Complying with Trihalomethane Reduction Requirements in Water Treatment Facilities

Book excerpt: Eight case studies from around the United States involving the reduction of trihalomethane in water treatment facilities. Includes information on finished water quality, treatment plant performance, and costs for each example. "From the Introduction: " In order to comply with the maximum contaminant level (MCL) for total trihalomethanes (TTHM), many utilities have modified their pre-oxidation and disinfection practices by switching to alternative oxidants and disinfectants in place of free chlorine. Examples of such modifications include the use of chlorine dioxide (C102), ozone (O3) or potassium permanganate (KMnO4) as pre-oxidants and disinfectants with free chlorine used as the final disinfectant, and the use of free chlorine as a pre-oxidant and disinfectant with combined chlorine (e.g., monochloramine (NH2Cl)) used as the final disinfectant. In fact, the final rule establishing an MCL for TTHM in November 1979 (EPA, 1979) was followed in March 1982 by a guidance document for utilities in which the EPA proposed treatment technologies which could be used to control trihalomethane (THM) levels. Three of the five "generally available" treatment methods included the use of chloramines or chlorine dioxide as alternative or supplemental disinfectants or oxidants, and the substitution of chloramines, chlorine dioxide, and potassium permanganate as pre-oxidants in place of chlorine. The proposal also included, as an additional treatment method which should be considered but which was not identified as "generally available," the use of ozone as an alternate or supplemental disinfectant or oxidant. These proposals were subsequently adopted by EPA in February 1983 (EPA, 1983). At the time