Enhanced solar evaporation using a photo-thermal umbrella: towards zero liquid discharge wastewater management

Rising water demands and depleting freshwater resources have brought desalination and wastewater treatment technologies to the forefront. For sustainable water management, there is a global push towards Zero Liquid Discharge (ZLD) with the goal to maximize water recovery for reuse, and to produce solid waste that lowers the environmental impact of wastewater disposal. Evaporation ponds harvest solar energy as heat for ZLD, 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 umbrella. By converting sunlight into only mid-infrared radiation where water is strongly absorbing, efficient utilization of solar energy and heat localization at the water surface through radiative coupling are achieved. The non-contact nature of the device makes it uniquely suited to treat a wide range of wastewater, and the use of commercially available materials enables a potentially low cost and scalable technology for the sustainable disposal of wastewater, with the added benefit of salt recovery.