Advantages of a ClO2/NaClO combination process for controlling the disinfection by-products (DBPs) for high algae-laden water

Chlorine dioxide (ClO 2 ) has been widely used in the process of preoxidation and disinfection as an excellent water treatment reagent. However, the inorganic by-products produced by ClO 2 , such as chlorite (ClO 2 − ) and chlorate (ClO 3 − ) are harmful to human health, and this has become a potential problem when using ClO 2 in drinking water treatment. In this study, ClO 2 alone and a ClO 2 /NaClO combination process were carried out to evaluate the algae removal efficiency of the treatment and the formation of disinfection by-products (DBPs: chlorite, chlorate, trihalomethanes and haloacetic acids) for high algae-laden water with 124.16 µg L −1 chlorophyll a (Chl.a) content. The results show that disinfection with 1.5 mg L −1 ClO 2 alone results in a ClO 2 − concentration exceeding 0.7 mg L −1 . ClO 2 preoxidation/ClO 2 disinfection is applicable for the control of effluent quality, but the ClO 2 − concentration still has an excessive risk when using 0.8 mg L −1 and 0.6 mg L −1 ClO 2 for the two process, respectively. In the ClO 2 /NaClO combination process, the ClO 2 − concentration is below 0.6 mg L −1 , and trihalomethane (THM) and haloacetic acid (HAA) concentrations are lower than 60% of the maximum contaminant levels (MCLs) set by the World Health Organization (WHO). Further, the formation of ClO 2 − is more effectively controlled by NaClO preoxidation/ClO 2 disinfection than ClO 2 preoxidation/NaClO disinfection.