Synergistic inactivation of Escherichia coli and MS-2 coliphage by chloramine and cupric chloride

Reaction of free chlorine with organic compounds in water during drinking water treatment may lead to the formation of potentially carcinogenic compounds known as trihalomethanes (THMs). Monochloramine and metals have been investigated as alternative disinfectants. However, the action of either disinfectant alone requires greater concentrations and longer contact times compared to free chlorine. This experiment evaluated the efficacy of combining monochloramine (1-2.5 mg/l) and copper in the form of cupric chloride (0.1-0.8 mg/l) to determine if inactivation of MS-2 coliphage and Escherichia coli was synergistic and thereby decreasing the concentration and contact time for adequate inactivation of these organisms. Combination of 5 mg/l monochloramine and 0.1-0.4 mg/l cupric chloride was sufficient to produce a 3 log₁₀ inactivation of MS-2 coliphage after 10 min. Nearly 120 min was required for the same log₁₀ inactivation of MS-2 using 5 mg/l monochloramine alone and less than a 0.5 log₁₀ reduction was observed after 120 min using 0.4 mg/l cupric chloride alone. A 6 log₁₀ reduction of E. coli was observed after 10- and 20-min exposures to 2.5 mg/l monochloramine and 0.8 or 0.4 mg/l cupric chloride, respectively. To achieve the same inactivation of E. coli using monochloramine alone, a concentration and contact time of 5 mg/l for 60 min was required. No inactivation of E. coli was observed after exposure to 0.4 or 0.8 mg/l cupric chloride after 60 min. Synergism was demonstrated in the inactivation of both organisms using the combined chloramine copper system.