IPDES Sludge/Biosolids Program
Sewage sludge is the solid, semisolid, or liquid untreated residue created during the wastewater treatment process. When treated and processed, sludge becomes biosolids, which are the stabilized residuals that settle from the water during the treatment process. Biosolids may be disposed of or beneficially re-used.
Biosolids Beneficial Reuse/Disposal Options
Because biosolids contain nutrients and organic matter, they are considered a beneficial resource by EPA and DEQ; therefore, the reuse of biosolids through land application is encouraged. When land applied, biosolids can be used as fertilizer to help improve and maintain productive soils and stimulate plant growth.
Before biosolids may be land applied, they must be treated to meet standards for pathogens, vectors, and metals. Biosolids treatment is designed to kill pathogens, stabilize organic matter, reduce odors, and minimize vector attraction.
Sewage Sludge/Biosolids may be disposed of by various means such as landfilling, incineration, or surface disposal (beneficial reuse).
Regulation of Biosolids
Regardless of whether biosolids are disposed of or beneficially reused, they are subject to certain federal, state, and local regulations. Any or all of the following regulations may apply to facilities that generate biosolids, derive a material from biosolids, land-apply biosolids, or own or operate a site where biosolids may be applied:
- Standards for the Use or Disposal of Sewage Sludge (40 CFR 503): Federal regulation that sets national standards for pathogens and certain heavy metals in sewage sludge; also defines standards for the safe handling and use of sewage sludge. The provisions of this regulation are applicable regardless of whether a permit is required.
- Environmental Protection and Health Act of 1972 (Idaho Code §39-1): State law that assigns responsibility for protecting human health and the environment to DEQ.
Additional information may be found on DEQ’s Sludge & Biosolids webpage.