Biocatalytic Removal of DB2 Azo Dye from Textile Effluent Using Soybean Residue Peroxidases Coupled with Fenton Oxidation

In this study, the catalytic potential of peroxidase enzymes obtained from soybean industrial residues was investigated for the decolorization of the azo dye Direct Blue 2 (DB2) in textile wastewater. Peroxidase fractions (15 ± 5 U/L) were extracted and partially purified by ion-exchange chromatography and applied to a pilot-scale effluent, achieving DB2 degradation rates of 1.48 mg/L·h in the presence of chemical additives. High-performance liquid chromatography confirmed dye removal and detected benzidine (1 mg/L) as a degradation byproduct. Acute toxicity tests using Vibrio fischeri showed minimal variation, with values of 8 TU for untreated wastewater and 7.94 TU after enzymatic treatment. A subsequent Fenton process was implemented as a polishing step, achieving up to 90% decolorization, a 30% reduction in organic matter, and complete elimination of toxicity at an FeSO4/H2O2 ratio of 1:2.4. The results demonstrate a sustainable strategy for pre-treating textile effluents containing azo dyes through the enzyme-based valorization of agro-industrial residues.