Turning seawater into clean drinking water in less than 30 minutes

Scientists have developed new technology that can turn seawater into clean drinking water in less than 30 minutes.

Researchers based in Australia used a metal-organic framework (MOF), a type of synthetic materials of lattice-like crystals made up of carbon and metal compounds, which form a porous honeycomb structure, to desalinate water.

The hollow framework of pores separates the salty solute within the brackish water or even saltier seawater, in a process known as molecular sieving. 

Under dark conditions, the framework absorbs salts and other impurities in the water in 30 minutes. The MOF itself is then regenerated for reuse in just four minutes, using sunlight to remove the adsorbed salts.  

The light-responsive MOF was used to filter harmful particles from water and generate 139.5 litres of clean water per kilogram of MOF per day.

Scientists say their technology is more energy-efficient than current desalination practices, including reverse osmosis, and could provide potable water for millions globally

Water scarcity is one of the largest global risks in the upcoming years, according to the World Economic Forum (WEF).

Thermal desalination processes by evaporation using solar energy are widely used to produce fresh water, but can be highly energy intensive. 

This new technology has been patented and scientists are discussing with potential industry partners to commercialise the technology. 

‘Sunlight is the most abundant and renewable source of energy on Earth,’ said Professor Huanting Wang from the Department of Chemical Engineering at Monash University in Australia. 

‘Our development of a new adsorbent-based desalination process through the use of sunlight for regeneration provides an energy-efficient and environmentally-sustainable solution for desalination.

Desalination – the process of turning undrinkable saline or salty water into drinkable water – has been used to address escalating water shortages globally. 

‘Due to the availability of brackish water and seawater, and because desalination processes are reliable, treated water can be integrated within existing aquatic systems with minimal health risks,’ Professor Wang said.

The World Health Organisation suggests good quality drinking water should have a total dissolved solid (TDS) of less than 600 parts per million (ppm). 

Monash researchers were able to achieve a TDS of less than 500 ppm in just 30 minutes and regenerate the MOF for reuse in four minutes under sunlight by rapidly releasing the adsorbed salts. 

MOFs were discovered in the 1990s and could have potential for use in hydrogen storage, solar energy and even mopping up toxic gasses from the air. 

They are a class of compounds consisting of metal ions that form a crystalline material with the largest surface area of any material known. 

They are so porous that they can fit the entire surface of a football field in a teaspoon. 

The research team created a dedicated MOF called PSP-MIL-53, which is photoreversible, meaning its functions can be changed from one to the other by light. 

‘These sunlight-responsive MOFs can potentially be further functionalised for low-energy and environmentally-friendly means of extracting minerals for sustainable mining and other related applications.’  

The new technology is different from a solar still, in which water evaporates and condenses into clean water. It takes a few minutes to wash salts out of the material with a small amount of water under sunlight.