CHLORINE DIOXIDE FOR LEGIONELLA CONTROL IN A HOSPITAL WATER SYSTEM: MONITORING FOR DISINFECTION BY-PRODUCTS

摘要

Chlorine dioxide (ClO2) has been used recently in the U.S. As an approach for disinfection of hospital water systems to prevent hospital-acquired Legionnaires’ disease. The Environmental Protection Agency Maximum Residual Disinfectant Level for chlorine dioxide is 0.8 mg/L. The disinfection byproducts of chlorine dioxide are chlorite (ClO2 -) and chlorate (ClO3 -) ions. The EPA Maximum Contaminant Level (EPA MCL) for chlorite is 1.0 mg/L. The levels of chlorite and chlorate generated during continuous chlorine dioxide disinfection of hospital water system have not been well studied. In an ongoing prospective study, we evaluated the efficacy of chlorine dioxide to control Legionella in a hospital water system and measured levels of ClO2, ClO2 - and ClO3 -. ClO2 is injected into the cold water main at 0.5-0.7 mg/L. Samples were collected bimonthly. After 18 months, the mean concentration (mg/L) of ClO2, ClO2 - and ClO3 - in cold water samples were 0.36, 0.18 and 0.06, respectively. In hot water samples the concentrations were 0.05, 0.28 and 0.06, respectively. The chlorine dioxide concentration in the hot water was significantly lower than the cold water (p=0.0001). Legionella positivity was 60% (12/20) at hot water outlets in August 2003, and was 50% (10/20) in June 2004 after 18 months of chlorine dioxide treatment. Chlorite concentrations have not exceeded the EPA MCL of 1.0 mg/L.