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Solar disinfection and evaluation of the thermal contribution to water purification

Solar water disinfection (SODIS) systems use the germicidal effects of UV (UVB-UBA) light and the thermal pasteurization effects of far infrared light for bacterial disinfection porpoises. Direct exposure of transparent plastic bottles filled with water to the sun is one of the most widespread methods for water disinfection in developing countries, along with the use of black containers to capture more IR radiation and thus heat the water up to 65 – 70 °C  (solar pasteurization). 

In order to evaluate this contribution to water purification, the research group “Water and Energy” from IMDEA Water in collaboration with researchers from the University of Cádiz and Jaén, has developed a research in which natural river water with low concentrations of wild bacteria strains (10–103 CFU/100 ml) was subjected to solar disinfection over the span of a year under different climatic conditions (temperate climate). After 6 h of sun exposure, SODIS was effective in all seasons for E. coli, Enterococcus spp. and total coliforms, although total disinfection was not achieved according to WHO standards (0 CFU/100 ml). Only for Enterococcus spp. complete inactivation was reached in the experiments corresponding to autumn and summer, with initial microbial populations of 102 CFU/100 ml. The most resistant microorganism was Clostridium perfringens that with initial concentrations of 10–103 CFU/100 ml, a 43% reduction was only achieved after the SODIS treatment in the best case.

The contribution of the thermal component was also studied under real-time conditions to separate this effect from the total SODIS process. Results have shown and confirmed that temperatures near the optimum growth temperature of the different microorganisms can have an antagonistic effect on solar disinfection and slow down the process.

The full article can be downloaded from here.