Before treatment, water entering a municipal facility may contain disease-causing microscopic organisms, such as bacteria and viruses, which are known as pathogens, or germs.

Federal law requires treatment to reduce pathogens: Treatment of biosolids to Class B standards eliminates 99 percent or more of the pathogens that exist in sewage sludge. Digesters and other forms of treatment kill pathogens originally found in solids.  It is the elimination of these pathogens that allow biosolids to be safely applied to agricultural and forest lands. Treatment of biosolids to Class A Exceptional Quality (EQ) standards completely eliminates pathogens. Accordingly, these materials may be used with very limited restrictions.

Ongoing research by utilities has continued to validate a technology-driven approach to reducing or eliminating pathogens in biosolids and shows low risk for the transmission of pathogens from land application sites to neighbors who live near application sites. No scientific studies have demonstrated any link between the existence of human pathogens in biosolids and illnesses in nearby residents. The conclusion that application of biosolids utilizing best management practices poses negligible health risks from pathogens is based on scientific research about pathogen survivability in the environment. Many pathogens do not survive passage through the collection and treatment system and through the additional treatment processes that further disinfect solids and effluent. (Raina M. Maier et al., Environmental Microbiology 512-13 (2000).)