Available at www.sciencedirect.com journal homepage: www.elsevier.com/locate/watres The effects of changing water flow velocity on the formation of biofilms and water quality in pilot distribution system consisting of copper or polyethylene pipes Markku J. Lehtola a,Ã , Michaela Laxander a , Ilkka T. Miettinen a , Arja Hirvonen c , Terttu Vartiainen b,c , Pertti J. Martikainen c a Laboratory of Environmental Microbiology, National Public Health Institute, Department of Environmental Health, P.O. Box 95, FI-70701 Kuopio, Finland b Laboratory of Chemistry, National Public Health Institute, Department of Environmental Health, P.O. Box 95, FI-70701 Kuopio, Finland c Department of Environmental Sciences, University of Kuopio, P.O. Box 1627, FI-70211 Kuopio, Finland article info Article history: Received 6 March 2006 Received in revised form 13 April 2006 Accepted 13 April 2006 Keywords: Biofilm Flow velocity Copper Plastic Microbes Abbreviations: AOC: Assimilable organic carbon ATP: Adenosine triphosphate CFU/ml: Colony forming units per milliliter HPC: Heterotrophic plate counts HGR: Maximum number of heterotrophic bacteria during the 14 day incubation of water MAP: Microbially available phosphorus TOC: Total organic carbon ABSTRACT We studied the effects of flow velocity on the formation of biofilms and the concentration of bacteria in water in copper and plastic (polyethylene, PE) pipes. The formation of biofilms increased with the flow velocity of water. The increase in microbial numbers and contents of ATP was clearer in the PE pipes than in the copper pipes. This was also seen as increased consumption of microbial nutrients in the pipeline system. This indicates that the mass transfer of nutrients is in major role in the growth of biofilms. However, the increased biomass of biofilms did not affect microbial numbers in the water. Rapid changes in water flow rate resuspended biofilms and sediments which increased the concentrations of bacteria and copper in water. The disturbance caused by the changing water flow was also seen as an increase in the particle counts and water turbidity recorded with online instrumentation. & 2006 Elsevier Ltd. All rights reserved. ARTICLE IN PRESS 0043-1354/$ - see front matter & 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.watres.2006.04.010 Ã Corresponding author. Tel.: +358 17 201371; fax: +358 17 201155. E-mail address: Markku.Lehtola@ktl.fi (M.J. Lehtola). WATER RESEARCH 40 (2006) 2151– 2160