CONCENTRATION OF TRIHALOMETHANES (THM) AND PRECURSORS IN DRINKING WATER WITHIN DISTRIBUTION NETWORKS
CORNELIA DIANA ROMAN, ANCA ELENA GURZAU, IRINA DUMITRASCU, CRISTIAN POP
ABSTRACT. Concentration of trihalomethanes (THM) and precursors in drinking water within distribution networks. Water chlorination is the disinfection method most widely used, having however the disadvantage of producing trihalomethanes (THM) as secondary compounds, which are included in the list of priority hazardous substances in water. THM formation is influenced by the raw water composition and chlorine from the disinfection process. This paper intends to highlight the individual values of the chemical compounds precursors of THM in the water network in order to correlate them with the evolution of THM concentration. The cities of Targu Mures and Zalau were chosen as the study area having surface waters with different degrees of contamination as the water source. Pre-treatment with potassium permanganate is used at the water treatment plant in Targu Mures, while pre-chlorination is used at the water treatment plant in Zalau. Water sampling was performed weekly between March-May, 2011 in three sampling points of each city, maintained during the period of study. Total THM and their compounds as well as THM precursors (oxidability, ammonium content, nitrites and nitrates) were measured. The water supplied in the distribution network corresponded integrally to the quality standards in terms of the analyzed indicators, including THM concentrations. The higher average THM concentrations in Zalau (52.01±14 μg/L) compared to Targu Mures (36.43±9.14 μg/L) were expected as a result of precursors concentration. In terms of THM compounds, they had similar proportions in the two localities, chloroform being clearly predominant, followed by dichlorobromoform and dibromochloroform, while bromoform was not identified. Statistical data analysis showed that the presence of THM precursors is correlated with the THM levels but not sufficient for their generation, even if they can be considered in general the basis of a valid prediction.
Keywords: drinking water, chlorination, precursors, THM.