Sustainable acid dye removal: A biocatalytic approach using glyoxal-immobilized oxidase enzymes

Abstract

Immobilized oxidase enzymes have been widely investigated for their potential to degrade dyes, and offer a promising approach for textile wastewater treatment. However, in many immobilization methods, a major obstacle in applying immobilized enzymes to wastewater treatment is the reliance on potentially toxic chemicals, in particular, crosslinking agents for covalent immobilization, which can introduce secondary risks to the aquatic ecosystem. This study evaluates the use of glyoxal, a less toxic alternative, as a crosslinking agent for immobilizing horseradish peroxidase (HRP) and laccase onto chitosan beads. The immobilized enzymes were tested for the removal of Acid Green 25 (AG 25) and Acid Red 1 (AR 1) dyes under various pH levels, temperatures, and contact times. At 30 °C and pH 6.5, the immobilized enzymes removed (80 −84) % of Acid Green 25 dye and 71 % of Acid Red 1 dye after 4 h. Characterization of the immobilized enzymes confirmed successful crosslinking and structural stability, while metabolite analysis suggested potential dye degradation pathways. By utilizing glyoxal at a lower concentration (0.4 %) compared to traditional glutaraldehyde methods (typically 0.8 %), this approach reduces chemical input and ecotoxicity while maintaining high dye removal efficiency. These findings highlight the potential of glyoxal-crosslinked immobilized enzymes on chitosan beads as a sustainable and effective solution for textile wastewater treatment. © 2025 Elsevier Ltd