Comparison of chlorine and chlorine dioxide disinfection in drinking water: Evaluation of disinfection byproduct formation under equal disinfection efficiency.

Disinfection efficiency and disinfection byproduct (DBP) formation are two important aspects deserving careful consideration when evaluating different disinfection protocols. However, most of the previous studies on the selection of disinfection methods by comparing DBP formation were carried out under the same initial/residual dose and contact time of different disinfectants, and such a practice may cause overdose or underdose of a certain disinfectant, leading to the inaccurate evaluation of disinfection. In this study, a comprehensive and quantitative comparison of chlorine (Cl) and chlorine dioxide (ClO) disinfection was conducted with regard to their DBP formation under equal disinfection efficiency. The microbial inactivation models as well as the Cl and ClO demand models were developed. On such basis, the integral CT (ICT) values were determined and used as a bridge to connect disinfection efficiency and DBP formation. For 3-log and 4-log reductions of Pseudomonas aeruginosa, ClO had 1.5 and 5.8 times higher inactivation ability than Cl, respectively. In the premise of equal disinfection efficiency (i.e., the ICT ratios of Cl to ClO = 1.5 and 5.8), the levels of total organic chlorine, total organic bromine, and total organic halogen formed in the Cl disinfection were significantly higher than those formed in the ClO disinfection. Among the 35 target aliphatic DBPs, trihalomethanes (THMs) and haloacetic acids (HAAs) were the dominant species formed in both Cl and ClO disinfection. The total THM levels formed in Cl disinfection were 14.6 and 30.3 times higher than those in ClO disinfection, respectively. The total HAA levels formed in Cl disinfection were 3.5 and 5.4 times higher than those in ClO disinfection, respectively. Formation of the target 48 aromatic DBPs was much favored in Cl disinfection than that in ClO disinfection, and the formation levels was dominated by contact time. This study demonstrated that ClO had significant advantages over Cl, especially at higher microorganism inactivation and lower DBP formation requirements.