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SOLAR DESALINATION TECHNOLOGY WORTH ITS SALT

25-07-2019
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Researchers at Monash University have developed energy-passive technology that is able to deliver clean drinking water to thousands of communities, simply by using photothermal materials and the power of the sun. It is a promising solution to water shortages in areas where grid electricity isn’t available.

Worldwide, an estimated 844 million people don’t have access to clean water, and one newborn dies every minute from infection caused by an unclean environment and lack of safe water.

Seawater desalination and wastewater recycling are two ways of easing the problem of water shortage, but conventional approaches are energy-intensive and based on the combustion of fossil fuels. In fact, water treatment uses about 3 per cent of world’s energy supply.

The researchers, led by Professor Xiwang Zhang from Monash University’s Department of Chemical Engineering, developed a robust solar steam generation system that achieves efficient and continuous clean water production from salty water with almost 100 per cent salt removal. Through precisely controlling salt crystallisation only at the edge of the evaporation disc, this novel design can also harvest the salts.

The feasibility and durability of the design have been validated using seawater from Lacepede Bay in south-eastern South Australia, and the researchers’ findings have been published in the international journal Energy & Environmental Science.

“Water security is the biggest challenge the world faces in the 21st century, especially as population grows and the effects of climate change take shape,” Professor Zhang says. “Developing and under-resourced communities feel the effects of these factors the most.

“Utilising solar energy for water treatment has been widely considered as one of the sustainable solutions towards addressing the scarcity of clean water in some communities, without sacrificing our environment or resources.

“Despite the significant progress achieved in material development, the evaporation process has been impeded by the concentration of salt on the surface, which affects the quality of water produced.”

The researchers created a disc using super-hydrophilic filter paper with a layer of carbon nanotubes for light absorption. A cotton thread, 1mm in diameter, acts as the water transport channel, pumping saline water to the evaporation disc.

The salty water is carried up by the cotton thread from the bulk solution to the centre of the evaporation disc. The filter paper traps the pure water and pushes the remaining salt to the edges of the disc.

The light absorbance was measured to 94 per cent across the entire solar spectrum. The disc also exhibited a rapid temperature increase when exposed to light in both dry and wet states, rising from 25 to 50°C and 17.5 to 30°C respectively within one minute.

The technology also has great potential in other fields, such as industry wastewater zero liquid discharge, sludge dewatering, mining tailings management and resource recovery. Future studies will look to extend the technology to these applications with industry support.

“Our study results advance one step further towards the practical application of solar steam generation technology, demonstrating great potential in seawater desalination, resource recovery from wastewater, and zero liquid discharge,” Professor Zhang says.

“We hope this research can be the starting point for further research in energy-passive ways of providing clean and safe water to millions of people, illuminating environmental impact of waste and recovering resource from waste.”

Professor Zhang is the Director of the ARC Research Hub for Energy-efficient Separation, which aims to develop advanced separation materials, innovative products and smart processes to reduce the energy consumption of separation processes that underpin Australian industry.

He has just received a $50,000 grant from Perpetual for a separate project looking at securing better water for rural Australia and the South-East Asian region.

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