In parts of India, you can tell what colour a factory dyed its fabric that week just by looking at the river next to it. One such dye is Methylene Blue. It is widely used by industries and can be difficult to remove once it enters water.
But researchers at the National Institute of Technology (NIT) Rourkela have now found a way to clean it up, using two materials that industries already throw away by the tonne.
How coal and steel waste became useful
The team, led by Prof Sunipa Bhattacharyya from the Department of Ceramic Engineering, along with research scholars Susant Mohapatra and Sourav Ranjan Satpathy, developed a wastewater-based ceramic adsorbent using fly ash, Ground Granulated Blast-Furnace Slag (GGBS), and kaolin clay.
Fly ash comes from coal combustion in thermal power plants, while GGBS is generated during steelmaking. Both pile up in enormous quantities and are notoriously hard to dispose of safely, a challenge other Indian innovators have tackled by turning fly ash into bricks for affordable housing.
What makes the choice of materials clever is that fly ash and GGBS are abundant and chemically suited to the job.
India produced over 340 million tonnes of fly ash in 2024-25. Fly ash and slag also contain silica and alumina, compounds that help such ceramic materials hold together and trap pollutants.
This simplicity helps keep the cost down and could make the process easier to scale up.
Instead of using fresh raw materials, Bhattacharyya’s team used waste that was already available. This helped them create a useful water-cleaning material at a much lower cost.
The simple science behind the dye removal
The process is simple. When dye-filled water passes through the ceramic, the Methylene Blue molecules stick to its surface. In this way, the dye gets trapped instead of remaining in the water.
This simplicity helps keep the cost down and could make the process easier to scale up.
This also matters for small and medium textile units. Many of them cannot afford expensive treatment systems or specialised staff, so a simpler process may be easier for them to adopt.
What sets this adsorbent apart is a deliberate omission. Many similar adsorbents use metakaolin, a form of clay that must be heated at high temperatures before use. Bhattacharyya’s team avoided this heating step and used raw kaolin clay instead.
“A notable aspect of our research is the use of raw kaolin clay rather than heat-treated metakaolin, which is commonly employed in geopolymer-based adsorbents,” she says, adding that avoiding the energy-heavy heating step made the process more sustainable and cost-effective.
The problem with dye-filled wastewater
Dye pollution damages far more than the colour of a river. Textile wastewater can carry dyes, surfactants, salts and heavy metals into rivers. In some places, this has made water unsafe for irrigation and aquatic life. Studies estimate that roughly 10 to 15 percent of dyes used in processing do not bind to fabric and wash into wastewater instead.
Methylene Blue can also break down into potentially carcinogenic aromatic compounds. Existing treatment technologies can work, but they are often expensive, energy-intensive and can create secondary waste. This puts them out of reach for many smaller industrial units.
95% dye removal at Rs 25-50 per kg
In laboratory testing, the ceramic adsorbent removed more than 95 percent of Methylene Blue dye from contaminated water. The cost of producing it works out to roughly Rs 25 to 50 per kilogram, making it far cheaper than many conventional treatment materials.
This mix of high efficiency and low cost is what makes the innovation significant. It has been tested in the lab, but it has also been designed with Indian industry’s cost realities in mind.
Dye pollution damages far more than the colour of a river.
The research has been published in the journal ChemistrySelect. It also aligns with two United Nations Sustainable Development Goals: SDG 6, Clean Water and Sanitation, and SDG 12, Responsible Consumption and Production.
From lab results to wider testing
The team’s next step is to shape the adsorbent into porous forms and test it against a wider range of pollutants beyond Methylene Blue, moving from a single proof of concept toward a more versatile water-treatment material.
If the next round of testing works, the idea could be useful beyond one region or one industry. Coal and steel waste are available in large quantities across India. A treatment method built from this waste could be easier to replicate in places where industrial waste and dye pollution exist together.
For now, the NIT Rourkela study offers a clear demonstration of circular thinking: two materials considered industrial burdens, combined into a third that solves an entirely different environmental problem.
Images courtesy of NIT Rourkela
