Promising New Desalination Method Operates without Electricity

Researchers at The Australian National University have introduced a novel desalination method that mitigates many of the adverse effects associated with traditional techniques and cuts energy consumption by approximately 80%.

Freshwater scarcity is becoming a critical issue worldwide, with some regions already relying on desalination to extract freshwater from ocean water. Currently, humans use about one-third of all freshwater discharges, a figure projected to increase to one-half by midcentury, especially in regions such as Israel, Mexico City, India, and Southern California.

Water availability may become the most significant crisis of this century, exacerbated by climate change, which affects snowpack, surface water evaporation, precipitation patterns, and atmospheric water content.

A 2018 World Bank Report Highlights Desalination’s Energy Demands

A 2018 World Bank report indicated that around 300 million people in over 150 countries depend on desalination, which consumes 3 kilowatt-hours per cubic meter (kWh/m3) of energy—ten times less than in 1970. However, desalination still accounts for one-fourth of the energy used for water provision, requiring about 100 billion kilowatt-hours of energy in 2018.

Current desalination techniques fall into two main categories: material-based methods like reverse osmosis, which uses high pressure to separate molecular species in water, and thermal methods, such as solar-based evaporation or freeze desalination.

However, these methods can harm marine life; heat, stress, or chemicals may kill small organisms, while larger creatures can be trapped against intake screens.

Moreover, they produce brine with a high salt content (over 30%) that, when discharged into the ocean, can damage ecosystems by sinking to the seabed.

Traditional Desalination Systems Require Costly Materials and Regular Maintenance

Traditional desalination systems also require costly materials that need regular cleaning and maintenance due to issues like membrane fouling, corrosion, and degradation.

They consume significant amounts of energy, ranging from 3 to 7 kWh/m³ for reverse osmosis and up to 100 kWh/m³ for other methods. While suitable for urban and industrial areas, these systems are often too large and expensive for use in developing countries or rural and remote regions.

New Method Utilizes Low-Grade Heat and Thermodiffusion for Desalination

The new method, detailed in Nature Communications, does not rely on electricity but instead utilizes low-grade heat from sunlight or industrial byproducts. It leverages thermodiffusion, a process where salt migrates towards the colder side of a temperature gradient. In this method, the water remains in its liquid phase throughout.

The research team, led by Ph.D. candidate Shuqi Xu, passed seawater through a narrow channel positioned between a top plate heated to over 60°C and a bottom plate cooled to 20°C.

These temperature values can be sourced from the environment. The setup produced low salinity water from the top region of the channel and high salinity water from the bottom.

In their experiment, the channel was half a meter long and one millimeter high, with flow rates between 1 and 16 milliliters per minute. After a single pass, cooler, saltier water was extracted, and warmer, less saline water was recirculated through the channel.

Each pass reduced salinity by 3%, allowing repeated cycles to lower seawater salinity from 30,000 ppm to below 500 ppm.

Thermodiffusive Desalination

“Our goal is to revolutionize desalination technology using low-temperature heat from our surroundings,” said Juan Felipe Torres, a professor at Australian National University and lead chief investigator. “Thermodiffusive desalination is the first thermal method that operates entirely in the liquid phase without requiring membranes or ion-adsorbing materials.”

Torres highlighted that thermodiffusive desalination is free from fouling, which could significantly impact large-scale desalination. Agriculture, which consumes about 69% of the world’s freshwater, requires water desalinated to about 95% of its original salinity.

Following their proof-of-concept, the team is developing a larger, multi-channel device to desalinate seawater for the drought-stricken southwestern Pacific island of Tonga, powered by a solar panel the size of a human face.

To conclude, Torres envisions thermodiffusive desalination as crucial for developing countries facing severe impacts of climate change, as it decentralizes desalination and enhances water security.

Read the original article on: TechXplore

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