Biodegradation of synthetic dyes using Aspergillus fumigatus-derived laccase immobilized in alginate matrices

The discharge of dye-contaminated industrial wastewater from textile and dye manufacturing industries poses serious environmental and health risks due to the persistence and toxicity of synthetic dyes, particularly azo compounds. Conventional treatment methods are often ineffective for complete dye removal and may produce secondary pollutants. We developed a green biocatalytic approach using laccase immobilized in sodium alginate beads for efficient dye removal. In this study, a soil-derived fungal strain (A19), identified as Aspergillus fumigatus, was screened using sugarcane bagasse as the growth substrate under submerged fermentation. Crude enzyme exhibited a specific activity of 1.122 mg/mL, which was purified through ammonium sulphate precipitation followed by Sephadex G-100 chromatography, resulting in a 1.92-fold increase in purity with a 75.57% recovery. SDS-PAGE confirmed the laccase molecular weight to be approximately 69 kDa. The purified enzyme was immobilized in sodium alginate beads. This achieved 88.33% decolorization of Congo red and 80.15% of Bromophenol blue within 120 h. Adsorption of both dyes followed the Langmuir isotherm model, indicating monolayer binding with maximum adsorption capacities of 0.09 mg/g for Congo red and 1.16 mg/g for Bromophenol blue. The stability and reusability of laccase were enhanced by immobilization in sodium alginate beads. FTIR analysis confirmed functional group shifts after treatment, and SEM-EDX data revealed elemental changes in dye-treated beads. This study demonstrates a green, cost-effective biocatalytic system using laccase immobilized in alginate beads for synthetic dye removal. The results highlight the enzyme's stability, efficiency, and potential for large-scale industrial wastewater treatment.