AWWA WQTC52940

Several studies have shownthat trihalomethanes (THMs) tend to be stable in distribution systems, whereas some of the haloacetic acid (HAA) species can be biodegraded in the absence of a residual disinfectant. This paper presents results from a bench-scale study on the biostability of the four THMs and all nine HAAs in adistribution system. They were placed at the effluent of a full-scale treatment plant, which uses a conventional treatment process with chlorine for primary disinfection and chloramines for secondary disinfection. Two parallel trains of reactors were set up: one receiving free chlorinated water; and the other chloraminated water. Each train was composed of two reactors in series: the upstream reactor received a positive disinfectant residual, and the downstream reactor received dechlor(am)inated water using sodium thiosulfate. Liquid and biofilm samples were collected under both cold and warm water conditions. Parallel samples were collected at the reactor influent to differentiate between the effectof the residence time and the impact of the biofilm. Includes 17 references, table, figures.