Effects of materials on biofilm formation
In every part of sanitary systems (for example: water storage tanks, pipes, shower heads), micro-organisms settle on the inner surfaces and form a biofilm. This biofilm forms a protective environment for the growth of legionella bacteria.
The formation of the biofilm depends on various characteristics: one of them is the type of pipe material. Various scientists investigated the effect of pipe materials that are frequently used in tap water systems in buildings: galvanised steel, polyvinyl chloride (PVC), polypropylene random copolymer (PPR), cross-linked polyethylene (PEX-c), stainless steel and copper.
The roughness of a material plays a major role in biofilm formation.
A rough pipe surface facilitates biofilm formation and thereby the attachment of bacteria along the pipe walls (Bohinc et al., 2014, 2016; Oder et al., 2015). This is illustrated in the figure below, which are 3D images based on atomic force microscopy. It illustrates the surface topography of 5 pipe materials before and after biofilm formation (adapted from Assaidi et al., 2018). The biomass is maximal on galvanised steel, while it is minimal on stainless steel. Moreover, galvanised steel surfaces harbour higher numbers of bacterial cells than stainless steel and the plastic materials.
As mentioned, copper is also frequently used in existing pipe systems, but rarely in distribution systems in new buildings. Although various sources show that copper limits the spread of Legionella through the bactericidal effect of copper ions, we do not want to go into this further here because the literature does not give a conclusive answer about the mechanisms involved. The bactericidal effect is presumably strongly dependent on other parameters, for example the effect of temperature on copper solubility (Proctor et al., 2015).
Research into biofilms is constantly evolving. With the development of new measurement techniques, interesting findings are emerging. Food for a future blog post.