ABSTRACT
In the first half of the 20th century, life expectancy in the United States increased dramatically, primarily because of water treatment, which greatly reduced the incidence of waterborne bacterial infections such as cholera, typhoid fever, and dysentery. The Safe Drinking Water Act of 1974 and its amendments of 1986 and 1996 are the primary pieces of federal legislation protecting drinking water supplied by public water systems. A standard process chain for water treatment consists of grit removal, flash mixing with chemicals, flocculation, sedimentation, filtering, and disinfection. The Clean Water Act of 1972 and subsequent legislation with the objective of reducing the discharge of pollutants to natural waters imposed standards on the secondary treatment of wastewater. A standard process chain for wastewater treatment consists of preliminary (physical), primary (physical and chemical), and secondary (biological) steps. In secondary treatment, microorganisms consume organic pollutants. Much industrial waste is incompatible with public treatment systems, so it is usually subject to pretreatment.
