Synthetic drinking water pipes can release substances into the water upon which bacteria can grow. The resulting biofilm on the pipe wall can lead to water-quality problems. The biomass production potential (BPP) test is used to assess pipe materials in this regard. In this project we provide a detailed description of BPP threshold values for the use of materials in distribution systems. We substantiate the variables in the BPP test and tabulate the regrowth levels in polyethylene (PE) connecting pipes.
Drinking water distribution systems, from the pumping station to the customer, make use of various types of pipe materials. The nature of these materials has changed significantly over the years. In the beginning classical pipe materials were used: steel, cast iron and later asbestos cement. Synthetic materials were then added to the assortment. But the accumulation of knowledge and experience can change perceptions. The use of synthetics brings with it the potential risk of regrowth – this is particularly true in the case of PE.
No unequivocal conclusion
KWR has developed a method to measure the biomass production potential (BPP) of materials. One assessment criterium for the BPP test has been incorporated into the regulations, alongside other test methods. However, the BPP test still raises many questions for PE suppliers. Research into the varieties of PE was part of the research agenda of the Biological Activity (2013-2017) theme group of the Joint Research Programme with the water utilities. But this research did not produce an unequivocal conclusion: the regrowth potential varied for the different PE types and producers, and no statistical difference was observed between the BPP values of the different producers or types. It therefore could not be concluded that a particular PE producer or type was the best (BTO report 2018-007). A degree of uncertainty therefore remains.
Practical guidelines for use of PE
KWR has recommended, as a precautionary measure, that PE use be limited. In practice, because of its specific advantages, PE is in fact being used in a number of situations by the water utilities and in installation construction. For this reason there is a greater need for practical guidelines for the use of PE.
The risk of undesirable, unacceptable regrowth is highest in connecting pipes. These pipes are not flushable, have relatively high residence times, higher temperature because of their shallower depth and partly-indoor installation, as well as a large contact surface (large conversion factor). The risk is lower in distribution mains, because of their better flow, lower conversion factor and greater cleaning options. The practical advantages of PE connecting pipes are also great (flexible, supplied in rolls). This project will contribute to a clearer formulation of the materials choice for connecting pipes.