Quenching of chlorination disinfection by-product formation in drinking water by hydrogen peroxide

Abstract

Reactions between chlorine disinfectants, dissolved organic matter, and other chemicals in water form a series of disinfection by-products (DBPs), including trihalomethanes (THMs) and haloacetic acids (HAAs), that are toxic and subject to increasingly stringent regulations. This paper explores effects on DBP formation produced by an alternative, non-chlorine-based secondary disinfectant comprised of silver and hydrogen peroxide (Ag +/H 2O 2) that is designed to provide long-lasting residual disinfection. Based on a series of laboratory experiments using simulated treatment and distribution systems, post-chlorination additions of the secondary disinfectant dramatically reduced the formation of halogenated DBPs. Five source waters were tested over a range of conditions, including various levels of chlorine dosing, bromine and organic carbon concentrations, pH and temperature. For surface and ground waters, DBP reductions at 24 h with the secondary disinfectant averaged 72±9% for THMs and 67±11% for HAAs after a 10-min chlorination period. The dramatic reduction in halogenated DBPs occurred for all tested source waters and all disinfection conditions. The likely mechanism is the reduction of chlorine to chloride by H 2O 2, which halts further reaction of chlorine with dissolved organic matter and other DBP precursors. Thus, H 2O 2 acts as a quenching agent, in addition to its residual disinfectant properties in combination with Ag +. This research shows a potential benefit of mixed disinfectants that provide a potentially viable option for controlling the formation of DBPs while maintaining effective disinfection.