This study examined the disinfection efficiency of free chlorine and monochloramine for improve water quality, but if sources of controlling biofilm organisms in a model pipe system. The composition of the pipe material microbial contamination (e.g., sediment, was found to be a major influence on disinfection efficiency. Bacteria grown on galvanized, tubercles, flocculated materials) are not copper, or PVC pipe surfaces were readily inactivated by a 1-mg/L residual of free chlorine or eliminated, deterioration will soon monochloramine. Biofilms grown on iron pipes treated with free chlorine doses as high as 4 recur.lO In practice, it is difficult to mg/L (3-mg/L residual) for two weeks did not show significant changes in viability, but if effectively apply these procedures to treated with 4 mg/L of monochloramine for two weeks, these biofilms exhibited a more than transmission mains and trunk lines 3-log die-off. Accumulation of corrosion products on iron pipes was found to interfere with without extreme effort, high costs, and free chlorine disinfection.

Previous research has shown a relationship between corrosion of an iron pipe and the protection of biofilm bacteria from disinfection. It is believed that the corrosion product reacts with chlorine disinfectants and prevents the biocide from penetrating the biofilm layer and inactivating the attached bacteria. The results of the current study show that even low levels of corrosion, i.e., <1 mpy, could interfere with free chlorine disinfection. High corrosion rates affected monochloramine disinfection. The research also suggested that the type of corrosion influences the efficiency of disinfection of the biofilm. Increases in the ratio of chloride and sulfate to bicarbonate (the Larson index) have been shown to be associated with pitting corrosion, which appears to interfere with disinfection more than general corrosion. Multiple linear regression models were able to predict approximately 75 percent of the variation in biofilm inactivation. Provided that low corrosion rates and Larson indexes are achieved, no one corrosion inhibitor is preferred over another to control biofilm bacteria. The authors recommend that water utilities monitor and control corrosion rates and Larson indexes to levels as low as feasible.

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