INVESTIGATION ON THE EFFECTIVENESS OF SUNLIGHT IN DISINFECTION OF DRINKING WATER

ABSTRACT

A safe or reliable year-round supply of drinking water remains a problem for at least one-third of the population of world, as effective filtration and chlorination are often beyond the financial means of the community. Boiling water before drinking is not always feasible, especially if fuel is expensive (financially or environmentally) or labour intensive to collect. Burning carbon-based fuels indoors in poorly ventilated dwellings can also have a significant impact on lung disease (K.G .McGuigan et al). A water treatment process that requires virtually no initial expense and absolutely no running cost would be of inestimable value to those most at risk of water-borne disease. This is the essential appeal of solar disinfection: to use a combination of irradiation by direct sunlight and solar heating to kill the water- borne pathogens in contaminated drinking water.

This study was conducted to determine the effectiveness of solar disinfection for the inactivation of E. coli and coliform bacilli bacteria. The study involved several experiments which included; test for colour, test for turbidity, test for biochemical oxygen demand, and bacteriological examination of both E-coli and coliform bacilli count.

Water samples were collected along Nairobi River for the study purpose.  Clear bottles of different sizes of both plastic and glass materials and which had been sterilized were filled with this water and placed in full, direct sunlight. Samples were taken at predetermined intervals and the temperatures were recorded during each sampling session. The viable bacteria count was enumerated using multiple tube method for coliform bacteria and membrane filtration technique for E-coli bacteria. Curves were obtained on the rate of inactivation on the bacteria and temperature rise from the results.

 

  Temperatures up to 46.0°C did not significantly inactivate E. coli and coliforms, therefore radiation or the synergistic effects of radiation accounted for the inactivation in samples exposed to sunlight.

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