Water distribution systems inside buildings: influence of “repeated treatments” on the ability of three materials to promote microbial growth

The main objective of this study was to evaluate the influence of “repeated treatments”, performed on three materials, on the potential of these materials to promote microbial growth. These three materials; copper, CPVC and a variety of PEX, are widely used in water distribution systems inside buildings. These materials were tested as new and in a degraded condition; achieved by treating the material 120 times with a succession of cleaning and disinfection procedures typical of those applied to distribution systems inside buildings (in terms of products, durations and concentrations) and representative of the service life of a system that suffers from contamination problems. The test method is the project European standard CEN TC164/WG3/AHG3 (Biomass Production Potential – BPP – Enhancement of Microbial Growth) and is based on the determination of the concentration of active biomass in the water phase and on the material, by assaying the microbial adenosine triphosphate (ATP), under so-called “semi-dynamic” conditions. The three materials studied differed significantly from each other in terms of their ability to promote microbial growth. Consequently, the promotion of microbial growth was found to be dependent on the type of material. The highest level of growth was observed for PEX (1520 pg ATP/cm2) with much lower levels for CPVC and copper (35 pg ATP/cm2 and 11 pg ATP/cm2 respectively). These tests also revealed the absence of any impact of the repeated treatments, performed on these three materials, on their ability to form biofilms (similar ATP content per cm2 for new and “treated” material), even though the treatments were observed to have slightly attacked the surfaces of the CPVC, PEX and copper materials. These repeated treatments probably do not modify the properties of the materials with regards to the ability of the micro-organisms to attach and proliferate. This study considered to a very limited extent the structural changes induced by the ageing of the materials under actual conditions of use: surface condition, scaling phenomena and corrosion. Tests under dynamic conditions, in pilot systems, which represent more closely the actual conditions in which the materials are used, could be conducted and the results compared with those obtained with the BPP test, for an optimal understanding of the risks of uncontrolled development of biofilms, relating to the properties of the materials