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WARNING! Sewage sludge is toxic. Food should not be grown in "biosolids." Join the Food Rights Network.


This article is part of the Food Rights Network, a project of the Center for Media and Democracy. Find out more here.

GroCo is a Seattle, WA product sold as fertilizer but made from sewage sludge.[1] Hundreds of communities across the U.S. sell toxic sludge products that are typically renamed biosolids and sold or given away as "fertilizer" or "compost" (and often even labeled or marketed as "natural" or "organic").

GroCo is a Class A Biosolids product that incorporates sawdust. The concentrated sewage sludge itself is labeled Class B Biosolids and is marketed separately as a King County Wastewater Treatment Division product recently "branded" Loop. 310 wet tons a day of this sewage sludge are trucked from the wastewater treatment plant and then spread directly on agricultural cropland (80 percent) and commercial forest land (15 percent). The remaining five percent is made into GroCo.[2]

According to one website:[3]

"King County operates several wastewater treatment plants in and around the Seattle, Washington area. Some of the biosolids from these plants are anaerobically-digested and dewatered to produce a biosolids "cake". The cake is either composted with sawdust to produce a product called GroCo or delivered directly to forest application sites as SilviGrow. King County has a long history of developing the SilviGrow program in association with the University of Washington College of Forest Resources. SilviGrow application to forest land is safe and beneficial. Trees fertilized with SilviGrow grow twice as fast as unfertilized trees. Thousands of forest land acres have been fertilized with SilviGrow.
"Recently, King County has entered into a partnership with Washington DNR, University of Washington, Sierra Club, Weyerhaeuser, and others in what's called the "Mountains to Sound Re-Greening Program." This program involves hundreds of volunteers in the restoration and revegetation of logging roads no longer needed along the scenic Interstate 90 corridor from Puget Sound to the east side of the Cascades. GroCo is being used to restore revegetate the unsightly, barren scars left by many old logging roads."

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External Resources


  1. Branded products containing sewage sludge, SludgeNews Website accessed June 3, 2010.
  2. Katrina Mendrey, Branding Biosolids Closes The "Loop" (sub. req'd.), BioCycle Magazine, June 2013, Vol. 54, No. 6, p. 21.
  3. Metropolitan Council - U.S. Biosolids Scene, Accessed November 12, 2010.
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