Characterization of young and mature biofilms in the nonchlorinated Danish drinking water distribution system

Biofilm is considered beneficial in the non-chlorinated Danish drinking water distribution systems, as it increases the microbiological stability. When introducing new pipe sections in the system, a biofilm develops on the new pipe wall. However, the influence of biofilm on the water quality in the short-term during the commissioning phase of new pipe sections remains poorly understood. Further, there is limited knowledge on the effect of upstream factors such as water quality, existing biofilm upstream the new pipe section, flow velocity, pipe material, etc. on the biofilm development and the composition of the mature biofilm.

This project followed biofilm development through 1.5 years in newly installed PE pipes at two locations (at a drinking water treatment plant (DWTP) and at a water storage facility near the consumer) receiving water from the same DWTP. In particular, water and biofilm samples were analysed for the following parameters: HPC22/37, ATP, DAPI, qPCR, and NGS.

The biofilm at both locations continuously developed over the first 6 months, after which the microbiological diversity reached a mature state. At this point, a principal component analysis showed different biofilm composition at the two locations. Besides having a higher diversity of microorganisms, the biofilm in the pipe at the water storage facility also had the highest microbiological activity. This difference was correlated with upstream factors in the system such as pipe materials. This knowledge will benefit utilities when commissioning new pipes in the existing network.