Application of Magnetite-Nanoparticles and Microbial Fuel Cell on Anaerobic Digestion: Influence of External Resistance

Abstract

In this paper, the application of magnetite-nanoparticles and a microbial fuel cell (MFC) was studied on the anaerobic digestion (AD) of sewage sludge. The experimental set-up included six 1 L biochemical methane potential (BMP) tests with different external resistors: (a) 100 Ω, (b) 300 Ω, (c) 500 Ω, (d) 800 Ω, (e) 1000 Ω, and (f) a control with no external resistor. The BMP tests were carried out using digesters with a working volume of 0.8 L fed with 0.5 L substrate, 0.3 L inoculum, and 0.53 g magnetite-nanoparticles. The results suggested that the ultimate biogas generation reached 692.7 mL/g VSfed in the 500 Ω digester, which was substantially greater than the 102.6 mL/g VSfed of the control. The electrochemical efficiency analysis also demonstrated higher coulombic efficiency (81.2%) and maximum power density (30.17 mW/ m2) for the 500 Ω digester. The digester also revealed a higher maximum voltage generation of 0.431 V, which was approximately 12.7 times the 0.034 V of the lowest-performing MFC (100 Ω digester). In terms of contaminants removed, the best-performing digester was the digester with 500 Ω, which reduced contaminants by more than 89% on COD, TS, VS, TSS and color. In terms of cost-benefit analysis, this digester produced the highest annual energy profit (48.22 ZAR/kWh or 3.45 USD/kWh). This infers the application of magnetite-nanoparticles and MFC on the AD of sewage sludge is very promising for biogas production. The digester with an external resistor of 500 Ω showed a high potential for use in bioelectrochemical biogas generation and contaminant removal for sewage sludge.

The Potential Use of Pseudomonas stutzeri as a Biocatalyst for the Removal of Heavy Metals and the Generation of Bioelectricity

“…Yaqoob et al (2023) used rotten rice as a substrate in their MFC, showing an internal resistance of 312.5 Ω using graphite as electrodes. They also mentioned that the increase in internal resistance decreased the mobility of electrons [61]. Likewise, Raychaudhuri et al (2023), in their MFCs, used rice mill wastewater as a substrate, achieving an internal resistance of 372.34 Ω using carbon electrodes, mentioning that high absorbed values of the chemical oxygen demand were due to the high porosity shown of the electrodes [62].…”

Application of Magnetite‐nanoparticles and Static Magnetic Field on a Microbial Fuel Cell in Anaerobic Digestion

“…The coulombic efficiency relies on the impedance or resistance of a bioelectrochemical system, and higher resistance leads to a decrease in the coulombic efficiency since it is difficult to retrieve electrons from a system with higher resistance [48] . Thus, the very high coulombic efficiency on the MFCMM digester is an indication that this digester recovered the greatest number of electrons [49] . Zhou et al [50] investigated the effect of static magnetic field on a bioelectrochemical system and found that static magnetic field reduced the internal resistance, particularly its diffusion resistance.…”

“…[48] Thus, the very high coulombic efficiency on the MFCMM digester is an indication that this digester recovered the greatest number of electrons. [49] Zhou et al [50] investigated the effect of static magnetic field on a bioelectrochemical system and found that static magnetic field reduced the internal resistance, particularly its diffusion resistance. Furthermore, due to low resistance, the use of static magnetic field resulted in abundance of Geobacter of almost 32.5%, and the high syntrophic interactions between exoelectrogenic and methanogenic microorganisms resulted in higher coulombic efficiency.…”