Process Optimization Strategy: An Efficient Approach for Degradation of Synthetic Direct Black 15 Dye by Citrobacter freundii

Abstract

Textile industrial effluent is contaminated with resilient azo dyes. This study focuses on incorporating biological approaches for effective dye degradation in treating textile industry waste water effluents. A bacterial strain Citrobacter freundii with the ability to break down synthetic textile dyes was identified. The optimal conditions for degradation were obtained using response surface methodology (RSM). Among the three variables (A- temperature; B- inoculum concentration; C- time), AC and BC showed the most significant impact on dye degradation (> 90%). Efficient degradation of around 90% was achieved for the direct black 15 dye utilized in this study. To validate the degradation process, both the treated and untreated direct black dyes were subjected to characterization by UV–visible spectroscopy, gas chromatography – mass spectrometry (GC–MS) and Fourier-transfer infrared spectroscopy (FTIR). Molecular docking studies revealed an interaction between azo dyes and enzymes namely laccase and peroxidase of Citrobacter freundii. Phytotoxicity assessment of the degraded dye in Vigna radiata seedlings confirmed the non-toxic nature of the degraded compounds. The results suggest that biodegradation by employing Citrobacter freundii is an effective alternative to degrade textile black dye.

Graphical Abstract