Disinfection observations on a major unfiltered water supply in Scotland

摘要

The Loch Katrine water supply to Glasgow was unfiltered until a new treatment works was completed in 2007. Disinfection observations on the unfiltered supply are reported here for the decade 1995-2004. On one half of the supply, raw water contamination by gulls led to annual final water microbiological failure rates up to 2.7%, which fell below 0.4% after introducing revised gull control measures. Seasonally in gull contamination contributed to marked seasonality in observed final water microbiological failure rates. A 14-min chlorine contact time at pH 5.8 realised all the effective disinfection; a longer second stage contact time at pH 8.6 provided no significant (P > 0.05} improvement. For a range of raw water Escherichia coli counts, a logistic regression model predicted probabilities of a final water E. coli failure that varied with quarterly period; this was consistent with seasonal factors, aside from raw water quality, contributing to probability of these failures.