Use of chlorine dioxide as alternative to chlorination in reverse osmosis product water

Enhanced bromate formation has been observed in desalination-derived drinking water containing bromide disinfected by chlorination under alkaline conditions. As an alternative to chlorine disinfection in drinking water, chlorine dioxide (ClO 2 ) was investigated to elucidate its performance in curtailing the bromate formation in the seawater reverse osmosis product water. The occurrence of disinfection by-products (DBPs), viz., chlorite, chlorate and trihalomethanes (THMs) was also monitored during the whole period of the tests at varying distances of 10, 50 and 3,500 m. Bromate concentrations throughout the trial were found to be <2 ppb indicating negligible or no bromate formation at the optimum residual ClO 2 in the range of 0.18–0.20 ppm. Chlorite (<0.01–0.1 ppm), chlo-rate (<0.05–0.14 ppm) and calculated total THMs were found to be within the range of the regulatory limits (<1) set by the World Health Organization (WHO). Biological analyses showed total coliforms and E. coli were negative indicating ClO 2 to be very efficient at the optimum residual in the range of 0.18–0.20 ppm. The chlorine dioxide generating system used in this test was found to be efficient in generating chlorine dioxide with minimum amounts of DBPs.