Poop to Power: Turning Wastewater into Clean Energy

Photograph of a City of Portland truck being fueled at an RNG fueling station located at the Columbia Boulevard Wastewater Treatment Plant
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 had been capturing 77 percent of biogas from its anaerobic digesters. We turned the biogas into electricity and heat for use at the City’s wastewater treatment plant in North Portland and sold a portion to a nearby roofing company for its manufacturing process. The rest was  flared, or 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 methane, or 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 is planned to be sold as truck fuel to displace dirty diesel. Some of the renewable gas also is planned to power City trucks. 

2018 –  Environmental Services opened a natural gas fueling station at the plant to supply some City trucks. The fueling station began delivering immediate clean air benefits by displacing dirty diesel. Climate benefits will be realized when the switch is made to renewable natural gas. 

2020 – Environmental Services and NW Natural completed the connection between the city’s wastewater treatment plant and the company’s pipeline. That connection will allow Environmental Services to distribute the renewable gas beyond the plant’s boundaries. 

2023  – Construction nears completion on the infrastructure that upgrades biogas to renewable gas. Once complete, RNG production will begin. The complex infrastructure uses water and pressure to clean biogas, extract methane, and remove impurities.

2024 - Environmental Services plans to test and refine systems in early 2024 and ramp up production in the following months. 

What is Biogas? 

Biogas is a byproduct of wastewater treatment as well as landfills, and occurs when organic materials such as poop or food waste break down or decompose.  Biogas is mostly methane (60 percent) and also contains carbon dioxide with smaller amounts of other gases. 

At the wastewater treatment plant, biogas is produced in large cylinders called digesters. In the digesters, anaerobic (without oxygen) microorganisms (tiny bugs) speed up the decomposition of those solids. The biogas can be used for heating or electricity. When refined by filtering out impurities, the resulting methane can be used as fuel. Methane from biogas is also called renewable natural gas, and can be used interchangeably with fossil fuel-produced gas. 

Energy Efficiency 

In addition to recovering resources, and transforming the waste materials received each day at the plant into valuable resources, Environmental Services also is working on 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.  

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. 


Diane Dulken

Public Information Officer

Josh Newman

Biogas Utilization Program Manager