The effect of corrosion control treatments and biofilm disinfection on unlined ferrous pipes

The occurrence of microbially related water quality problems has long been a concern to consumers and to water suppliers. Microbially related water quality problems are of particular interest because ferrous materials have been found to support larger populations of attached microorganisms (biofilms) even in the presence of disinfectants. These systems are now being required to implement corrosion control programs to reduce the quantities of lead and copper that leach from plumbing materials into the finished water. Many utilities have reservations about the implementation of a corrosion control program because most corrosion inhibitors contain phosphorus, which is an essential nutrient for microbial growth.; It is therefore the purpose of this research to investigate the numerous interactions between disinfectants (free chlorine and monochloramine) and several corrosion control methods and determine how they influence microbial growth in distribution systems.; To investigate these numerous interactions, studies were conducted using bench-scale and pilot-scale facilities, chemostats, and various other laboratory systems. Bench-scale facilities consisted of continuous flow annular reactors using unlined ductile iron or unlined mild steel materials. Pilot-scale facilities consisted of a 5-loop system of 4-inch mild steel pipe located at the Bozeman Water Treatment Plant. A series of experiments were conducted, using each type of facility, to evaluate the effect that various combinations of disinfectant and corrosion control treatments would have on distribution biofilms.; Results from these experiments have demonstrated that use of an effective corrosion control treatment will typically reduce microbial populations within the distribution system. Our studies have shown that corrosion products have a significant influence on the amount of microorganisms that a pipe material can support. Goethite (alpha-FeOOH), the most common corrosion product found in distribution systems, is of particular importance because it is able to adsorb and transform humic substances to more bioavailable forms, resulting in increased substrate for attached microorganisms. This study has demonstrated that an effective corrosion control program will reduce the amount of goethite formed on a ferrous pipe, and will consequently reduce the amount of bioavailable carbon on the surface and reduce habitat for problematic microorganisms.