AWWA WQTC60655

Many utilities are challenged by problems associated with disinfection byproduct (DBP) control. Alternative strategies available for reaching goals include: moving the point of chlorine application downstream; splitting the overall chlorine dose between two points of application; or, utilizing alternative oxidants. Both potassium permanganate and chlorine dioxide have shown to reduce DBP formation. More specifically, as an effective oxidant and a successful disinfectant for Cryptosporidium, chlorine dioxide (ClO₂) has shown especially promising results. Though ClO₂ doses are limited by the formation of inorganic DBPs, ClO₂ forms fewer regulated organic DBPs compared to chlorine. The primary objectives of this study were to systematically test: the impact on DBP formation under alternative strategies and oxidants at the pilot scale level; and, evaluate the use of ClO₂ under preoxidant and primary disinfectant scenarios by the quantification of organic DBP formation at the bench scale. Generally, both alternative strategies in chlorine dosing resulted in a decrease in DBP formation measured at the 24-hour sample point. Moreover, as the chlorine dose was reduced, DBP formation decreased as well. Total trihalomethane (TTHM) and haloacetic acid (HAA5) formation were reduced by an average of 27 and 16 percent, respectively, when splitting the chlorine dose and by 11 and 7 percent, respectively when moving the point of chlorination downstream from the rapid mix to mid-flocculation. When moving the entire dose of chlorine to post sedimentation, the TTHM and HAA5 formation was reduced by about 50 percent. The alternative oxidants were also successful at reducing DBP formation: 36 and 53 percent for TTHM under preoxidation with KMnO₄ and ClO₂ respectively, and 39 and 55 for HAA5 formation, respectively. The impact of ClO₂ as a preoxidant or primary disinfectant on TTHM and HAA5 formation was evaluated on four source waters. Under the primary disinfection condition, TTHM and HAA5 formation at the 24-hour sample point was reduced by an average of 50 and 34 percent, respectively. Under preoxidation, the TTHM formation was reduced by an average of 33 percent, while the HAA5 formation actually showed an average increase of 27 percent. Includes 20 references, tables, figure.