Speciation and kinetics of trihalomethanes formation in drinking water supplies

Trihalomethanes (THMs) are formed in drinking water supplies as a result of chlorination which are carcinogenic in nature and may cause the diseases like bladder cancer, colon cancer etc. This study aims at establishing the concentration range and speciation, of THMs in the drinking water supplies of eastern part of India. The results delineated significantly higher concentration of THMs (231–484 μg/L) exceeding the maximum allowable limit prescribed by IS 10500 (2012) and USEPA (2011). Speciation of THMs revealed predominance of chloroform followed by CHBr2Cl and CHBrCl2. However, bromoform was not detected in any of the samples. This may be due to absence of bromide ion below detection limit (< 0.01 mg/L). Effects of contact time, pH and chlorine doses on THMs formation were also investigated. The study indicated increase in THMs with increasing contact time and chlorine dose. The increase in THMs was directly proportional to the applied chlorine dose. The rate of reaction of THMs formation increased as the pH of water was increased from 6 to 9. Meanwhile, THMs were not detected in the pH range below 5 because at this pH chlorine does not react and remains as elemental chlorine. Kinetics of THMs formation and chlorine decay followed first-order reactions. THM formation kinetics were determined using Clark and Kavangauh models. Validation of the models revealed that Clark model (error of prediction, 5.913) predicted THMs formation more accurately than Kavangauh (error of prediction, 19.71). The models may have considerable utility, particularly for evaluating the potential of THM formation in the distribution system following post disinfection with chlorine.