The effects of chlorine and pipe material on biofilm development and structure were studied in a model reclaimed water distribution system using annular reactors (ARs). The initial chlorine dose of influents in ARs with polycarbonate pipes and cast iron pipes was 3.59 and 10.15 mg/L, respectively, which could maintain the reclaimed water quality (HPC 102–103 CFU/mL). The chlorine and pipe material influenced the bacterial community. Biofilms formed faster and to a greater extent in ARs with cast iron coupons (HPC 107 CFU/cm2) compared to those with polycarbonate coupons (HPC 105 CFU/cm2). Using polymerase chain reaction (PCR) and denaturing gradient gel electrophoresis (DGGE) analysis, it was found that Gammaproteobacteria were prevalent in all cases with polycarbonate pipes, whereas with cast iron pipes microbial populations were affiliated with the phylum Proteobacteria, including the classes Alphaproteobacteria, Betaproteobacteria, Gammaproteobacteria and Deltaproteobacteria, followed by the phyla Bacteroidetes and uncultured bacterium.

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