Assessing bacterial growth potential in a model distribution system receiving nanofiltration membrane treated water

This study was designed to assess the extent of bacterial growth in a model distribution system fed with the water treated by nanofiltration (NF) membranes under controlled conditions. The three NF membranes were used in improving the quality of tap water in a lab-scale process. The changes in total cell counts and culturable heterotrophic bacteria in both bulk water and biofilm were monitored during transport of NF permeate water through the model distribution system. The NF membranes were capable of removing the assimilable organic carbon (AOC) contents, but not low enough to restrict bacterial growth. Bacterial adhesion and cellular proliferation were observed in the NF permeate-fed systems, which were apparently characterized by the increase in the fraction of culturable heterotrophic bacteria and the relative abundance of alpha-Proteobacteria in bacterial community of biofilms. The overall specific cell growth rate which indicates the growth potential in the whole system was calculated as 0.07-0.08 day(-1). Results indicate that the NF permeate water has some potential to support bacterial growth in a distribution system, although the NF membrane is able to improve the quality of drinking water. Consequently, proper care should be taken to secure biostability to acceptable levels. (C) 2012 Elsevier B.V. All rights reserved.