Comparative assessment of chlorine reactivity and trihalomethanes formation potential of three different water sources

Abstract

Trihalomethanes (THMs) are carcinogenic compounds formed during water chlorination. Nature of source water and treatment conditions significantly influence its formation. Chlorine reactivity and trihalomethanes formation potential of water samples taken from three different sources such as the sea, open reservoir, and Palar river subsoil were assessed for a period from 2013 to 2017 with respect to key determinants. UV absorbance (254 nm) values of all the water samples (n = 175) varied from 0.033 to 0.09 with dissolved organic carbon (DOC) ranged between 1.08–1.88, 0.69–2.15, 0.66–1.98 mg/L for seawater, open reservoir and Palar subsoil water respectively. Though UV absorbance (UV254) was positively correlated with DOC content, specific UVA254 (SUVA254) did not correlate with DOC. Consistent nonlinear increase in chlorine demand with increasing dose and time was observed which differs in magnitude for three water sources. THM formation potential followed the order: Reservoir > Seawater > Palar subsoil. The seasonal average of THMs (5 mg/L dose; 24 h contact time) was the highest for open reservoir water samples ranging from 151.62 (southwest monsoon)-198.25 μg/L (post northeast monsoon) as compared to that of the seawater (max. 105.60 μg/L) and Palar subsoil water (max. 119.66 μg/L). Among the three sources, THM in open reservoir water sample only exhibited positive correlation with its DOC. Water quality parameters such as pH, temperature, dissolved oxygen, nitrate, total nitrogen failed to establish a clear correlation with THMs yield, which indicated the overriding influence of simultaneous occurring reactions. Among all the parameters chlorine demand appeared to be a better surrogate to predict trihalomethanes formation regardless of water sources.