98 

 

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Replace old, existing equipment with  2 new turbo blowers and fine bubble diffusers in lower 
plant. Also replace digester gas mixing system with linear motion mixers. Completed in 2012.  
Reduced plant energy consumption by 15%.  

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Install sub-meter for lower plant - Sub meter was installed which allows staff to monitor energy 
consumption of the lower plant and the upper plant.  Having more precise consumption info 
enables plant staff to make better operational decisions with the goal of conserving energy. 
 
 

ENERGY GENERATION & RECOVERY  

•

 

Indication of management commitment (e.g., standard operating procedures; board/executive 
management renewable energy conversion policy, including quantitative goals developed and 
shared with stakeholders)   

•

 

Internal energy sources evaluated (e.g., biogas, hydropower, heat in wastewater), and/or 
renewable energy sources evaluated on an ongoing basis (e.g., solar, wind, co-digestion)  

•

 

Recovery of digester gas in a combined heat and power (CHP) system, and boilers in place (for 
process and building heating)   

•

 

Conversion of digester biogas to electricity and heat, and/or transportation fuel Yes   

•

 

Solar panels, wind turbines, heat recovery, in conduit hydro, and/or hydroelectric power 
generation systems installed  

Performance Measures & Results 

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Install solar power plant. 420 mW solar power plant provides 7% of plant power at a discounted 
rate.  No capital cost to the City.  

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Install Fats Oil and Grease (FOG) Receiving Station with the goal of doubling biogas production 
through codigestion so that cogen power production can be increased.  

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Project completed, biogas production doubled.    

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Install second Cogen Engine to make use of increased biogas production, and make Gresham 
WWTP energy net zero.  

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Project completed.  Gresham WWTP has been energy net zero since March 2015.  Gresham 
WWTP produces more energy than it consumes.  Plant powered by 100% renewable energy 
produced on site by solar panels and two 400 kW cogen engines.  Projected payback period is 7 
years.  

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Make use of available energy grants and incentives.  

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Approximately $9.5 million dollars was spent on energy related projects in the past 10 years.  
38% of the funding was provided in the form of grants and incentives from the Oregon 
Department of Energy and the Energy Trust of Oregon.  

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Generation of renewable energy credits.  REC’s are being generated and given to Energy Trust of 
Oregon in exchange for incentive payment.  REC’s are registered with the Western Renewable 
Energy Generation Information System (WREGIS) an independent, renewable energy tracking 
system for the region.