Enhancement on the microbial extracellular electron transfers by modified lignin materials: Application on decolorization of azo dye

In the process of biodegradation of azo dye, redox mediators (RMs) were found to signifi-cantly enhance the removal efficiency. In this work, biodegradable RMs deriving from lignin-based monomers were prepared via peroxidation to investigate whether similar chemicals present in lignin-rich streams from biorefineries could be used for biological treatment of azo dyes. The as-prepared RMs were characterized by fourier transform infrared spectroscopy (FTIR), gas chromatography-mass spectrometer (GC-MS), cyclic voltammetry and electron paramagnetic resonance, and the degradation metabolites were analyzed by high performance liquid chromatography (HPLC). The induction of RMs accelerated the extracellular electron transfer, resulting efficient methyl orange (MO) decolorization. The decolorization efficiency of MO motivated by the products of vanillin peroxidation were increased from 20% to 95% in 12 h. Moreover, the products deriving from syringaldehyde peroxidation increased the efficiency from 40% to 85% in 24 h. The degradation results of the two RMs were well fitted by zero-order and first-order kinetic models. Under saline condition, the strain still remained a high and stable removal effi-ciency to MO in the presence of RMs, making it acceptable to be applied in the practical wastewater. The extracellular electron transfers and metabolic products were explored to unveil the mechanisms of enhancement. This study could provide a new route for the functional utilization of lignin-resource and a theoretical guidance for efficient biodegra-dation of azo dye wastewater. (c) 2021 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).