Characteristics of Biofilm Community Formed in the Chlorinated Biodegradable Organic Matter-Limited Tap Water

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Abstract
The aim of this study was to characterize the influence of free chlorine residual on biofilm formation in a chlorinated system in which the biodegradable organic matter (BOM) was limited. The biofilm community was characterized through a community-level physiological profile (CLPP) that was generated using the Biolog GN microplate-based community-level assay. The chlorinated system was run at chlorine residual concentrations of 0.3, 0.5, and 1.0 mg l−1 with the provision of BOM-limited tap water (0.01 mg l−1 as assimilable organic carbon and 0.06 mg l−1 as biodegradable dissolved organic carbon). For comparison, an unchlorinated system was operated in parallel under the same condition. The number of viable heterotrophic bacteria in the biofilm that formed in the chlorinated system over the 3 months of operation averaged 7.2×103, 4.8×10, and 1.6×10 CFU cm−2 for the chlorine residual concentrations of 0.3, 0.5, and 1.0 mg l&minus1, respectively. In the unchlorinated system, the average bacterial content was 1.1×106 CFU cm−2. Using measures of substrate utilization rate, substrate utilization diversity, and metabolic potential index (MPI), the CLPP patterns demonstrated that the metabolic potentials of the biofilm communities decreased markedly as the chlorine residual levels increased. In particular, the community level of the biofilm that formed in the system with chlorine residual concentration of 1.0 mg l−1 was the lowest of any biofilm under the tested conditions. The results implied that chlorine residual had a positive biocidal effect on the metabolic potential and/or functional potential of the biofilm community, especially when the BOM level was low. In addition, BOM limitation by itself was not sufficient to control biofilm formation.

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