Biofilms consist of a layer of mucus (film) in which microorganisms (e.g., bacteria, algae, fungi, protozoa) are embedded. Biofilms are formed when microorganisms settle at interfaces. They form predominantly in aqueous systems, either on the water surface or at an interface to a solid phase.

In principle, however, all interfaces of biofilms may be overgrown: between gas and liquid phases (e.g., free water level), liquid and solid phases (e.g., gravel at the bottom of the water), or between different liquid phases (e.g., oil droplets in the water). The interface on which the biofilm is formed is called substratum.

Due to the existing in the pipeline network biofilm may cause damage to health due to the concentrated accumulation of bacteria and microorganisms. Biofilms are often perceived in everyday life as a “mucus layer” or “coating”. Other, colloquial designations are growth, residue film or sewer films.


Probability of bacteria in the Biofilm


The thermal disinfection

Bacteria and other microorganisms are killed at a temperature of more than 70 ° C in a short time. For thermal disinfection, therefore, at least the water heater and, if possible, the entire pipeline network, including the removal fittings, are heated to more than 71 ° C for at least three minutes.

Periodic disinfection (Legionella switching of the regulating valves within the circulation line, usually once a week) with full disinfection volume flow followed by cooling by inflowing cold water allows safe legionella-free supply of hot water distribution systems. However, the loss of lime in the pipe network – depending on the region above 60 °C – causes major problems, depending on the pipe material used and the degree of hardness of the fresh water. Particularly problematic proved the previously used iron materials.

For thermal disinfection in homes, etc., the temporary danger of scalding at the extraction point must be taken into account. The set target temperature in the hot water tank of a heating system without circulation should not be below 55 °C. Modern heating controls for small heating systems increase the storage temperature daily for a short time at least once or at regular intervals.

Naturally, thermal disinfection only covers the hot water network for the fresh water. However, legionella can multiply massively in cold water, because in modern heated buildings, the cold water supply network can warm up to over 20 °C. If there are additional structural defects (pipes of too large dimensions, laying in supply lines with poorly insulated hot water pipes or heating pipes), the cold water temperature can rise to over 25 °C.


Biofilms lead to higher energy costs