Disinfecting Biofilms in a Model Distribution System

This study examined the disinfection efficiency of free chlorine and monochloramine for controlling biofilm organisms in a model pipe system. The composition of the pipe material was found to be a major influence on disinfection efficiency. Bacteria grown on galvanized, copper, or PVC pipe surfaces were readily inactivated by a 1‐mg/L residual of free chlorine or monochloramine. Biofilms grown on iron pipes treated with free chlorine doses as high as 4 mg/L (3‐mg/L residual) for two weeks did not show significant changes in viability, but if treated with 4 mg/L of monochloramine for two weeks, these biofilms exhibited a more than 3‐log die‐off. Accumulation of corrosion products on iron pipes was found to interfere with free chlorine disinfection.