Monochloramine and Chlorine Dioxide as Alternative Disinfection Met Meth For Legionella Control: Results of Pilot-studies in a Model Plumbing

摘要

Legionnaires’ disease can be prevented by eradication of Legionella from the water systems ofhospitals, industrial plants, apartment and office buildings. Currently recommended methods forLegionella pneumophila inactivation are thermal disinfection and hyperchlorination. However, eachhas significant disadvantages such that alternative disinfection approaches are needed.Monochloramine (NH2Cl) and chlorine dioxide (ClO2) are potential alternatives to chlorine that havereceived much attention in recent years. Monochloramine is considered to be a good secondarydisinfectant due to its stability, better prevention of bacterial re-growth, superior ability to penetratebiofilm, reduced disinfection by-products (DBPs), and no taste and odor problems. But little is knownabout the efficacy of monochloramine against environmentally grown Legionella, especially againstbiofilm-associated Legionella. Chlorine dioxide is a strong oxidant with no taste and odor problemsand minimal generation of DBPs. However, use of chlorine dioxide has been limited because ofdifficulties with safe on-site production. A new chlorine dioxide generating system (Halox, BridgeportCT) uses an electrochemical process that appears to be safe, and easy-to-control. The objective of thisstudy was to compare the efficacy of monochloramine, chlorine dioxide and chlorine againstLegionella and heterotrophic bacteria in a model plumbing system at pH 7.0 ~ 8.0 and temperature of25°~30°C. Monochloramine and chlorine were tested at a single dose of 2.0 mg/L and 4.0 mg/L as Cl2individually. Chlorine dioxide was tested at a single dose of 2.0 mg/L as ClO2 and at an initial dose of2.0 mg/L followed by maintaining a 0.5 mg/L residual within the system.A 99.9% inactivation (3-log reduction from initial population) of Legionella in both biofilmand planktonic phases was observed within 0.5 hours of contact for chlorine, monochloramine andchlorine dioxide at all the concentration tested in this study. Results showed that monochloramine at a