Biosolids is the soil-like residue of materials removed from sewage.
In 1991, the Water Environment Federation (WEF) recognized the term biosolids. By 2004, the word Biosolids was used universally. Biosolids is the soil-like residue of materials removed from sewage during the wastewater treatment process. During treatment, bacteria and other macroscopic organisms break down sewage into simple and more stable forms of organic matter. The organic matter combined with bacterial cell masses, settles out to form biosolids. According to USEPA, biosolids that meet treatment and pollutant content criteria can be safely recycled and applied as fertilizer to sustainable improve and maintain productive soils and stimulate plant growth.
Biosolids in their liquid form resemble muddy water containing 1-10% solids. During the second phase of the treatment, the biosolids may be dehydrated turning into
a cake with the texture of a wet sponge. In this stage, it contains 11-40% solids.
As of 2002 in the United States, about 60% of all biosolids were beneficially used as fertilizer for growing crops. Biosolids that meet the Class B treatment and pollutant criteria, in accordance with USA Standards for the use or disposal of sewage sludge, Title 40 Code of Federal Regulations Part 503 (40 CFR 503) can be applied to land with formal site permit restrictions, and strict record keeping. Biosolids that meet Class A pathogen reduction requirements, or (PFRP) Process to Further Reduce Pathogens, have the least restrictions on use. PFRPs include composting, heat drying, heat treatment, thermophilic aerobic digestion, beta or gamma ray irradiation, and pasteurization.
The National Research Council published in July 2002, Biosolids Applied to Land:
Advancing Standards and Practices. The NRC concluded that there was no documented scientific evidence stating biosolids regulations have failed to protect public health. Despite the NRCs ruling, there is persistent concern on possible adverse health issues. The NRC noted that further research was needed and made approximately 60 recommendations addressing public health concerns, scientific qualms, and gaps in scientific data relating to the sewage sludge standards. As of 2004, the USEPA has had insufficient funding to implement the NRC recommendations.
In 1997 the United States, municipal wastewater treatment plants annually produced about 7.7 million dry tons of biosolids. In 1999, about 6.8 million dry tons were produced according to sources relying on USEPA estimates. The NRC states, about 5.6 million dry tons was the normal US annual biosolids production rate for 2002.
https://www.epa.gov/biosolids/2002-national-research-council-report-biosolids-and-epas-response