Advances and feasibility of biocatalytic technologies for dye removal

The expanding dye and dye-related industries have led to the production of large volumes of dye-containing wastewater streams. Without adequate treatment, the wastewater could pollute the environment and give rise to health concerns. Biocatalytic technologies provide a channel of treating the wastewater. These technologies involve immobilizing dye-degrading enzymes particularly laccase and peroxidase, and microorganisms on or in suitable supports to enhance their activities, stability, efficiency, and recyclability. This review provides the latest advances in biocatalytic technologies and their feasibility. Based on this review, laccase has been immobilized on supports comprising PEDOT-PPy-COOH/Pt, nanocellulose from quinoa husks, calcium alginate, delignified spent grain, polymeric membrane, and metal-organic frameworks to treat different dyes with efficiencies ranging from 39% to 100%. Peroxidase has been immobilized on calcium alginate, Fe3O4 nanoparticles, cationic maize starch, and graphene oxide-SiO2 for treatment of various dyes with efficiencies in the range of 40–100%. The dye-degrading ability of azoreductase is often harnessed through immobilization of microbial cells which contain multiple enzymes in them and are frequently able to decolorize more than 90% of the dyes tested. An immobilized azoreductase has been successfully produced but showed lower dye-degrading efficiencies of 18.3–58.3%. The performance of biocatalysts can be affected by multiple factors, making optimization of the operating conditions important. The use of green support materials could reduce the cost of biocatalysts and the associated environmental concerns. A versatile biocatalyst or biocatalyst mixture is beneficial to degrade the complex pollutants in dye-containing wastewater.