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Waste-to-energy system to supply renewable electricity, heat at West Point Treatment Plant


King County’s West Point Treatment Plant is making a powerful example of waste recycling.The plant is now operating a new cogeneration system that turns digester gas generated during the treatment process into electricity and heat.


A new cogeneration system at King County’s West Point Treatment Plant is now using a waste byproduct of sewage treatment and turning it into renewable electricity and heat that helps run the plant.

“This facility puts King County on the path to operating one of the nation’s first carbon-neutral wastewater utilities, and helps us meet our goals for the use of renewable energy,” said King County Executive Dow Constantine at a celebration to launch the new project.

Digester gas is a naturally occurring byproduct of the wastewater solids treatment process and an excellent source of renewable energy. With the addition of the new facility, the Wastewater Treatment Division will produce the equivalent of the energy used by almost 6,000 homes. 

Though much of the heat and energy will be harnessed for the plant’s operational needs, some of the electricity generated at the plant will be sold to Seattle City Light under an agreement reached in 2010.

The new system replaces an end-of-life cogeneration facility that was taken offline in 2007 after 23 years of service. Since the opening of West Point in 1966, its raw sewage pump engines and hot water boilers have been powered by digester gas generated during the treatment process. And waste heat from plant process has been put to good use in keeping digesters warm.

Because of investments in energy conservation, renewable energy production and carbon and nutrient recycling, the division is 70 percent of the way to being carbon-neutral in its operations. King County hopes to have one of the nation’s first carbon-neutral wastewater utilities of its size.

The cogeneration project is funded in part by an $8.2 million grant from the federal Environmental Protection Agency.

More information is available on the Web at


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