The Phosphorus Story: Sustainable Nutrient Management at the Robert W. Hite Treatment Facility Englewood PWO Seminar – February 7, 2019 Dan Freedman, MWRD Nate 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) The Lucifer of Liege by Guillaume Geefs Image by Luc Viatour 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 ‐ John Lemieux, flickr.com 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 How was Phosphorus by Joseph Wright of Derby 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/ 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 Asimov from Asimov on Chemistry
Image source ‐ John Lemieux, flickr.com Image source ‐Image source ‐ https://lystek.com/ https://lystek.com/ Image source – DC Comics 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/ Where is all the Phosphorus?
Image source: BioPandit Where is all the Phosphorus?
Image source – Y. Arthur‐Bertrand, Corbis Image source – Robert Garvey, Corbis
Image source – UNEP
Image source – National Geographic Image source – Elena Elisseeva, Shutterstock
The Phosphorus Cycle (Source: UNEP)
Image source ‐ John Lemieux, flickr.com Image source ‐ https://lystek.com/ Why we care: Water quality issues
Off-line Reservoirs South Platte River
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, Robert W. Hite Treatment Facility (RWHTF) Background Robert W. Hite Treatment Facility (RWHTF)
North Secondary
South Secondary
Solids 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
Combined Heat and Power (Energy) Average ~4.5 MW 38% plant electricity
Biosolids (Nitrogen) Effluent (Water) 107 dry tons/day (2017) Average ~134 mgd 1.64 tons/day plant available nitrogen No District water rights 75% applied on private property 85% of S. Platte 6 months/year 25% applied on METROGRO Farm N Denver Water can reuse up to 120 cfs The District’s Phosphorus Initiative The Regulatory Timeline
Reg. 85 Voluntary Interim Limits? Reg. 31 and Incentive Program Barr/Milton TMDL
TP (mg/L) 1.0 0.7 0.7 0.1 2019 2027 2037 The Phosphorus Initiative
The Problem: Why phosphorus is regulated GOAL To find the most effective and sustainable phosphorus The Cost of Compliance: Financial incentive to figure management approach our way through this through an intensive study phase of biological The Current Plan: phosphorus removal, Environmental and social phosphorus recovery, reasons for innovation watershed impact studies, and tertiary facilities The Current Plan
4 Angles
Liquid stream 1 TP removal
Solids TP 2 removal 3 4 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
• Two‐stage process: anaerobic (release) and aerobic (uptake)
Adapted from WEF MOP 8, 2010 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
MLR Effluent PE
Clarifier Anaerobic Anoxic Aerobic (Anoxic Swing)
100% RAS Liquid Stream Phosphorus Removal: NSEC
• 12 AB‐SC Trains • 4 Sidestream Tanks Gravity Thickeners (CaRRB) • 4 Gravity Thickeners Aeration Tanks (1 of 12) (in the vicinity)
Sidestream Tanks (1 of 4) NSEC Baseline Process Schematic Conventional A2O Process Schematic Alternative Novel Sidestream Configuration Liquid Stream Phosphorus Removal: NSEC
Enhanced 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 Results TP = 0.58 mg-P/L OP = 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
70 100 95 60 Intentional EBPR 40% of Facility in 100% of Facility in Off EBPR EBPR 90 50 85
40 80 75 30 70 Cake solids, % Chemical, lbs/dt 20 65 60 Capture Efficiency, % 10 55 0 50 1‐Jan‐15 11‐Apr‐15 20‐Jul‐15 28‐Oct‐15 5‐Feb‐16 Date
Cake solids, % Polymer, lbs/dt Ferric, lbs/dt Capture Efficiency, % Consequences of EBPR Operation
Primary Treatment Secondary Treatment
Return Activated Sludge (RAS)
Centrifuge
Phosphorus Recovery Centrate (recycle flow) Digester Less than 1% of the flow but 25% of the Phosphorus Load Solids Stream Phosphorus Recovery Effective and Sustainable Phosphorus Management
5 Drivers for Phosphorus Management 1. Phosphorus Recycle Control 2. Biosolids Dewatering 3. Struvite Reduction 4. Phosphorus Index 5. 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 Systems
Intentional Precipitation of Struvite
NH4MgPO4●6H2O Two primary recovery system types Digestate = AirPrex™ Centrate and Stripped WAS Filtrate = WASSTRIP/Ostara
5 in Germany 4 in the Netherlands 1 Belgium 1 in China Phosphorus Recovery Pilot Work
Hypothesis: 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
Nutrient and cation Development Pilot testing WAS sampling and Pilot testing of and utilization release mass balances AirPrex of steady‐ pretreatment across solids precipitation and state process with anaerobic processing recovery model using digestion and Benchtop BioWin sludge Ostara Pearl WAS release PAR 1280 dewaterability pilot tests initiation assessment
2011 2015 Jan June–Aug Aug 2016 Oct 2016– 2015 2016 2016 Jun 2017 How does AirPrex work?
Reactor is aerated which strips the CO2 Magnesium is dosed to the reactor from the reactor and raises the pH causing struvite to precipitate CO2 Mg
Digester effluent is fed to AirPrex effluent, stripped of phosphorus, AirPrex reactor is sent to dewatering centrifuges
AirPrex Centrifuge Biosolids Reactor Anaerobic Digestion Centrate
Struvite settles and is pumped out and cleaned Struvite How does Ostara+WASSTRIP work?
Phosphorus is released into the liquid stream and separated from the biosolids WASSTRIP Process Low P Anaerobic Biosolids Dewatering Phosphorus‐stripped WAS from Thickening Digestion the WASSTRIP reactor is thickened Centrate Caustic is added to High P Centrate from dewatering is high in ammonia and raise the pH is combined with liquid stream from WASSTRIP Caustic
Mg Ostara Pearl effluent, stripped of Magnesium is dosed to the reactor, phosphorus, is recycled back to mainstream causing struvite to precipitate
Struvite Struvite pearls settle and are pumped out and cleaned 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
300 Orthophosphorus 250 Particulate Phosphorus 200
150
100 Phosphorus, mg/L 50
0 Typical Untreated Mg:P Mg:P Mg:P 0.7:1 1.4:1 1.7:1
• 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
30%
25%
20%
15% Digestate AirPrex
Cake Solids, % 10%
5%
0% 012345 Polymer Dose, lb/hr 8.7% reduction in wet tons hauled 17% 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
1000 70%
900 60% 800
700 50%
600 40% 500 30% 400
300
20% Phosphorus Total to Soluble
200 10% P Concentration in Final Released WAS, mg/L WAS, Released Final in Concentration P 100
0 0% 4-Feb 19-Feb 6-Mar 21-Mar 5-Apr 20-Apr
Soluble P Particulate P Soluble to Total Phosphorus Struvite Quantification
Comparison of Methods for Quantifying Struvite in Biosolids • 8% of biosolids is struvite at full‐scale 30% 14% • “Test train” averaged 23% less struvite than “control train” 25% 12%
10% 20%
8% 15%
6%
10% Struvite Reduction in Biosolids 4%
Struvite Concentration in Biosolids, % of Total TS 5% 2%
0% 0% Acid Cake Test Mass Balance on XRD Soluble Mg
Test Control Reduction Key Results from Pilot Studies
Struvite Formation Recycle Control Dewaterability Potential (Modeling) P Recovery System % Reduction in % Increase in % Reduction in Struvite Formation %P Reduction Final Cake Solids Polymer Potential Ostara w/ 30 ‐ 45% Combined ~70 – 90% 7 ‐ 13% Inconclusive WASSTRIP AirPrex 25% 83% 15 ‐ 20% 17% Full-Scale AirPrex Process Complexity Full-Scale Ostara/WASSTRIP Process Complexity Summary of Findings AirPrex Ostara + WASSTRIP
Phosphorus Recycle Reliable Recycle Control Less stable and more complex process Control
Polymer 23% polymer reduction 10% polymer reduction Improve Biosolids Dewaterability Truck Hauls 8% reduction 7% reduction
Digesters 25% reduction digester struvite 30 ‐ 45% reduction digester struvite Struvite Reduction Significant reduction in dewatering Significant reduction in dewatering Dewatering nuisance struvite nuisance struvite Improvement over chemical Improvement over chemical Phosphorus Index sequestration sequestration
Product Recovery 25% ‐ 35% product recovery 70%+ product recovery
Significant increase in equipment and Process Complexity Simple, reliable system system complexity
Return on Investment 9 years (low risk) 17 years (higher risk) Full-Scale Implementation of AirPrex
• Nuisance Struvite and Dewaterability Improvements Project (PAR 1280) Ductbank • Project Delivery / Work Packages (WP) SCPI • 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 Ductbank North Gallery Full-Scale Implementation of AirPrex
• Work Package No. 1 ‐ In Construction
PRF Bldg
Reactor Piers
North Tunnel Full-Scale Implementation of AirPrex • Work Package No. 2 ‐ Award in late Q1/2019
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 MgCl2 and FeCl3 Storage and Conveyance
867 ‐ PRF FeCl3 Delivery • Two rail spurs • Six 10,000+ gal Storage Tanks FeCl3 FeCl3 Uses • Digesters • EPC • Dewatering • Centrate Holding • DAF MgCl2 and FeCl3 Storage and Conveyance
867 ‐ PRF Tank Retrofit • Three Storage Tanks each FeCl3 Chemical • New Fused HDPE Piping MgCl2 • New MgCl2 pumps (PC) Phosphorus Recovery Facility Construction
Struvite Washing Struvite Pumping and Load Out
Anti‐foam Electrical
Aeration Blowers Stair Tower Air Piping Reactor
Sludge Feed MgCl2
Sludge Return Overflow
Reactor Bldg.
North Gallery The Future of Phosphorus Management The Future of Phosphorus Management Tertiary Facilities ($300M+)
Image Rendering from 2013 Facility Plan
Flocculation & Sedimentation Complex Filter Complex
Thank You! Questions? [email protected] [email protected]