Biocatalytic degradation of carbamazepine with immobilized laccase-mediator membrane hybrid reactor

Abstract

Carbamazepine (CBZ) is one of the most recalcitrant pharmaceutically active compounds routinely detected in wastewater effluent-impacted environment. Biocatalytic degradation with enzymes such as laccase provides a promising approach for the elimination of CBZ. However, the relatively low redox potential of laccase makes its efficient CBZ degradation difficult. Therefore, an environmentally benign and effective mediator is required. In this study, three natural phenolic compounds, namely p-coumaric acid (PCA), syringaldehyde (SYR), and acetosyringone (ACE), were investigated as redox mediators for the enzymatic removal of CBZ by both free and immobilized laccase. Among the tested mediators, PCA resulted in the optimal CBZ removal performance with 60% removal rate (20μM initial CBZ) after 96h incubation with immobilized laccase in a conventional suspension system. The degradation of CBZ was then carried out in a membrane hybrid reactor with the effluent recirculating through suspended biocatalytic TiO2 nanoparticles. The effect of operation parameters including PCA concentrations, initial enzyme activity and operational flux on CBZ removal were investigated. Further CBZ metabolites study identified 10,11-dihydro-10,11-dihydroxy-CBZ (CBZD), 10,11-dihydro-10,11-epoxy-CBZ (CBZE) and acridone as the major metabolites of CBZ oxidation by laccase. The toxicity tests determined by algal viability using the fluorometric indicator alamarBlue indicated that the CBZ treatment via the hybrid reactor could effectively remove the toxicity of parent CBZ compound.