Enhanced anaerobic treatment of azo dye wastewater via direct interspecies electron transfer with Fe3O4/sludge carbon

In this study, enhancement of anaerobic treatment of azo dye wastewater with Fe3O4/SC is investigated. Fe3O4/sludge carbon (SC) is prepared from waste activated sludge using a simple impregnation method. Two identical laboratory-scale upflow anaerobic sludge blanket reactors with a working volume of 1.5 L are filled with 2 g/L of SC (reactor 1) and 2 g/L of Fe3O4/SC (reactor 2). Another reactor (reactor 0) is operated as a control. FTIR, XPS, SEM, and BET results indicate that Fe3O4 is successfully loaded on the SC. Addition of Fe3O4/SC to the reactor results in high chemical oxygen demand (78.13%) and color (97.60%) removal rates. Furthermore, Fe3O4/SC effectively decreases the amount of aniline generated and increases CH4 production. The Fe3O4/SC anaerobic system is stable with fast recovery in terms of both organic matter removal and aniline control with high toxic substance concentrations and fluctuating organic loads. Moreover, Fe3O4/SC greatly enhances enzymatic activity and sludge granulation, which could greatly improve anaerobic reactor stability. High electron transport system and conductivity values and the enrichment of Geobacter and Methanosaeta species confirm that direct interspecies electron transfer occurs with Fe3O4/SC in the reactor. These results provide a scientific basis for further applications to azo dye wastewater treatment and promote resource utilization of waste sewage sludge.