skip to main content

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

Biosolids...a sustainable choice

Biosolids are the nutrient rich organic product of wastewater treatment - a never ending resource. We are using biosolids to return valuable nutrients and carbon to the land. Research shows that biosolids enriches soils and keep them productive and healthy!

King County's Loop® biosolids are recycled as a fertilizer and soil conditioner in agriculture and forestry, and a portion of our biosolids is composted by a private company and sold as GroCo for use in landscaping and gardening.

If you have any questions or comments, please don't hesitate to contact us.

All about biosolids

All about biosolids
Find basic information on Loop® biosolids: what they are, where they come from, and what we  do with them.


Garden compost
GroCo is a soil-enhancing compost made with Loop biosolids. Find out more about GroCo, including where to get it.


What we're doing to minimize climate change 
Learn how carbon in Loop biosolids is stored in the soil and reduces greenhouse gas emissions.

projects icon

Our soil improvement projects
Come find out more about how we're using Loop® to improve soils and plants in Washington.

safety icon

Safety and regulations
Get the facts on biosolids safety and the regulations governing the production and use of Loop biosolids.

question-mark Hot topics
Concerned about something you've heard recently about biosolids? Get the facts here. 
FAQ icon

Find answers to the most common questions about Loop, biosolids, and King County's Loop biosolids program.

links icon

Documents & Links
Download brochures, reports and technical papers and find helpful links to more information on biosolids and related topics.

Loop video gallery

(external link)

Biosolids News

Related agencies