IIT-M’s cheap solution to make brackish water potable

It may soon become possible to convert brackish water into drinking water at about 12 paisa per litre right on the kitchen table by using a potential difference of just 1.8 volts, thanks to researchers at the Indian Institute of Technology, Madras (IIT-M).

Sustainable approach

The researchers used a stack of tissue paper and carbonised it at high temperature to make graphene. Graphite electrodes were then coated with the graphene produced in the lab. When a small potential is applied to the electrodes, the brackish water gets deionised to become potable water. The results were published in the peer-reviewed journal ACS Applied Materials & Interfaces, published by the American Chemical Society.

“An electrode for such deionisation purposes should have high surface area, high electrical conductivity and high porosity,” says Mr. Soujit Sen Gupta, a coauthor of the paper from the Department of Chemistry (DoC), IIT Madras. “The graphene coating gives both high surface area and conductivity.” To render the graphene porous, silica precursors were added to the graphene and removed subsequently. The removal of silica makes the graphene porous while retaining its structural integrity.

When the electrodes are dipped into brackish water and 1.8 volt potential is applied to the electrodes, the sodium and chloride ions move towards respective electrodes and get adsorbed. In about five minutes, the brackish water turns into potable water with less than 500 parts per million (ppm) of sodium chloride, which is less than the permissible limit for drinking water. Further reduction is possible to bring the concentration below 100 ppm, the scientists say.

Filters will last 10 years

Compared with reverse osmosis, which is energy intensive and causes 65-70 per cent of water of the water to be rejected as waste, the wastage is only 25 per cent in the case of capacitive deionisation (CDI) technology, and it can work independent of the grid using solar energy. A prototype has been developed and tests are under way. “At the core of the technology are carbon-based electrode materials with high adsorption capacity,” says Prof. T. Pradeep, corresponding author of the paper from the Department of Chemistry, IIT-M.

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