EXAMINING THE RELATIONSHIP BETWEEN IRON CORROSION AND THE DISINFECTION OF BIOFILM BACTERIA

Previous research has shown a relationship between corrosion of an iro n pipe and the protection of biofilm bacteria from disinfection. It is believed that the corrosion product reacts with chlorine disinfectant s and prevents the biocide from penetrating the biofilm layer and inac tivating 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 monochlorami ne disinfection. The research also suggested that the type of corrosio n 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 appear s to interfere with disinfection more than general corrosion. Multiple linear regression models were able to predict approximately 75 percen t of the variation in biofilm inactivation. Provided that low corrosio n rates and Larson indexes are achieved, no one corrosion inhibitor is preferred over another to control biofilm bacteria. The authors recom mend that water utilities monitor and control corrosion rates and Lars on indexes to levels as low as feasible.