Formation potential of trihalomethanes (THMs) in blended water treated with chlorine

This study was conducted in the laboratory to assess the formation potential of trihalomethanes (THMs) in blended water under various treatment conditions. Three batches of water samples prepared by mixing desalinated (product) water and ground brackish water with three different proportions (i.e. 1:2, 1:5 and 1:10 - brackish:product water) were treated with three concentration levels of calcium hypochlorite and collected after 24 and 48 h. Other treatment runs were conducted under three different temperatures of 25, 35 and 45 °C. Results of the study indicated that brominated THMs (i.e. bromoform (CHBl₃) and dibromochloromethane (CHClBr₂)) were the dominant components of the THMs formed in blended water. Results also showed that the total THMs (TTHMs) levels decreased as the portion of product water in the blended samples increased from 2 to 10. Results revealed that bromoform levels decreased and chloroform increased as the product portion increased. In this study, the TTHMs slightly increased as the chlorine dose increased from 1 to 5 ppm and as high as 175 ppb of TTHMs formed when the temperature of the water increased from 25 to 45 °C.