Water distribution system biofilms can be important sources of microbial contamination into the water supply. The growth and composition of these biofilms depend on a variety of factors including pipe material and the water matrix. In an effort to advance microbial water quality, and/or reduce the formation of disinfection byproducts, many water utilities are changing their treatment practices. These changes can include adding UV treatment, and/or a change in the disinfectant residual. Both of these could alter biofilm composition, and are being addressed in this investigation (AwwaRF project #3087). By using a flow-through laboratory model and molecular techniques we characterized and compared the composition of biofilms formed under various chemical treatments (chlorine, monochloramine, and chlorine dioxide) at typical concentrations, with and without upstream UV treatment, using the same source. Tap water from a soft surface water source (Halifax, Canada), was first passed through granular activated carbon filters to remove any residual disinfectant before entering the annular reactors. Annular reactor coupons made of cast iron or polycarbonate, were used to represent and compare pipe materials. Controls without any additional disinfectant residual were also included. Biofilm samples were removed from the coupons at defined intervals, and total DNA was extracted. Samples were also cultured on R2A medium for heterotrophic plate count, and full sweeps were harvested to extract DNA from cultivable bacteria for comparison to direct DNA isolation. The DNA samples from both sources were then used to identify the composition of the biofilm bacterial community using the PCR-DGGE (denaturing gradient gel electrophoresis) technique. Universal primers for a variable region of the 16S rRNA gene were used to amplify bacterial DNA.
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