Applying Extractive Nutrient Recovery for Managing Phosphorus in Sidestreams and Biosolids

Transcription

1 Applying Extractive Nutrient Recovery for Managing Phosphorus in Sidestreams and Biosolids Wendell Khunjar PhD, PE May 11, 2017

2 Embracing the new resource management paradigm Source water Drinking Water Treatment Water Water Resource Recovery Facility Wastewater Treatment Plant Biosolids Nutrient Products Wastewater Generation Other products e.g., bioplastics, cellulose Energy

3 Nutrient management has historically assumed unlimited energy and resources 12 kwh/kg N Haber Bosch Process N 2 NH 3 Phosphorus mining Apatite ortho-p Non-Bioavailable Nutrient 0.9 to 2.3 kwh/kg N Treatment Bioavailable Nutrient Nitrogen Gas Apatite (P) Potash Ore (K) Low nutrient content water

4 Extractive recovery is an effective nutrient management strategy Haber Bosch Process N 2 NH 3 Phosphorus mining Apatite ortho-p Non-Bioavailable Nutrient Treatment Bioavailable Nutrient Extractive Nutrient Recovery Recovery facilitates Reuse Offsets Energy Demand Offsets Resource Demand

5 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

6 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

7 Magnesium Struvite (NH 4 MgPO 4 6H 2 O) Most commonly recovered P product at WRRFs Formation at ph > 8 Characteristic Magnesium struvite Monoammonium phosphate Chemical formula MgNH 4 PO 4-6H 2 O NH 4 H 2 PO 4 (NH 4 ) 2 HPO 4 Average price/metric tonne $100 - $600 $570 - $615 $420 - $680 Grade (N-P-K) Water solubility at 20 C Insoluble g/l g/l 588 g/l Application description Typical application rates* Spread on soil Normally spread or mixed in soil 255 lb/a 142 lb/a 160 lb/a Diammonium phosphate Normally spread or mixed in soil

8 Magnesium Struvite Recovery Concept Solids Stream Influent Headworks Primary Clarification BNR Secondary Clarification Disinfection Effluent Septage WAS Thickener Anaerobic Digestion Thickener Filtrate Nutrient Recovery Option Struvite Dewatering Filtrate Dewatering Biosolids

9 Sludge liquor Magnesium Struvite Recovery Concept Solids Stream Airprex Nuresys Process limits MgCl 2 Polymere Digested sludge Air AirPrex reactor Struvite Buffer tank Washwater Centrifuge Dewatered sludge Back charge to WWTP Separation

10 Magnesium Struvite Recovery Concept Liquid Stream Influent Headworks Primary Clarification BNR Secondary Clarification Disinfection Effluent Septage WAS WAS release Thickener Anaerobic Digestion Thickener Filtrate Nutrient Recovery Option Dewatering Filtrate Dewatering Biosolids Struvite

11 Magnesium Struvite Recovery Concept Liquid Stream Name of Technology Pearl 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)

12 Magnesium Struvite Recovery What Have We Learned? 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

13 Magnesium Struvite Recovery What Have We Learned? PS WAS release Thickener Filtrate Nutrient Recovery Option Thickener Dewatering Filtrate WAS Anaerobic Digestion Nutrient Recovery Option Dewatering Biosolids If goal is to minimize struvite in digester o o Redirect P, Mg and Ca around digester Precipitate P, Mg and Ca before digester If goal is to minimize struvite downstream of digester o o Redirect P, Mg and Ca around digester Precipitate P, Mg and Ca after digester All processes still require provisions for acid cleaning of lines

14 Magnesium Struvite Recovery What Have We Learned? TP removal/recovery is variable and needs to be considered in evaluation Account for formation and capture of struvite fines Dewatering Influent Effluent Recovery Reactor Ortho-P removal/recovery TP removal/recovery

15 Magnesium Struvite Recovery What Have We Learned? Dewaterability benefits varies per technology and is site specific Pilot work is necessary to quantify in advance of installation Technology Site Polymer Demand Reduction (%) Cake Solids % Increase Ostara + WASSTRIP Clean Water Services?? 2.5 F. Wayne Hill 22 1 Moenchengladbach 15 3 Berlin-Wassmannsdorf 20 3 to 4 Airprex Echten 15 3 Amsterdam-West 25 3 Salzgitter 15 2

16 F. Wayne Hill Water Resource Reclamation Facility

17 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

18 Process Flow Diagram

19 Tertiary Process Flow Diagram

20 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

21 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 Raw INF Grit tank YR Sludge Grit BRB A1 BRB C3+C4 BRB A2 BRB B1 BRB B2 BRB C5+C6BRB C7 BRB C8 BRB C1+C2 Tertiary Clarifier Metal Salt Tertiary Caustic Influent (SV)7 Sec Scum Influent (SV)17 Combined Filter Effluent - Pre O3 Infl Anaerobic Digesters Bioreactor21 Dewatered Sludge

22 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

23 How does WASSTRIP help? Influent Primary Clarification P-Release Tank 5 Stage BNR Secondary Clarification RAS To Tertiary Treatment PS Rotary Drum Thickening Anaerobic Digestion WAS WASSTRIP Dewatering Centrifuges Nutrient Recovery Filtrate EQ Centrate EQ MgCl 2 NaOH Nutrient Recovery Cake Struvite Pellets Filtrate / Centrate

24 How does WASSTRIP help? + acetate (100% VFA) + PSL (some VFA) + WAS only

25 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 Year 1 Capital Costs $ 13.75M $ 13.08M $ 13.46M $ 4.60M $ 4.60M $ 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

26 Nutrient Recovery Facility WASSTRIP + Recovery startup on 7/7/15

27 WASSTRIP Tank Inner tank: 98,000 gallons Constant Volume 1 2 hrs HRT Outer tank: 280,000 gallons Elevation Varies < 6 hours HRT

28 WASSTRIP Modifications PS 2.5% TSS WAS 1.5% TSS To RDTs Variable level here to control HRT and wide spot for thickening

29 Observations from 1+ Year Operations P-release working well, P levels as expected No supplemental Mg required Fines loss experienced TP removals are improving

30 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

31 Robert W. Hite Treatment Facility

32 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

33 Nutrient recovery is a component of the phosphorus initiative 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! Slide courtesy MWRD

34 Nutrient Recovery Concepts Applicable to RWHTF 220 mgd facility with Bio-P PS WAS WAS release Thickener Filtrate Thickener Anaerobic Digestion Nutrient Recovery Option Pre-dewatering recovery Recovery from digested sludge matrix e.g., Airprex Nutrient Recovery Option Dewatering Filtrate Dewatering Post-dewatering recovery Recovery from filtrate and centrate e.g., Ostara + WASSTRIP Biosolids

35 Project Approach Struvite Recovery from Digested Sludge OR Struvite Recovery from WAS P-release Filtrate and Centrate Driver Break recycle loop Biosolids dewatering costs Struvite scaling Phosphorus loading on soils Product recovery Data to support Pilot (Ostara and Airprex), WAS release testing, Modeling Airprex Pilot WAS Release Digester Pilot Modeling Pilot (Airprex) Modeling Pilot (Ostara and Airprex) Modeling

36 Additional considerations for RWHTF Impact of P recovery on Deammonification P recovery downstream deammonification Applicable to post-dewatering option only Centrate Slipstream Recovery Reactor Centrate DMX Return to plant Pre-thickened WAS Release Filtrate P product

37 Additional considerations for RWHTF Impact of THP Thickened Primary Solids 5.1% TS Dilution water as necessary Digestion Waste Activated Sludge Pre-thickening WAS Release WAS dewatering Thermal Hydrolysis 0.7% TS 3.0% TS 16 to 18% TS 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

38 Concluding Thoughts

39 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

40 Wendell Khunjar 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)