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Natural Resources and Parks

King County, Washington

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Sept. 9, 2010

Garden bounty feeds a crowd at South Treatment Plant harvest lunch

Local farmers, soil scientists dish the dirt on biosolids safety and benefits

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Roasted potatoes, garden fresh salads and herbed salmon accompanied a helping of expert testimonial by local farmers and scientists about the safety and benefits of biosolids today at King County’s South Treatment Plant.

About 50 people, including elected officials, area farmers and staff from several clean-water utilities, attended a luncheon that featured dishes prepared with the produce recently harvested from the plant’s biosolids demonstration garden in Renton.

“Biosolids were once considered a useless byproduct of our treatment process,” said Pam Elardo, interim director of King County’s Wastewater Treatment Division. “With education and research, we have become more aware that biosolids are a valuable product and an important part of our agency mission to create resources from wastewater to benefit our region.”

Since the 1970s, King County’s clean-water utility has recycled 100 percent of the biosolids produced at its Renton and Seattle facilities and currently produces about 116,000 tons of this popular product each year. Prior to the adoption of the federal Clean Water Act in 1972, the biosolids were commonly dumped into Puget Sound. Some wastewater agencies continue to landfill or incinerate it.

About 70 percent of the King County’s biosolids are used on hops and wheat crops in eastern Washington. The rest is used in forestry projects, such as fertilizing land on the Mountains to Sound Greenway, or made into GroCo compost, a consumer-grade product popular with local gardeners.

“GroCo is similar to other compost, but it has many advantages,” Dr. Craig Cogger, a soil science expert with Washington State University. “It’s a more consistent product and a reliable, slow-release source of nitrogen. Like other well-prepared composts, the pathogens have been killed, so it’s safe for home garden use.”

“Biosolids recycling is an example of resource recovery at its finest,” said Kate Kurtz of the urban farm collective Alleycat Acres in Seattle, which, with the use of biosolids, has produced and donated 500 pounds of fresh produce to the Beacon Hill Food Bank. “What starts as waste in our sewers gets turned into a resource for use in urban areas. It’s effective and sustainable.”

King County has partnered with local universities for nearly 30 years to study the safety of biosolids on soils, crops, wildlife, and water quality. Research results have consistently found that biosolids promotes lush plant growth, increases crop yields, nourishes depleted soils, and reduces erosion. Biosolids use also enables farmers to reduce their use of herbicides and chemical fertilizers. Studies also show that produce grown using biosolids compost is safe to eat, healthy, and delicious.

Additional information about King County’s biosolids recycling program efforts and research is available online at

People enjoy clean water and a healthy environment because of King County's wastewater treatment program. The county’s Wastewater Treatment Division protects public health and water quality by serving 17 cities, 17 local sewer distric
ts and more than 1.5 million residents in King, Snohomish and Pierce counties. Formerly called Metro, the regional clean-water agency now operated by King County has been preventing water pollution for nearly 50 years.

Note to editors and reporters: Visit the WTD Newsroom, a portal to information for the news media about the Wastewater Treatment Division, King County Department of Natural Resources and Parks at

Related information

Reclaimed water & biosolids demonstration garden


King County Wastewater Treatment