Biochar from Waste Rice Husks and Double Hydroxide Layers Can Filter Toxic Dyes from Water

     Plant matter burned under very low oxygen conditions, or pyrolysis, is known as biochar, charcoal-like matter that has several important uses, including sequestering carbon and releasing it slowly to plants, improving soil fertility. It is also used as a water filtration material, along with its relative, activated carbon, which is burned with oxygen, 

     Research published in the journal Sustainable Chemistry and Pharmacy found that biochar made from waste rice hulls, an abundant form of agricultural waste, can effectively filter toxic dyes in wastewater when double hydroxide layers are added. Toxic synthetic dyes, some of which are carcinogenic, are used in textile manufacturing, leather processing, paper production, and aquaculture. These dyes can cause problems when they get into wastewater, including reducing light penetration, disturbing aquatic ecosystems, and polluting drinking water sources. Thus, materials that can adsorb dyes from wastewater offer hope of preventing such problems.

     According to Anthropocene Magazine, researchers from Florida International University first made the biochar from rice husks. After this, they augmented the process 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.”

     The paper’s introduction notes two industrial dyes targeted in the research, Brilliant Green and Malachite Green, explaining their toxicity below:

“Brilliant Green and Malachite Green are two widely utilized synthetic dyes in sectors like textiles and aquaculture; however, their application presents significant environmental and health concerns. Brilliant Green is often utilized for dyeing silk, wool, and leather, and it also serves as a staining agent in microbiology. Nonetheless, extended contact with this dye may lead to skin irritation, allergic responses, and respiratory issues. Furthermore, it presents a significant environmental risk because of its resistance to biodegradation, enabling it to remain in aquatic ecosystems and lead to prolonged contamination (Mittal et al., 2008). Malachite Green raises even greater toxicological issues. This substance is associated with significant health risks, such as skin and respiratory irritation, possible organ damage, and is regarded as a potential carcinogen (Srivastava et al., 2004). In aquaculture, although it is advantageous for managing parasites, its application may result in reproductive issues, mutations, and lasting environmental contamination in aquatic organisms (Hashimoto et al., 2011). The findings underscore the critical necessity for improved handling protocols, effective disposal strategies, and the innovation of sustainable alternatives to reduce their negative effects on health and the environment.”

     The paper’s conclusion notes:

“The Mg–Al LDH@RH composite proved to be an effective adsorbent for the removal of toxic dyes such as Brilliant Green (BG) and Malachite Green (MG) from wastewater. Characterization analyses confirmed that Mg–Al LDH@RH possesses a crystalline rhombohedral structure with a high specific surface area of 118.78 m2 g−1, while the presence of hydroxyl, silicate, and aromatic functional groups enabled dye uptake through electrostatic attraction, ion exchange, and π–π stacking interactions.”

     The use of crop residues for biochar-based water filtration adds to the potential uses of crop waste. Just a few days ago I wrote about them as a potential feedstock for the production of bioplastics, or more properly, bio-based polymers. I also noted in another post just days ago that biochar production is by far the most used durable carbon removal method for carbon offsetting used by tech companies. If more can be sourced from India and Pakistan, where burning of crop residues is a very significant seasonal environmental problem, that could help mitigate it.

      

 

References:

 

Researchers recycle rice husks into a wonder material that removes toxic dyes from water. Anthropocene Team. Anthropocene Magazine. August 10, 2026. Researchers recycle rice husks into a wonder material that removes toxic dyes from water

Waste-to-resource approach: Sustainable synthesis and life cycle assessment of rice husk char-supported Mg–Al layered double hydroxide for dye biosorption. Noel Abhick Lawrence, Shaziya Siddiqui, Runit Isaac, Islam Ibrahim, George V. Belessiotis, Mohammad Saood Manzar, Nuhu Dalhat Mu'azu, and Nazrul Haq. Sustainable Chemistry and Pharmacy. Volume 52, August 2026. Waste-to-resource approach: Sustainable synthesis and life cycle assessment of rice husk char-supported Mg–Al layered double hydroxide for dye biosorption - ScienceDirect