Biosolids

[2] Some sewage sludge can not qualify as biosolids due to persistent, bioaccumulative and toxic chemicals, radionuclides, and heavy metals at levels sufficient to contaminate soil and water when applied to land.

In contrast, biosolids refers to treated sewage sludge that meets the EPA pollutant and pathogen requirements for land application and surface disposal.

[8] Challenges faced when increasing the use of biosolids include the capital needed to build anaerobic digesters and the complexity of complying with health regulations.

There are also new concerns about micropollutions in sewage (e.g. environmental persistent pharmaceutical pollutants), which make the process of producing high quality biosolids complex.

[9] Encouraging agricultural use of biosolids is intended to prevent filling landfills with nutrient-rich organic materials from the treatment of domestic sewage that might be recycled and applied as fertilizer to improve and maintain productive soils and stimulate plant growth.

Biosolids may contain macronutrients nitrogen, phosphorus, potassium and sulphur with micronutrients copper, zinc, calcium, magnesium, iron, boron, molybdenum and manganese.

[5][11][12] The United States Environmental Protection Agency (EPA) has set numeric limits for arsenic, cadmium, copper, lead, mercury, molybdenum, nickel, selenium, and zinc but has not regulated dioxin levels.

[16] In 2014, the City of Charlotte, North Carolina, discovered extreme levels of polychlorinated biphenyls (PCBs) in their biosolids after being alerted by that illegal PCB dumping was taking place at regional waste water treatment plants across the state.

[20] In 2023, Arturo A. Keller at the Bren School of Environmental Science & Management within the University of California, Santa Barbara began working on solutions to eliminate these PFAS, including creating bio-char fertilizers from the bio-solids.

[23][24] In the United States the EPA mandates certain treatment processes designed to significantly decrease levels of certain so-called indicator organisms, in biosolids.

[38] The European Union (EU) was the first to issue regulations for biosolids land application; this aimed to put a limit to the pathogen and pollution risk.

The Water Environment Federation (WEF) sought a new name to distinguish the clean, agriculturally viable product generated by modern wastewater treatment from earlier forms of sewage sludge widely remembered for causing offensive or dangerous conditions.