Removal of triclosan via peroxidases-mediated reactions in water: Reaction kinetics, products and detoxification

This study investigated and compared reaction kinetics, product characterization, and toxicity variation of triclosan (TCS) removal mediated by soybean peroxidase (SBP), a recognized potential peroxidase for removing phenolic pollutants, and the commonly used horseradish peroxidase (HRP) with the goal of assessing the technical feasibility of SBP-catalyzed removal of TCS. Reaction conditions such as pH, H2O2 concentration and enzyme dosage were found to have a strong influence on the removal efficiency of TCS. SBP can retain its catalytic ability to remove TCS over broad ranges of pH and H2O2 concentration, while the optimal pH and H2O2 concentration were 7.0 and 8 mu M, respectively. 98% TCS was removed with only 0.1 U mL(-1) SBP in 30 min reaction time, while an HRP dose of 0.3 U mL(-1) was required to achieve the similar conversion. The catalytic performance of SBP towards TCS was more efficient than that of HRP, which can be explained by catalytic rate constant (K-CAT) and catalytic efficiency (K-CAT/K-M) for the two enzymes. MS analysis in combination with quantum chemistry computation showed that the polymerization products were generated via C-C and C-O coupling pathways. The polymers were proved to be nontoxic through growth inhibition of green alga (Scenedesmus obliquus). Taking into consideration of the enzymatic treatment cost, SBP may be a better alternative to HRP upon the removal and detoxification of TCS in water/wastewater treatment. (C) 2016 Elsevier B.V. All rights reserved.