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Re‐Thinking Enhanced Biological Phosphorus Removal
James BarnardPatrick Dunlap
13 July 2018
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Bardenpho Pilot Plant 1972
The purpose of the dead zone was to allow relative adjustments to the other zones
100 m3/d
Some early observations… Pilot Plant
Barnard 100 m3/d pilot 1972
• Fermenter resulted from basin configuration and not deemed important
• Excellent phosphorus removal resulted
• Phosphorus profile shown in ellipses
• Performance could not be replicated in laboratory
• Barnard suggested organisms (PAO) should pass through anaerobic phase with low ORP which triggered EBPR
• Suggested Phoredox process by adding an anaerobic zone up front
Concept of passing all PE through AN Zone Become standard with early designs
These were followed by others such as UCT, JHB & Westbank
FirstAcinetobacterandthenAccumulibacteridentifiedasPAO
VFA from Fermenters
Westbank Process Incorporated a Fermenter(While also allowing for Primary Effluent bypass around the Anaerobic Zone) (Knight & Piesold, 1984)
TN < 6 mg/ℓ BOD < 5 mg/ℓ TSS < 2 mg/ℓ TP < 0.15 mg/ℓMixing energy 0.15 hp/kcf
X
Westside Regional WWTP
Primary Anaerob Anoxic 1 Anoxic 2 Anoxic 3 Aerobic 1 Aerobic 2 Aerobic 35.36 20.56 2.20 1.84 1.60 0.50 0.20 0.03Bioreactor Profile
Phosphorus by Zone
0.00
1.00
2.00
3.00
4.00
5.00
6.00
7.00
8.00
9.00
10.00
Prim
ary
Anaerob
Anoxic 1
Anoxic 2
Anoxic 3
Aerobic 1
Aerobic 2
Aerobic 3
Phosph
orus
mg/L
Note P uptake in Anoxic Zone
Tetrasphaera‐like PAO can denitrify and uptake P under anoxic conditions
South Cary, NC
4Q
AX
AN
AER
Ferment
AX
AX
AEREffluent
WAS
Influent
Bardenpho plant
RAS Fermentation
Stroud, R and Martin, C. (2001) South Carey Water Reclamation Facility’s Nutrient Removal Modifications and Reduction Success, Town of Carey, NC, Proceedings of WEFTEC2001
Based on Lamb Patent (1994) to ferment some RAS to provide VFA for PAO
Charlotte NC (CNC) Process
• Experiment at McDowell Creek
• Worked in summer but not well in winter
• Probable cause – over‐mixing at 20 W/m3 (0.75 hp/kcf)
9
WASFermenter
Primary Effluent
VFA
Anoxic Aeration
RAS Fermentation
Stokholm‐Bjerregaard (2015)
• In mid 90s the RAS Fermentation process was developed
• Fraction of RAS, long fermenter HRT, no supplemental carbon
• Now >60 of these processes worldwide, mostly in Denmark
• Recent patent by Kruger comes out of this tradition
Carousel Plant Henderson NV60 ML/d – Upgraded to BNR
Ortho-P for May 2010
0
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010
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010
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5/11/
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5/13/
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2010
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2010
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2010
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2010
Phos
phor
us (m
g/L)
ANA Eft SPS SCC Final Eft
Switching off a mixer in the anaerobic zone resulted in In‐plant Fermentation
Experiment at Metro Denver
Cavanaugh, L., Carson, K., Lynch, C., Phillips, H., Barnard, J. and McQuarrie, J. (2012) A Small Footprint Approach for Enhanced Biological Phosphorus Removal: Results from a 106 mgd Full‐Scale Demonstration. Proceedings of the 85th Annual Water Environment Federation Technical Exhibition and Conference, New Orleans, LA, October 2012.
ItemTotal plant flow 100 mgdTotal RAS flow 104 mgdRAS to Fermenter 24 mgdTotal Ferm. volume 1.36 mgdHRT 1.25 hAnaerobic SRT 1 dayGR. Th. Overflow 5.4 mgdORP end of Fermenter
‐230mV
RbCOD in GTO 320 mg/L Mixing energy 0.08 hp/kcf
Phosphorus Removal by RAS Fermentation – Metro Denver
0
5
10
15
20
25
0.0
0.5
1.0
1.5
2.0
2.5
3.0
10/4/201
1
10/6/201
1
10/8/201
1
10/10/20
11
10/12/20
11
10/14/20
11
10/16/20
11
10/18/20
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10/20/20
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10/22/20
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10/24/20
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10/26/20
11
10/28/20
11
10/30/20
11
11/1/201
1
11/3/201
1
11/5/201
1
11/7/201
1
11/9/201
1
11/11/20
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11/13/20
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11/15/20
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11/17/20
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11/19/20
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11/21/20
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11/23/20
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11/25/20
11
11/27/20
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11/29/20
11
12/1/201
1
12/3/201
1
12/5/201
1
mg‐TSS/L
mg‐P/L
NSEC Effluent TP
NSEC Effluent PO4‐P
NSEC Effluent TSS
Cavanaugh, L., Carson, K., Lynch, C., Phillips, H., Barnard, J. and McQuarrie, J. (2012) A Small Footprint Approach for Enhanced Biological Phosphorus Removal: Results from a 106 mgd Full‐Scale Demonstration. Proceedings of the 85th Annual Water Environment Federation Technical Exhibition and Conference, New Orleans, LA, October 2012.
Why Conventional EBPR selected for Accumulibacter
Accumulibacter species don’t ferment ‐ need supply acetic & propionic acid?
short anaerobic residence time
relatively weak anaerobic conditions (ORP > ‐150 mV)
due to nitrates in RAS and DO concentrations in primary effluent
Many AN zones are over‐mixed:
surface agitation and DO entrainment prevents deeper anaerobic conditions
Standard mixing energy 20 W/m3 (0.75 hp/kcf)
When 2 W/m3 (0.08 hp/kcf) is adequate (huge saving in energy) and does not entrain air
Too much primary effluent low in VFA and high in DO going to AN zone, thus reducing AN SRT and raise ORP 14
Deeper Anaerobic Zones Select for Fermenting PAO’s
Advantages of PAOs like Tetrasphaera that can ferment :
ferment glucose and amino acids and other higher carbon forms and store phosphorus
produce VFA that allow a population of Accumulibacter to grow alongside them, and
can denitrify and uptake P under anoxic conditions
Completely independent of wastewater characteristics
It would appear an ORP of less than < ‐250 mV is needed to select for Fermenting PAOs
Longer AN SRT (1.5 to 2.0 days) for fermenting RAS or mixed liquor
Can be achieved when passing primary effluent to anoxic zone
Use PS fermentate when available to reduce required SRT
Reduce dilution by limiting RAS to fermenter to between 10 and 20%
Reduce mixing energy to less than 2 W/m3 (0.08 hp/kcf) for top entry mixers15
16
Examples of S2EBPR Processes(As classified by WERF S2EBPR Project)
1.5dto2dSRTforRASonly8to12hwhenfeedingfermentate
POSSIBLE EXPLANATION OF RAS FERMENTATION
17
OHO Other heterotrophsFAC Facultative bacteriaTSA Tetrasphaera ACC Accumulibacter
Gravity thickener overflow
ACC
OHOHy
droly
sis
FAC
TSA
VFA
P
RAS (10%)
RbCOD
Hydr
olysis
And the latest ‐ Wakarusa KS
18
On‐line April, 20182 mgd – no primaries Side‐stream mixed liquor fermentation Eventually – BardenphoEBPR kicked in May 20, 2018
Conversion of McAlpine, Charlotte to S2EBPR
Nitrate reduction may not be required
• Reverse flow of one or two basins
• Convert to S2EBPR
• 10 to 20% of RAS
• Add GTE to Fermenter
• Increase RAS to anoxic zones
19
AN
Feed
Possible Future Ae
ratio
n
Pilot D
emo
RAS
FC
Keep one Pass asAnaerobic or Construct New UnitSplitter
Box
Gravity Thickeners
Existin
g aeratio
n ba
sins
Gravity thickener overflow
Existin
g an
aerobic
zone
s
•Undisputable benefit of S2EBPR •Independent of wastewater characteristics•Easily retro‐fitted to existing plants•PAOs need anaerobic conditions (<‐250 mV ORP)•Reduce mixing energy to avoid air entrainment•Reliable removal to lower than 0.1 mg/L P•Modeling catching up
Take home Message
QUESTIONS ?
21
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