A new SolWat technology has been developed that uses exclusively solar energy, called Large Open SolWat, as a possible tertiary treatment in a WWTP. This photochemical-photovoltaic hybrid system has a water disinfection reactor on a photovoltaic module, which consists of a pumping system that constantly cools the surface of the module by means of a thin film of water, and another open disinfection reactor with full solar exposure that stores the water sample during treatment. The water sample used was the wastewater effluent after secondary treatment of a WWTP. Large Open SolWat was operated with a flow rate of 8.9 L/min for the sample volumes of 4.2 and 6.2 L. The experiments took place on sunny days with climatic variability. Microbiological, physicochemical and photovoltaic performance analyses of the system were carried out. The results showed that good quality reclaimed water was obtained after a 4-hour SODIS treatment under real sunlight, which could be used for other purposes according to Spanish (RD 1620/2007) and European (R(EU) 2020/741) regulations. Simultaneously, the system generated energy with an energy efficiency that improved by 15 - 21% compared to the reference PV module, as a consequence of the successful cooling of the module temperatures (between 16.2 - 30.6°C during the experiments) with waste water. This would thus increase the performance and lifetime of the PV module. The energy generated could be used to self-supply the pumping system and to meet the energy demand of a WWTP in the future.

The results of this research showed a successful breakthrough in SolWat technology and demonstrated the feasibility of an appropriate and efficient use of water and energy.