Scaling up of Open SolWat for WWTP: Use of 380 Wp grid-connected modules and adaptation to R(EU) 2020/741

The large-scale Open SolWat system was evaluated as a possible tertiary treatment for WWTPs. It uses solar energy to disinfect secondary wastewater effluents and generate photovoltaic power. The prototype combines an open disinfection reactor on a photovoltaic module (380 Wp), with active cooling using a free-falling water film, driven by a pumping system and collected in an external tank. Four experiments were conducted under sunny conditions, with sample volumes of 50 L (Exp.#1) and 30 L (Exp.#2, Exp.#3, Exp.#4), after a 4 h SODIS exposure. The results indicated that Open SolWat improved the energy efficiency of its PV module by 8.0 ± 1.6 %, thanks to cooling module temperatures between 19.09 and 23.43 °C, with water temperatures around 33.31 ± 1.11 °C. This allowed average energy production of 1217–1270 Wh, compared to 1114–1193 Wh for a reference module. The system also achieved bacterial reductions of up to 3 log 10 in the treated samples of the summer tests (Exp.#3: 99.92 % and Exp.#4: 99.96 %), meeting the C and D qualities of Regulation (EU) 2020/741 for agricultural irrigation. Efficiency was lower in spring tests due to shading problems. It is suggested that a pre-filtration stage be included in future studies to improve reclaimed water quality. • Large-scale Open SolWat as a possible tertiary treatment in a WWTP for reclaimed water and energy production • Assessment of solar disinfection in secondary wastewater effluents • Obtaining reclaimed water suitable for use in accordance with R(EU)2020/741 • Improvement of the energy efficiency of photovoltaic modules, with >8.0 ± 1.6 %, through active water cooling