Using the waste created by one of the world’s staple foods, researchers have made a filter that can clean water. They converted discarded rice husks into a sponge-like filter that can remove polluting industrial dyes such as the ones released by textile, leather, and other industries.
The low-cost material could help clean waterways while reducing agricultural waste. The researchers published their findings in the journal Sustainable Chemistry and Pharmacy.
Many industries such as textile manufacturing, leather processing, paper production and aquaculture use synthetic dyes. These industrial dyes persist in aquatic environments for a long time, “diminishing light penetration, disturbing aquatic ecosystems, and polluting drinking water sources,” the researchers write in the paper. Many of these dyes are toxic and some can be carcinogens.
Manufacturers can remove these dyes from wastewater before it is released into the environment. One of the most promising, cost-effective, and sustainable method for the removal of dyes are materials that can adsorb dyes, that is, soak them up on the surface via physical or chemical mechanisms.
The team at Florida International University set out to make such an adsorbent from waste rice husks. Rice is the most-eaten food globally. The world produces over 540 million tonnes of rice every year, and discards some 136 million tonnes of the outer husk of the grains.
To make the water filter, the researchers first heat waste husks in a low-oxygen environment. This converts the organic material into biochar, a sponge-like material with a very high surface area and a porous network that can trap contaminants.
But the researchers boosted the performance of the biochar by combining it with special materials called layered double hydroxides, which are clay-like minerals composed of layers of magnesium and aluminum hydroxide sheets with charged ions and water molecules trapped in the spaces between the layers.
In laboratory tests, the material captured brilliant green and malachite green dyes, two commonly used industrial dyes. The material was also reusable. The researchers found that it could be reused at least five times without losing its efficacy. They now plan to test the material on other dyes, heavy metals and various contaminants found in real-world water samples.
Source: Noel Abhick Lawrence et al, Waste-to-resource approach: Sustainable synthesis and life cycle assessment of rice husk char-supported Mg–Al layered double hydroxide for dye biosorption, Sustainable Chemistry and Pharmacy, 2026.
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