Biosolids

Biosolids is a term coined in the United States that is typically used to describe several forms of treated sewage sludge that is intended for agricultural use as a soil conditioner. Although sewage sludge has long been used in agriculture, concerns about offensive odors and disease risks from pathogens and toxic chemicals may reduce public acceptance of the practice. Modern use of the term biosolids may be subject to government regulations, although informal use describes a broader range of semi-solid organic products separated from sewage.

Description of biosolids in conformance with local regulations may reduce confusion; but some use an expanded definition including any solids, slime solids or liquid slurry residue generated during the treatment of domestic sewage including scum and solids removed during primary, secondary or advanced treatment processes. Use of alternative terms like solids or wastewater solids may be preferable for non-conforming biosolids.

Biosolids may be defined as organic wastewater solids that can be reused after suitable sewage sludge treatment processes leading to sludge stabilization such as anaerobic digestion and composting.

Alternatively, the biosolids definition may be restricted by local regulations to wastewater solids only after those solids have completed a specified treatment sequence and/or have concentrations of pathogens and toxic chemicals below specified levels.

The United States Environmental Protection Agency (USEPA) defines the two terms - sewage sludge and biosolids - in the Code of Federal Regulations (CFR), Title 40, Part 503 as follows: sewage sludge refers to the solids separated during the treatment of municipal wastewater (including domestic septage), while biosolids refers to treated sewage sludge that meets the USEPA pollutant and pathogen requirements for land application and surface disposal. A similar definition has been used internationally.

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