Global Water Crisis Can Be Solved By An Unlikely Ally -- Sunlight!

Freshwater makes up less than 3% of the world's total water supply. Due to climate change, deforestation, and changing demographic habits, this already scarce resource is getting scarcer in many countries.

Currently, 1.42 billion people live in areas with moderate to very high water vulnerability, including 450 million adolescents, and this number is expected to rise in the coming decades.

UniSA's Future Industries Institute researchers have created a groundbreaking new process that could alleviate water tension for millions of people, especially those living in some of the world's most impoverished and deprived populations.

Via highly effective solar evaporation, a team led by Associate Professor Harlan Xu has perfected a technique for obtaining fresh water from seawater, brackish water, or polluted water, providing enough daily fresh drinking water for a family of four from only one square meter of source water.

"Using solar evaporation to produce fresh drinking water has received a lot of attention in recent years, but previous methods have proven too expensive to be realistic," says Assoc Prof Xu.

"We've solved such inefficiencies, and our system can now provide enough freshwater to meet many realistic needs at a fraction of the cost of conventional technologies like reverse osmosis," says the researcher.

Photothermal Machine

A highly effective photothermal structure sits on the surface of a water stream. It converts sunlight to heat, concentrating energy specifically on the surface to quickly evaporate the liquid's uppermost component.

Other researchers have looked at similar technologies, but previous attempts have been plagued by energy leakage. "Previously, many experimental photothermal evaporators were only two-dimensional," says Dr. Xu.

"We've created a strategy that not only avoids solar energy leakage but also extracts additional energy from the bulk water and surrounding atmosphere, resulting in a device that runs at 100% efficiency for solar input and draws up to 170 percent from the water and environment."

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Design Elements

Assoc Prof Xu and his team created a three-dimensional, fin-shaped, heatsink-like evaporator compared to other researchers' two-dimensional structures.

Their architecture transfers excess heat from the evaporator's top surfaces (i.e., solar evaporation surface) to the fin surface for water evaporation, thereby cooling the top evaporation surface and achieving zero energy loss during solar evaporation.

As a result of the heatsink method, all surfaces of the evaporator remain cooler than the ambient water and air, allowing more energy to flow from the higher-energy outer atmosphere into the lower-energy evaporator.

"We are the world's first researchers to remove energy from bulk water during solar evaporation and use it for evaporation, which has made our process effective enough to produce between 10 and 20 liters of fresh water per square meter per day," says the team.

Performance and Maintenance

In addition to its performance, the system's practicality is improved because it is constructed entirely of low-cost, sustainable, and readily available materials.

Assoc Prof Xu explains, "One of our key goals for our study was to deliver for realistic uses, so the products we used were simply purchased from the hardware store or supermarket."

"The only exception is photothermal materials, but even there, we're using a rapid and cost-effective technique," he says.

The machine is not only simple to install and deploy, but it is also simple to manage, as the photothermal mechanism stops salt from accumulating on the evaporator floor. The system could be used in conditions where other desalination and purification systems will be financially and operationally unviable due to its low cost and ease of maintenance.

In rural areas, reverse osmosis systems are too costly, says Prof Xu. The new technology could be a low-cost alternative. It is easy to set up and virtually free to run, he says. "This technology has the potential to offer a long-term clean water solution to individuals and societies that can't afford other alternatives."

Other Practical Applications

Apart from drinking water, Assoc Prof Xu says his team is looking at various other applications for the technology, including wastewater treatment in industrial operations.

"There are several possible ways to apply the same technologies," he says, "but we are really at the start of a fascinating journey."

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