Development and structure of drinking water biofilms and techniques for their study

1. SUMMARY Drinking water systems are known to harbour biofilms, even though these environments are oligotrophic and often contain a disinfectant. Control of these biofilms is important for aesthetic and regulatory reasons. Study of full-scale systems has pointed to several factors controlling biofilm growth, but cause-and-effect relationships can only be established in controlled reactors. Using laboratory and pilot distribution systems, along with a variety of bacterial detection techniques, insights have been gained on the structure and behaviour of biofilms in these environments. Chlorinated biofilms differ in structure from non-chlorinated biofilms, but often the number of cells is similar. The number and level of cellular activity is dependent on the predominant carbon source. There is an interaction between carbon sources, the biofilm and the type of pipe material, which complicates the ability to predict biofilm growth. Humic substances, which are known to sorb to surfaces, appear to be a usable carbon source for biofilms. The finding offers an explanation for many of the puzzling observations in full scale and laboratory studies on oligotrophic biofilm growth. Pathogens can persist in these environments as well. Detection requires methods that do not require culturing.