AWWA WQTC60734

AWWA WQTC60734 Formulation and Decay of THMs and HAAs in Five Full-Scale Distribution Systems
Conference Proceeding by American Water Works Association, 11/15/2004

Baribeau, Helene; Boulos, Lina; Haileselassie, Hiriti; Singer, Philip; Nichols, Cora; Schlesinger, Savita; Williams, Sherry; Gullick, Richard

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This AwwaRF and U.S. Environmental Protection Agency (USEPA) sponsored research study investigated factors affecting the formationand decay of disinfection byproducts (DBPs) under actual distribution system conditions. Fullscaledistribution system samplings were conducted over a one-year period at two freechlorinated systems and two chloraminated systems. In addition, one chloraminated system, withperiodical 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 ofgeneral water quality parameters. This manuscript presents THM4 and HAA9 results obtained atthe participating utilities, and a discussion of observed factors affecting the formation and decayof DBPs in full-scale distribution systems.As expected, THM4 and HAA9 concentrations were higher in the warmer months than in thecolder months in both free chlorinated and chloraminated systems. In the free chlorinatedsystems, 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 ageincreased. In both free chlorinated and chloraminated systems, pipe material and diameter was not observedto affect THM4 and HAA9 concentration and speciation.The chloraminated systems that periodically switch to free chlorine allowed confirmation ofseveral trends: THM4 and HAA9 concentrations increased with increasing water temperature,although the magnitude of increase in HAA9 concentrations due to temperature was not as highas the increase in THM4 concentrations; THM4 and HAA9 concentrations were higher duringthe free chlorination period than during the chloramination periods; THM4 and HAA9concentrations increased with increasing water age when free chlorine was used as finaldisinfectant, whereas DBP concentrations remained relatively uniform during chloramination; and, the magnitude of increase in HAA9 concentration during chlorination was less than theincrease observed for THM4. Includes figures.