Enhanced disinfection efficiencies of solar irradiation by biogenic silver

Solar disinfection (SODIS) is a very inexpensive and easy-to-run water-treatment process that is widely used in third world countries to decrease the number of waterborne diseases and mortality. However, it does have a number of disadvantages, including the long time needed for complete disinfection, especially during cloudy days, and the possible regrowth of germs during subsequent storage of the water. We tested whether the addition of low concentrations of biogenic silver, which is nanosilver produced on a bacterial scaffold of Lactobacillus fermentum , to the treatment process would improve the disinfection process in general and, more specifically, retard the growth of germs during water storage. Biogenic silver was found to accelerate the inactivation of Escherichia coli by SODIS by approximately twofold. This effect was more pronounced during the first 3 h of the disinfection process and was better than when TiO 2 was added. Biogenic silver which was immobilized on zeolite or polysulphone (PSF) to create a reusable formulation enhanced SODIS during the first 3 h, with the Ag–PSF formulation giving the best results. Ag–PSF released silver more slowly to the surrounding water, making it a more suitable formulation for drinking water disinfection, and it prevented germ regrowth during storage of the treated water.