AWWA WQTC60734

This AwwaRF and U.S. Environmental Protection Agency (USEPA) sponsored research study investigated factors affecting the formation and decay of disinfection byproducts (DBPs) under actual distribution system conditions. Fullscale distribution system samplings were conducted over a one-year period at two free chlorinated systems and two chloraminated systems. In addition, one chloraminated system, with periodical switches to free chlorine for nitrification control, was closely monitored before, during, and after the disinfectant change. Monitoring parameters included the four trihalomethanes (THM4), the nine haloacetic acids (HAA9) and N-nitrosodimethylamine (NDMA), along with a suite of general water quality parameters. This manuscript presents THM4 and HAA9 results obtained at the participating utilities, and a discussion of observed factors affecting the formation and decay of DBPs in full-scale distribution systems. As expected, THM4 and HAA9 concentrations were higher in the warmer months than in the colder months in both free chlorinated and chloraminated systems. In the free chlorinated systems, THM4 concentrations increased as water age increased and chlorine residual decreased, a trend observed for all samplings. In the chloraminated systems, THM4 concentrations were relatively stable as water age increased. In both free chlorinated and chloraminated systems, pipe material and diameter was not observed to affect THM4 and HAA9 concentration and speciation. The chloraminated systems that periodically switch to free chlorine allowed confirmation of several trends: THM4 and HAA9 concentrations increased with increasing water temperature, although the magnitude of increase in HAA9 concentrations due to temperature was not as high as the increase in THM4 concentrations; THM4 and HAA9 concentrations were higher during the free chlorination period than during the chloramination periods; THM4 and HAA9 concentrations increased with increasing water age when free chlorine was used as final disinfectant, whereas DBP concentrations remained relatively uniform during chloramination; and, the magnitude of increase in HAA9 concentration during chlorination was less than the increase observed for THM4. Includes figures.