ABSTRACT
Biofilms may appear as a patchy mass in some pipe section or as a uiniform film along the inner walls of a storage tank. They may consist of a monolayer of cells in a microcolony or can be as thick as 10 to 40 mm, as in algal mats, reservoir bottom sediments, or raw water intake structures. These biofilms often provide a variety of microenvironments for growth that include aerobic and anaerobic zones due to the oxygen diffusion limitation within the biofilm. Biofilms are initially formed when pioneering organisms enter the distribution system and become entrapped in some slow-flow area, line obstruction, or dead-end section. Thus, there is a progressive diversity brought into the biofilm as the site becomes populated with a variety of bacteria, protozoans, nematodes, and worms. Coliform organisms are heterotrophic bacteria that may become colonized in the distribution system biofilm.
