Just what is a Biofilm? A biofilm is a complex structure of bacteria living as a community within a sticky slime layer of their own making. Biofilms can attach to any surface that stays wet. Biofilms are a developmental process, and as the sticky polymers that produce the slime attach to a surface and build up, their appearance under magnification resemble microscopic mushrooms and streamers. Biofilms are a water issue because such films support accumulation of bacterial colonies and can result in a mat capable of causing pipe corrosion or clogging problems. Bacteria biofilms within water distribution systems are somewhat protected from low level disinfection methods, so they can cause a number of water quality problems, depending on the type of bacteria cultures present in the biofilm. Biofilms pose a variety of health risks in a water distribution system.
Pseudomonas aeruginosa is one opportunistic pathogen known to produce biofilms and it can cause animal disease. If chunks of this type of biofilm break loose and move into water supply pipelines, health officials will see the affect. Nitrification within a water distribution system is caused by biofilms. The nitrifying bacteria within such biofilms can oxidize residual ammonia left over from chloramination to produce nitrate and nitrite in the treated water as it moves through a distribution system. A higher nitrate level at the tap than that in the raw water source, especially in a system using chloramines for disinfection, is a good indicator of biofilm induced nitrification within the distribution system.
At one time biofilms were believed to be simple biomass clusters of a single bacterium. However, research in the 1990s has found that biofilms can contain more than one species of bacteria. These bacterial colonies have also been found to be much more complex structures than originally thought, sometimes containing voids, channels, cavities, pores and filaments with bacterial cells arranged in clusters or layers. These interstitial voids allow for good mass transfer within the biofilms, making exchange of substrate and products between the water phase and the bacterial cultures possible. There may be synergistic relationships, yet to be discovered, between different bacteria species within the same biofilm.
Finally, there are a number of microbial processes, which occur as the result of biofilms on surfaces and have beneficial industrial and environmental applications. Some examples include biomineralization to help recover precious metals from wastewater, bioremediation of hazardous waste sites, biofiltering of industrial water, and forming biobarriers to protect soil and ground water from contamination.