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Biofilm Basics

fouling on biofilm basics page

Biofilm fouling of high efficiency fill in a cooling tower

What are biofilms?

The understanding of what biofilms are and how they can affect efficiency of recirculating water systems has grown exponentially over the last 20 years (refer to “Biofilms” book, by Characklis and Marshall). Biofilms in the simplest of terms are consortiums of living microorganisms that grow on surfaces in contact with water. These growths or deposits are made up of the organisms themselves and various metabolites such as proteins and polysaccharides which are excreted and hold the mass together and adhere it to surfaces. In real world environments (natural or industrial as opposed to controlled laboratory settings), biofilms also contain a variety of inorganic materials (fine sand/silt, corrosion products if the underlying surface is metal, mineral scales, precipitated metals, etc.) which contribute to the stability of the biofilm structure, and therefore the difficulty in disrupting and removing biofilms.

In addition, note the distinction between viable biofilm and the disinfected structure that could possibly be treated with dispersant to be removed.

Biofilm fouling on a tube sheet in a heat exchanger

Biofilm fouling on a tube sheet in a heat exchanger

How do biofilms affect the industrial water business?

Although biofilms are mostly water, they form an insulating film that can result in approximately 13% energy loss from a 1/32-inch thick layer formed on chiller tubes and other heat transfer surfaces in a cooling system. In addition, biofilm deposits on metal surfaces promote corrosion of the metal. This is termed “microbially induced corrosion” (MIC), biocorrosion, or “under-deposit corrosion”. Thus control and removal of biofilm is extremely important for the industrial water treatment industry. In general, it takes 100 to 1000 times as much biocide to kill the sessile (surface-attached) organisms in a biofilm as planktonic (free-floating) organisms in solution.




Corrosion deposits which have accumulated on the inner surfaces of a water injection pipeline. The black color of the deposit is due to the presence of iron sulfide, a corrosion byproduct resulting from biofilm activity in the deposit.

More on biofilm science

The Center for Biofilm Engineering at Montana State University is one of the main sources of scientific information about biofilms, what they are, how they are formed and how they impact their environments. More on biofilms.