Rice Straw-Derived Magnetic Hydrothermal Carbon Accelerates Anaerobic Azo Dye Biodegradation Through Enhanced...

In the present study, Fe₃O₄@hydrothermal carbon was prepared successfully using rice straw waste. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) analysis confirmed that the material had rich and strong redox-active centers on its surface, indicating that it has potential to be used as a redox mediator for electron transfer. Fe₃O₄@hydrothermal carbon was added into the anaerobic sludge treatment system for the collaboration of dye decolorization. The results showed that azo dye decolorization efficiency reached the maximum value (98.3%) with the presence of Fe₃O₄@hydrothermal carbon, which was 16.6% higher than control reactor (without Fe₃O₄@hydrothermal carbon added). In addition, Fe₃O₄@hydrothermal carbon exhibits good reusability and the dye decolorization rates in the "anaerobic sludge-material" combining system were significantly higher than that in the "sludge-alone" system during the semi-continuous wastewater treatment process. Mechanistic investigations revealed that the enhanced decolorization is driven by a synergistically constructed interspecies electron transfer pathway. Specifically, the addition of Fe₃O₄@hydrothermal carbon improved the formation of the extracellular polymeric substance (EPS), which had positive effects on sludge stability and its interaction with the material. CV and electron transport system (ETS) activity analysis showed that the sludge exhibited high electrochemical activities with the support of the material, which led to a high electron transfer efficiency between the electron-donating and accepting microbial pairs in the treatment system. The high-throughput sequencing analysis showed that the structure of the microbial community changed during the semi-continuous treatment process; Megasphaera and Clostridium accounted for more than 87.5% of the total abundance of the bacterial community in the anaerobic sludge with material addition. Driven by the material-mediated process, these enriched functional taxa exhibited a high electron transfer efficiency between electron-donating and accepting pairs, accelerating the catalytic cleavage of azo bonds and ultimately improving the overall anaerobic treatment performance.