Modeling of trihalomethane (THM) formation via chlorination of the water from Dongjiang River (source water for Hong Kong's drinking water)

The Dongjiang River is the major source of drinking water supply for Hong Kong. The deterioration of the water quality of the Dongjiang River and excessive trihalomethanes (THMs) in the tap water of some districts in Hong Kong have become causes for public concern. The main objective of the present study is to investigate and model THM formation due to the chlorination of the Dongjiang River water under different chlorination conditions. The results showed that the total THM formation ranged between 11.7 and 91.8 mg L^{- 1} and that control of the levels was primarily due to the reaction time and the Br^- level in the water. Bromide concentration was a key factor in determining bromine-containing THM formation and consequently the speciation of THMs. Higher concentrations of bromide shifted THM species to more-bromine-containing ones, while the kinetics reflected the competing halogenation reactions. As the two mixed-halogen THMs had high cancer potency, the cancer risk of total THMs appeared to reach a peak at a bromide concentration ranging between 218 and 262 mg L^{- 1} (with a bromide to dissolved organic carbon molar ratio (Br^-/DOC) ranging between 15 and 18 mM/mM).