Walk past a textile manufacturing unit and the scene can be full of colour — bright fabrics moving through machines, vats of dye transforming plain cloth into vibrant shades, and water being used through several stages of the process.
But once those colours have done their job, they can become an environmental problem.
The wastewater released by textile industries can contain synthetic dyes that are difficult to break down. Among them are azo dyes, a group of synthetic colourants known for their chemical stability. If untreated wastewater enters rivers or other water bodies, these pollutants can pose risks to aquatic ecosystems and may also have implications for human health.
Now, researchers at the Indian Institute of Technology Guwahati have found a biological way to tackle one such dye, using something much smaller than the industrial systems that usually treat wastewater: bacteria.
A bacterium that eats away at the problem
The researchers have identified a novel bacterium called Brevundimonas sp. AJZ05, which was isolated from a native textile effluent discharge site.
In laboratory experiments, the bacterium degraded 98.50% of Direct Blue-6 (DB-6), a commonly used synthetic azo dye.
Textile wastewater can contain dyes that are difficult to break down and harmful to water bodies. Photograph: (Biopol Chemicals Limited)
Azo dyes contain a chemical structure called an azo bond (–N=N–). This bond contributes to their strong colour and stability but also makes them difficult to remove through conventional wastewater treatment.
The researchers found that Brevundimonas sp. AJZ05 produces an enzyme called azoreductase. This enzyme can attack the azo bond, helping break down the dye.
Using a statistical optimisation technique called Response Surface Methodology, the team identified conditions that simultaneously improved dye degradation and azoreductase production. Under these optimised conditions, the bacterium achieved 98.50% degradation of DB-6, along with 0.761 U/mL of azoreductase activity.
But there was another important question: What happens to the dye after it breaks down?
It is not just about making water look clean
Simply removing the colour from wastewater does not necessarily mean that the pollution has disappeared. Some treatment processes can make water look cleaner while leaving behind potentially harmful compounds.
The IIT Guwahati researchers therefore analysed the metabolites formed during the bacterial degradation process and assessed their toxicity.
Elaborating on the research, Dr Selvaraju Narayanasamy, Associate Professor, Biochemical and Environmental Engineering Laboratory, Department of Biosciences and Bioengineering, IIT Guwahati, said, “A key feature of the study is that we went beyond measuring colour removal. Our research team analysed the metabolites formed during the biodegradation process and assessed their toxicity.”
The bacterium uses an enzyme called azoreductase to break down the dye.
Photograph: (Project Cece)
The degradation products were found to be non-toxic after bacterial treatment, indicating that the process can potentially transform the dye into safer compounds rather than only making contaminated water appear visually cleaner. Through this research, they have demonstrated a promising biological route towards safer and more sustainable wastewater treatment.
The bacterium also showed tolerance to several metal ions. This could be useful because real industrial wastewater can contain a mixture of contaminants rather than a single pollutant.
From laboratory to industry
For now, the work is at the laboratory stage, but the researchers are already looking at how the bacterial approach could be developed for real-world use.
Speaking about the current status of the research and the real-world applications, Dr Selvaraju Narayanasamy added, “We are now working towards translating the laboratory-scale findings into a practical and scalable wastewater treatment technology. The next step involves immobilising Brevundimonas sp. AJZ05 in a suitable support matrix to improve its stability, operational performance and reusability.”
The treated dye broke down into non-toxic compounds, making the process a promising wastewater solution. Photograph: (Fibre2Fashion)
The team plan to develop a continuous treatment system for azo-dye removal from textile wastewater, with the long-term goal of advancing the microbial platform towards industrial application.”
The research, supported through the Prime Minister’s Research Fellowship and with support from IIT (BHU), Varanasi, was published in Environmental Geochemistry and Health.
If developed further, this tiny bacterium could become part of a much larger solution: treating industrial wastewater while reducing dependence on energy-intensive, chemical-heavy processes. It is a reminder that sometimes, a cleaner approach to a major environmental problem can begin with something as small as a microbe.
