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Mitigating Greenhouse Gases From Biological Wastewater Treatment Plants. Rob Stephenson and Charles Liao Paradigm Environmental Technologies Inc. Outline . Energy and GHGs at a WWTP Biogas energy potential in sludge WWTP as a bioenergy centre
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Mitigating Greenhouse Gases From Biological Wastewater Treatment Plants Rob Stephenson and Charles Liao Paradigm Environmental Technologies Inc.
Outline Energy and GHGs at a WWTP Biogas energy potential in sludge WWTP as a bioenergy centre Sludge pre-treatment and advanced co-generation Example: Lulu Island WWTP Conclusions
How WWTPs generate GHGs • By consuming electricity and natural gas • By generating CO2 from biological wastewater treatment • By generating excess microorganisms that: • Require trucking and disposal • Rot, forming CH4, CO2, N2O
Activated sludge wastewater treatment Electricity is used for blowers to aerate wastewater For organic load of incoming sewage: ~ 50% is converted to CO2 ~ 50% is converted to bacteria
Anaerobic digestion of sludge Anaerobic Digesters >15 days pumping, mixing, heating at 37ºC Stabilize primary sludge, waste activated sludge Generate biogas (60-65% CH4, 35-40% CO2) Poor Efficiency ~30% destruction of WAS ~60% destruction of primary sludge
Energy recovery systems Typical Co-generation Efficiency 30% conversion of biogas to electricity 50% recovery of waste heat
Heat generation at a WWTP Typical Boiler Efficiency 80 - 90% to useable heat
GHG impacts for land application of sludge Aerobic Degradation: C5H7O2N + 5O2 -> 2H2O + NH3 + 5CO2 (sludge) Anaerobic Degradation: 2C5H7O2N + 6H2O -> 5CH4 + 2NH3 + 5CO2
GHG impacts for landfilling sludge Anaerobic Degradation: 2C5H7O2N + 6H2O -> 5CH4 + 2NH3 + 5CO2 Aerobic Degradation: C5H7O2N + 5O2 -> 2H2O + NH3 + 5CO2
GHG impacts for sludge incineration Sludge Combustion: C5H7O2N + 6.25O2 -> 3.5H2O + NO + 5CO2 Fuel Combustion: CH4 + 2O2 -> CO2 + 2H2O
Biogas energy potential of sludge for a WWTP serving 1 million people • 30% conventional, 42% ARES • 40 – 50% recovery of waste heat (3) 5¢/kWh electricity, 3¢/kWh natural gas
Why WWTPs are net energy consumers • Energy Uses • Aeration for secondary wastewater treatment • Heating, pumping, mixing anaerobic digesters • Sludge conveying and dewatering • Hauling and disposal of residual sludge • Potential for Energy Recovery • Anaerobic digestion • Co-generation
Why does WAS digest so poorly? Extremely tough cell membranes retard degradation in anaerobic digesters Conventionally, VSr of WAS ≤ 30% • limits biogas production MicroSludge increases VSr of WAS to up to 90% • maximizes biogas production
WAS pre-treatment options • Heat • Freezing • Chemicals • Enzymes • Shear • Pressure
Sheer Forces Lyse Cells WAS liquefied WAS liquefied 12,000 psi 700 mph Cell disrupter valve LYSED CELLS IMPACT RING TWAS (INTACT CELLS) VALVE STEM VALVE SEAT LYSED CELLS
How MicroSludge can make anaerobic digesters work better After MicroSludge Before MicroSludge
Advanced Reciprocating Engine System • ARES: High efficiency, low emissions gas engine • US DOE, Caterpillar, Cummins, Waukesha Engine • Biogas to electricity efficiency: 42% now, target 50% • (Conventional efficiency 30%) • Reduces NOX by 90%
Synergy of MicroSludge + ARES + * Estimate from GVRD
Example of Lulu Island WWTP Lulu Island WWTP services 170,000 people and businesses in Richmond, BC treating 80,000 m3/day of wastewater
How WWTPs can minimize GHG generation • Maximize conversion of sludge to biogas • Maximize co-generation efficiency • Displace non-renewable energy with biogas energy • Minimize quantity of sludge hauled off site: • Landfill • Land application • Incineration
Conclusions • Cities are flush with bioenergy potential • Guaranteed supply • Guaranteed buyer • Infrastructure already exists • New innovations of (1) MicroSludge • + (2) ARES co-generation: • Transform municipal WWTPs from • energy blackholes into • renewable energy showpieces
Ode to sludge • Sludge, oh sludge - • Vile yucky muck! • By treating wastewater, • We haul it from cities by truck. • But farmers don’t want it. • And it’s too wet to burn. • So anaerobically digest it. • And do Mother Nature a good turn.