The Occurrence and Control of Disinfection By-Products (DBPs) in Two Water Treatment Plants Utilizing the Same Source

The influence of disinfection by-products (DBPs) on the operation and design of water treatment plants has been increasing since the early studies by Rook on trihalomethanes (THMs) (Stevens, 1977). Work conducted in the 1980s identified the existence of nonvolatile halogenated organics (non-THM organics), of which the majority produced by chlorination were haloacetic acids (HAAs), within the HAAs, dichloroacetic acid (DCAA) and trichloroacetic acid (TCAA) were the dominant members. Concern over potential health effect led the U.S. Environmental Protection Agency (USEPA) to set a maximum contaminant level (MCL) for total THMs and HAAs. The disinfectant/disinfection by-product rule (D-DBP Rule) currently proposed by the USEPA will lower the MCL for THMs and HAAs. Past and pending DBP regulations have provided a momentum to seek a better understanding of how these compounds are formed as well as how their production can be controlled. Drinking water utilities are preparing for these major changes. An investigation was conducted to examine disinfection options that would ensure minimization of DBP formation and conform to disinfectant-disinfection by-product regulations. Primary issues were the types of disinfectants applied (chlorine, chlorine dioxide, chloramines and/or ozone). The study was conducted at two public drinking water treatment plants that derive their water from one source; the Delaware River. Each plant was associated with a different chemical environment that affected DBP formation. The effects of implementing different disinfection options on DBP formation were evaluated at pilot plants for various water conditions. Analyses were conducted for disinfectant residuals, organic by-products (trihalomethanes and haloacetic acids). Promising DBP elimination strategies were also investigated utilizing the pilot treatment facilities. Results have shown that DBP control was accomplished by the focus on removal of the precursors through granular activated carbon (GAC), reverse osmosis and coagulation. After the DBPs had formed it was possible to remove them by subsequent GAC and coagulation treatment.