United States increases, the percentage of the population directly discharging to POTWs is projected to increase to 88% by 2016 (EPA 2000a). The ability to effectively treat and return wastewater and sewage sludge to the environment in a protective manner is of paramount importance from both a public-health and an environmental perspective. In partial recognition of this fact, Congress passed the CWA of 1972 and the federal government has contributed $61.1 billion in grants and $16.1 billion in low-interest loans to municipal and local governments between 1972 and 1999 for capital construction costs to provide necessary support for wastewater and sewage-sludge treatment and disposition of biosolids (EPA 2000a). Approximately 40% of that amount has been used for sewage sludge treatment and disposition of biosolids (Peavy et al. 1985). Sewage sludge is generated in several treatment processes that generally include primary (from primary clarification) and secondary (from secondary clarification) sewage sludge. The general process of treating wastewater and sewage sludge is illustrated in Figures 2–1 and 2–2.
EPA is responsible under Section 405 of the CWA to promulgate regulations for sewage sludge use or disposal. The CWA Amendments of 1987 added special provisions that required EPA to identify toxic pollutants and set sewage-sludge standards that are “adequate to protect public health and the environment from any reasonably anticipated adverse effect of each pollutant” (emphasis added). Recognizing that sewage-sludge production will continue to increase and that sewage sludge possesses many potential beneficial properties for agricultural production, federal and state agencies have long advocated the recycling of it as biosolids through land application (EPA 1981, 1984, 1991). The other primary options for sewage sludge disposition are to bury it in a landfill or to incinerate it. Although these latter options possess inherent risks and environmental difficulties, these options are beyond the scope of this report (see Chapter 1).
Of the 16,000 POTWs in the United States, approximately 8,650 generate sewage sludge that must be used or disposed of at least annually (Wisconsin Department of Natural Resources, unpublished data, 2001). Based on data from 37 states, approximately 5,900 of these sewage sludge generators (68%) either land apply or publicly distribute over 3.4 million dry tons of biosolids each year (see also End Use Practice section of this chapter). Most of this recycling use is conducted without public opposition and with no documented adverse health effects. However, recent allegations of adverse health effects have received media and congressional attention. Chapter 3 assesses the epidemiological evidence and approach for health effects associated with biosolids production and application, but does not systematically investigate these allegations. Rather, the report examines the process by which the regulations were established and determines whether advances in risk-assessment methods warrant a revisiting of the process.