Synthetic materials in contact with drinking water may affect microbial water quality by releasing growth-promoting substances. Various tests are being used for assessing the microbial growth-supporting potential of such materials. The biofilm formation potential (BFP) method is based on determining the concentration of active biomass (as adenosine triphosphate (ATP)) on the surface of a material incubated in slow sand filtrate (surface to volume ratio 0.15/cm) at 25°C during a period of 16 weeks. In addition to attached biomass (biofilm), suspended biomass is also produced. The amount of suspended biomass is a significant fraction (20-70%) of the total biomass production, depending of the type of material. Therefore, it is concluded that the production of suspended biomass should be included in evaluating the growth-promoting properties of materials in contact with drinking water. Consequently, the BFP test has been adapted to the biomass production potential (BPP) test, with BPP including BFP and suspended biomass production (SBP), as pg ATP/cm2. The defining criteria for BPP values for materials require further investigation into the effects of water quality on biofilm formation and the relationship between BPP values and regrowth problems.

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