We regulate the wastewater treatment plants that produce biosolids and the businesses that apply biosolids for farmers, including how this material is treated, tested, and used.

Biosolids are a product of wastewater treatment systems. Rich in organic material and nutrients, biosolids are used by farmers across Washington to grow a variety of crops like wheat, corn, grass hay, and hops. Proper oversight, testing, and application ensures biosolids benefit farmers and soil without leaching nutrients into surface or groundwater.

Learn about biosolids

  • Research on biosolids
  • How wastewater treatment plants make biosolids
  • Pollutants and pathogens in biosolids
  • Biosolids use in Washington

Permitting and forms

Biosolids laws & rules