The Role of Biofilm and Sediment Accumulation and of Chlorine Tolerance in Bacterial Regrowth

This report was produced for the Urban Water Research Association of Australia, a now discontinued research program.

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Report No UWRAA 99

February 1996

SYNOPSIS

Problems of coliform non-compliance, which could not be linked to contamination events, were experienced in the Sydney drinking water distribution system during the late 1970’s. Bacterial regrowth was subsequently found to be responsible for a proportion of the high coliform counts, with both Aeromonas hydrophila and klebsiella oxytoca dominant in the regrowth within the system. The aim of this project was to determine the role of biofilm and sediment accumulation and of chlorine tolerance in the regrowth of these two organisms.

Analysis of flushing samples, collected from within Sydney’s drinking water distribution system, resulted in the isolation of total coliforms and A. hydrophila, but not K. oxytoca, from within any of the sampled zones. A significantly higher number of total coliforms, A. hydrophila and heterotrophic plate count bacteria were isolated from biofilms/sediments within two of the four zones sampled. The absence of Klebsiella-type bacteria, in this sampling period, may have been the result of low winter temperatures or of a more effective control of these organisms by the management program adopted.

Resistance of Kl. oxytoca to chlorine was related to the formation of aggregates during growth. In addition, these bacteria were able to recover after chlorine injury and grow on the organic matter supplied by lysed cells.

Measures for the control of bacterial regrowth should include the removal of biofilms, sediments and cell aggregates before disinfection, as well as the reduction of sediment and organic materials entering the system. Other control measures should include the maintenance of a chlorine residual throughout the system and the implementation of routine flushing programs.

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