Research on Inorganic Disinfection By-Products in Combined Disinfection of Chlorine and Chlorine Dioxide

In this paper, inorganic disinfection by-products formation rules and amount in the process of combined disinfection of chlorine and chlorine dioxide were investigated in three kinds of commonly used pipe materials. We investigated two types of combined disinfection, which included: (1) adding chlorine first and then adding chlorine dioxide; and (2) adding chlorine and chlorine dioxide together with different proportions. Results indicated that chlorine levels were the highest in PVC pipe and lower in metal pipes for both kinds of combined disinfection. The difference between the two types of combined disinfection was that in the way of adding chlorine and chlorine dioxide together, chlorite levels in the ductile iron pipe increased with the increase of chlorine in the mixed disinfectant. While, for the way of adding chlorine first and then adding chlorine dioxide, chlorite levels were higher in ductile iron pipe than in stainless steel from the beginning to the end. The results would be a useful guide for many municipalities and communities using combined disinfection in determining disinfectant dosage, proportions of disinfectants and so on.