The application of beneficial biofilms during commissioning of new drinking water PE pipes in Aarhus, Denmark

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 distribution network, a biofilm develops on the new pipe wall influenced by the water quality, the existing biofilm upstream the new pipe section, flow velocity, pipe material, etc. However, the influence of biofilms on the water quality in the short-term during the commissioning phase of new pipe sections remain poorly understood. This paper aims to analyse the short-term effect of the developed biofilm in newly installed drinking water PE pipes on the water quality to be able to optimize the commissioning procedure for installing new pipe sections in the existing pipe network to improve water safety for the consumers. Background Production of drinking water in Denmark is mainly based on groundwater that undergoes a simple treatment of aeration and filtration before entering the distribution network. No chemicals are added to prevent growth of microorganisms during production, distribution or at the consumers tap. Under normal conditions, no pathogenic microorganisms are observed in the production and distribution of drinking water in Denmark. During commissioning of new PE pipes in the exiting distribution network, biofilm will start to develop on the surface when water enters the new pipe. The water company will need to flush the new pipes until the water meets the required drinking water criteria defined by the water authority (HPC22 <200 CFU/mL). The flushing period will be determined by several factors like groundwater quality, pipe material and flow velocity. During the flushing period, all water is discharged to the sewer system until it meets the drinking water criteria above. A factor that is poorly understood is the role of biofilm development in the pipe and how it affects the water quality in the short-term during pipe commissioning. Methodology & Results This study contains the following parts: 1) During commissioning of a new PE pipe section in the City of Aarhus, Denmark the microbiological status was monitored for both water and surface biofilm. 2) Detailed field and laboratory analysis of the diversity, abundance and activity of microorganisms capable of establishing a biofilm in newly installed PE pipes in the distribution system. In particular, water and biofilm samples were analysed for the following parameters: HPC22/37, ATP, DAPI, qPCR, NGS (Next Generation Sequencing) and biotic/abiotic particles using BACMON. 3) Analysis of water samples from flushing of the pipe and colonies from positive HPC22/37 agar plates by molecular microbiological methods to investigate if any pathogenic microorganisms were present in water samples and on agar plates (data in preparation). 4) Documentation and evaluation of a new procedure for commissioning new pipe sections with extended focus on consumer water safety and water use. Significance of the study Based on data from several molecular microbiological methods and a new online microbiological sensor (BACMON), the study will give clear evidence if the increased measures of HPC22/37 during the commissioning process of new pipes will result in any health risk to the consumer. With knowledge from the study, the current protocols for commissioning new pipe sections will be optimized to reduce water use during the flushing period. The study highlights the importance of maintaining the natural biofilm in the non-chlorinated drinking water distribution system with regards to the water quality.