Stand-Alone, Solar-Powered Devices for Water Disinfection
Authors: Chinello Enrico , Hashemi Mohammad H. , Modestino Miguel Antonio , Schuettauf Jan-Willem , Coulot Laurent , Ackermann Mathieu , Gerlich Florian , Faes Antonin , Psaltis Demetri , Moser Christophe 
Published: February 2020

Over one billion people currently lack access to safe potable water. Those communities, often isolated or settled in remote locations, are thus constantly exposed to a severe health threat due to waterborne pathogens (e.g. cholera, typhus, etc.). It is therefore evident that unavailability of drinking water directly hampers hygiene, education and ultimately societal development.
Chemical treatments are commonly employed to remove organic contaminants from water. The injection of a certain dose of chlorine or chlorinated compounds is the most reliable route to ensure disinfection and avoid back-contamination as the water is distributed. On-site electrochemical generation of chlorinated compounds appears promising due to its high versatility, cost-effectiveness and ease to employ. Such reactors require electricity to operate; this constrains their applicability to locations and communities where the grid is accessible. Nevertheless, solar energy is usually abundant is countries affected by lack of potable water.
To tackle scarcity of pathogens-free water in low-income countries, we have developed a novel solar-powered electrochemical platform. Thus, we intend to employ chemical disinfection via the injection of chlorinated compounds into the water batch. The products of choice are chlorine or sodium hypochlorite, two of the most utilized disinfecting agents. The solar-electrochemical device comprises: (i) cutting-edge photovoltaic arrays (possibly illuminated by a solar concentrator, depending on the technology of choice) and (ii) an optimized electrochemical reactor employing state of the art electrocatalysts. We have assessed the performances in terms of efficiency, chemical throughput and cost-effectiveness for different photovoltaic technologies: crystalline silicon arrays of multi-junction cells. The latter was illuminated by a novel solar concentrator, which employs linear millimetric movements to track the sun, thus replacing rotational trackers.
We have conducted experimental studies and simulations in our work. For each photovoltaic technology, we have estimated the annual chemical productivity. Further analyses evaluated the photovoltaic surface needed and the cost of water disinfection, for the benchmark case of a small-scale hospital. Additionally, we have compared a solar-powered sodium hypochlorite generator and a solar-driven reactor employing ultraviolet lamps for water disinfection.
Our study highlighted that the solar-electrochemical platform we have developed is a viable option of removal of waterborne pathogens from surface waters in low-income countries. We have identified crystalline silicon as the photovoltaic technology with the highest readiness to have an impact; multi-junction technologies are likely to follow similar pathways in the next years. Despite ultraviolet radiation could provide water disinfection at a lower cost, the applicability of such technology is hampered by higher need of maintenance and replacements, and by the lack of a residual disinfection effect.
Stand-alone, solar-powered reactors for chlorine and sodium hypochlorite generation are foreseen to have a significant impact in communities where sun power is abundant but drinkability of surface water is hindered by pathogens and other organic contaminants.