The Effects of Nanoscale Zerovalent Iron on Microbial Fuel Cells in the Start-up Process

Municipal sludge contains carbon-rich material that can be used in microbial fuel cells (MFCs) to generate electrical power. However, manufactured nanoparticles found in sewage pose a potential risk in MFCs although the extent of this is still unclear. In this study, MFCs using sludge containing two types of nanoscale zerovalent iron (nZVI) as substrates are investigated. It is found that in the MFC start-up process, the maximum output voltage of the green synthesized nZVI (g-nZVI) group and chemically synthesized nZVI group (c-nZVI) decreases to 202.5 mV and 94.7 mV, respectively. Meanwhile the maximum output voltage of the control group is higher than 500 mV. These outcomes are attributed to a high concentration of nZVI being inhibited during the start-up phase, and nZVI makes no essentially significant change in generating electricity despite MFCs being started successfully. Concerning the results on the rate of removing chemical oxygen demand, scanning electron microscope, and electrochemical characterization indicate that green synthesized nZVI, compared to chemically synthesized nZVI, reveals less antibacterial activity to microbial community in anode. The electronic properties of MFCs are lightly affected due to the mature biofilm adhering to the anode's electrode surface. Finally, nZVI can effectively extend and stabilize the output voltage of the produced electricity by releasing Fe3+ ions.