Enhancement on the Microbial Extracellular Electron Transfers by Modified Lignin Materials: Application on Decolorization of Azo Dye

Abstract

Background: Extracellular electron transfers (EETs) are mainly involved in anaerobic respiration of quinone-respiring strains, which is applicable in many fields, such as microbiological fuel cell, bio-hydrogen production, anoxic denitrification, and bio-reduction of azo dyes. However, this kind of instinctive function of microbes was nonspecific and low efficient, which needed to be improved by addition of exogenous redox mediators (RMs). In this work, vanillin, syringaldehyde and p-hydroxybenzaldehyde, as the precursors of lignin, were functionally modified to RMs in effort to accelerate the bio-reduction azo dyes.Results: The results showed that the decolorization efficiency of MO motivated by modified vanillin were increased from 20% to 95% in less than 12 h. And the modified syringaldehyde was increased to 85% in 24h. According to GC-MS, the modified products of vanillin and syringaldehyde were mainly kinds of phenols, ketones and quinones. The RMs exhibited better electrochemical performances by CV measurement and the •OH radicals were found according to EPR. Under saline condition, the strain, in the presence of RMs, still exhibited a high and stable removal efficiency to MO.Conclusions: The novel RMs of biodegradation to azo dyes were prepared from lignin monomers. The RMs based on bio-materials are environment-friendly and have a remarkable effect in biodegradation of azo dyes. This work may provide a new route for the functional utilization of lignin-resource and a theoretical guidance for efficient biodegradation of azo dye wastewater.