AWWA WQTC56942

The objective of this study was to investigate and determine the influence of distribution system infrastructure on bacterial regrowth. In terms of "distribution system infrastructure" this was limited to pipeline material. Past research as cited in this report has connected the type of piping material with regrowth. Therefore, the focus was on piping material rather than an overall general condition (e.g. aging) of the distribution system. This emphasis on piping material is also consistent with utilities' prioritization of replacement of unlined cast-iron pipe, which can be a major contributor to water quality degradation in the distribution system. While there are other contributing factors (e.g. disinfectant residual, corrosion control) to bacterial regrowth, the study of these factors was outside the scope of this study. However, the influence of these factors was necessary to understand the results. This chapter summarizes the conclusions from this study and provides guidance for utilities to assist them in understanding and controlling regrowth in their system, specifically with respect to infrastructure materials, organics, and disinfectants. Samples of the influent water to the reactors were collected and analyzed for pH, temperature, chlorine residual, alkalinity, TOC, and HPC by utility personnel at each reactor location, and certified laboratories were used for analyses of these samples. Coupons were removed from the reactors, replaced with a coupon of similar material, and placed into sterile wide mouth screw-topped test tube filled with sterile phosphate-buffered saline (PBS) or sterile water prior to sealing for transport and analysis. The tubes were stored on ice and sent by overnight delivery to Montana State University for analysis of biofilm HPC levels. Coupon biofilm analysis was conducted within 24 hours of sampling. Includes figures.