Abstract:
Chlorine may kill microbes in contaminated water by disrupting their metabolism and protein synthesis processes but it does not kill all pathogenic bacteria, cysts, viruses and protozoa at normal dosages. The present study was designed to evaluate the inactivation efficiency of chlorine doses against selective pathogenic bacteria in a prototype distribution network. Shigella flexneri causative agent of Shigellosis and Campylobacter jejuni causative agent of Campylobacteriosis were selected as model organisms. Isolation and purification of S. flexneri and C. jejuni was carried out from Ratta Amral, a site associated with serious water quality issues according to an earlier study conducted for HEC project no. 20-874/HEC/R&D/07/379 entitled as ―Monitoring of drinking water within the distribution network of Rawalpindi and Islambad‖. Chlorine disinfection studies were conducted in two phases i.e. Bench Scale and Lab Scale. For Bench scale studies, selected chlorine dosages against S. flexneri (107 CFU/mL) were 0.5, 1, and 1.25 mg/L whereas for Campylobacter jejuni (107 CFU/mL) selected chlorine dosages were 0.5 and 1 mg/L. Samples were taken at different time intervals of 0, 10, 15, 30, and 45 minutes. For lab scale studies survival of S. flexneri and C. jejuni was investigated at 1.25, 1.5 and 1 mg/L, respectively. Samples were taken at time intervals of 0, 30, 45, 60, 75 and 90 minutes. Bench scale results indicated that S. flexneri and C. jejuni showed 7-log reduction at CT values of 56.25 and 15 mg-min/L. Lab scale studies revealed that addition of humic matter increased the chlorine demand of water and both bacteria showed complete inactivation at CT value of 90 and 45 mg-min/L. TOC determination of organic matter at different time intervals revealed that bacterial load decreases with decrease in organic load. Detection of trihalomethanes including chloroform, bromodichloromethane and dibromochloromethane was also determined using gas chromatography. Chloroform concentration was highest among total trihalomethanes formed at different time intervals and their formation increases with increase in contact time and dissolved organic carbon as determined by absorbance of chlorinated water samples at UV254 nm using UV-Vis spectrophotometer.
