Biosolids are the nutrient-rich organic material produced by treating wastewater solids. After processing and treatment, they can be beneficially recycled as a fertilizer and soil amendment.
Wastewater flows to treatment plants from homes, businesses, and industries.
Wastewater pumped from septic systems is also delivered to the treatment plant. Biosolids have been recycled safely by King County for more than 25 years. In some parts of the country, biosolids have been used for over 70 years. The Water Environment Federation recently investigated several long-term application programs. They found that sites with cumulative biosolids loadings equivalent to more than 600 years of annual agronomic rates showed very little, if any, negative impact on the soil-plant system and on water resources.