The Phosphorus Story: Sustainable Nutrient Management at the Robert W. Hite Treatment Facility

Englewood PWO Seminar – February 7, 2019Dan Freedman, MWRDNate Brown, Stantec

Agenda

• Background on Phosphorus• Robert W. Hite Treatment Facility Background• The District’s Phosphorus Initiative• Liquid Stream Phosphorus Removal• Solids Stream Phosphorus Recovery• The Future of Phosphorus Management

Background on Phosphorus(The Most Interesting Element in the World)

What even is Phosphorus?• In Greek mythology, Phosphorus was the god “Light Bringer” otherwise known as The Morning Star (aka the planet Venus)

• The Latin translation of Phosphorus is Lucifer

Image source ‐ https://lystek.com/Image source ‐ John Lemieux, flickr.com

The Lucifer of Liege by Guillaume GeefsImage by Luc Viatour

How was Phosphorus first discovered?• Discovered in 1669 by Hennig Brand whilst searching for the “philosopher’s stone”

• Brand attempted to create the stone through distillation of salts by evaporating urine

• Through the process he produced a material that made a brilliant white light, hence the name phosphorus

Image source ‐ https://lystek.com/

The Alchymist, In Search of the Philosopher’s Stone, Discovers Phosphorus, and prays for the successful Conclusion of his operation, as was the custom of the Ancient Alchymical Astrologers

by Joseph Wright of Derby

Why is Phosphorus important?“Life can multiply until all the phosphorus is gone, and then there is an inexorable halt which nothing can prevent. We may be able to substitute nuclear power for coal, and plastics for wood, and yeast for meat, and friendliness for isolation—but for phosphorus there is neither substitute nor replacement.”

‐Isaac Asimovfrom Asimov on Chemistry

Image source ‐ https://lystek.com/Image source ‐ John Lemieux, flickr.com Image source ‐ https://lystek.com/

Who is Phosphorus?While working at a nuclear power plant, Dr. Alex Sartorius was expose to radioactive material as a result of a nuclear reactor failure. His body transformed into live Phosphorus and turns to flame whenever he is in contact with air. He is now known as Doctor Phosphorus!

Image source ‐ John Lemieux, flickr.com Image source ‐ https://lystek.com/

Image source – DC Comics

Where is all the Phosphorus?

Image source: BioPandit

Where is all the Phosphorus?

Image source ‐ https://lystek.com/Image source ‐ John Lemieux, flickr.com

Image source – UNEP

The Phosphorus Cycle (Source: UNEP)

Image source – National Geographic

Image source – Robert Garvey, CorbisImage source – Y. Arthur‐Bertrand, Corbis

Image source – Elena Elisseeva, Shutterstock

South Platte RiverOff-line Reservoirs

Prehearing Statement, Regs #31 and #85, Rulemaking Hearing, March 12, 2012, Colorado Water Quality Control Division, December 9, 2011.

Phased Total Maximum Daily Load to Achieve pH Compliance in Barr Lake and Milton Reservoir, Colorado, Barr Lake and Milton Reservoir Watershed Association, May 2013,

Why we care: Water quality issues

Robert W. Hite Treatment Facility (RWHTF) Background

Robert W. Hite Treatment Facility (RWHTF)

North SecondaryNorth Secondary

South SecondarySouth Secondary

Solids HandlingSolids Handling

• 1.8 million population equivalent service area, 220 MGD plant rating• Separate secondary processes, with combined solids handling and 

sidestream treatment

Resource Recovery at the RWHTF

Effluent (Water)Average ~134 mgd

No District water rights85% of S. Platte 6 months/year

Denver Water can reuse up to 120 cfs

Biosolids (Nitrogen)107 dry tons/day (2017)1.64 tons/day plant available nitrogen75% applied on private property25% applied on METROGRO Farm

Combined Heat and Power (Energy)Average ~4.5 MW

38% plant electricity

N

The District’s Phosphorus Initiative

The Regulatory Timeline

2019 2037

Reg. 85 Voluntary Incentive Program

Reg. 31 andBarr/Milton TMDL

TP (mg/L) 1.0 0.7 0.7 0.1

Interim Limits?

2027

The Phosphorus InitiativeThe Problem:

Why phosphorus is regulated

The Cost of Compliance:Financial incentive to figure

our way through this

The Current Plan: Environmental and social

reasons for innovation

GOALTo find the most effective 

and sustainable phosphorus management approach 

through an intensive study phase of biological 

phosphorus removal, phosphorus recovery, 

watershed impact studies, and tertiary facilities

The Current Plan4 Angles

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2

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Liquid stream

TP removal

SolidsTP

removal

Liquid Stream Phosphorus Removal

Quick Note on Terminology• Biological phosphorus removal (BPR) – refers to the incorporation of phosphorus into biomass during cellular growth

• Enhanced biological phosphorus removal (EBPR) – refers to the intentional selection of polyphosphate‐accumulating organisms (PAOs) through the conditioning of biomass in anaerobic zones (i.e., no nitrate or oxygen present)

• Bio‐P – colloquial phrase used to describe either BPR or EBPR

EBPR Mechanisms

Adapted from WEF MOP 8, 2010

• Two‐stage process: anaerobic (release) and aerobic (uptake)

Liquid Stream Phosphorus Removal: SSEC

• South Secondary Improvements Project (PAR 1085)

• Completed in 2015• Demolished a high‐purity oxygen activated sludge process

• Constructed a 3‐stage anaerobic‐anoxic‐oxic (A2O) activated sludge process

• Rated for 114 MGD max. month flow• Currently treats approx. 60% of the total plant secondary influent – not running in Bio‐P mode

Liquid Stream Phosphorus Removal: SSEC

Anaerobic(Anoxic Swing) Anoxic

PE

100% RAS

Effluent

Clarifier

Aerobic

MLR

Liquid Stream Phosphorus Removal: NSEC

Aeration Tanks (1 of 12)

Sidestream Tanks (1 of 4)

Gravity Thickeners

• 12 AB‐SC Trains• 4 Sidestream Tanks(CaRRB)

• 4 Gravity Thickeners (in the vicinity)

NSEC Baseline Process Schematic

Conventional A2O Process Schematic

Alternative Novel Sidestream Configuration

Liquid Stream Phosphorus Removal: NSECEnhanced Biological Phosphorus Removal (EBPR) Pilot Project (PAR 1171)

Two Anaerobic RAS Reactors

Temporary Gravity Thickener Overflow Feed

EBPR Pilot Study Parameters

• 8‐month full‐scale demonstration period• 15‐30% RAS rate through anaerobic zone• 0.3 to 0.5‐day anaerobic SRT• 1.3‐hr anaerobic HRT• 80‐100% centrate returned to NSEC CaRRB• 100% gravity thickener effluent conveyed to anaerobic zone• Low mixing energy in anaerobic zones

EBPR Pilot Study Phase I ResultsTP = 0.58 mg-P/LOP = 0.10 mg-P/L

Full-Scale Sidestream EBPR Implementation

• Sidestream Nutrient Removal Project (PAR 1237)• Construction completed in Jan 2018• Retrofit two CaRRB to Sidestream Anaerobic Reactors (SAR)• Up to 50% RAS (52 MGD) and 100% GTE (7 MGD) to anaerobic zones

North Secondary aeration basins

Consequences of EBPR Operation

• 2011‐2012 pilot study observations suggest that effluent quality is directly related to digested sludge dewatering recycle loads.

Consequences of EBPR Operation

Consequences of EBPR Operation

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1‐Jan‐15 11‐Apr‐15 20‐Jul‐15 28‐Oct‐15 5‐Feb‐16

Capture Effic

iency, %

Chem

ical, lbs/dt

Cake so

lids, % 

Date

Cake solids, % Polymer, lbs/dt Ferric, lbs/dt Capture Efficiency, %

40% of Facility in EBPR

100% of Facility in EBPR

Intentional EBPR Off

Consequences of EBPR Operation

Return Activated Sludge (RAS)

Secondary Treatment

Centrate (recycle flow)

Primary Treatment

Digester

Centrifuge

Phosphorus Recovery

Less than 1% of the flow but 25% of the Phosphorus Load

Solids Stream Phosphorus Recovery

Effective and Sustainable Phosphorus Management

5Drivers for Phosphorus Management1. Phosphorus Recycle Control2. Biosolids Dewatering3. Struvite Reduction4. Phosphorus Index5. Product Recovery

1 lb of phosphorus equates to 8 lbs of struvite.7,000 lbs of phosphorus enter the RWHTF each day!

Established Phosphorus Recovery SystemsIntentional Precipitation of Struvite

NH4MgPO4●6H2O

Two primary recovery system types

Digestate = AirPrex™ Centrate and Stripped WAS Filtrate = WASSTRIP/Ostara

5 in Germany4 in the Netherlands1 Belgium1 in China

Phosphorus Recovery Pilot WorkHypothesis:Removing phosphorus in the sidestream will: Improve our effluent quality Reduce operating costs Pilot Technologies: Digestate Recovery (i.e., AirPrex) WAS Phosphorus Stripping

(i.e., Ostara WASSTRIP)

AirPrex™ phosphorus removal pilot test, summer 2016

Phosphorus Recovery Pilot Work

Pilot testing WAS release 

pretreatment with anaerobic digestion and 

sludge dewaterabilityassessment

Oct 2016–Jun 2017

Aug2016

PAR 1280 initiation 

Nutrient and cation

sampling and mass balances across solids processing 

2015 June–Aug2016

Pilot testing of AirPrex

precipitation and recovery 

BenchtopWAS release 

tests 

Jan2015

Ostara Pearl pilot

2011 2016

Development and utilization of steady‐

state process model using 

BioWin

How does AirPrex work?

Anaerobic Digestion

Centrifuge

Centrate

BiosolidsAirPrexReactor

Struvite

Digester effluent is fed to AirPrex reactor

Reactor is aerated which strips the CO2from the reactor and raises the pH

Magnesium is dosed to the reactor causing struvite to precipitate 

CO2 Mg

Struvite settles and is pumped out and cleaned

AirPrex effluent, stripped of phosphorus, is sent to dewatering centrifuges

How does Ostara+WASSTRIP work?

Thickening DewateringAnaerobic Digestion

WASSTRIPProcess

Struvite

Biosolids

Centrate

Phosphorus‐stripped WAS from the WASSTRIP reactor is thickened

Phosphorus is released into the liquid stream and separated from the biosolids

Low P

High P Centrate from dewatering is high in ammonia and is combined with liquid stream from WASSTRIP

Caustic

Mg

Caustic is added to raise the pH

Magnesium is dosed to the reactor, causing struvite to precipitate 

Struvite pearls settle and are pumped out and cleaned

Ostara Pearl effluent, stripped of phosphorus, is recycled back to mainstream

AirPrex Pilot Study• Pilot on site from June thru August 2016• Reactor operated continuously at a flow of 11 gpm

• Centrisys CS10‐4 centrifuge operated 6 –8 hours per day

• Mg:P molar dosing ratio varied between 0.7:1 – 1.7:1

AirPrex Pilot Phosphorus Recycle Load Control

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Typical Untreated Mg:P0.7:1

Mg:P1.4:1

Mg:P1.7:1

Phosph

orus, m

g/L

Orthophosphorus

Particulate Phosphorus

• OP and TP were observed to decrease in the centrate as the Mg:P molar dosing ratio increased to 1.4:1

• At 1.7:1 Mg:P molar ratio, OP was lowest while TP increased –potentially due to fines loss

AirPrex Pilot Dewaterability Improvements

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5%

10%

15%

20%

25%

30%

0 1 2 3 4 5

Cake Solids, %

Polymer Dose, lb/hr

Digestate

AirPrex

8.7% reduction in wet tons hauled17% decrease in polymer consumption

WAS Phosphorus Stripping Pilot Study• Pilot testing conducted from October 2016 through May 2017

• Batch fed phosphorus stripping reactor (48‐hr SRT)

• Filter press system for thickening

WAS Phosphorus Stripping Pilot Study• TWAS combined with TPS in Digester Pilot System (16‐day SRT)

• “Control train” received unstripped WAS, “test train” received phosphorus‐stripped WAS

• WAS used in pilot is from SSEC while operating in Bio‐P mode (centrate recycle to NSEC)

WAS Phosphorus Stripping Process

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4-Feb 19-Feb 6-Mar 21-Mar 5-Apr 20-Apr

Solu

ble

to T

otal

Pho

spho

rus

P C

once

ntra

tion

in F

inal

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ease

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AS,

mg/

L

Soluble P Particulate P Soluble to Total Phosphorus

Struvite Quantification

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Acid Cake Test Mass Balance onSoluble Mg

XRD

Struvite

Redu

ction in Biosolid

s

Struvite Con

centratio

n in Biosolid

s, % of T

otal TS

Comparison of Methods for Quantifying Struvite in Biosolids

Test Control Reduction

• 8% of biosolids is struvite at full‐scale• “Test train” averaged 23% less struvitethan “control train”

Key Results from Pilot Studies

P Recovery System

Struvite Formation Potential (Modeling) Recycle Control Dewaterability

% Reduction in Struvite Formation 

Potential%P Reduction % Increase in Final Cake Solids

% Reduction in Polymer

Ostara w/ WASSTRIP 30 ‐ 45% Combined ~70 – 90% 7 ‐ 13% Inconclusive

AirPrex 25% 83% 15 ‐ 20% 17%

Full-Scale AirPrex Process Complexity

Full-Scale Ostara/WASSTRIP Process Complexity

AirPrex Ostara + WASSTRIP

Phosphorus Recycle Control 

Reliable Recycle Control Less stable and more complex process

Improve Biosolids Dewaterability 

Polymer 23% polymer reduction 10% polymer reduction

Truck Hauls 8% reduction 7% reduction

Struvite Reduction Digesters 25% reduction digester struvite 30 ‐ 45% reduction digester struvite

Dewatering Significant reduction in dewatering nuisance struviteSignificant reduction in dewatering 

nuisance struvite

Phosphorus Index Improvement over chemical sequestrationImprovement over chemical 

sequestration

Product Recovery   25% ‐ 35% product recovery 70%+ product recovery

Process Complexity Simple, reliable system Significant increase in equipment and system complexity

Return on Investment 9 years (low risk) 17 years (higher risk)

Summary of Findings

Full-Scale Implementation of AirPrex

• Nuisance Struvite and Dewaterability Improvements Project (PAR 1280)

• Project Delivery / Work Packages (WP)• WP 0 – Owner Pre‐procurement• WP 1 – Inground Utility Relocates / Reactor Piers• WP 2 – Balance of Plant

• Anticipated completion Q4 2019

• CNP (AirPrex™ Supplier) Involvement• WP 0 – Equipment• WP 2 – Reactor Fabrication, erection, coating as a subcontractor to WP 2 General Contractor

SCPI

Ductbank

Ductbank

North Gallery

Full-Scale Implementation of AirPrex• Work Package No. 1  ‐ In Construction

North Tunnel

PRF Bldg

Reactor Piers

Full-Scale Implementation of AirPrex

Major WP 2 Components• MgCl2 Storage, Pumping, and Conveyance• Digested Sludge Pumping and Conveyance• New Phosphorus Recovery Facility Bldg.• Recovery Reactor• Stair Tower• Access Manway

• Work Package No. 2  ‐ Award in late Q1/2019

MgCl2 and FeCl3 Storage and Conveyance

FeCl3

FeCl3 Delivery• Two rail spurs• Six 10,000+ gal

Storage Tanks

FeCl3 Uses• Digesters• EPC• Dewatering• Centrate Holding• DAF

867 ‐ PRF

MgCl2 and FeCl3 Storage and Conveyance

FeCl3

MgCl2

Tank Retrofit• Three Storage

Tanks each Chemical

• New Fused HDPE Piping

• New MgCl2 pumps (PC)

867 ‐ PRF

Phosphorus Recovery Facility Construction

Aeration Blowers

Anti‐foam

Struvite Washing and Load Out

Electrical

Struvite Pumping

Stair Tower

North Gallery

Reactor

Reactor Bldg.

Air Piping

Sludge Feed

Sludge Return

Overflow

MgCl2

The Future of Phosphorus Management

The Future of Phosphorus Management

Tertiary Facilities ($300M+)

Flocculation & Sedimentation Complex Filter Complex

Image Rendering from 2013 Facility Plan

Thank You! Questions?dfreedman@mwrd.dst.co.usnathan.brown@stantec.com