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AWWA ACE58292
- Understanding and Optimizing Chlorine Interactions during Coagulation
- Conference Proceeding by American Water Works Association, 06/15/2003
- Publisher: AWWA
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To minimize disinfection byproduct (DBP) formation, three general optimizationoptions are available to conventional treatment plants that chlorinate prior to or at the rapidmix: lower the level of chlorine dosed at the rapid mix and re-chlorinate; move the pointof chlorination downstream of the rapid mix; or, switch to a different pre-disinfectant/oxidant. Bench-scale results indicated that lowering the pre-chlorination dose and rechlorinatingafter the sedimentation basin such that a target distribution system residual (1mg/L at 24 hours) is maintained, yielded lower chlorine consumed and lower totaltrihalomethanes (TTHMs) and haloacetic acids (HAA5) formed after 24 hours (up to 23% and33%, respectively, after 5 days). This observed behavior could be explained by theavailability of natural organic matter (NOM) to react with chorine to form halogenated byproducts.The first objective of this study was to assess and evaluate the conditions under whichoptimizing preoxidation is effective in controlling DBPs. Chlorine dose, point of chlorineapplication and the use of other preoxidants (chlorine dioxide, potassium permanganate andmixed oxidant) were evaluated. Chlorine dose levels were varied to achieve three watertreatment goals: inorganic oxidation, bio-growth control and CT. Moving the point of chlorineapplication from the rapid mix to mid-flocculation to post sedimentation was evaluated. Thealternative preoxidants were dosed to achieve inorganic oxidation and biogrowth control andre-chlorinated (post sedimentation) to yield CT and a target distribution system residual.The second objective was to understand the interactions of chlorine with NOM duringcoagulation, flocculation and sedimentation (CFS), particularly the solid / liquid phaseformation of halogenated DBPs. Relating these results to those obtained from the firstobjective enables the integration of fundamentals into applicable engineering, therebyobtaining the full spectrum of understanding. Includes 3 references, tables, figures.
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