DETERMINATION OF OPTIMUM CONDITIONS FOR AN ENERGY EFFICIENT SOLAR WATER DISINFECTION SYSTEM

Abstract

Worldwide about 1 billion people have no access to safe drinking water and the problem is most severe in developing countries. 20 to 50 liters of safe and clean drinking water is needed by each person on this earth per day. Over $150 billion is needed by developing countries to setup a drinking water supply system. However such sum is not easy to generate. Conventional treatment methods like filtration and chemical treatment require facilities and materials that are not economically feasible for such countries. This calls for alternatives like boiling of water. A common perception is that boiling kills all the microorganisms in water. However, it was observed that heating the water to 600C for 5 minutes served the purpose equally well. In current research a pasteurization unit was developed that used solar energy to achieve the required temperature. The unit built was cost effective and can disinfect water through solar water pasteurization. Initially a lab scale disinfection unit was established in which pasteurization temperature was achieved through electric current and optimum conditions for the disinfection of two pathogens i.e. Escherichia coli and Salmonella Typhimurium were determined through lab tests. E. coli was inoculated at 107 CFU/mL while S. typhi was inoculated at 105 CFU/mL in the feed tank of lab scale unit. Complete reduction of E. coli to 0 CFU/mL was observed by heating water for 3 minutes at 50o C while S. Typhi was observed to reduce to 0 CFU/mL by heating water for 6 minutes at 60o C. This was followed by design of a full scale solar disinfection unit. 50o C was achieved by solar water heater in 3 hours while 60o C was achieved in 4 hours. Turbidity had no effect on thermal disinfection of drinking water.