4 Angles. Pilot-scale Evaluation of AirPrex for Phosphorus Management. Innovation Program Phosphorus Initiative JTAC 4/22/2017

Transcription

1 Pilot-scale Evaluation of AirPrex for Phosphorus Management JTAC Innovation Program Phosphorus Initiative 4 Angles Liquid stream TP removal Solids TP removal

2 Phosphorus Initiative: Solids Stream Phosphorus Removal GOAL To find the most effective and sustainable phosphorus management approach through an intensive study phase of phosphorus recovery technologies under the phosphorus initiative Internal Sidestreams Primary Treatment Secondary Treatment Return Activated Sludge (RAS) Centrifuge Centrate (recycle flow) Digester Phosphorus Recovery Less than 1% of the flow but 25% of the Phosphorus Load 4 2

3 Phosphorus Recovery Pilot Work DIGESTATE RECOVERY PILOT WORK 5 Effective and Sustainable Phosphorus Management 5 Measures for Success 1. Break the phosphorus recycle loop 2. Biosolids dewatering costs 3. Struvite scale issues for O&M 4. Phosphorus loading on soils 5. Recovery of a finite resource 1 lb of phosphorus equates to 8 lbs of struvite. 7, lbs of phosphorus enter the RWHTF each day! 6 3

4 AirPrex Pilot Testing Hypothesis: Will create a controlled environment to precipitate struvite from District solids to simultaneously address: Break P-Recycle Loop Biosolids Dewatering Struvite Issues Phosphorus Index Product Recovery 7 Proven Innovation Full Scale Installations: 5 in Germany 4 in the Netherlands 1 Belgium 1 in China Other US Pilot Investigations: Miami, FL Stevens Point, WI Fox River, IL Fond du Lac, WI Meridian, Idaho Pima County, AZ 8 4

5 How Does AirPrex Work? Digester effluent is fed to AirPrex reactor Reactor is aerated which strips the CO2 from the reactor and raises the ph CO2 Anaerobic Digestion AirPrex Magnesium is dosed to the reactor causing struvite to precipitate Mg AirPrex effluent, stripped of phosphorus, is sent to dewatering centrifuges Biosolids Centrifuge Centrate Struvite settles and is pumped out and cleaned Struvite 9 AirPrex Pilot Pilot onsite from June 6 th through August 3 rd Reactor operated continuously at a flow of 11 gpm Centrisys CS1-4 centrifuge operated 6 8 hours per day Mg:P molar dosing ratio varied between.7:1 1.7:1 1 5

6 Sampling and Testing Protocol Weekly water quality analyses Daily dewatering analyses Over 3 water and solids analyses! Parameter Reactor Centrifuge Influent Underflow Effluent Influent Centrate Cake ph Temperature Total Solids (TS) Volatile Solids (TVS) Total Ca, Mg, Fe, K, Na Dissolved Ca, Mg, Fe, K, Na Orthophosphate Total Phosphorus Water Extractable Phosphorus Acid cake Struvite Test Ammonium Conductivity Total Alkalinity COD EPS 11 Modeling Thermodynamic modeling to model nuisance struvite formation potential upstream and downstream of the digesters and recovery technologies Struvite Tool (Office of Water Programs, Sacramento, California) Visual Minteq (KTH, Sweden) BioWin Effects of reduction in recycle phosphorus would have on Bio P performance 12 6

7 Driver 1: Phosphorus Recycle Control Phosphorus, mg/l Typical Untreated Mg:P.7:1 Orthophosphorus Mg:P 1.4:1 Particulate Phosphorus Mg:P 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 13 Driver 1: Phosphorus Recycle Control Secondary Effluent Soluble P, mg/l No Recovery Secondary Effluent Soluble P Digestate Centrate Recycle Soluble P Centrate Recycle Soluble P, mg/l Reducing recycle soluble phosphorus concentrations from 4 mg P/L to 3 mg P/L would result in a decrease in secondary effluent OP 14 7

8 Driver 2: Dewatering Performance Chemical Pounds per Dry Ton / Cake %TS % of Facility 1% of Facility in EBPR Intentional EBPR Turned Off 5. Jan 15 Feb 15 Apr 15 May 15 Cake %TS Jul 15 Sep 15 Oct 15 Polymer lbs/dt Fe lbs/dt Dec 15 Feb 16 Capture Efficiency Mar 16 May Capture Efficiency (%) While more economically sustainable than chemical precipitation, Bio P does have significant impacts on full scale operations Driver 2: Dewatering Performance Cost Centers: $ Polymer consumption $ Wet mass of biosolids for hauling and dispersal Tracked cake total solids and polymer consumption Polymer dose varied in 5 active pound/dry ton increments Higher average centrifuge hydraulic pressures for AirPrex treated 16 8

9 Solids Correction Dry Mass MgCl 2 NH4MgPO4 6H2O Generated in AirPrex Total solids Digestate Airprex Apx Eff Centrifuge Biosolids f b Product f p Centrate f c f p + f c + f b = 1 Fraction of struvite in biosolids matrix f b Fraction of struvite fines in centrate f c Fraction of struvite that settles and is pumped out as product f p 17 Solids Correction Dry Mass Acidification tests performed on dewatered biosolids to estimate total struvite Untreated cake struvite content ~5.3% AirPrex treated cake struvite content ~11.7% ~6.4% increase in struvite - 8% retention in cake Digestate AirPrex Apx Eff Centrifuge Biosolids f b ~8% Product f p Centrate ~2% f c ~ Assumed negligible based on centrate TP at optimal operation 18 9

10 Solids Correction NH 4 MgPO 4 6H 2 O Ammonia and water evaporate from struvite in the temperature range of 55 o C to 25 o C NH 4 + 6H 2 O = 51.4% of struvite mass Traditional TS concentration test measures a portion of struvite mass as water, underestimating total solids in sample This affects metrics traditionally used for assessing sludge dewaterability Solids Correction Method Corrected TS concentration measurement Ongoing work to determine actual extent of struvite evaporation Assumed 51.4% loss of struvite due to evaporation Digestate TS correction: % % AirPrex effluent TS correction: % % Wet tons calculation: % 2 1

11 AirPrex - Dewaterability Complete Dataset Cake % Total Solids (Uncorrected for Struvite) 29% 27% 25% 23% 21% 19% 17% 15% AirPrex Effluent Digestate data points analyzed Polymer Dose (Active Pounds per Hour) 8.9 % reduction in wet tons hauled 21 AirPrex Dewaterability Sorted - 1 gpm, 9% OP removal Cake % Total Solids (Uncorrected for Struvite) 29% 27% 25% 23% 21% 19% 17% 15% AirPrex Effluent Polymer Dose (Active Pounds per Hour) Digestate 61 data points analyzed 12.44% reduction in wet tons hauled 22 11

12 AirPrex Dewaterability Paired Dataset CAKE % TOTAL SOLIDS (UNCORRECTED FOR STRUVITE) 29% 27% 25% 23% 21% 19% 17% 15% AirPrex Digestate POLYMER DOSE (ACTIVE POUNDS PER HOUR) 2 data points analyzed 8.7% reduction in wet tons hauled 17.6% decrease in polymer consumption 23 Sensitivity Analysis of Assumptions Assumptions on product recovery and evaporated TS mass do impact the estimation of wet tons hauled per day 24 12

13 AirPrex Biosolids Dewatering Costs 8.7% reduction of biosolids hauled Untreated Biosolids 21 Hauled Truckloads After AirPrex Treatment 19 Hauled Truckloads Difference of 2 truckloads per day or 73 truckloads per year! Approximately 15 2% decrease in polymer use 25 Driver 3: Nuisance Struvite Reduction 14 Reduced Mg Feed 8 Reduced Mg Feed Pre AirPrex, Post AirPrex, and Centrate Struvite Production, lb/d /9 6/19 6/29 7/9 7/19 7/29 Untreated Digestate Airprex Treated Digestate Pre AirPrex, Post AirPrex, and Centrate Struvite Production, lb/d /9 6/19 6/29 7/9 7/19 7/29 Untreated Centrate Treated Centrate Significant reduction of struvite mass predicted between untreated and AirPrex treated 26 13

14 Driver 3: Digester Struvite Reduction Struvite Production in Digesters, ppd P 2, 15, 1, 5, No Recovery AirPrex Treated Modeling efforts in BioWin show a reduction in struvite production from 18, lb/d to 13, lb/d with digestate phosphorus recovery 27 Driver 5: Product Recovery 15 tons of phosphorus recovered annually Potential distribution Composters Fertilizer manufacturers Potential uses Turf grass Alfalfa 28 14

15 Driver 5: Product Recovery Struvite Product - Metals Analysis Pollutant "High Quality" Pollutant Concentration Limits (mg/kg) Pilot MAP Results (ppm) Lab Analysis from Previous Pilot (ppm) Arsenic 41 BDL 2 Cadmium 89 BDL BDL Copper Lead Mercury Molybdenum 1 < 75.8 Nickel 42 BDL BDL Selenium 1 BDL Zinc There is currently no limit for Molybdenum for High Quality while rules are awaiting EPA investigation. Ceiling limit is 75 ppm. 2. Levels were below detection limit Struvite product produced by Airprex is well below limits of high quality pollutant concentrations Driver 5: Product Recovery Struvite Product - Pathogen Testing Class A: maximum density of fecal coliform < 1 MPN per gram total solids (dry weight basis) 2 Samples were taken for pathogen testing using fecal coliforms July 19: 1 MPN/g TS August 2: Investigate fecal coliform with drying time Fecal Coliforms Drying Test (MPN/g TS) Sample Date Initial 24hr 48hr 8/2/ Current testing of product shows Airprex struvite may be within Class A categorization for biosolids 15

16 AirPrex Pilot Testing Results Phosphorus Recycle Control Reliable OP and TP Reduction Biosolids Dewaterability Polymer ~17% polymer reduction Truck Hauls ~8.7% reduction hauled mass Struvite Reduction Phosphorus Index Product Recovery Digesters Dewatering ~25% reduction digester struvite Significant reduction in dewatering nuisance struvite Accumulation of phosphorus in biosolids 25% 35% product recovery 31 Phosphorus Recovery Pilot Work PHOSPHORUS WAS STRIPPING AND CENTRATE RECOVERY PILOT WORK 32 16

17 Ostara Pearl First installation 28 Calgary Edmonton Saskatoon 33 How Ostara+WASSTRIP Works WASSTRIP Process Phosphorus stripped WAS from the WASSTRIP reactor is thickened Thickening Low P Anaerobic Digestion Dewatering Biosolids Caustic is added to raise the ph Caustic Mg High P Centrate Phosphorus is released into the liquid stream and separated from the biosolids Ostara Pearl effluent, stripped of phosphorus, is recycled back to mainstream Centrate from dewatering is high in ammonia and is combined with liquid stream from WASSTRIP Struvite Magnesium is dosed to the reactor, causing struvite to precipitate Struvite pearls settle and are pumped out and cleaned 34 17

18 Phosphorus Stripping Pilot Test Pilot October 216 to ongoing Evaluate features and benefits of WAS phosphorus stripping Dewatering performance Nuisance struvite reduction Batch WAS phosphorus stripping reactor with thickening press 35 Phosphorus Stripping Pilot Test Control Train receives TWAS, test train receives stripped TWAS Two separate activated sludge trains allows for centrate recycle to be fed to North; control train reflects bio P with recycle control 36 18

19 Nuisance Struvite and Dewaterability Improvements Project Secondary Effluent Soluble P, mg/l No Recovery Digestate Centrate & Stripped Filtrate Secondary Effluent Soluble P <.1 Centrate Recycle Soluble P Centrate Recycle Soluble P, mg/l 37 Digester Nuisance Struvite Production 2, Struvite Production in Digesters, lb/d 16, 12, 8, 4, 25% No Recovery Digestate Centrate & Stripped Filtrate Method of determination: Mass balance on measured analytes BioWin modeling XRD analysis 45% Anaerobic Digestion 38 19

20 Biosolids Production 5 Biosolids Production, tpd No Recovery Digestate Centrate & Stripped Filtrate Dry Mass, dtpd Total Mass, wtpd 39 Preliminary Pilot Testing Results Phosphorus Recycle Control Digestate Reliable OP and TP reduction Phosphorus Stripping Assessing need for lamella plate settlers Biosolids Dewaterability Polymer ~17% polymer reduction Awaiting additional testing Truck Hauls ~8.7% reduction hauled mass ~6.6% reduction hauled mass Struvite Reduction Digesters Dewatering ~25% reduction digester struvite Significant reduction in dewatering nuisance struvite due to limiting OP ~55% reduction digester struvite Significant reduction in dewatering nuisance struvite due to limiting Mg Phosphorus Index Improvement over chemical sequestration Improvement over chemical sequestration Product Recovery 25% 35% product recovery 7%+ product recovery 4 2

21 Next Steps Complete WAS phosphorus stripping digester pilot Complete Business Case Evaluation for phosphorus recovery systems Select a path forward for near term implementation 41 21