Exposure time as a disinfecting index in a solar water disinfecting system

Contaminated water is mainly responsible for most water-born diseases. Solar disinfecting of water is considered one of the best alternative methods of water disinfecting systems. Because the inactivation of micro-organisms is done either by heating to a disinfecting temperature or by exposure to ultraviolet solar radiation, a solar hot box (SHB) is used in this study as a solar disinfecting apparatus. A mathematical model of the SHB is presented and its governing equations are solved numerically. It is found that the exposure time corresponding to the water disinfecting temperature is affected by some parameters such as environmental conditions (ambient temperature, wind speed and solar radiation). A mathematical correlation between two nondimensional parameters (exposure time ratio and heat loss ratio) is presented. It is found that the minimum efficiency of the SHB used for water disinfecting systems is about 35%