Effect of Magnet Powder (Fe3O4) on Aerobic Granular Sludge (AGS) Formation and Microbial Community Structure Characteristics

Magnet powder (Fe3O4) could affect the growth and biodegradation ability of microbes by producing a magnetic field and iron ion. In this study, the enhancement of aerobic granulation by adding Fe3O4 was performed to evaluate the effects of different Fe3O4 concentrations (0, 0.4, 0.8, 1.2, and 1.6 g/L) on sludge granulation. Fe3O4 had a positive effect on the formation and growth of aerobic granular sludge (AGS) during the start-up period. In addition, the Fe3O4 concentration at 0.4-1.2 g/L promoted COD removal compared to the sequencing batch reactor (SBR) without Fe3O4. The three-dimensional excitation emission matrix (3D EEM) indicated that 0.8 g/L Fe3O4 addition could accelerate the granulation by stimulating extracellular polymeric substance (EPS) secretion which was an advantage for enhancing granule size. Meanwhile, microbial richness and diversity of AGS was significantly affected with Fe3O4 addition by high-throughput sequencing. Furthermore, dominant groups contributing to granule formation, COD removal, and nitrifying denitrifying were identified under different Fe3O4 concentrations.