Solar Disinfection of Drinking Water

Rojko, Christine

Etd

Solar Disinfection of Drinking Water

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Over 30% of the population in developing countries is in need of access to safe drinking water. The 875 million cases of diarrhea and 4.6 million deaths that occur each year due to a lack of a safe water supply occur primarily in these countries. It is estimated that these countries will need over $150 billion to establish full drinking water supply system coverage. Conventional methods of drinking water disinfection, such as chemical treatment, heat pasteurization, and filtration, require facilities, materials, and fuel that may not be readily available or feasible to attain. An alternative treatment option is to utilize solar energy, which has been shown to inactivate pathogens through pasteurization and radiation effects. This research was conducted to determine the effectiveness of solar disinfection for the inactivation of E. coli. Turbidity, sample volume, exposure time, and bottle size were varied. Experiments were conducted by adding E. coli to water samples (phosphate buffered saline with or without added montmorillonite clay or pond water) in clear drinking water test bottles. The bottles were then placed in full, direct sunlight. Samples were taken at predetermined intervals and solar intensity, weather conditions, and water temperatures were recorded during each sampling session. The viable bacterial count was enumerated using the pour plate method to determine log inactivation achieved. Laboratory experiments were also conducted to determine the effects of heating only on the inactivation of E. coli. Sample volumes from 1 to 2 L and turbidity values ranging from <1 ntu to approximately 100 ntu did not significantly affect inactivation levels when samples were exposed to sunlight for at least 4 hours. In samples with 0 ntu turbidity, a minimum cumulative intensity of 20.8 J/cm2 of wavelengths below 400 nm was required for a 7-log inactivation of E. coli. In samples with up to 100 ntu, a maximum fluence of 99.8 J/cm2 was required. Temperatures up to 46.0Â°C did not significantly inactivate E. coli, therefore radiation or the synergistic effects of radiation and heating accounted for the inactivation in samples exposed to sunlight.

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