Controlling DBPs with monocholoramine

he proposed Disinfectants/Disinfection By-products (D/DBP) Rule and the Enhanced Surface Water Treatment Rule (ESWTR) have prompted an industrywide evaluation of disinfection and treatment practices.1,2 One of the least expensive methods of limiting DBP formation is to use monochloramine instead of free chlorine to maintain a distribution system residual. Monochloramine limits free chlorine contact time. An understanding of DBP formation rates will allow microbial inactivation goals to be balanced with DBP control goals. This article examines the effect of common water quality variables on DBP Balancing disinfection with control of disinfection by-products (DBPs) requires an understanding of how common water quality variables such as chlorine dosage and contact time, temperature, pH, and total organic carbon (TOC) affect both processes. This article examines how these variables affect the concentrations of trihalomethanes (THMs) and haloacetic acids (HAAs) at the shorter contact times associated with the use of chloramines, rather than chlorine, for residual disinfection. Five case studies evaluated DBPs in five water sources of differing quality. The most important variables were TOC and chlorine contact time, but chlorine dosage, pH, and temperature also had an effect. Response to some variables was linear; response to others was nonlinear. In most water sources, THM concentrations were greater than HAA concentrations, but in some the reverse was true. DBP concentrations must be investigated under a range of conditions to determine the best way to use chlorine disinfection while minimizing concentrations of DBPs. For executive summary, see page 174.