Innovative Phosphorus Control to Turn Struvite Headaches into Increase Revenue Peter Schauer, Rob Baur, Brett Laney PNCWA 2010
Contents Where does the phosphorus go in BPR? How can WASSTRIP improve recovery? Benchtop Testing but can it be modeled? Pilot Testing What did we learn? 2
Phosphorus Removal in BPR Plants Phosphorus accumulates in the cell mass and is removed with the daily waste activated sludge Anaerobic solids processing release of P, Mg, and N in recycle streams Some metal phosphate precipitation in sludge Struvite precipitation in sludge Remaining released Mg, P and ammonia in return streams 20 30% of the phosphorus load on the activated sludge process is in the recycle streams 3
Struvite recovery in return streams Primary Treatment (Sludge Settles to Bottom) Secondary Treatment (Bacteria Break Down Organics) Fermentor Sludge Thickener Sludge Thickening Anaerobic Digestion Chemical Sludge 90% Phosphate Removed 20% Ammonia Removed Ostara Reactor Dewatering Centrifuge Solids to Land Application Crystal Green R Slow Release Struvite Fertilizer Pellets 5-28-0 10%MG 4
Patent Pending WAS and VFArich fermentate combined in release tank Diverted to recovery process in liquid after thickening Less favorable conditions for struvite in digesters 5 US patent 7,604,740 that protect the WASSTRIP system and process technological advances, and world-wide patent rights are reserved to Clean Water Services, Oregon, USA.
What do we need to know about WASSTRIP Design information for stripping tank How much VFA needed to strip phosphorus? The rate of P and Mg release in the tank? Production of ammonia? Impact on downstream processes? Can it be modeled with BioWin? 6
Previous Studies Phosphorus and Magnesium Release Ratios Truckee Meadows WWTP Empire WWTP 7
Truckee Meadows WWTP Release during endogenous fermentation and when adding VFA Relatively fast initial release (<16 hours) Short SRT BPR plant Release Ratio, Mg/P 0.5 0.4 0.3 0.2 0.1 0.0 Endogenous With Acetic Acid 0 20 40 60 80 Time, hours Phosphorus Conc, mg/l 160 140 120 100 80 60 40 20 0 Endogenous With Acetic Acid 0 20 40 60 80 Time, hours Magnesium Conc, mg/l 50 40 30 20 10 0 Endogenous With Acetic Acid 0 20 40 60 80 Time, hours 8
Empire WWTP Endogenous release Achieved >50% release Steady release for 70 hours Phosphorus Conc, mg/l 400 350 300 250 200 150 100 50 0 Test 1 Test 2 Test 3 0 50 100 150 70% Time, hours Release as % of TP 60% 50% 40% 30% 20% 10% Test 1 Test 2 Test 3 0% 0 50 100 150 Time, hours 9
Laboratory Test Anoxic conditions maintained using closed containers Two tests using VFA addition One endogenous release test 10
Endogenous Release Tests 0.30 Mg : P release consistent 0.25 0.20 0.15 0.10 Phosphorus release from 0.05 PAO up to 48 hours 0.00 Release Ratio, mg Mg / mg P 0 20 40 60 80 100 120 Time, hours 200 250 Concentration, mg/l 180 160 140 120 100 80 60 40 20 0 NH3-N VFA 0 24 48 72 96 120 Time, hours P Released, mg/l 200 150 100 50 0 0 24 48 72 96 120 Time, hours o-po4 Mg 11
VFA-Enhanced Release Round 1 Results from P were inconsistent Result from Mg showed little additional release with more VFA 140 40 P per L of WAS, mg 120 100 80 60 40 20 0 75 mg VFA / L RAS 186 mg VFA / L RAS 374 mg VFA / L RAS 571 mg VFA / L RAS Mg per L of WAS, mg 35 30 25 20 15 10 5 0 75 mg VFA / L RAS 186 mg VFA / L RAS 374 mg VFA / L RAS 571 mg VFA / L RAS 0 50 100 150 200 Time, min 0 50 100 150 200 Time, min 12
VFA-Enhanced Release Round 2 Very little difference in release rates based on VFA addition 160 35 Conc, mg OP/L of WAS 140 120 100 80 60 40 20 0 119 mg VFA/L RAS 185 mg VFA/L RAS 278 mg VFA/L RAS 417 mg VFA/L RAS 0 100 200 300 Time, min Conc, mg Mg/L of WAS 30 25 20 15 10 5 0 119 mg VFA/L RAS 185 mg VFA/L RAS 278 mg VFA/L RAS 417 mg VFA/L RAS 0 100 200 300 Time, min 13
VFA-Enhanced Release Summary of VFA to VSS ratios Round 1 mg VFA / mg VSS Round 2 mg VFA / mg VSS Test 1 0.010 0.015 Test 2 0.025 0.023 Test 3 0.051 0.035 Test 4 0.077 0.051 14
Modeling Results Endogenous Anaerobic hydrolysis from 0.5 0.025 300 300 P Concentration, mg/l 250 200 150 100 50 Lab Data Modeling Data VFA Concentration, mg/l 250 200 150 100 50 Lab Data Modeling Data 0 0 50 100 150 Time, hours 0 0 50 100 150 Time, hours 15
Modeling Results VFA-Enhanced PAO Sequestration rate from 6 day -1 to 0.45 day -1 120 VFA sequestration half-saturation rate was changed from 5 mg/cod/l to 0.03 mg COD/L Magnesium Concentration, mg/l 100 80 60 40 20 0 Test #1 Model #1 Test #2 Model #2 Test #3 Model #3 Test #4 Model #4 0 100 200 300 Time, min Phosphorus 16
Implications of Modeling 0.006 0.0012 P release Rate per VSS, hr -1 0.005 0.004 0.003 0.002 0.001 0.000 Phosphorus Release Magnesium Release 0.00 0.02 0.04 0.06 0.08 0.10 0.0010 0.0008 0.0006 0.0004 0.0002 0.0000 Mg release Rate per VSS, hr -1 VFA / VSS 17
Pilot Test Complete-Mix Continuous Operation Waste Activated Sludge Fermenter Thickener Overflow 18
Pilot Test Operation Started in April 2010 Plant shifted into Nutrient Removal season Alum addition Fermenter start-up Adjusted FTO and WAS flow Detention Time Ratio of VFA to PAOs 19
Pilot Test Results Shift between bio-p and chem-p Fermenter Operation Generally release 20-30% of the TP Reasonable detention time Above 0.15 mg VFA/mgVSS 20
Pilot Test Results Percent Phosphorus Release versus VFA/VSS Ratio % Phosphorus Release 45% 40% 35% 30% 25% 20% 15% 10% 5% 0% 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 VFA/VSS Ratio, m g/m g Residence Time < 8 hr Residence Time > 8 hr 21
Pilot Test Results Percent Phosphorus Release verus Residence Time % Phosphorus Release 45% 40% 35% 30% 25% 20% 15% 10% 5% 0% VFA/VSS < 0.013 0.020 > VFA/VSS > 0.013 VFA/VSS > 0.02 0 2 4 6 8 10 12 14 16 Residence Time, hr 22
Implications for Durham AWWTF Dry Weather Wet Weather Scenario 1 Scenario 2 Scenario 3 WAS Flow, mgd 0.34 0.42 0.42 0.42 FTO Flow, mgd 0.58 0.58 0.58 0.58 FTO VFA Concentration, mg/l 437 203 100 100 FTO used for WASSTRIP, % 25 50 100 50 HRT, hours 10.2 7.0 5.0 7.0 mg VFA / mg VSS 0.026 0.021 0.021 0.010 23
Implications for Durham AWWTF Dry Weather Wet Weather Scenario 1 Scenario 2 Scenario 3 FTO VFA, mg/l 437 203 100 100 FTO for WASSTRIP, % 25 50 100 50 Phosphorus Release, lb/d 314 334 334 147 Magnesium Released, lb/d 103 103 103 21 Potential Struvite, lb/d 1,120 1,120 1,120 224 24
Phosphorus Mass Balance Typical Operation Influent 1,400 lbs/d Liquid Treatment Process Effluent 30 lbs/d 500 lbs/d Solids Treatment Process Sludge 1,370 lbs/d 25
Phosphorus Mass Balance Phosphorus Recovery Liquid Treatment Process Effluent 30 lbs/d 200 lbs/d Solids Treatment Process Struvite (as P) Sludge 385 lbs/d 985 lbs/d 26
Phosphorus Mass Balance WASSTRIP Influent 1,400 lbs/d Liquid Treatment Process Effluent 30 lbs/d 200 lbs/d Solids Treatment Process Struvite (as P) Sludge 385 lbs/d 985 lbs/d 25% reduction in Mg Addition 27
Conclusions Appears to be an upper limit on impact that VFAs can have on phosphorus release rates. Release rates anticipated using existing tankage will be adequate for Phosphorus and Magnesium release using WASSTRIP Chem P versus Bio P has a large influence 28
Next Steps Determine the overall impact to the treatment plant Overall economics Impacts from ph Impact on Dewaterability 29
B&V - 30 Discussion