Optimizing a Pure Oxygen Wastewater Treatment Plant Randal W. Samstag, PE, BCEE CarolloTemplateWaterWave.pptx Principal Technologist Outline • HPO Basics • HPO Upgrade Case Studies – West Point WWTP Pilot Plant – Bellingham Post Point WWTP CarolloTemplateWaterWave.pptx • Conclusions 2 The High Purity Oxygen (HPO) Process • Invented by Union Carbide Corp. in early 1970s • “High Purity Oxygen” CarolloTemplateWaterWave.pptx – Cryogenic Plant (95 – 99%) – Pressure Swing Adsorption (88 – 93%) – Vacuum Swing Adsorption (88 – 93%) 3 HPO Upgrade Case Studies • West Point WWTP HPO Pilot Plant • Bellingham Post Point WWTP CarolloTemplateWaterWave.pptx – HPO Modifications Project – Nitrogen Removal Upgrades 4 CarolloTemplateWaterWave.pptx West Point WWTP Pilot Plant 5 West Point HPO Test Facility • 4-stage HPO pilot facility (Lotepro) – 20-30 gpm – SRT: 1-2 days • Mar - Dec 1988 • 3 modes evaluated: – Plug Flow – Contact/Reaeration CarolloTemplateWaterWave.pptx – Anaerobic Selector w/ Plug Flow Wef2003Samstag.ppt CarolloTemplateWaterWave.pptx HPO Test Facility Schematic Wef2003Samstag.ppt 7 CarolloTemplateWaterWave.pptx SVI, mL/g Settleability Data from HPO Test Facility 900 800 700 600 500 400 300 200 100 0 Min Ave Max 8 The Culprits • Microscopic evaluation found filaments – Thiothrix II – Type 021N CarolloTemplateWaterWave.pptx • Sulfur oxidizing aerobes Wef2003Samstag.ppt Influence of SRT and Temp on PAO Washout Aerobic SRT (Days) Nitrifier Washout PAO Washout 14 12 10 EBPR and Nitrification 8 6 EBPR 4 2 No EBPR 0 CarolloTemplateWaterWave.pptx Nocardia Washout 10 15 20 25 30 Temperature (Degrees C) Mammais and Jenkins, 2001 PAO Have Higher Floc Density • PAO form Neisser-positive cell clumps • Compact flocs settle faster than highly filamentous sludges CarolloTemplateWaterWave.pptx • Bio P organisms have a higher density than typical zoogleal or filamentous organisms Schuler and Jang, 2007 CarolloTemplateWaterWave.pptx Bellingham Post Point WWTP 12 The Bellingham Post Point WWTP • 20 mgd capacity HPO activated sludge plant • 10 ton/day pressure swing absorption HPO system CarolloTemplateWaterWave.pptx • Three HPO basin stages Settleability History • Average SVI of 170 mL/g from 1999 to 2004 • Filament caused settleability problems – Type 1701 (Low DO) – Type 1863 (Low SRT) CarolloTemplateWaterWave.pptx • Periodically high VFA feed from influent sewer and from solids dewatering operation 3-4 days per week leading to slime bulking 14 Idea for Improvement – Anaerobic Selector • Provide zone for uptake of VFA • Encourage growth of phosphorus accumulating organisms (PAO) • Increasing population distribution of PAO increases floc density CarolloTemplateWaterWave.pptx • PAO have a compact morphology and higher density than other typical activated sludge bacteria (Schuler and Jenkins) • Experience at three other HPO plants (SE Essex SD, Hyperion, SE San Francisco) 15 The HPO Modifications Project • Improve settleability by converting first stage to anaerobic selector • Replace aerators to improve oxygen transfer • Add variable speed drives to mixers to improve control and save power CarolloTemplateWaterWave.pptx • Selectors added capacity for interim operation until major capacity upgrade could be completed 16 SVI History Before and After Conversion to Anaerobic Selector Comparison of SVI and MCRT 350 3.5 Aerobic CarolloTemplateWaterWave.pptx 3.0 250 2.5 200 2.0 150 1.5 100 1.0 50 0 07/17/05 Anaerobic SVI 7/Avg ml/g 12/14/05 0.5 MCRT 7/Avg Days 05/13/06 10/10/06 03/09/07 08/06/07 01/03/08 0.0 06/01/08 MCRT (Days) SVI (mL/g) 300 The Original Aerators • Conventional conically shaped low speed aerators with bottom impellors CarolloTemplateWaterWave.pptx • Estimated standard aerator efficiency (SAE) 3.2 pounds of oxygen per hour per horsepower New Aerators • m2t Technologies • Flat-bladed surface aerators without bottom impellers CarolloTemplateWaterWave.pptx • Initial estimate of SAE (second stage conditions) – 4.0 pph/hp Low Speed Testing for First Stage Aerators CarolloTemplateWaterWave.pptx • Tested to deliver 0.5 ft per second velocity at the bottom of the test tank at low speed in first stage (anaerobic / aerobic) High Speed Testing CarolloTemplateWaterWave.pptx • Test-tank tested at approximately 3.9 pph/hp under high speed conditions simulated for second stage Simulation of Variable Speed Control • Savings only occur when aerators are under-loaded 16 Dissolved Oxygen Concentrations (mg/L) • Simulations by Michael Stenstrom of UCLA indicated up to 35% savings in power with VSD control 14 DO1 DO2 DO 3 12 10 8 6 4 2 0 5 10 15 CarolloTemplateWaterWave.pptx Time (hours) 20 25 Summary Comparison Performance Description Aerobic (2006) Anaerobic (2007) Difference (%) 7.2 6.7 -6.8% 1,291 1,212 -6.5% 1.21 1.15 -5.7% 155.71 126.77 -22.8% Estimated Mixer Power (hp) 222.2 125 -77.9% Estimated Oxygen Power (hp) 215.2 201.6 -6.8% Estimated Total Power (hp) 437.5 326.6 -34.0% O2 (tpd) O2 (lb/mgal) O2 (lb/lb BOD) CarolloTemplateWaterWave.pptx SVI (mL/g) Project Budget • Total cost - $670,000 • Puget Sound Energy grant - $330,000 CarolloTemplateWaterWave.pptx • City of Bellingham cost - $340,000 24 CarolloTemplateWaterWave.pptx Comparison of Operating Modes Actual Bellingham Operation Anaerobic Selector Operation - 2007 HPO Operation - 2006 • 100% Aerobic • 67% Aerobic • 2.2 Days Aerobic SRT • 1.6 Days Aerobic SRT • 157 mL/g SVI • 126 mL/g SVI • 2,400 mg/L MLSS • 2,900 mg/L MLSS 25 Comparison of Operating Modes Actual Bellingham Capacity CarolloTemplateWaterWave.pptx HPO Operation - 2006 20 MGD Capacity Anaerobic Selector Operation - 2007 22 MGD Capacity 10 Percent Increase 26 What About BNR Conversions? • Concerns about HPO CarolloTemplateWaterWave.pptx – CO2 accumulation -> low pH -> suppresses nitrification – As SRT increases HPO becomes less and less economical compared to fine bubble – Examples: • • • • • LOTT (Olympia, Washington) Denver Metro Indianapolis Bellingham All abandoned HPO for BNR 27 Oxygen Supply Cost as function of SRT HPO: New VPSA HPO Plant AAS: New Diffused Aeration System $800 $700 Unit Cost of Oxygen ($/ton) $600 $500 $400 $300 $200 CarolloTemplateWaterWave.pptx $100 $0 1.5 2.5 SRT (Days) 8.0 28 CarolloTemplateWaterWave.pptx HPO Conclusions 29 Conclusions from the HPO Test Facility CarolloTemplateWaterWave.pptx • Anaerobic selectors at the HPO test facility failed because low SRT, low temperature prevented formation of an environment supportive of EBPR. PAO were washed out. Wef2003Samstag.ppt 30 Conclusions from the Post Point Project • Anaerobic selector provided a way to control settleability by encouraging PAO and taking up excess VFA • Improved oxygen transfer efficiency of new aerators saved power • Variable speed control of DO provided power savings and improved process control • The upgrade provided a 10 Percent capacity increase for interim operation CarolloTemplateWaterWave.pptx • For BNR upgrade, fine bubble was more economical 31 Thank you! Questions? CarolloTemplateWaterWave.pptx Randal Samstag [email protected] 206-684-6532 (office) 206-851-0094 (mobile) Generalized Conclusions about HPO CarolloTemplateWaterWave.pptx The Initial Claims Experience • Less O2 consumption • O2 consumption depends more on SRT than on DO • Better settling sludge • Little evidence of better settleability at a given SRT • Can operate at a higher MLSS • If settling is not better, no justification for higher MLSS • Smaller tank volume required • If settling is not better, no justification for smaller tanks • More power efficient than conventional aeration • Power efficiency depends on SRT • Can be used for nitrification • High CO2 decreases pH and inhibits nitrification 33 CarolloTemplateWaterWave.pptx MLSS Showed Indications Phosphorus Accumulating Organisms 34 Recent SVI and SRT Data from West Point WWTP West Point SVI and SRT Data CarolloTemplateWaterWave.pptx SRT (day) Linear (SVI) 30 per. Mov. Avg. (SVI) 30 per. Mov. Avg. (SRT (day)) Linear (SRT (day)) 450 9.0 400 8.0 350 7.0 300 6.0 250 5.0 200 4.0 150 3.0 100 2.0 50 1.0 0 12/4/05 12/4/06 12/4/07 12/3/08 12/3/09 SRT (Days) SVI (mL/g) SVI 0.0 12/3/10 35 Summary Comparison Operation Description Aerobic (2006) Anaerobic (2007) Difference (%) Flow (mgd) 12.2 12.1 -0.8% BOD (ppd) 12,852 12,994 1.1% 1,763 2,057 14.3% Total SRT(days) 2.2 2.4 6.5% Aerobic SRT (days) 2.2 1.6 -40.3% 13.3 7.4 -78.8% Temp (Deg C) 17.57 17.24 -1.9% O2 Purity (%) 88% 89% 1.4% MLSS (mg/L) CarolloTemplateWaterWave.pptx DO (mg/L) CarolloTemplateWaterWave.pptx Comparison of Operating Modes Typical Operating Assumptions Classical HPO Operation • 100% Aerobic Anaerobic Selector Operation • 85% Aerobic • 1.5 Days Aerobic SRT • 2.5 Days Aerobic SRT • 200 mL/g SVI • 120 mL/g SVI • 1,700 mg/L MLSS • 2,200 mg/L MLSS 37 Comparison of Operating Modes Capacity Impact CarolloTemplateWaterWave.pptx Classical HPO Operation 13 MGD Capacity Anaerobic Selector Operation 17 MGD Capacity 30 Percent Increase 38
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