An overview of immobilized enzyme technologies for dye and phenolic removal from wastewater

Global water pollution caused by dye and phenol contaminants has been reported to have reached an alarming level. These hazardous contaminants pose significant threats to humans and ecosystem, due to their toxicity, carcinogenicity, and mutagenicity. Various technologies have emerged for dyes and phenols removal from wastewater, such as physical adsorption, chemical oxidation, ozonation, extraction, and electrochemical treatments. However, these conventional methods are constrained by low efficiency and stability, high cost, and formation of harmful by-products. In recent years, there has been growing interest towards the development of immobilized enzyme technologies because they are more economical, effective and eco-friendly. Among various enzymes, peroxidases have generated extraordinary interest attributed to their ability to catalyze reactions of a variety of undesirable pollutants, such as dyes and phenol effluents. Immobilization of enzyme can enhance its catalytic efficiency, improve storage and operational stabilities, as well as allow enzyme recovery and reusability. Although numerous existing immobilized enzymatic systems have been established, their practical applications are limited due to mass transfer restriction, lack of feasibility for scaling-up and continuous operations, and difficulty for separation of immobilized enzymes from reaction mixtures. Therefore, much attention has been devoted to the immobilization of enzymes on nano-structured materials. In the current review, effects of process parameters on immobilized enzymes for applications in both dye and phenol treatment are discussed and summarized. Recent advanced technologies as well as challenges and future perspectives for research and development in this field are also highlighted.