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In addition to reducing energy use, King County set a renewable energy goal of generating and consuming the equivalent of 50% of its energy needs through renewable sources. The renewable energy sources captured through WTD’s operations are playing a significant role in meeting that goal.

With the West Point cogeneration facility online, all of the Wastewater Treatment Division facilities can now produce the equivalent of the energy used by almost 6000 average Pacific Northwest homes.

The Energy Program looks for additional opportunities for WTD to invest in renewable energy production. Mindful of environmental, operational and financial considerations, the Energy Program reviews existing infrastructure, analyzes data and makes recommendations that expand WTD's ability to generate more electricity and heat onsite.

Through the development of strategic partnerships with local utility companies, the Energy Program is often able to secure outside funding to offset costs.

Creating and using its own renewable fuel reduces WTD's carbon footprint, insulates ratepayers from volatile energy prices and further establishes WTD's self-reliance and independence from outside fuel sources.

Biogas put to use

SP scrubbing towers
Scrubbing towers at South Plant

Since 1966, WTD has been capturing and cleaning gas produced anaerobically by the microbes consuming wastewater solids in large digester tanks. Some biogas is converted into electricity via cogeneration engines, and some of it is scrubbed and sold to local utility companies. Scrubbing the gas removes carbon dioxide and other impurities, making it suitable to run engines and import into natural gas pipelines.

South Plant processes biogas and uses about 20 percent of it to power the boilers heating the digester tanks. The rest of the pipeline-quality biogas is sold to a local utility company for use as natural gas in local homes and businesses.   The availability, use, and sale of biogas not only reduce the amount of energy WTD needs to purchase but also reduce WTD’s carbon footprint.

Sometimes excess biogas must be burned off, or flared. For the safety of its employees and nearby communities, treatment plants must have a way to manage biogas when energy recovery systems are offline for routine maintenance or repairs. For example, in 2011, South Plant’s gas-scrubbing equipment was damaged, and all of its gas was flared while the problem was being fixed.

For more information about resource recovery, please contact us at: