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Disinfection efficiency of ozone was determined in various types of water at different pH (6, 7 and 8) values and temperatures (15, 25 and 35 °C) for E. coli and Salmonella. Three different applied ozone concentrations (1.5, 1.7, and 2 mg/L) in the gas phase were applied, and samples were taken at different time intervals to determine microbial survival using spread plate count (SPC) and ozone residual. Highest microbial inactivation was observed in distilled water with applied ozone concentration of 2 mg/L in the gas phase. Survival of E. coli was higher at pH 8 and 15 °C as comparedtolower pH values and temperatures as depicted by the inactivation kinetics of the test microbes used in the study. Salmonella showed 5 and 6 log removal after contact time of 45 and 60 sec, respectively, at 2 mg/L. Disinfection of mixed culture showed relatively more survival of E. coli; as 3 and 4 log removal of E. coli and 4 and 5 log removal of Salmonella was observed after 45 and 60 sec. [ABSTRACT FROM AUTHOR]

The aim of this study was to monitor microbial water quality and residual chlorine in drinking water supplies at the treatment plant and in the water distribution network of Ratta Amral, Rawalpindi, Pakistan. The drinking water quality in the distribution network was performed by collecting samples from water source, over head reservoir and residential taps and for analyzing chemical and microbial parameters. The samples were analyzed for physico-chemical indicators (total chlorine, free chlorine residual, turbidity, total dissolved solids and conductivity) and bacterial indicators (total and fecal coliforms). The average value of total chlorine at filtration plant was found to be ranging between 0.0 to 1.3 mg/l. Chlorine residue via distribution network available at consumer end was below detectable level at all sampling sites. The study is in progress to monitor the drinking water quality in the twin cities of Rawalpindi and Islamabad. [ABSTRACT FROM AUTHOR]