Solar disinfection of viruses (SODIS): inactivation of coliphages MS2 and phiX174, human adenovirus and echovirus in water from Switzerland and India

Access to safe drinking water remains a challenge in many regions of the world. New methods to treat drinking water are constantly developped and improved in both in industrialised countries and in developing countries. SODIS is an interesting household-level disinfection technique that simply consists of pouring water into a PET bottle and exposing it to sunlight for at least 6 hours. Bacteria are efficiently inactivated by sunlight during SODIS, but the efficiency of SODIS on virus removal is much less studied. In this work, the inactivation of bacteriophages MS2 and phiX174, and human echovirus and adenovirus was studied in three different waters, two from India and one from Switzerland. Good removal (4 logs in 6 hours at 22°C and a fluence rate of 600 1.34 kJ/cm2) of MS2 was achieved in Swiss tap water, while less efficient inactivation was achieved in both Indian waters for MS2 and echovirus (1 log in 6 hours at 22°C and a fluence rate of 1.34 kJ/cm2). Both phiX174 and adenovirus were much more resistant to SODIS disinfection and less than 1 log of inactivation was obtained in Swiss tap water for phiX174. However, inactivation was not significantly different from the dark control in Indian water and for all experiments with adenovirus. Echovirus was inactivated similarly than MS2 and adenovirus was equally slow as phiX174. An increased temperature during SODIS enhanced inactivation substantially; 6 logs in 6 hours could be expected at 45 °C and with a fluence rate of 1.34 kJ/cm2. Indirect-solar inactivation was responsible for the MS2 removal, while direct inactivation via sunlight absorption of genome was not occurring during SODIS. We argue that iron could be responsible for the formation of reactive oxygen species which react with the viruses and yield their inactivation. The slower inactivation in Indian waters was probably due to the quenching effect of the higher concentration of organic matter. Removal of echoviruses during SODIS could be sufficient (4 logs in 6 hours) particularly at higher temperatures and for water with a low organic matter content. In contrast, SODIS may not be effective to remove Adenoviruses.