Deterioration of drinking water quality in UV treated house-hold water storage tanks. (c2002)

Abstract

In countries with short and unreliable drinking water supplies, such as Lebanon, the microbial regrowth problem is exacerbated due to the intermittent regime of supplying water to consumers that necessitates the storage of water in house - hold tanks for long periods. The aim of this study was to investigate the microbial changes that occur in Lebanon drinking water supplies after the treatment point, in the house - hold water storage tanks. This study showed that there is an existing microbial regrowth problem in Lebanon drinking water that is more pronounced in the house - hold water storage tanks in the summer where the temperature is high. Furthermore, this study indicated a significant increase in the bacterial numbers upon storage for 4 and 7 days with no significant difference between bacterial numbers at 4 and 7 days. This bacterial number was found to be high in the polyethylene tank than in the cast iron tank. The sediments dry weight (mg) was calculated and found to be higher in the polyethylene tank than in the cast iron tank; this in tum attributes to a higher bacterial number in the polyethylene tank since sediments provide nutrients for bacteria to flourish grow and multiply. Microbial biofilms were found in this study to attach more on the polyethylene tank than on the cast iron tank. The biofilm growth was found to be independent of the temperature and the availability of nutrients, as such increasing the public health concern. Pseudomollas VlJsiCliiaris was found to be dominant in the sediments and the different levels of drinking water in the house - hold water storage tanks experimental setups, whereas in the biofilm experimental setup Psetldomollas citrrJIlel/olis was found to be dominant; the gram-positive bacteria in the biofilm experimental setup occurred at a higher percentage compared to that in the sediments and water experimental setups with the prevalent dominance of Rhodococc/IJ spp. Little difference was observed between the types of microorganisms found in the source, sediments, water and the biofilm experimental set ups performed in this study. Coliforms were not detected in all of the experimental set ups. The gram-negative identified bacteria from the sediment, water and the biofilm showed a prevalent multiple antibiotic resistances characteristic that was most directed towards chloramphenicol, whereas the gram-positive bacteria showed resistance to bacitracin and sulphamethoxazole/trimethoprim, and penicillin.