerated anoxic conditions thatpromote simultaneous N-D
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Page 21 Water Technologies
Lower Oxygen Delivery Can Lead toSuperior Nitrification
Increasing Oxygen Delivery inAnoxic Tanks to ImproveDenitrification
Unusual Titles for Papers
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INCREASING oxygen delivery in anoxic tanks to
IMPROVE Denitrif ication
Sounds backwards, huh?
Wouldnt denitrification be better with no oxygen
delivery in anoxic tanks?
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Page 23 Water Technologies
Case Study: Hammonton, NJ WWTP
Increasing O2delivery in aerated anoxic tanks improves denitr ification
175
150
125
100
75
50
25
0
Outer Middle Inner
O2Demand,
lbs/hr
Channel
By increasing O2delivery in outer channel NO3-N dropped from 2.8 mg/l to 1.6 mg/l!
O2Supply Before
O2Supply After
O2Demand
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Page 24 Water Technologies
Hammonton, NJ WWTP
Nitrogen Balance
Q: With 0.3 mg/l nitrate, how muchdenitrification is due to recycle?
Influent N to be nitrified @ 200 lbs/day
N denitrified @ 197 lbs/day
N in recycle @ 13 lbs/day
N denitrified due to simultaneous N-D@ 184 lbs/day
A: More than 93% is denitrified due to
simultaneous N-D!
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Page 25 Water Technologies
Compared nitrifiers from:
1. Orbal plants with aerated anoxicreactors
2. Nitrification plants with conventional
upfront non-aerated anoxic tanks
University of Wisconsin F.I.S.H. Study
Found different types of nitrifiersfor two different types of plant:
NITROSOMONAS typical ammonia oxidizer for most nitrification
plants, including those with non-aerated anoxic reactors NITROSPIREA dominant ammonia oxidizer for plants with aerated-
anoxic reactors
NITROBACTER dominant nitrite oxidizer
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Page 26 Water Technologies
University of Wisconsin F.I.S.H. Study
NITROSPIREA:
The dominant ammoniaoxidizer in systems wherethere is simultaneousnitrifcation-denitrification
A nitrifier that is very good
at going dormant There are a lot of
dormant nitrifiers in ourBNR designs
Staging with aerated anoxic reactors infront is a good way to increase (evendouble) the nitrifier population.
Nitrifier population does not exclusively
depend upon the amount of ammoniaentering the plant.
Under typical conditions:
10,000 units
50% active 50% inactive
With increased dormant population:
25,000 units
20% active 80% inactive
Dormant Nitr ifiers
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Page 27 Water Technologies
Nine Springs WWTP: Madison, WI
Conventional FB plant with upfront anaerobic tank
Operates at a 10 day SRT side by side test with one side beingaerated anoxic
Loading MLSS eTN eP CFM/lb of BODConventional: 14 2800 15 0.4 1100Aerated Anoxic: 26 4100 11 0.2 673
Anaerobic Aerobic (fine bubble)
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Page 28 Water Technologies
Denitrification
Shortcut Pathway
5-step pathway:
Ammonia nitrite nitrate
nitrite nitrogen gas
3-step Shortcut pathway (in
aerated anoxic tanks):
Ammonia nitrite nitrogen gas
Requires 33% lesscarbon
Explains lack of nitrite oxidizers inOrris Albertsons Phoenix study
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Page 29 Water Technologies
Aerated Anaerobic
It sounds too odd
But works in designs with LARGEaerated anoxic tanks and limited
oxygen
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Page 30 Water Technologies
McMinnvil le, Oregon WWTP
Two 3-channel Orbal Basins
1stchannel operates asaerated anaerobic channel
2ndchannel operates as
aerated anoxic channel 1.52 m.gal. Aeration Volume per
basin
Four 50 hp Drives
0.07 mg/l eff. P required Designed for 8 day sludge age
0.5 mg/l eff. ammonia required
Only 18% of total basin volume isaerobic
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Page 31 Water Technologies
McMinnvil le, Oregon WWTP
P-removal Performance
Typical Municipal Plant
Operates first channel with discsat 29 rpm less than 10% of thetotal oxygen (aerated anaerobic)
Second channel operates with70% of the air and a zero DO(aerated anoxic)
Effluent ammonia at 0.2 mg/l (with 8 day sludge age)
Sol. P from Orbal/FC is 0.03 mg/l
Total P from Orbal/FC is 0.1 mg/l
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Page 32 Water Technologies
System A SAE @ 3 lbs/hp-hr
DO levels 0 - 2 - 4
alpha @ 0.9
power draw @ 544 hp
System B
SAE @ 3 lbs/hp-hr
DO levels 0 - 2 - 4
alpha @ 0.9
power draw @ 444 hp
Comparison of Two Identical Aeration Systems
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Page 33 Water Technologies
Case Study @ Lit tle Lower Miami, OH
Adding more O2at Zero DO saves power DO
Operating Condi tions: DO levels and alpha/FCF same
Aerobic Zone 12mg/l DO0.7 FCF
Aerated Anoxic Zone0 mg/l DO0.9 FCF
Aerobic Zone 24mg/l DO0.5 FCF
Add more O2where absorption rateis greatest
Add less O2 where absorption rateis less
Add less O2where absorption rateis less
Actual Optimized
800
700
600
500
400
300
200
100
0
Aerated Anoxic Opt imizat ion Recommendations
OxygenDelive
red,
lbs/d
Actual Optimized Actual Optimized
O2absorbedfrom aerators(AOR)
UnabsorbedO2fromaerators(FCF)
Total O2Supplied (lb/hr)
Actual Optimized DifferenceFor AOR 1050 1000
For FCF 583 322
Total 1633 1322 22.5% less
Power Use 544 HP 444 HP 22.5% less
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Page 34 Water Technologies
Anammox Bacteria
Nitrogen Removal Efficiency at Centralized Domestic
Wastewater Treatment Plant in Bangkok, Thailand
VLR @ Nongkhaem: BOD NI 32.8 11.8E 3.8 6.7
Of the several plants (8) in the study, Anammox type
bacteria was only present at the Nongkhaem plant
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Page 35 Water Technologies
Anammox Bacteria
2.5 mgd Orbal plant with primaries
Ratio of BOD:N@ 3.5:1 (105 mg/l BOD 30 mg/l TKN)
Effluent ammonia @ 0.1 mg/l Effluent nitrate @ 2 mg/l
AnammoxPathway:
50% of the ammonia oxidized to NO2-N
50% of the ammonia uses NO2-N for oxygen supplier
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Page 36 Water Technologies
Where do we go from here?
Blending erobic With naerobic
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Page 37 Water Technologies
50,000 gpd Pilot Study in Singapore
Roof Installation Roof with Canvas
Gas Holder Installation Digester with Gas Holder
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Page 38 Water Technologies
With DAFT and Anaerobic Digestion
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Page 39 Water Technologies
BOD Extraction and Digester Recycle
Plant main gate
ConstructionTemporaryAccess
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Page 40 Water Technologies
Prime Float Normal Loading Conditions
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Page 41 Water Technologies
Prime Float High Solids Loading Conditions
(Simulate Captivator)
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Page 42 Water Technologies
Test Plans and Summary for High Solids Loading Condit ions
High Solids LoadingConditions
Biosolids TSS Loading/Influent BOD Loading
DAF performance,Removal Efficiencies, %
Targeted Actual TSS BOD CODBase Case 2.7 3.5 98 93 96
Base Case +10 ppm FeCl3 2.7 3.1 99 95 96Base Case + 5 ppm FeCl3 2.7 3.1 97 97 96
DAF
System
DAF Influent
Biosolids Flow, TSS Source
Q Inf = 30 gpm,
BOD = 400 mg/L
TSS = 375 mg/L
Q R = 6 gpm, TSS = 6000 mg/L
DAF Float Sludge, 3.5%
DAF Effluent, to Aeration Tanks
BOD = 50 mg/L, TSS = 35 mg/L
FeCl3,
0 - 10 ppm
Primary
Clarifier
Contact
Tank
Influent Flow
QDAF = 18 gpm,
Directly To Aeration Tanks
Q= 18 gpm
BOD = 320 mg/L
TSS = 210 mg/L
Half of raw influent was treated by combined primary clarifier and contact tank (CT) + DAF:
DAF effluent BOD = 50 mg/L with total removal of 88%: 20% removed by clari fier and 68% removed by CT + DAF
DAF effluent TSS = 35 mg/L with to tal removal of 91%: 44% removed by clari fier and 47% removed by CT + DAF
Estimated reduction in aeration requ ired = 0.5*Q*(320-50)/(Q*320) = 42% based on BOD balance
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Page 43 Water Technologies
Sand Island WWTP, Hawaii
Currently no secondary treatment
Upgrade cost estimate: $1.2 Billion
Power Cost: $0.21/kW
Limited land area for upgrade
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Page 44 Water Technologies
Aeration Energy Reduction/Biogas Production
Conventional Mode BE/DR
2700 kW Energy used 1300 kW1800 kW Energy recovered 4800 kW
Total revenue gain of $8M/year
Total surplus of $6M/year
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Remembering Wellington Donaldson
He had great ideas.
But for the most part they were:
ignored
neglectedforgottennot used
Maybe now we are finally back on the right
course