Biosolids are the organic materials obtained by the treatment of sewage in municipal wastewater treatment facilities. Sewage sludge is the material resulting from settling and screening of solid materials in sewage. Biosolids differ from sewage sludge in that they undergo additional physical, chemical, and biological processing to control odors and remove disease-causing organisms, toxins, and some heavy metals.
An estimated 6.9 million dry tons of biosolids were generated in 1998. It is projected that by 2010, 8.2 million dry tons will be generated. About 17% of biosolids are landfilled, while the remainder are recovered and used (about 1.5 million dry tons for energy production).