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

The World Economic Forum recognizes water crises as a major global risk that has arisen from the depletion of natural freshwater resources due to agricultural, industrial and municipal use, while generating vast amounts of wastewater. This poses a sustainability challenge that currently threatens 4 billion people worldwide and is expected to become more severe with population growth and economic development. Desalination of seawater and inland brackish water has emerged as a solution to meet this increasing water demand. However, desalination plants produce concentrated brine as a byproduct, the disposal of which is detrimental to land vegetation and the aquatic ecosystem, thereby having a significant environmental impact. Thus, there has been a push towards maximizing water recovery for reuse from industrial wastewater and desalination brine to achieve zero-liquid discharge (ZLD) such that the final waste is a solid.

Evaporation ponds, as a final step of ZLD harvest solar energy as heat for zero-liquid discharge, but require large land areas due to low evaporation rates. In this paper, Akanksha K. Menon et. al., 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.

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