In Kuopio, Finland, it has been built a pilot scale drinking water distribution system with copper and plastic (polyethylene) pipes. With this system we have studied how pipeline materials and flow regime affect water quality and biofilms. In plastic pipes, biofilms reached steady state faster than in copper pipes and microbial community structure was affected by the piping material. Increase in the flow velocity of the water from 0.03 m/s to approximately 0.3 m/s increased significantly the formation of biofilms. Increased biomass in biofilms had no effect on the bacterial concentrations in water, but even a small disturbance in flow regime detached bacteria and metals from biofilms and sediments to water. Chlorine eliminated effectively bacteria from biofilms of plastic pipes, but in copper pipes the disinfection efficiency was weaker, and was depending on the age of the biofilms.
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