Design, construction and testing of an improved solar water disinfection system (SODIS)

This study improves on the conventional SODIS design to make it more effective and increase its acceptability. An improved SODIS was designed to allow polyethylene teraphalate (PET) bottles serving as reactors to be under approximately 97% sunrays’ cover, and with a provision for a heat absorber. The improved SODIS was tested for inactivation of microorganisms by loading it with eight PET bottles filled with water containing 10 5 to 10 7 CFU/100 ml of Escherichia coli. The test was conducted simultaneously with a conventional SODIS, consisting of an improvised rooftop arrangement, containing same quantity of water-filled bottles with same concentration of E. coli . The two systems were placed close to each other, and exposed to direct sunlight for seven hours each day, on six different days. Ambient temperature was measured with a general-purpose thermometer. The thermometer was inserted into one bottle on each system to measure (representative) temperature. At hourly time intervals, a bottle was taken out from each system for enumeration of E. coli concentration. Hourly ambient and bottle temperatures were read simultaneously. The improved SODIS achieved a temperature of 4 °C above ambient and 1 °C above the conventional SODIS. In all the experiment days, complete inactivation of E-coli below detectable limit (less than 1 CFU/100 ml) was achieved at the fourth hour of exposure to sunlight by the improved SODIS and sixth hour by the conventional SODIS. The inactivation rates, K, for E. coli were 0.53 and 0.46 for the improved SODIS and the conventional (rooftop) SODIS, respectively.