Biofilm in water systems: formation, problems and solutions

In simple terms, a biofilm consists of microorganisms such as bacteria, fungi, protozoa or algae that are embedded in a layer of slime and deposited on a surface.

These communities of microorganisms are very well adapted to their environment. This is because the microorganisms organised in biofilms use metabolic properties of the other species they cohabit with or their protective mechanisms to multiply in biofilms.

Biofilm formation

Some types of bacteria can form a slime layer (extracellular polymeric substances, EPS) with which they adhere to surfaces. This layer forms the basic structure of biofilms.

This structure grows and ultimately makes it easier for microorganisms to colonise. This leads to the lateral expansion of the biofilms and the formation of three-dimensional structures consisting of several layers. The biofilm begins to spread.

This structure, a so-called extracellular matrix, offers protection against chemical and thermal disinfection measures, for example. This makes it almost impossible to completely remove a biofilm once it has formed.

In certain areas, such as water pipes, biofilm can form after just a few days, even if quality of the water is high.

Where do biofilms form?

Biofilms form on stones in a stream bed, for example, but also on the inside of water pipes, a fact that can play a major role in the hygiene of tap water.

In the human body, biofilms can be found on implants, where they can cause health problems. However, they can also fulfil useful functions by preventing the colonisation of pathogenic germs in the gastrointestinal tract.

Why do biofilms cause problems?

Although in nature biofilms can be very useful, e.g. for self-cleaning processes in soil and water or for binding carbon dioxide, they pose a major problem in other areas. The microorganisms in biofilms that cause disease in humans include the Legionella bacteria or pseudomonas (e.g. Pseudomonas aeruginosa). The latter can cause various infections such as. pneumonia, urinary tract infections or wound infections. Other pathogens that are often found in biofilms are Staphylococcus epidermidis, Staphylococcus aureus, Escherichia coli or Candida albicans.

Biofilm in the water installation

A low flow rate or dead legs – water stagnation – in drinking water installations favour the formation of biofilm. This, in turn, makes it easier for harmful bacteria to spread.

Once the slime layer has reached a certain thickness, parts of it detach from the pipe due to the force of the flowing water and settle elsewhere in the system. People can come into contact with these bacteria via taps, shower heads and siphons.

Waterborne germs can also be introduced into medical devices such as endoscopes during the final rinse in the cleaning process.

Hospitals, therefore, resort to manual water filtration using membrane filters, especially for immunocompromised patients. Due to their hollow fibre membrane technology, these sterile water filters stop all waterborne germs, including legionella (e.g. Legionella pneumophila) and pseudomonas.