Effect Of Pipe Materials And Microbial Community Structure On Biofilm Formation And Chlorine Resistance Of Drinking Water Distribution System

Microorganisms form biofilm in the drinking water distribution system(DWDS)and cause a series of drinking water safety problems such as water quality deterioration and pipe corrosion.Recently,many researchers have focused their attention on the impact of hydrodynamic conditions and other factors on microbial biofilm,but ignored the impact of the pipe material itself and microbial community structure on the biofilm formation and chlorine resistance.In the present study,five common and representative bacteria which are more resistant to chlorine in DWDS were selected and attached to five typical pipe materials by single,dual and multiple species respectively to discuss the impact of pipe material and microbial community structure on the formation of biofilm and chlorine resistance of DWDS,hoping to provide theoretical support for ensuring the safety of drinking water microorganisms in DWDS.The main research contents and conclusions are as follow:(1)The impacts of pipe material on the biofilm formation and chlorine resistance of single species biofilm were studied.In terms of biofilm formation,cast iron pipe> polypropylene(PPR)≈ polyethylene(PE)> copper pipe> stainless steel pipe(SS).Acidovorax,Bacillus and Acinetobacter had the most biofilm biomass in all pipes except PPR pipe,while Microbacterium also had more biofilm biomass in PPR pipe.In PE,PPR and copper pipe,bacteria secreted more extracellular polymeric substance(EPS)contents.Some bacteria also have different EPS contents in different pipe materials,such as Sphingomonas have more EPS contents in copper pipe.Single-species biofilm in different pipe materials may have diverse chlorine resistance mechanisms.More stable EPS could better protect microorganisms against the influence of disinfectants;the metal pipe would react with the disinfectant and reduce the disinfection effect,in particular,the corrosion products of cast iron pipes could effectively protect microorganisms.Except Bacillus exhibited better chlorine resistance in all pipe materials due to it would form spores to resist to chlorination,chlorine resistance of the bacteria was also various in different pipes.(2)The impacts of pipe material on the interspecific relationship were studied,and the influence of pipe material and interspecific relationship on the biofilm formation and chlorine resistance of dual-specific biofilm was discussed.In PE and PPR pipes,most of the dual-species groups were neutralism relationship.In SS pipe,most of the groups were synergism relationship.In copper and cast iron pipes,most of the groups were competition relationship.The impact of interspecific relationship on biofilm biomass was not as significant as that of pipe material.The biofilm biomass of dual-species groups in cast iron pipe was still more than that of PE and PPR pipes,the biomass of the dual-species biofilm in copper pipe was less than that in SS pipe.The interspecific relationship of some dual-species biofilm was various for the different pipes,and the same bacteria may play different role in dual-species biofilm.The interspecific relationship also affected the chlorine resistance of dual-species biofilm.In SS pipe,the chlorine resistance of dual-species biofilm is stronger than that of the other pipes.In PE pipes,most of the dualspecies groups containing Bacillus exhibited better chlorine resistance,while in cast iron pipes,the addition of Microbacterium made the dual-species biofilm exhibited better chlorine resistance.(3)The impacts of pipes on the community-intrinsic properties were studied,and the effects of pipes and the community-intrinsic properties on the biofilm formation and chlorine resistance of multi-species biofilms were discussed.Community-intrinsic properties improved the multi-species biofilm biomass.Except for the dual-species biofilm in the SS pipe,multispecies biofilm in the other pipes had the most biofilm biomass.Some multi-species biofilms had different biofilm biomass in different pipes.The group without Sphingomonas had more biofilm biomass in metal pipes;the group without Acidovorax had more biofilm biomass in cast iron pipe,but less biofilm biomass in SS and copper pipes;the biofilm biomass of the group without Bacillus had more biofilm biomass but less in cast iron pipe.Community-intrinsic properties allowed all community members to share the chlorine resistance effect,so as to protect microorganisms during the disinfection process.Some multi-species groups may have different chlorine resistance in different pipe materials.The chlorine resistance of the group without Bacillus was better,but worse in other four pipe materials;the group without Acidovorax exhibited worse chlorine resistance in two plastic pipes and cast iron pipe,but better chlorine resistance in SS and copper pipes.