Enhanced anaerobic digestion of landfill leachate based on a novel redox mediator: Synergistic mechanism of enhancing extracellular electron transfer

Abstract

The presence of recalcitrant compounds and toxic substances in landfill leachate results in low anaerobic digestion (AD) efficiency and poor methane production performance. Strengthening the extracellular electron transfer of microorganisms represents an effective approach to promote the AD of landfill leachate. In this study, a novel redox mediator (FeNC-RM) was synthesized through the combination of metal and non-metal doping, intensifying the stable operation of the landfill leachate AD system. Through characterization techniques including X-ray photoelectron spectroscopy and X-ray diffraction, it was observed that FeNC-RM possesses a larger specific surface area, abundant functional groups, and exceptional electrochemical performance. By adding FeNC-RM, the stability and efficiency of the medium-temperature AD system in the treatment of landfill leachate were improved: Obtained a high removal of chemical oxygen demand which was increased by 30 % compared to the control group and enhanced the specific methanogenic activity by 57.5 % compared to the control group. The electron transport system (ETS) activities of the experimental groups with the addition of RMs were all significantly higher than those of the control group, and the ETS activity of the sludge from the FeNC-RM group was 79.6 % higher than that of the control group. Through a comprehensive analysis of the underlying mechanism, it was determined that three aspects synergistically facilitated electron transfer: FeNC-RM, endowed with electrochemical capabilities, assumed a pivotal role in establishing a conduit for electron transport, thus promoting the synthesis of extracellular humic substances and augmenting electron transport activity. Furthermore, the microbial community was optimized by FeNC-RM, thereby fostering a co-nutritional mechanism between hydrolytic acidification bacteria and methanogens, establishing a direct interspecific electron transport pathway. In this study, an “endogenous + exogenous” electron transport model based on the enhanced extracellular electron transport pathway facilitated by FeNC-RM was proposed. This study offered valuable contributions to the advancement of anaerobic treatment technology for landfill leachate.