Modeling the formation and assessing the risk of disinfection by-products in water distribution systems.

The effect of water quality parameters and operation conditions of water treatment on the formation of trihalomethanes (THM) and haloacetic acids (HAA) in pilot-scale reactor and water distribution system were investigated. Results indicated that dissolved organic carbon and THM formation increased while the concentration of free chlorine decreased along the length of pipeline from the water treatment plant; but HAA formation showed no relationship with the pipeline length. THM concentration was predicted with hydraulic analytic software, namely WaterCAD. The predicted THM data were within +/-10% of measurements; HAA had a relatively high error of +/-16% due to complex bio-decomposition reactions occurred in the distribution system. Both the hazardous quotient and cancer risk of THM in the water distribution system of an advanced water treatment plant were much lower than those of a conventional water treatment plant; there was no significant difference in hazard quotient and cancer risk of HAA in the above two water distribution systems.