1 Sidestream Treatment for Nutrient Removal and Recovery PNCWA Webinar April 23, 2015 1200 – 1300 PST H. David Stensel, PhD, PE University of Washington Water Environment Resarch Foundation Nutrient Challenge Program Wastewater Engineering: Treatment and Resource Recovery 5 th Edition (2013) G. Tchobanoglous, H.D. Stensel, R. Tsuchihashi, F. Burton Metcalf & Eddy, McGraw-Hill
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Sidestream Treatment for Nutrient Removal and Recovery
PNCWA Webinar April 23, 2015
1200 – 1300 PST
H. David Stensel, PhD, PE University of Washington Water Environment Resarch Foundation Nutrient Challenge Program
Wastewater Engineering: Treatment and Resource Recovery 5th Edition (2013) G. Tchobanoglous, H.D. Stensel, R. Tsuchihashi, F. Burton Metcalf & Eddy, McGraw-Hill
Motivation for Sidestream Treatment
• Helps meet more stringent effluent nutrient concentration goals
• Save energy • Reduce carbon addition • Sustainable environmental Engineering
• Centrate + return activated sludge in separate aeration basin before mainstream – Higher MLSS and higher nitrification rate/unit volume – Decreases oxygen transfer needs in mainstream – Plants with conventional plug flow configurations more easily
accommodate this design – Nitrifiers produced in sidestream seed the mainstream reactor
• bioaugmentation
• hi [Centrate and return activated sludge reaeration basin (CaRRB)
Nitro-bacteria oxidize NO2 to NO3
Nitroso-bacteria oxidize NH4 to NO2
Quick review on nitrification/denitrification Nitrification is by two steps Uses oxygen and alkalinity
Overall two-step process
→
+ -4 2 3
- +2 5 7 2 2
1.0 NH + 1.404 O + 0.0743 HCO
0.985 NO + 0.0149 C H O N + 1.911H + 1.03 H 0
→
- + -2 2 4 2 3 2
-3 5 7 2
1.0 NO + 0.473 O + 0.005 NH + 0.020 CO + 0.005 HCO + 0.005 H O
1.0 NO + 0.005 C H O N
+ -4 2 2 3
- +3 5 7 2 2
1.0 NH + 1.86 O + 0.02 CO +0.079 HCO +
0.981 NO + 0.0197 C H O N + 1.902 H + 1.02 H O→
Biological denitrification uses carbon and produces alkalinity
3 4 3
2 5 7 2 2 3 2
NO H 0.33NH 1.45 CH COO
0.5N 0.33 C H O N 1.60H O 1.12HCO 0.12CO
− + + −
−
+ + +
→ + + + +
Acetate Nitrate
Alkalinity Nitrogen gas
• Heterotophic bacteria oxidize a carbon substrate with NO3-N or NO2-N • produce alkalinity, 1 mole/mole
Needs carbon (BOD)
Produces alkalinity
Alkalinity is an important issue with regard to nitrification efficiency in sidestream treatment • Digester produces alkalinity from
deamination and ammonia production – NH3 + CO2 + H2O NH4(HCO3)
• 1.0 mole alkalinity produced per mole NH3
• Nitrification uses 2.0 moles alkalinity per mole of NH3 oxidized
• Can get the other 1.0 mole from biological reduction of NO3 or NO2 produced
Needs carbon
Many Treatment Schemes used for sidestream nitrification
AT3, BAR, MAUREEN, CaRRB, InNitri
(carbon addition, anoxic tank, percent RAS added)
• May be entirely aerobic or anoxic/aerobic • Add and/or produce alkalinity • SRT of 3 to 5 days • HRT ~ 0.4 to 0.5 hrs
Proposed for bioaugmentation of nitrification
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New York City AT-3 Process (26th Ward plant) MAUREEN IS A MODIFIED VERSION
BioAugmentation Reaeration (BAR) or Regeneration Denitrification-Nitrification (R-D-N) • RAS added to plug flow nitrification tank • HRT of 1-2 hrs • May have ~1 hr anoxic zone in front end • Nitrifiers grown at similar conditions as mainstream • RAS alkalinity may be sufficient as flows may be 20-100 times centrate flow
• Postanoxic with external carbon and primary effluent • Minimal NO3/NO2 to feed to Enhanced Biological P Removal Process • No internal recycle in RAS reaeration process • HRT ~ 1 to 2 hrs
proposed for EBPR systems
• Has been used for separate sidestream treatment • SRT of ~ 10 days • Alkalinity and external carbon can be added • Mix during fill • Intermittent aeration may be used during react period
In these schemes sidestream nitrifiers have same SRT as the activated
sludge in the mainstream • What if the sidestream nitrifiers can be kept in the
mainstream reactor longer? – Much greater impact of bioaugmentation
• There may be a way! • Grown them in aerobic granular sludge
Nitritation-denitritation is done in the SHARON Process
• Not named after someone named Sharon
• Single Reactor High Activity Ammonium Removal Over Nitrite
Nitritation – Not Nitrification
• Ammonia oxidation to only NO2
• 25% less oxygen is required
Nitroso-bacteria oxidize NH4 to NO2
→
+ -4 2 3
- +2 5 7 2 2
1.0 NH + 1.404 O + 0.0743 HCO
0.985 NO + 0.0149 C H O N + 1.911H + 1.03 H 0
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Nitrification - Denitrification
75% O2
25% O2
40% Carbon
60% Carbon
Nitrification-Aerobic Denitrification-Anoxic
1 mol Nitrite (NO2-)
1 mol Nitrite (NO2-)
1 mol Nitrate (NO3-)
½ mol Nitrogen Gas (N2)
1 mol Ammonia (NH3/ NH4 +)
Autotrophs Heterotrophs
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Nitritation - Denitritation
75% O2
60% Carbon Nitritation -Aerobic
Denitritation -Anoxic
1 mol Nitrite (NO2-)
1 mol Nitrite (NO2-)
½ mol Nitrogen Gas (N2)
1 mol Ammonia (NH3/ NH4 +)
Heterotrophs
Autotrophs
Advantages; 25% Reduction in Oxygen Demand 40% Reduction in Carbon (e- donor) Demand 40% Reduced Biomass Production
How do you stop NH3 oxidation to only NO2 (nitritation)?
• Short SRT for high temperature centrate treatment (<1.5 d) • Low pH • Low DO concentration • Elevated NH3 toxic to NO2 oxidizers (higher pH encourages free
ammonia toxicity) • Cyclic aeration helps
SHARON PROCESS in operation at New York City Wards Island WWTP (400 Mgd) Since December 2010. Two Trains with capacity of 1.0 Mgal/d of centrate treatment In each train
30-40ºC500-1500 mg/L NH3-N
Carbon
Heat Exchangers OXIC ANOXIC
6-9 Q RecycleNitrified & Denitrified Effluent
No ClarifierHRT ~ SRT
Dewatering Sidestream
Alkalinity
Wards Island SHARON Process
New York City SHARON PROCESS 1.0 Mgal/day (Recirculation anoxic to
• Sensitive to elevated NO2-N (<40 mg/L) • Sensitive to free NH3-N • Reversible inhibition by DO
Produces a large very dense granular floc- long SRT possible
9/25/2013 -40-
1 mol Nitrate (NO3
-)
0.57 mol Nitrite (NO2
-) 1 mol Nitrite
(NO2-)
1 mol Ammonia (NH3/NH4
+) 0.44 mol N2 0.11 mol NO3-N
Autotrophic Aerobic Environment
25% O2
40% O2
40% Carbon
60% Carbon
Heterotrophic Anoxic Environment
ANAMMOX
11% Carbon ANaerobic AMMonia OXidation
Comparison of sidestream N removal processes
Process Deammonification Nitritation/Denitritation Nitrification/Denitrification
Oxygen demand 1.84 g O2/g NH4-N
3.21 g O2/g NH4-N 4.25 g O2/g NH4-N
Acetate COD demand
0.7 g acetate COD/g N
4.0 g acetate COD/g NO2-N
6.7 g acetate COD/g NO3-N
Biomass production 0.12 g biomass VSS/g NH4-N
1.45 g biomass VSS/g NH4-N
2.12 g biomass VSS/g NH4-N
Advantages of deammonification: No carbon for anammox Small amount of carbon for NO3 removal 57% less aeration energy than nitritation/denitritation 25% less alkalinity than nitritation/denitritation Less sludge production
*acetate used as an example
Variety of Deammonification Processes Used in many facilities world wide
• Stable deammonification achieved in single reactor
• Deammonification accomplished in attached growth or suspended growth reactors
• Anammox biomass forms dense granular sludge
• Process operation tied to DO and pH measurements
• Cyclic aeration at low DO may be used – Air On: pH decreases due to nitritation – Air Off: pH increases due to NO2/NO3 removal
NH3-N load 0.70 – 1.2 kg N/m3-d SRT 40 to 50 d (granules) 10-15 d (floc)
3 L
L3
L 33
3
L
QNoNH -N load = N = V
V No= Q N
N = kg NH -N/m -d
No = kg NH -N/mAt No = 1,000 mg/L, N = 0.70, V/Q = 1.4 days
@ 1.0 kgN/m3-d The O2 demand = 140 mg/L-h
ANITATMMox-Single stage moving bed biofilm reactor (MBBR) process
NH3-N load 0.70 – 1.2 kg N/m3-d SRT > 20 d AnoxKaldness plastic media TypeM 1200 m2/m3
50 percent fill fraction
Nitritation – Anammox -CANON
Anammox AOB • NH4+O2àNO2
• NH4+NO2àN2
AOB: 1NH4+ + 1.5 O2 → 1 NO2
- +1 H2O + 2 H+
Anammox: 1NH4+ + 1.3 NO2
- 1 N2 + 0.3 NO3-
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→
Increase aeration
Management options for phosphorus-rich sidestream flows
• Minimize variable loads to secondary treatment process – Equalization
• Remove phosphorus from recycle stream – Chemical treatment of sidestream flow
• Add alum or ferric – Convert soluble P to particulate P – Remove particulate P to biosolids
– Phosphorus recovery and reuse – Sidestream EBPR
Phosphorus Recovery
• Phosphorus is a finite resource on the earth
• Necessary for all living species (humans, food plants etc)
• Using it once and throwing it away is not within sustainable resources or environment principles
P and N are recovered as struvite in crystalizers
• Struvite – MgNH4PO4●6H2O
• Molar ratios – Mg:N:P = 1:1:1
• Mass ratios – Mg:N:P = 1.77:0.45:1.0
• Percent N and P – N = 4.2 % – P = 9.4 %
Struvite crystallization recovery processes
AirPrexr process Cone-shaped fluidized bed- Multiform Harvest
Crystalactor® NuReSys® process Ostara Pearl® process Phosnix® process PHOSPAQTM process
Generally typical process parameters HRT ~ 1.0 hr MgCl2 and NaOH added for pH control Hydrodynamics vary with reactor design
Pearl® process
Example of crystallizer system
Ostara Pearl®,Tigard, Oregon Durham WWTP
Multiform Harvest, Yakima, WA
~ 85% P removal ~ 15% N removal
~ 80-90% P removal
Other issues with P recovery • About 20-23% of influent P recovered • Struvite formation in digester and effluent piping • WAS P release before digester
Stripping CO2 by aeration indigester promotes internal struvite precipitation
Summary • Digester centrate return can increase
mainstream N and P load by 15-30% • Sidestream loads adds hinders reliably
meeting low effluent N and/or P concentrations.
• A variety of process options have been shown for sidestream management of nutrients – each with its own advantages and unique
process considerations.
Summary • Nitrification bioaugmentation • Reduce carbon and energy for N removal –
SHARON Process • Almost eliminate carbon, reduce energy, reduce
alkalinity needs – Deammonification/Anammox process
• For sustainable environmental engineering practice, deammonification for nitrogen and struvite recovery for phosphorus are most attractive