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 Khunjarwkhunjar@hazenandsawyer.com

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)