EVALUATION OF DRINKINK WATER DISINFECTION DEPENDING ON ESCHERICHIA COLI AS A POLLUTION INDICATOR

Abstract

This study was suggested to evaluate the chemical treating systems of drinking water in the city of Al-Kut by studying Escherichia coli as a pollution indicator; 60 sample were collected(15 sample each) from:(A) Drinking water treatment tanks;(B) Sewage tanks; (C) Domestic tanks and (D) Distilled water. All samples had transported using clean and sterile containers under cooling to the lab, then the samples were inoculated in MacConkey’s broth at 44°C for 18 h with an inverted Durham’s tube to trap the gas liberated and lactose fermented at that temperature; then the samples cultured at the(Cruickshank et al., 1975) conventional media (MacConkeys', Eosin-Methylin Blue (EMB) and Blood agars). Gram stain were made to prove the presence of Gram negative bacilli, then motility test was made then the biochemical tests (Triple Sugars iron, indole, Simmons' citrate utilizing tests) were carried out to identify the bacteria. A dense bacterial growth was recorded in all samples that were collected from the sewage with a significant importance from that of domestic tanks and chemical treatment tanks. Bacterial count was done by tenfold serial dilution with ringers' solution for all samples, then a quantity of 1 ml from each dilution was poured with modified nutrient agar at 55°C then left to solidify and incubated at 37°C for 18h. bacterial count showed differences between groups, these differences were significantly important in that of B-group than that of C-group which overcomes these samples of A-group. No reported growth of D-group derived samples. The study proved that the conventional method of water disinfection by Chlorine is not so effective for complete bacterial depopulation, although the level was globally accepted.