Microorganisms in drinking water distribution systems can impact water quality and create regulatory concerns for utilities that involve disinfection residuals, densities of coliforms, and concentrations of disinfection by products. While there are microorganisms suspended in distribution water, most of the organisms are attached to the surfaces of pipes in biofilms. The City of Philadelphia Water Department (PWD) obtains water from the Delaware River and Schuylkill River. Treated waters from these sources are mixed and stored in the East Park Reservoir. Concern for water quality in portions of the distribution system fed from that reservoir, part of the mixed district, has focused on the difficulty in maintaining a disinfectant residual. These problems are most acute during the summer months when temperatures are warmer, and they correlate with increased utilization of energy sources for bacterial growth, observations that suggest the cause of decline in disinfectant residuals is a biological phenomenon. Water treatment by PWD includes the addition of ammonia to form chloramines, and this may exacerbate the problem of biofilm growth by providing substrates for nitrifying organisms.

The research that we propose focuses on microbial biofilm growth within the East Park Reservoir distribution system. Our objectives, divided into two phases, are to assess the ecology of the distribution system biofilm and to identify effective treatment regimes to control biofilm growth. In the first phase, we propose to identify the organisms present, find out where they come from, determine whether they rely on organic carbon for growth, assess the stability of the community composition, and determine whether they harbor indicator organisms or pathogens. In the second phase we will test different disinfectant agents for their ability to inactivate distribution system biofilms and assess the impact of reducing organic carbon concentrations on biofilm growth.

Knowledge of the ecology of the distribution system biofilm community composition is important to identifying effective treatment strategies. However, prokaryotic microorganisms, the Bacteria and Archaea, while some of the most widely distributed and abundant organisms on Earth, remain largely unexplored because they are difficult to isolate in culture. Molecular microbial methods that do not depend upon growth in culture, but rather identify organisms from extracts of microbial DNA obtained from the environment, have revolutionized microbial ecology. We will apply these methods to samples from the distribution system and from laboratory-based reactors, combined with activity measurements made with the reactors, to accomplish our objectives.

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