AWWA JAW57436

The authors provide the results of a study investigating factors affecting biofilm accumulation in bench-scale distribution systems using both synthetic and real waters. The effects were assessed by measuring the accumulation of heterotrophic plate count bacteria per unit area in an annular reactor. The results showed that the disinfectant residual was the most important factor in terms of controlling biofilm. The highest biofilm levels were observed under conditions in which a high level of easily biodegradable organic matter was present and there was no disinfectant residual. Although a number of investigations have been conducted to examine the formation of biofilms in both real and model distribution systems, there is relatively limited information from controlled experiments that have systematically investigated the various factors influencing the extent of biofilm formation. The authors' purpose in conducting this research was to quantify the effects of the following factors: chlorine or monochloramine residual, concentration of easily biodegradable organic matter, shear (i.e., flow velocity), pipe material, and temperature. The results of this investigation have important practical implications for control of biofilms in distribution systems. North American practice is generally to maintain a residual in the distribution system, in part for biofilm control. However, the results of this study suggest that the residual should be defined based on a variety of factors and that interactions among the various factors are important in determining the extent of distribution system biofilm accumulation. Includes 29 references, tables, figures.