Improving the efficacy of solar water disinfection by incremental design innovation

Solar water disinfection (SODIS) is a simple, affordable, yet effective method for treating drinking water in under-resourced communities. It has been scientifically proven, internationally recognized, and benefiting many people worldwide. However, the treatment time of the existing protocol is long (6 h or 2 consecutive days when the sky is sunny or partly cloudy, respectively). Previous studies showed that the method could be considerably shortened if the water temperature could be raised to over 50 °C, in order to trigger a powerful synergy between optical and thermal inactivation mechanisms of sunlight. This work has developed a new SODIS container design that can achieve the water temperature range that is conducive to synergistic SODIS inactivation, which has been overlooked by previous work that endeavored to enhance SODIS. Factors that could affect the water-heating performance of a SODIS container were systematically evaluated and subsequently aggregated to create the new design. Extensive field experiments were conducted to assess the disinfection efficacy of the new design under actual, and often unfavorable, weather conditions in a rural community. While still maintaining the simplicity, affordability, and portability of the original SODIS protocol, the new design can disinfect water much more effectively. In head-to-head comparisons with conventional SODIS bottle, the new design could achieve on average 74, 30, and 12 % more reductions of total coliforms than the bottle, in the conditions of at least half a day of strong sunshine, partly cloudy with some sunshine, and completely cloudy, respectively.