GUWAHATI: Researchers at the Indian Institute of Technology Guwahati (IIT Guwahati) have developed a biological approach to treat textile wastewater containing toxic azo dyes, using a novel bacterium that degraded 98.50% of a commonly used synthetic dye under optimised laboratory conditions.
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The study demonstrated the ability of Brevundimonas sp. AJZ05 to degrade Direct Blue-6 (DB-6), a widely used synthetic dye. The researchers also found that the products formed after bacterial treatment were non-toxic, suggesting that the process could potentially transform the dye into safer compounds rather than simply removing its visible colour.
Textile wastewater can contain azo dyes that are difficult to remove because of their stable chemical structure. These dyes contain an azo bond (–N=N–), which contributes to their colour and chemical stability and can make them resistant to conventional treatment processes.
According to the researchers, untreated textile effluents can pose risks to aquatic ecosystems and may also have implications for human health. Conventional chemical and physicochemical treatment methods can be energy-intensive and may generate secondary pollutants.
To develop an alternative approach, the researchers isolated Brevundimonas sp. AJZ05 from a native textile effluent discharge site. The bacterium was found to produce azoreductase, an enzyme capable of breaking down the azo bond responsible for the colour and stability of the dyes.
Using a statistical multi-objective optimisation approach based on Response Surface Methodology, the team simultaneously optimised dye degradation and azoreductase production. Under the optimised conditions, the bacterium achieved 98.50% degradation of DB-6, along with an azoreductase activity of 0.761 U/mL.
Dr Selvaraju Narayanasamy, Associate Professor at the Biochemical and Environmental Engineering Laboratory, Department of Biosciences and Bioengineering, IIT Guwahati, said an important part of the study was analysing the metabolites produced during the biodegradation process and assessing their toxicity.
“The degradation products were found to be non-toxic after bacterial treatment,” Dr Narayanasamy said, adding that the findings indicate the process could potentially transform the dye into safer compounds rather than only making contaminated water appear visually cleaner.
The researchers are now working to move the findings beyond the laboratory scale. The next stage involves immobilising Brevundimonas sp. AJZ05 in a suitable support matrix to improve its stability, operational performance and reusability.
Another finding from the study was the bacterium’s tolerance to several metal ions. According to the researchers, this could be useful because industrial wastewater often contains complex mixtures of contaminants.
The research was supported by the Ministry of Education through the Prime Minister’s Research Fellowship, with support from the Department of Chemical Engineering and Technology, IIT (BHU), Varanasi.
The findings were published in the peer-reviewed journal Environmental Geochemistry and Health. The paper was co-authored by Ajithkumar Veluchamy, Jothika Jeyabalan and Dr Selvaraju Narayanasamy from IIT Guwahati, along with Dr Ankur Verma from the Department of Chemical Engineering and Technology, IIT (BHU), Varanasi.