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Biosolids Recycling

For more information about the Biosolids Recycling Program, please send us an email message or contact us at: 

King County Wastewater Treatment Division
Resource Recovery
201 S. Jackson Street
Mail Stop: KSC-NR-0512
Seattle, WA 98104
Phone: 206-477-5557
Fax: 206-684-2057

What we're doing to minimize climate change

Sequestering Carbon with Loop biosolids

Fertilizing with carbon-rich Loop allows us to:

  • Increase plant growth, which helps remove CO2 from the atmosphere and deposits more plant residues in the soil.
  • Reduce the use of synthetic fertilizers, which are fossil fuel intensive to produce.
  • Increase soil carbon storage (C sequestration).

By sequestering carbon and avoiding synthetic fertilizers, we offset over 42,000 tons of CO2 equivalents in 2012. That's like taking 8,000 cars off the road! 

Soil Carbon Sequestration and Reforestation at Island Center Forest

In the summer of 2009 we began testing options to restore vegetation to a site with drastically disturbed soils in Island Center Forest. Previously, soils on the Vashon Island site were "borrowed" for use as daily cover for the adjacent landfill, leaving behind a pit where the remaining soils are so degraded they cannot support a healthy ecosystem. The use of composted organic residuals will improve soil health and enhance vegetation growth. The long term objective for the site is to restore a healthy forest ecosystem.

The demonstration project is being used by researchers to evaluate the potential of organic residuals to store carbon in the soil. Vegetation and soils are widely recognized as carbon storage sinks. Adding carbon to soils and enhancing growth of vegetation is known as terrestrial sequestration. Enhancing the natural processes that remove carbon dioxide (CO2) from the atmosphere and store it in soils and vegetation is thought to be one of the most cost-effective ways of reducing atmospheric levels of this greenhouse gas. Reforestation of degraded sites, such as borrow pits and gravel mines, offers a significant opportunity for maximizing carbon sequestration.

Island Center Forest

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The borrow pit before restoration.

Installing research plots, September 2009

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Plots were seeded with grasses, prior to winter planting of tree seedlings. Tree planting with community volunteers, January 2010

Future vision for the site.... bs_foresttrail_250

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King County Climate Change