Bio decolorization of the oil soluble azo dye toluidine Red by Halomonas strain A3

Synthetic dye wastewater is a significant environmental concern, particularly due to its extensive usage in industries such as textiles, printing, and dyeing. Traditional methods for treating wastewater with synthetic dyes are often seen as costly and inefficient, primarily because of the dyes' robust chemical nature. In light of these challenges, there has been a growing interest in recent years in the use of biodegradation. This method utilizes specific microorganisms capable of breaking down these stubborn pollutants, offering a more sustainable and effective solution for their removal. Given the limited detailed studies on the bacterial decolorization of oil-soluble (solvent-soluble) azo dyes, there is a significant need to address this issue. The ability of salt-tolerant bacteria named Halomonas strain A3 to decolorize an oil soluble azo dye, Toluidine Red was investigated. Decolorization conditions, including initial dye concentration, pH, NaCl percent (w/v), and incubation temperature, were optimized using the one-factor-at-a-time method with dye as the sole carbon and energy source. The ultraviolet-visible spectrophotometric method, high-performance liquid chromatography, and gas chromatography mass spectrometry analyses were used to investigate the decolorization mechanism at optimum condition, including 25 ppm dye concentration, 5% (w/v) NaCl, pH 6.5, and incubation temperature of 35 °C. Compared to the parent dye, the ultraviolet-visible scan of the supernatant suggested that the degradation mechanism was the main reason for color removal rather than inactive surface adsorption. HPLC analysis confirmed this conclusion. The final compounds produced from TR degradation were identified as benzene diazonium (m/z 105 ± 1) and 3-Phenyl-acrylic acid (m/z 149 ± 1). According to the results, Halomonas strain A3 is a practical alternative for degrading effluents containing oil-soluble azo dyes in salty conditions. A pathway for dye degradation was predicted based on the obtained intermediate and final products.