Influence Factors And Control Methods Of Biofilm Growth In Drinking Water Distribution Networks

Although drinking water distribution system (DWDS) is extreme environments with oligotrophic conditions where a disinfectant residual is commonly maintained, microorganisms are able to survive within DWDS, in particular by attaching to the internal surfaces of pipes forming biofilms. These biofilms could be associated with several unpleasant problems in DWDS such as deterioration of water quality, corrosion of pipe walls and causing secondary pollution due to undesired microorganisms are released into bulk water. In order to explore effective and efficient control methods of biofilms in DWDS, a full scale, non-circulated experimental pipeline facility and a full scale, semi-circulated experimental pipeline facility located in the water plant of city SX, east China, were used to simulate the growth of biofilm and biofilms growing in different material, lining, shear stress and condition were sampled. In this paper, traditional plate count techniques and modern molecular biology techniques were used to explore the influence of material, lining, shear stress and stagnation on growth and development of biofilm and explore effective and efficient control methods of biofilms. The results of the research are as follows:(1)Material and lining have a significant impact on biomass and bacterial community composition of biofilms in DWDS. Bacteria with strong resistibility to chlorine such as Alphaproteobacteria, Sphingomonas and Methylobacterium are easier to grow on the inner surface of HDPE pipe, rather than ductile cast iron pipes with cement-lining.(2)Shear stess has a slight impact on biomass and bacterial community composition of mature biofilm in DWDS, while relative activity (RNA transcription number) will increase as shear stress increases.(3)The cohesion of biofilm forming during stagnation is poor and these biofilms are sensitive to shear stress change. Gammaproteobacteria, Nevskia and Blastomonas are gradually becoming dominant while Rubrobacter, Bacillus, Hyphomicrobium are gradually becoming inferior during stagnation in DWDS.(4)Combination of shock chlorination and flushing is an effcient method to remove biofilms from inner pipe wall. Ideally, shock chlorination should precede flushing.