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

Akanksha K. Menon, Iwan Haechler+3 more|arXiv (Cornell University)|May 24, 2019

Solar-Powered Water Purification MethodsEnergy30 references3 citations

TL;DR

This paper proposes a passive, non-contact photo-thermal umbrella that enhances solar evaporation by over 100% through radiative coupling, converting sunlight into mid-infrared radiation absorbed by water. The system enables efficient, scalable zero liquid discharge wastewater treatment with salt recovery using low-cost, commercially available materials.

ABSTRACT

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.

Motivation & Objective

• Address the global challenge of sustainable water management amid rising demand and dwindling freshwater resources.
• Overcome the limitations of conventional evaporation ponds, which suffer from low evaporation rates and require large land areas.
• Develop a passive, non-contact method to enhance solar evaporation for zero liquid discharge (ZLD) wastewater treatment.
• Enable efficient, scalable, and low-cost wastewater treatment with recoverable salts using commercially available materials.
• Achieve high water recovery while minimizing environmental impact of wastewater disposal.

Proposed method

• Design a photo-thermal umbrella that selectively converts solar radiation into mid-infrared (mid-IR) radiation, which is strongly absorbed by water.
• Utilize radiative coupling to localize heat at the water surface without physical contact, minimizing thermal losses.
• Employ materials with high solar absorption and selective mid-IR emission to maximize energy utilization efficiency.
• Ensure non-contact operation to allow treatment of diverse wastewater types without fouling or clogging.
• Leverage commercially available materials to enable low-cost, scalable deployment for real-world ZLD applications.
• Optimize the device geometry and material properties to enhance evaporation rates through targeted thermal radiation.

Experimental results

Research questions

• RQ1 Can a non-contact, passive device significantly enhance solar evaporation rates beyond conventional evaporation ponds?
• RQ2 How effective is radiative coupling via mid-infrared emission in localizing heat at the water surface for improved evaporation?
• RQ3 To what extent can a photo-thermal umbrella achieve over 100% enhancement in evaporation using only sunlight and selective thermal emission?
• RQ4 Can this system be applied to a wide range of wastewater types without degradation or fouling?
• RQ5 What is the potential for scalability and cost-effectiveness in real-world zero liquid discharge wastewater treatment systems?

Key findings

• The photo-thermal umbrella enhanced evaporation rates by more than 100% compared to conventional solar evaporation processes.
• The system achieved efficient heat localization at the water surface through selective mid-infrared emission, minimizing thermal losses.
• The non-contact design enabled treatment of diverse wastewater streams without fouling or clogging.
• The use of commercially available materials supports low-cost, scalable deployment for industrial and municipal wastewater applications.
• The technology enables high water recovery with solid residue (salt) production, supporting zero liquid discharge goals.
• Radiative coupling between the umbrella and water surface significantly improved energy utilization efficiency.