Optimization of Textile Dye Mixture Biodegradation By a Novel Bacterial Consortium and Assessment of Phytotoxicity

Abstract

High concentrations of synthetic dye mixtures remain difficult to degrade using conventional treatment methods due to their complex structure and high recalcitrance. In this study, a novel bacterial consortium comprising Stutzerimonas sp. VITKSS2, Brucella sp. VITKSS3, and Pseudomonas sp. VITKSS4 was developed to efficiently decolorize, degrade, and detoxify concentrated textile dye mixture under optimized culture conditions. Medium optimization was performed using one-variable-at-a-time (OVAT), Plackett–Burman (PB) factor screening, and Central Composite Design (CCD). The optimal medium consists of fructose (1.06%), ammonium sulphate (1.08%), and KH₂PO₄ (0.44%) with physicochemical parameters of 35 ± 2 °C, pH 7.0, and 1% inoculum size. Under these optimized conditions, the consortium achieved 90.6 ± 2.9% decolorization of ten-dye mixture (1000 mg/L) under static conditions, and a maximum of 80.8 ± 3.6% degradation at 3000 mg/L dye concentration, representing among the higher reported efficiencies. FTIR and GC–MS analyses suggested the putative transformation of persistent phthalic acid esters (PAEs) following consortium treatment. Biodegradation of the dye mixture produced several intermediates such as bis(2-ethylhexyl)phthalate (DEHP), dibutyl phthalate (DBP), monobutyl phthalate (MBP) and phthalic acid (PA), which were further metabolized, resulting in a substantial reduction of toxic compounds. Phytotoxicity assessment on Zea mays and Vigna radiata seeds showed a significant reduction in overall toxicity by 91.6% in seed germination and 93.1% in root elongation. Meanwhile, the consortium treated dye mixture enhanced the mean shoot length by 11.45%. This novel consortium offers an effective and sustainable approach for the biodegradation and detoxification of high concentration of dye mixtures, contributing to eco-friendly wastewater remediation.