AWWA JAW27637

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 93-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. The author suggests that water utilities use a strong disinfectant (such as free chlorine, chlorine dioxide or ozone) for primary disinfection, then convert the residual to chloramines for secondary disinfection in the distribution system. Includes 34 references, tables, figures.