Self-recoverable voltage reversal in stacked microbial fuel cells due to biofilm capacitance

Prevalence of Escherichia coli in electrogenic biofilm on activated carbon in microbial fuel cell

For a better understanding of the distribution of depth-dependent electrochemically active bacteria at in the anode zone, a customized system in a microbial fuel cell (MFC) packed with granular activated carbon (GAC) was developed and subsequently optimized via electrochemical tests. The constructed MFC system was sequentially operated using two types of matrice solutions: artificially controlled compositions (i.e., artificial wastewater, AW) and solutions obtained directly from actual sewage-treating municipal plants (i.e., municipal wastewater, MW). Notably, significant difference(s) of system efficiencies between AW or MW matrices were observed via performance tests, in that the electricity production capacity under MW matrices is < 25% that of the AW matrices. Interestingly, species of Escherichia coli (E. coli) sampled from the GAC bed (P1: deeper region in GAC bed, P2: shallow region of GAC near electrolytes) exhibited an average relative abundance of 75 to 90% in AW and a relative abundance of approximately 10% in MW, while a lower relative abundance of E. coli was found in both the AW and MW anolyte samples (L). Moreover, similar bacterial communities were identified in samples P1 and P2 for both the AW and MW solutions, indicating a comparable distribution of bacterial communities over the anode area. These results provide new insights into E. coli contribution in power production for the GAC-packed MFC systems (i.e., despite the low contents of Geobacter (> 8%) and Shewanella (> 1%)) for future applications in sustainable energy research. KEY POINTS: • A microbial community analysis for depth-dependence in biofilm was developed. • The system was operated with two matrices; electrochemical performance was assessed. • E. coli spp. was distinctly found in anode zone layers composed of activated carbon.

High electrical energy harvesting performance of an integrated microbial fuel cell and low voltage booster-rectifier system treating domestic wastewater

To harvest directly usable electrical energy from real domestic wastewater, a new power management system (PMS), transistor-based low voltage boosters followed by a voltage rectifier (LVBR), was developed and tested for its energy harvesting performance. Three air-cathode MFCs were individually linked with LVBs, which were electrically stacked in parallel and then connected with a single voltage rectifier (MFC-LVBR). The MFC-LVBR system could increase V_MFCto 11.9 ± 0.6 V without voltage reversal, which was capable of charging a lithium-ion batteryand supercapacitor-based power banks. When the integrated MFC-LVBR system was linked with a lithium-ion battery, the highest normalized energy recovery (NER_COD) of 0.76 kWh/kg-COD (NER_volumeof 0.22 kWh/m³) was achieved with a minimal energy loss of 14.4%, whichwas much higher than those previously reported values.Furthermore, the electrical energy charged in the lithium-ion battery successfully powered a DC peristaltic pump requiring a minimum operating power of 0.46 W.

Electrochemical impedance spectroscopy applied to microbial fuel cells: A review

Electrochemical impedance spectroscopy (EIS) is an efficient and non-destructive test for analyzing the bioelectrochemical processes of microbial fuel cells (MFCs). The key factors limiting the output performance of an MFC can be identified by quantifying the contribution of its various internal parts to the total impedance. However, little attention has been paid to the measurement conditions and diagrammatic processes of the EIS for MFC. This review, starting with the analysis of admittance of bioelectrode, introduces conditions for the EIS measurement and summarizes the representative equivalent circuit plots for MFC. Despite the impedance from electron transfer and diffusion process, the effect of unnoticeable capacitance obtained from the Nyquist plot on MFCs performance is evaluated. Furthermore, given that distribution of relaxation times (DRT) is an emerging method for deconvoluting EIS data in the field of fuel cell, the application of DRT-analysis to MFC is reviewed here to get insight into bioelectrode reactions and monitor the biofilm formation. Generally, EIS measurement is expected to optimize the construction and compositions of MFCs to overcome the low power generation.

Microbial fuel cell driven mineral rich wastewater treatment process for circular economy by creating virtuous cycles

The aim of this work is to study for concurrent harvesting bioelectricity and struvite mineral from mineral rich wastewater containing with nitrogen (N) and phosphorous (P) contents using MFCs and a chemical precipitation system. Whole reaction was constructed to sequentially run hybrid reactor (consisting of MFCs and struvite precipitation), gravitational sedimentation, nitrogen purging and MFCs. The MFCs generated around 6.439 ± 0.481 mA and 2.084 ± 0.310 mW as I_max and P_max, respectively under 2g/l of COD. More than 70% of C source, and around 95% of P and N sources have been removed. Struvite mineral was precipitated in the hybrid reactor after the injection of Mg²⁺ and collected in sedimentation tank. Economic feasibility and beneficial concerns were carefully investigated, and it is proposed for applications in the "decentralised treatment process" of agriculture and livestock wastewater in order to realise circular and strong economy in agriculture by creating virtuous cycles.

In situ groundwater remediation with bioelectrochemical systems: A critical review and future perspectives

Groundwater contamination is an ever-growing environmental issue that has attracted much and undiminished attention for the past half century. Groundwater contamination may originate from both anthropogenic (e.g., hydrocarbons) and natural compounds (e.g., nitrate and arsenic); to tackle the removal of these contaminants, different technologies have been developed and implemented. Recently, bioelectrochemical systems (BES) have emerged as a potential treatment for groundwater contamination, with reported in situ applications that showed promising results. Nitrate and hydrocarbons (toluene, phenanthrene, benzene, BTEX and light PAHs) have been successfully removed, due to the interaction of microbial metabolism with poised electrodes, in addition to physical migration due to the electric field generated in a BES. The selection of proper BESs relies on several factors and problems, such as the complexity of groundwater and subsoil environment, scale-up issues, and energy requirements that need to be accounted for. Modeling efforts could help predict case scenarios and select a proper design and approach, while BES-based biosensing could help monitoring remediation processes. In this review, we critically analyze in situ BES applications for groundwater remediation, focusing in particular on different proposed setups, and we identify and discuss the existing research gaps in the field.

Controlling Voltage Reversal in Microbial Fuel Cells

Microbial fuel cell (MFC) systems have been developed for potential use as power sources, along with several other applications, with bacteria as the prime factor enabling electrocatalytic activity. Limited voltage and current production from unit cells limit their practical applicability, so stacking multiple MFCs has been proposed as a way to increase power production. Special attention is paid to voltage reversal (VR), a common occurrence in stacked MFCs, and to identifying the mechanisms underlying this phenomenon. We also proposed realistic perspectives on stacked MFCs in an effort to control and suppress VR by balancing the kinetics in the system, such as using enriched electroactive microorganisms or altering the circuitry mode.

Elimination of voltage reversal in multiple membrane electrode assembly installed microbial fuel cells (mMEA-MFCs) stacking system by resistor control

Voltage reversal (VR) in series connection of multiple membrane electrode assembly installed microbial fuel cells (mMEA-MFC) is eliminated by manipulating the resistor control. Discharge test results collected from two mMEA-MFCs initially operated (designated as P1 and P2) confirm that the performance of P2 exceeds that of P1. Thus, driving P1 and P2 as serially stacked MFCs generate the VR in P1. Controlling the inserted resistor adjust the current production of P2 to maintain balance with P1, and the VR in P1 is eliminated in the operation of stacking mode. Thus, manipulating the internal resistance provide an applicable approach to suppress VR in the stacking of mMEA-MFCs system.