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Poop to Power: Turning Waste into Clean Energy

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Environmental Services has been harvesting biogas – a byproduct of sewage treatment – for years, generating heat and electricity to power the plant while selling a portion to a local business. But even with this reuse, some methane is still burned off, released to the environment as carbon dioxide.

From Poop to Power 

Through the Poop to Power Project, Portland is on its way to maximizing the reuse of the methane produced at the treatment plant and turning this waste into a valuable resource. The resulting renewable natural gas (RNG) will be used to replace dirty diesel in commercial vehicles. 

Environmental Services aims to create a triple win for the public. Creating renewable fuel from Portland’s poop is projected to eliminate 21,000 tons a year of climate-altering emissions, generate upwards of $3 million a year in revenue for ratepayers, and replace over one million gallons of vehicle fuel with clean renewable natural gas. 

Graphic with three blue circles with white icons in the center. The first, an image of a cloud with the text "Co2" inside and an arrow pointing down has the following text: "Climate. Cut greenhouse gas emissions by 21,000 tons annually." The next icon has an image of a gas pump with a leaf it and has the following text: "Revenue. Generate upwards of $3 million in revenue a year for the city." The third has a truck, "Clean air. Replace 1.34 million gallons of dirty diesel truck fuel with clean RNG per year.

Project Progress

Before 2017  – Environmental Services captures 77 percent of biogas from its anaerobic digesters. We turn the waste methane into electricity and heat for use at the City’s wastewater treatment plant in North Portland and sell a portion to a nearby roofing company for its manufacturing process. The rest is flared, meaning released to the environment as carbon dioxide. 

2017 – City Council authorized Environmental Services to build the infrastructure to capture and clean almost 100 percent of the plant’s biogas, and to enter into a partnership with NW Natural to distribute the resulting renewable natural gas (RNG). Funneling the RNG into NW Natural’s pipeline allows a wider distribution. To maximize the environmental, community, and revenue benefits, the RNG will be marketed as truck fuel to displace dirty diesel. Some of the RNG also will power City trucks. 

2018 –  Environmental Services opened a natural gasfueling station at the plant to fuel City trucks. It supplies conventional natural gas now but will switch to renewable natural gas once RNG production begins. The fueling station is delivering immediate clean air benefits by displacing dirty diesel. Climate benefits will be realized when the switch is made to RNG. 

2020  – Environmental Services began testing the new system in the fall 2020. Full production is expected in 2021. 

What is Biogas? 

Biogas is produced in the digesters at the wastewater treatment plant. In the digesters, biogas is released when anaerobic microorganisms breakdown the solids from the wastewater treatment process. Biogas is mostly methane (60 percent) and carbon dioxide with smaller amounts of other gases.   

Biogas is collected in the digesters and then sent to a biogas upgrading facility at the treatment plant where it is “refined,” or cleaned. This process removes other gases like hydrogen sulfide, siloxane, and water vapor. The final product can be used as fuel for cars and trucks.  

Why Convert Poop to Power? 

Harnessing biogas that is produced as a by-product of the wastewater treatment process helps fight climate change and is an important step in creating a low-carbon future. The alternative is to burn the gas through a flare, which means releasing the methane and carbon dioxide into the atmosphere. By turning these gases into renewable energy, we keep these harmful greenhouse gases out of the atmosphere and put them to a beneficial use.  

Energy Efficiency 

Resource recovery is not just about transforming the waste materials received each day at the plant, but it is also about efficiently using our current resources. Environmental Services has teams dedicated to finding ways to use energy efficiently throughout the treatment process. Their work reduces energy use and saves ratepayers money.  

The new fueling station at the plant allows Environmental Service to start converting some City vehicles from gasoline and diesel to renewable natural gas. This will reduce greenhouse gas emissions and improve air quality in Portland. The Poop to Power Project is a local, renewable source of fuel that can produce enough to fuel the majority of Portland’s fleet.

Our Work Continues 

The future holds great opportunities to address global challenges. We can find solutions that are equitable, resilient, financially feasible, and improve public and environmental health. Resource recovery does all those things. By finding and recovering all that is valuable in our wastewater, we can shift to a more sustainable future – one where our current needs are met without compromising the ability of future generations to meet their own needs.