This chapter briefly reviews why biosolids are a public-health concern, states the task addressed by the committee, sets forth the committee’s activities and deliberative process in developing the report, and describes the organization of the report.
Sewage sludge is defined in the Part 503 rule as the solid, semi-solid, or liquid residue generated during the treatment of domestic sewage in a treatment works. The term biosolids is not used in the Part 503 rule, but EPA (1995) defines biosolids as “the primarily organic solid product yielded by municipal wastewater treatment processes that can be beneficially recycled” as soil amendments. Use of the term biosolids has been controversial because of the perception that it was created to improve the image of sewage sludge in a public-relations campaign by the sewage industry (Rampton 1998). For the purposes of this report, the committee considers sewage sludge to be the solid, semi-solid, or liquid residue generated during treatment of domestic sewage, and biosolids to be sewage sludge that has been treated to meet the land-application standards in the Part 503 rule or any other equivalent land-application standards.
It is estimated that approximately 5.6 million dry tons of sewage sludge are used or disposed of annually in the United States, of which approximately 60% are used for land-application or public distribution (see Chapter 2). On the basis of data from EPA (1999a) and USDA (1997), EPA estimates that approximately 0.1% of available agricultural land in the United States is treated with biosolids. Biosolids are a complex mixture that may contain organic, inorganic, and biological pollutants from the wastewaters of households, commercial establishments, and industrial facilities and compounds added or formed during various wastewater treatment processes. Such pollutants include inorganic contaminants (e.g., metals and trace elements), organic contaminants (e.g., polychlorinated biphenyls [PCBs], dioxins, pharmaceuticals, and surfactants), and pathogens (e.g., bacteria, viruses, and parasites). Sewage-sludge treatment processes are intended to reduce the volume and organic content of biosolids and to reduce the presence of pathogens but retain beneficial properties for soil-amendment and land-reclamation purposes. Figure 1–1 provides a simplified schematic of how biosolids are produced and illustrates how the content of biosolids can vary depending on the wastewater streams and the variations in treatment processes. See Figures 2–1 and 2–2 in