Optimal loading of α-Fe₂O₃ continually promotes microbial metabolism and extracellular electron transfer in the iron-reducing bacteria-driven microbial electro-Fenton system

Both iron-reducing bacteria (IRB) and iron are loaded to anode during the microbial electro-Fenton (MEF) system, which simultaneously achieves the refractory wastewater treatment and iron circulation. Meanwhile, the amounts of iron play a pivotal role in both performance of microbial electrochemical system (MES) and regulation of the microbial community and metabolism. Therefore, additional α-Fe 2 O 3 was adopted in MEF system, and then the regulation mechanism for anodic microorganism was thoroughly revealed in this study. When α-Fe 2 O 3 loading increased to 2 mg/cm 2 , phenol removal rate improved by 3.8 times and the anaerobic biofilm thickness of 1000 μm on the anode surface; following, current density increased by 96.2 % and current resistance reduced by 50.5 %. Metatranscriptomic sequencing indicated that α-Fe 2 O 3 could improve microbial metabolism activity via up-regulating the enzymes associated with tricarboxylic acid cycle (TCA cycle). Meanwhile, Shewanella abundance increased 326-fold, and α-Fe 2 O 3 up-regulated the expression of Type II secretion system and cytochrome c synthesis, promoting extracellular electron transfer (EET) process via direct contact pathway. Overall, this study provided a novel strategy for optimizing the performance of MEF system.