Applying Extractive Nutrient Recovery for Managing Phosphorus in Sidestreams and Biosolids
Wendell Khunjar PhD, PE
May 11, 2017
Embracing the new resource management
paradigm
Source
water
Drinking
Water
Treatment
Wastewater
Generation
Wastewater
Treatment
Plant
Water
Biosolids
Energy
Nutrient
Products
Water
Resource
Recovery
Facility
Other productse.g., bioplastics,
cellulose
Nutrient management has historically
assumed unlimited energy and resources
Haber Bosch Process
N2 NH3
Phosphorus mining
Apatite ortho-P
Non-Bioavailable
Nutrient
Bioavailable
NutrientTreatment
Nitrogen Gas
Apatite (P)
Potash Ore (K)
Low nutrient
content water
12 kWh/kg N
0.9 to 2.3 kWh/kg N
Extractive recovery is an effective nutrient
management strategy
Haber Bosch Process
N2 NH3
Phosphorus mining
Apatite ortho-P
Non-Bioavailable
Nutrient
Bioavailable
NutrientTreatment
Extractive Nutrient
Recovery
Recovery facilitates Reuse
Offsets Energy Demand
Offsets Resource Demand
Beyond recovery - What other benefits can be
observed at full-scale WRRFs?
Reduction of operating costs
Offsets due to reduction in aeration and
supplemental carbon, metal salt
coagulant, polymer
Reduction in sludge quantity and hauling
costs
Offset from revenue sharing
Benefits to operations and
maintenance
Minimize nuisance scaling
Reduce chemical demand
Beyond recovery - What other benefits can be
observed at full-scale WRRFs??
Benefits to nutrient removal reliability
Reduce impact of sidestream on mainstream
Benefits to treatment capacity
Regain lost volume and pumping capacity
Increase overall capacity for nutrient removal
Changes to biosolids quality
Drier or wetter cake
Phosphorus and nitrogen cake characteristics
Magnesium Struvite (NH4MgPO4·6H2O)
Most commonly recovered P product at
WRRFs
Formation at pH > 8
Characteristic Magnesium struviteMonoammonium
phosphateDiammonium phosphate
Chemical formula MgNH4PO4-6H2O NH4H2PO4 (NH4)2HPO4
Average price/metric
tonne$100 - $600 $570 - $615 $420 - $680
Grade (N-P-K) 5-29-0 11-52-0 18-46-0
Water solubility at 20 °C Insoluble - 0.2 g/L 328 - 370 g/L 588 g/L
Application description Spread on soilNormally spread or mixed
in soil
Normally spread or mixed in
soil
Typical application rates*255 lb/A 142 lb/A 160 lb/A
Magnesium Struvite Recovery Concept Solids Stream
HeadworksPrimary
ClarificationBNR
Secondary
ClarificationDisinfection
ThickenerAnaerobic
Digestion
Dewatering Biosolids
EffluentInfluent
WAS
Septage
Thickener Filtrate
Dewatering Filtrate
Nutrient
Recovery
OptionStruvite
Magnesium Struvite Recovery Concept Solids Stream
Centrifuge
MgCl2 Polymere
Dewatered
sludge
AirWash-
water
Slu
dg
e
liq
uo
r
Back charge
to WWTP
Digested
sludge
AirPrex®
reactor
Buffer
tank
Sepa-
ration
Struvite
Process limits
Airprex Nuresys
Magnesium Struvite Recovery Concept Liquid Stream
HeadworksPrimary
ClarificationBNR
Secondary
ClarificationDisinfection
ThickenerAnaerobic
Digestion
Dewatering
Nutrient
Recovery
Option
Biosolids
EffluentInfluent
WAS
Septage
Thickener Filtrate
Dewatering Filtrate
Struvite
WAS release
Magnesium Struvite Recovery ConceptLiquid Stream
Name of
TechnologyPearl®
Multiform
Harvest™NuReSys™ Phospaq™ Crystalactor™
Type of reactor upflow fluidized bed upflow fluidized bed CSTR CSTR with diffused air upflow fluidized bed
# operating
facility (as of
2016)
14 3 9 9 4
Magnesium Struvite Recovery
• All processes provide effective ortho-P removal
• Combining WAS P strip liquor + centrate for struvite
recovery increases recovery potential significantly
• Recovery potential from liquid stream is higher than from solids
stream
What Have We Learned?
Magnesium Struvite RecoveryWhat Have We Learned?
• If goal is to minimize struvite in
digester
o Redirect P, Mg and Ca around
digester
o Precipitate P, Mg and Ca before
digester
• If goal is to minimize struvite
downstream of digester
o Redirect P, Mg and Ca around
digester
o Precipitate P, Mg and Ca after
digester
ThickenerAnaerobic
Digestion
Dewatering
Nutrient
Recovery
Option
Biosolids
WAS
Thickener Filtrate
Dewatering Filtrate
WAS release
Nutrient
Recovery
Option
PS
All processes still require provisions for acid cleaning of lines
Magnesium Struvite Recovery
• TP removal/recovery is variable and needs to be
considered in evaluation
• Account for formation and capture of struvite fines
What Have We Learned?
Influent Effluent
Recovery
Reactor
Dewatering
Ortho-P removal/recovery TP removal/recovery
Magnesium Struvite Recovery
Dewaterability benefits varies per technology and is site specific
Pilot work is necessary to quantify in advance of installation
What Have We Learned?
Technology Site Polymer Demand
Reduction
(%)
Cake Solids % Increase
Ostara +
WASSTRIP
Clean Water Services ?? 2.5
F. Wayne Hill 22 1
Airprex
Moenchengladbach 15 3
Berlin-Wassmannsdorf 20 3 to 4
Echten 15 3
Amsterdam-West 25 3
Salzgitter 15 2
F. Wayne Hill Water Resource Reclamation Facility
F. Wayne Hill WRC – Nutrient Recovery
Project
• Gwinnett County DWR
• 60 MGD advanced WWTP
• 0.08 mg/L TP effluent limit
• Bio-P and chemical trim for P-
removal
• Influent TP ~ 9 mg/L
Process Flow Diagram
Tertiary Process Flow Diagram
Background Struvite & Phosphorus Issues
2009 – Replaced Bioxide with Mg(OH)2 in collection system
▪ Resulted in struvite formation in centrate lines, centrifuges, digester complex
▪ High soluble Mg content in digester – very low PO4-P in centrate
Accepting sludge from 22 mgd Yellow River Bio-P plant
▪ Substantial increase in P load
▪ Substantial risk for increased struvite formation
▪ Increased recycle P
Project Approach
• Bench Scale testing of P release from WAS
• Whole plant sampling of Mg, P, Fe, Ca
• Pilot scale testing of WASSTRIP and Ostara and Multiform
Harvest
• Whole plant process modeling
• Business case evaluation
Grit tank
BRB 5-10- A1BRB 5-10- A2 BRB 5-10- B1 BRB 5-10- B2 BRB 5-10- C5+C6 BRB 5-10- C8BRB 5-10- C1+C2BRB 5-10- C3+C4 BRB 5-10- C7
Anaerobic Digesters
Dewatered Sludge
Grit
Tertiary Clarifier Metal Salt
Combined Filter Effluent - Pre O3 Infl
Tertiary Caustic
Sec Scum
Bioreactor21
Raw INF
YR Sludge
Influent (SV)7
Influent (SV)17
Plant Mass Balance - Mg
Estimated 7,000 lb/day Struvite Leaving in Cake and in nuisance precipitation
Removes amount of P expected to be released (~ 40% of influent P load)
Explains very low PO4-P in centrate
How does WASSTRIP® help?
Primary Clarification 5 Stage BNR
Secondary
Clarification
Rotary Drum
Thickening Nutrient
Recovery
To Tertiary
Treatment
Influent
WAS
RASP-Release
Tank
Struvite Pellets
PS
Filtrate
EQ
Centrate
EQ
NaOH
MgCl2
Filtrate / Centrate
Nutrient
Recovery
WASSTRIP
Anaerobic
Digestion
Cake
Dewatering
Centrifuges
How does WASSTRIP® help?
+ acetate (100% VFA)
+ PSL (some VFA)
+ WAS only
Net Present Cost Analysis – Results
Summary of Net Present Costs
Alternative 1a
Ostara
WASSTRIP Mg
Alternative 1b
Ostara
WASSTRIP
No Mg
Alternative 1c
Ostara
Centrate
No Mg
Alternative 2a
Ferric at
Digesters Mg
Alternative 2b
Ferric at
Centrate No Mg
Total Capital
Costs$ 13.75M $ 13.08M $ 13.46M $ 4.60M $ 4.60M
Year 1 Capital
Costs $ 9.75M $ 11.41M $ 11.30M $ 1.52M $ 1.52M
Year 1 O&M $ (200,000) $ (94,700) $ (91,000) $ 724,200 $ 861,000
Total Net
Present Cost$ 7.04M $ 10.86M $ 10.74M $ 20.55M $ 23.14M
Nutrient Recovery Facility –
WASSTRIP® + Recovery startup on 7/7/15
WASSTRIP® Tank
Inner tank:
98,000 gallons
Constant Volume
1 – 2 hrs HRT
Outer tank:
280,000 gallons
Elevation Varies
< 6 hours HRT
WASSTRIP® Modifications
Variable level here to control HRT and “wide spot” for thickening
PS2.5% TSS
WAS1.5% TSS
To RDTs
Observations from 1+ Year Operations
• P-release working well, P levels as
expected
• No supplemental Mg required
• Fines loss experienced
• TP removals are improving
Observations from 1+ Year Operations
• Prior to project:
• Centrate lines high pressure
cleaned twice per month
• Struvite in centrifuges and
upstream piping
• No struvite clogging
issues since startup
• Only issue, struvite cleaning of
centrate feed pumps twice
Robert W. Hite Treatment Facility
District is implementing a phosphorus initiative
to proactively manage nutrients
Project is positioning MWRD for the
future • Minimize sidestream load
• Minimize nuisance struvite,
• Meet future nutrient limits (0.1 mg TP/L)
• Maximize solids treatment capacity
Nutrient recovery is a component of the
phosphorus initiative
Slide courtesy MWRD
5 Measures for Success
1. Break the phosphorus recycle loop
2. Struvite-scale issues for O&M
3. Biosolids dewatering costs
4. Phosphorus loading on soils
5. Recovery of a finite resource
1 lb of phosphorus equates to 8 lbs of struvite.7,000 lbs of phosphorus enter the RWHTF each day!
Nutrient Recovery Concepts Applicable to
RWHTF
Pre-dewatering recovery
• Recovery from digested sludge matrix
• e.g., Airprex
ThickenerAnaerobic
Digestion
Dewatering
Nutrient
Recovery
Option
Biosolids
WAS
Thickener Filtrate
Dewatering Filtrate
WAS release
Nutrient
Recovery
Option
PS
Post-dewatering recovery
• Recovery from filtrate and centrate
• e.g., Ostara + WASSTRIP
220 mgd facility with Bio-P
Project Approach
Struvite
Recovery from
Digested Sludge
Struvite Recovery
from WAS P-release
Filtrate and
Centrate
OR
Driver Data to support
Break recycle loop
Pilot (Ostara and Airprex),
WAS release testing,
Modeling
Biosolids dewatering costs
Airprex Pilot
WAS Release Digester
Pilot
Struvite scaling Modeling
Phosphorus loading on
soils
Pilot (Airprex)
Modeling
Product recoveryPilot (Ostara and Airprex)
Modeling
Additional considerations for RWHTF
• P recovery downstream deammonification
• Applicable to post-dewatering option only
Impact of P recovery on Deammonification
Recovery Reactor
DMX
P product
Pre-thickened WAS Release Filtrate
Centrate Slipstream
CentrateReturn to plant
Additional considerations for RWHTFImpact of THP
Thickened Primary Solids
Waste Activated Sludge
Pre-thickening WAS dewateringThermal
Hydrolysis
Digestion
5.1% TS
0.7% TS
3.0% TS
16 to 18% TS
Dilution water as necessary
WAS Release
• Pre and post-dewatering options are compatible with THP• Implementing THP requires installation of new infrastructure common to all
technologies
• Installation of THP will require new post-dewatering reactors
• Installation of THP will enhance pre-dewatering reactor capacity
Concluding Thoughts
Nutrient recovery is a viable treatment
option NOW!
Cost and operational improvements at WRRFs
• Offsets due to reduction in aeration and supplemental carbon,
metal salt coagulant, polymer
• Reduction in sludge quantity and hauling costs
• Offset from revenue sharing
• Minimize nuisance scaling
• Reduce chemical demand
• Reduce impact of sidestream on mainstream
• Regain lost volume and pumping capacity
• Increase overall capacity for nutrient removal
• Drier or wetter cake
• P/N cake characteristics
Wendell [email protected]
http://www.werf.org
1. State of Science and Market Assessment Report (NTRY1R12a)
2. Technology Matrix – Nutrients (NTRY1R12m)
3. Case Studies of Full-scale Facilities Performing Nutrient
Recovery Report (NTRY1R12b)
4. TERRY – Phosphorus with user guide tutorials (NTRY1R12t)
5. Innovative Extractive Nutrient Recovery Technologies Report
(NTRY1R12)