Characterization of Non-Enteric Bacterial Regrowth in the Water Supply Distribution Network from a Eutrophic Reservoir

1989 
An area of a distribution network receiving organically rich treated water was studied for a period of one year to gain further understanding of the regrowth of bacteria in a water distribution network. These bacteria are considered to be harmless to man. Surveys additional to this study confirmed that enteroviruses and pathogenic bacteria (as defined by EC directives) were absent, consistent with the general absence of coliforms. Fixed points were sampled regularly for bacteriological analysis and for relevant physical and chemical parameters. Heterotrophic plate counts were carried out using standard methods and a study was conducted to test alternative techniques. It was found that bacterial regrowth occurred close to the treatment works and longer retention resulted in little increase in plate counts. Monochloramine residuals of 0.26mg/l or less did not prevent regrowth. The assimilable organic carbon concentration decreased through the distribution system and increased following booster chlorination. Plate counts showed a seasonal pattern peaking in the spring and autumn and decreasing in the summer and winter. The predominant genera of bacteria were Pseudomonas, Alcaligenes and Aeromonas with maximum counts of 17,000, 23,000 and 1,700 CFU/ml respectively. Heterotrophic plate counts using the R2A medium, spread plate method and 7 day incubation period were on average 190 times greater than counts using the UK standard method. The increase in count gained by using the alternative method was greatest at the sampling points furthest from the treatment works.
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