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 (Cl₂) and chlorine dioxide (ClO₂) disinfection was conducted with regard to their DBP formation under equal disinfection efficiency. The microbial inactivation models as well as the Cl₂ and ClO₂ 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-log₁₀ and 4-log₁₀ reductions of Pseudomonas aeruginosa, ClO₂ had 1.5 and 5.8 times higher inactivation ability than Cl₂, respectively. In the premise of equal disinfection efficiency (i.e., the ICT ratios of Cl₂ to ClO₂ = 1.5 and 5.8), the levels of total organic chlorine, total organic bromine, and total organic halogen formed in the Cl₂ disinfection were significantly higher than those formed in the ClO₂ disinfection. Among the 35 target aliphatic DBPs, trihalomethanes (THMs) and haloacetic acids (HAAs) were the dominant species formed in both Cl₂ and ClO₂ disinfection. The total THM levels formed in Cl₂ disinfection were 14.6 and 30.3 times higher than those in ClO₂ disinfection, respectively. The total HAA levels formed in Cl₂ disinfection were 3.5 and 5.4 times higher than those in ClO₂ disinfection, respectively. Formation of the target 48 aromatic DBPs was much favored in Cl₂ disinfection than that in ClO₂ disinfection, and the formation levels was dominated by contact time. This study demonstrated that ClO₂ had significant advantages over Cl₂, especially at higher microorganism inactivation and lower DBP formation requirements.

Yang Pan

Dr., Nanjing University

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