Impact of Booster Chlorination on THM Production: A Simulated Analysis

Abstract

Chlorine is commonly used in drinking water treatment as both a primary disinfectant and as a secondary disinfectant to carry a residual in the distribution system. The continuing formation of disinfection by-products (DBPs), including trihalomethanes (THMs), due to reactions between residual chlorine and natural organic matter (NOM) has led utilities and researchers to seek innovative ways of managing disinfectant residuals. One such management strategy that has been proposed is the use of booster chlorination (re-chlorination), but relatively little research has been done on this topic. Previous research has indicated that the rates of chlorine consumption and THM formation remain the same under re-chlorination conditions. For this study, a model water comprised of NOM extracted from Lake Drummond, Virginia was chlorinated under two scenarios: one representing conventional chlorination, and one representing booster chlorination. Chlorine consumption and THM formation were monitored over a 72-hour time period, and the results show that both THM formation and chlorine consumption were the same under both scenarios. The results of this study also confirm the findings of previous research that THM formation and chlorine consumption are linearly correlated, even under re-chlorination conditions. Additional work is ongoing as part of this study to explore the effect of booster chlorination on chlorine consumption and THM formation in distribution systems using hydraulic models.