Enhanced solar evaporation using a photo-thermal umbrella for wastewater management

Zero-liquid discharge is an emerging wastewater management strategy that maximizes water recovery for reuse and produces a solid waste, thereby lowering the environmental impact of wastewater disposal. Evaporation ponds harvest solar energy as heat for zero-liquid discharge, but require large land areas due to low evaporation rates. Here, we demonstrate a passive and non-contact approach to enhance evaporation by more than 100% using a photo-thermal device that converts sunlight into mid-infrared radiation where water is strongly absorbing. As a result, heat is localized at the water’s surface through radiative coupling, resulting in better utilization of solar energy with a conversion efficiency of 43%. The non-contact nature of the device makes it uniquely suited to treat a wide range of wastewater without contamination, and the use of commercial materials enables a potentially low-cost and highly scalable technology for sustainable wastewater management, with the added benefit of salt recovery. By passively evaporating water from waste streams, evaporation ponds work with different waste streams but need large areas due to low evaporation rates. This study shows that a photo-thermal device converting sunlight into mid-infrared radiation could enhance evaporation and reduce land needs.