Loop is a natural soil amendment. Using Loop replenishes the earth and closes the nutrient loop that begins when harvested plants remove nutrients from the soil.

As it has for the past 40 years, King County produces Loop from solids extracted during the wastewater treatment process. Using Loop as a soil amendment closes the nutrient loop wherein harvested plants take nutrients from soil, humans obtain nutrients from the plants, and then we return nutrients to soil with Loop. Loop is an endlessly renewable resource restoring carbon and nutrients to the land for the good of plants, people, and Puget Sound.

Loop delivers a full suite of macro- and micronutrients, making it a superior source of plant food over synthetic fertilizers. It has a proven ability to improve soil structure thereby reducing runoff and erosion. Held to rigorous standards by both the EPA and the State of Washington, Loop is safe. Choosing to use Loop as a soil amendment reduces greenhouse gas emissions into the atmosphere. It has enriched Pacific Northwest landscapes as an ingredient in the commercial product GroCo since 1976.

Why is Loop awesome?

How Loop® Biosolids are Made

What are biosolids and how are they made? In this video, staff from King County Wastewater Treatment Division show how they transform raw wastewater into Loop® biosolids. After the transformation is complete, the endlessly renewable soil amendment is used to fertilize farms, forests, and gardens.

Take a tour of King County’s Wastewater Treatment Plants to see for yourself how Loop is made.