Disinfection Byproduct Control with Chlorine Dioxide and OtherAlternative Oxidant Strategies

摘要

Many utilities are challenged by problems associated with disinfection by-product (DBP) control. Alternativernstrategies available for reaching goals include; moving the point of chlorine application downstream; splittingrnthe overall chlorine dose between two points of application; or utilizing alternative oxidants. Both potassiumrnpermanganate and chlorine dioxide have shown to reduce DBP formation. More specifically, as an effectivernoxidant and a successful disinfectant for Cryptosporidium, chlorine dioxide (ClO2) has shown especiallyrnpromising results. Though ClO2 doses are limited by the formation of inorganic DBPs, ClO2 forms fewerrnregulated organic DBPs compared to chlorine. The primary objectives in this study were to systematically test a)rnthe impact on DBP formation under alternative strategies and oxidants at the pilot scale level; and b) evaluaternthe use of ClO2 under preoxidant and primary disinfectant scenarios by the quantification of organic DBPrnformation at the bench scale.rnGenerally, both alternative strategies in chlorine dosing resulted in a decrease in DBP formation measured at thern24-hour sample point. Moreover, as the chlorine dose was reduced, DBP formation decreased as well. TTHMrnand HAA5 formation were reduced by an average of 27 and 16 percent, respectively, when splitting the chlorinerndose and by 11 and 7 percent, respectively when moving the point of chlorination downstream from the rapidrnmix to mid-flocculation. When moving the entire dose of chlorine to post sedimentation, the TTHM and HAA5rnformation was reduced by about 50 percent. The alternative oxidants were also successful at reducing DBPrnformation: 36 and 53 percent for TTHM under preoxidation with KMnO4 and ClO2 respectively, and 39 and 55rnfor HAA5 formation, respectively.rnThe impact of ClO2 as a preoxidant or primary disinfectant on TTHM and HAA5 formation was evaluated onrnfour source waters. Under the primary disinfection condition, TTHM and HAA5 formation at the 24-hourrnsample point was reduced by an average of 50 and 34 percent, respectively. Under preoxidation, the TTHMrnformation was reduced by an average of 33 percent, while the HAA5 formation actually showed an averagernincrease of 27 percent.