AWWA JAW55402

Drinking water regulations emphasize monitoring at the plant effluent, but water quality can deteriorate between the plant and the customer's tap. Although the fate of disinfectants and disinfection byproducts (DBPs) has been examined in controlled, constant laboratory conditions, research has not fully investigated their fate in full-scale distribution systems. This study tracked changes in the concentrations of chlorine and dissolved organic halogens (DOX) as a function of water residence time (RT) in two full-scale drinking water distribution systems. Free and total chlorine concentrations decreased with increasing RT in the distribution system. Pipe size also influenced chlorine decay, especially in warm water; at similar RTs, chlorine concentrations were lowest in small-diameter pipes, greater in the main pipes, and greatest in the batch incubations. Corrosion byproducts in pipes appeared to be the major factor affecting chlorine decay in the distribution system; chemical instability of some DBPs and the presence of microbial biomass seemed to be the main factor influencing DOX. Numerous factors affect water quality in the distribution system - pipe materials, diameter, presence of corrosion byproducts and biofilm, RT, water temperature, disinfectant residuals, and hydraulic conditions. To preserve the high water quality obtained by expensive treatment processes, water providers need a better understanding of how that quality can degrade in the distribution system. Armed with this information, they can make better determinations of disinfectant dosages to comply with regulatory requirements and protect their supplies at all points of the distribution system. Includes 45 references, tables, figures.