Applications of Redox Mediators in the Treatment of Organic Pollutants by Using Oxidoreductive Enzymes: A Review

Abstract

An enzymatic approach has attracted much interest in the remediation/degradation of various organic pollutants present in the wastewater coming out of industries. The treatment of several pollutants sometimes causes problems due to the recalcitrant nature of the compounds. However, these recalcitrant compounds were degraded/transformed by enzymes in the presence of certain redox mediators. These redox mediators enhanced the range of substrates and efficiency of degradation of the recalcitrant compounds by severalfold. Enzymes whose potential has been exploited for this purpose are laccases, lignin peroxidases, manganese peroxidases, horseradish peroxidases, turnip peroxidases, bitter gourd peroxidases, and others. Several redox mediators have been reported in the literature but very few of them are frequently used, for example, 1-hydroxybenzotriazole, veratryl alcohol, violuric acid, 2-methoxy-phenothiazone, 3-hydroxyanthranilic acid, anthraquinone 2,6-disulfonic acid, 2,2-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid), N-hydroxyacetanilide, phenol red, 3,3′,5,5′-tetramethyl benzidine; dichlorophenol red, 2,2′,6,6′-tetramethylpiperidine-N-oxyl radical, syringaldehyde and acetosyringone, and others. In the near future the enzyme–redox mediator combined treatment of aromatic compounds present in the industrial effluents/wastewater will play a vital role. Use of the enzyme–redox mediator system certainly will enhance the chances of remediation of a wide spectrum of aromatic compounds present in various industrial effluents.