Innovative Phosphorus Control to Turn Struvite Headaches into Increase Revenue. Peter Schauer, Rob Baur, Brett Laney PNCWA 2010

Transcription

1 Innovative Phosphorus Control to Turn Struvite Headaches into Increase Revenue Peter Schauer, Rob Baur, Brett Laney PNCWA 2010

2 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

3 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

4 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 %MG 4

5 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.

6 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

7 Previous Studies Phosphorus and Magnesium Release Ratios Truckee Meadows WWTP Empire WWTP 7

8 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 Endogenous With Acetic Acid Time, hours Phosphorus Conc, mg/l Endogenous With Acetic Acid Time, hours Magnesium Conc, mg/l Endogenous With Acetic Acid Time, hours 8

9 Empire WWTP Endogenous release Achieved >50% release Steady release for 70 hours Phosphorus Conc, mg/l Test 1 Test 2 Test % Time, hours Release as % of TP 60% 50% 40% 30% 20% 10% Test 1 Test 2 Test 3 0% Time, hours 9

10 Laboratory Test Anoxic conditions maintained using closed containers Two tests using VFA addition One endogenous release test 10

11 Endogenous Release Tests 0.30 Mg : P release consistent Phosphorus release from 0.05 PAO up to 48 hours 0.00 Release Ratio, mg Mg / mg P Time, hours Concentration, mg/l NH3-N VFA Time, hours P Released, mg/l Time, hours o-po4 Mg 11

12 VFA-Enhanced Release Round 1 Results from P were inconsistent Result from Mg showed little additional release with more VFA P per L of WAS, mg 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 mg VFA / L RAS 186 mg VFA / L RAS 374 mg VFA / L RAS 571 mg VFA / L RAS Time, min Time, min 12

13 VFA-Enhanced Release Round 2 Very little difference in release rates based on VFA addition Conc, mg OP/L of WAS mg VFA/L RAS 185 mg VFA/L RAS 278 mg VFA/L RAS 417 mg VFA/L RAS Time, min Conc, mg Mg/L of WAS mg VFA/L RAS 185 mg VFA/L RAS 278 mg VFA/L RAS 417 mg VFA/L RAS Time, min 13

14 VFA-Enhanced Release Summary of VFA to VSS ratios Round 1 mg VFA / mg VSS Round 2 mg VFA / mg VSS Test Test Test Test

15 Modeling Results Endogenous Anaerobic hydrolysis from P Concentration, mg/l Lab Data Modeling Data VFA Concentration, mg/l Lab Data Modeling Data Time, hours Time, hours 15

16 Modeling Results VFA-Enhanced PAO Sequestration rate from 6 day -1 to 0.45 day VFA sequestration half-saturation rate was changed from 5 mg/cod/l to 0.03 mg COD/L Magnesium Concentration, mg/l Test #1 Model #1 Test #2 Model #2 Test #3 Model #3 Test #4 Model # Time, min Phosphorus 16

17 Implications of Modeling P release Rate per VSS, hr Phosphorus Release Magnesium Release Mg release Rate per VSS, hr -1 VFA / VSS 17

18 Pilot Test Complete-Mix Continuous Operation Waste Activated Sludge Fermenter Thickener Overflow 18

19 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

20 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

21 Pilot Test Results Percent Phosphorus Release versus VFA/VSS Ratio % Phosphorus Release 45% 40% 35% 30% 25% 20% 15% 10% 5% 0% VFA/VSS Ratio, m g/m g Residence Time < 8 hr Residence Time > 8 hr 21

22 Pilot Test Results Percent Phosphorus Release verus Residence Time % Phosphorus Release 45% 40% 35% 30% 25% 20% 15% 10% 5% 0% VFA/VSS < > VFA/VSS > VFA/VSS > Residence Time, hr 22

23 Implications for Durham AWWTF Dry Weather Wet Weather Scenario 1 Scenario 2 Scenario 3 WAS Flow, mgd FTO Flow, mgd FTO VFA Concentration, mg/l FTO used for WASSTRIP, % HRT, hours mg VFA / mg VSS

24 Implications for Durham AWWTF Dry Weather Wet Weather Scenario 1 Scenario 2 Scenario 3 FTO VFA, mg/l FTO for WASSTRIP, % Phosphorus Release, lb/d Magnesium Released, lb/d Potential Struvite, lb/d 1,120 1,120 1,

25 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

26 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

27 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

28 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

29 Next Steps Determine the overall impact to the treatment plant Overall economics Impacts from ph Impact on Dewaterability 29

30 B&V - 30 Discussion