Excess surface area in bioelectrochemical systems causes ion transport limitations

Pulse-opencircuit voltammetry: A novel method characterizes bioanode performance from microbe-electrode interfacial processes

Bioanode is a key component of bioelectrochemical systems, but the methods characterizing its resistance distribution are lacked. We propose a novel pulse-opencircuit voltammetry (POV) based on the analytical principle clarified from the electron flow pathways of microbe-electrode interfacial processes (MEIPs). A dual-cathode cell is designed to provide an experimental platform for ensuring precise data acquisition of bioanodes. This POV method enables to measure steady state polarization curves and ohmic potential loss curves by integrating potentiostatic discharge and current interruption techniques. They determines reaction resistance (R_B,act) and ohmic resistance (R_B,ohm) of biofilm with the assistance of impedance spectroscopy measuring material resistance. The results of various bioanodes demonstrate that R_B,act is the principal limiting factor and its value relies on catabolism state. Whilst R_B,ohm is relevant to extracellular electron transfer behaviors. They are two useful indicators of the dynamic evaluation of biofilm. We anticipate that this method together with the cell platform is accessible to users and has wide applications in bioanode construction and electroactive bacteria investigation.

The characteristic of electrode of degradation of bio-electrochemical system based on in-situ ultrasonic monitoring: Biofilm and ion precipitation

Electrode interface behavior is a decisive factor affecting the performance of bio-electrochemical systems, and traditional monitoring methods cannot provide real-time feedback. Therefore, in situ ultrasonic monitoring was performed to continuously monitor the formation process of electroactive biofilm and salt precipitation on the cathode surface. The results showed that biofilm was attached to the cathode surface first. Then, Ca²⁺ and Mg²⁺ precipitation gradually invaded the biofilm and accumulated between the cathode and the biofilm. The electrochemical performance of the biofilm adhesion and initial ion invasion process was improved. However, the electrochemical performance of the precipitation layer was decreased, while the operation time increases. In this paper, based on the air cathode scaling analyzing a new method for monitoring the electrode interface of bio-electrochemical system was provided, and the performance was recovered by using reverse electric field.

Substrate salinity: A critical factor regulating the performance of microbial fuel cells, a review

Substrate salinity is a critical factor influencing microbial fuel cells (MFCs) performance and various studies have suggested that increasing substrate salinity first improves MFC performance. However, a further increase in salinity that exceeds the salinity tolerance of exoelectrogens shows negative effects because of inhibited bacterial activity and increased activation losses. In this review, electricity generation and contaminant removal from saline substrates using MFCs are summarized, and results show different optimal salinities for obtaining maximum performance. Then, electroactive bacteria capable of tolerating saline environments and strategies for improving salinity tolerance are discussed. In addition to ohmic resistance and bacterial activity, membrane resistance and catalyst performance will also be affected by substrate salinity, all of which jointly contribute the final overall MFC performance. Therefore, the combined effect of salinity is analyzed to illustrate how the MFC performance changes with increasing salinity. Finally, the challenges and perspectives of MFCs operated in saline environments are discussed.

The effect of additional salinity on performance of a phosphate buffer saline buffered three-electrode bioelectrochemical system inoculated with wastewater

In bioelectrochemical system (BES), phosphate buffer saline (PBS) is usually used to achieve a suitable pH condition, which also increases electrolyte salinity. A series of factors that change with salinity will affect BES performance. To simplify the scenario, a three-electrode BES is used to investigate how additional salinity affects the performance of a 50 mM PBS-buffered BES. Results demonstrated that current production decreased with increasing salinity and the dominant exoelectrogens were not inhibited with the addition of 200 mM NaCl. The distribution of system resistance was analyzed by electrochemical impedance spectroscopy. Compared to the decreased solution and biofilm resistance, the increased interfacial resistance that accounted for up to 97.8% of total resistance was the dominant reason for the decreased current production with the increasing additional salinity. The effects of additional salinity on acetate degradation and columbic efficiency were also analyzed.

Recent development of biofuel cell based self-powered biosensors

BFC-based SPBs have been used as power sources for other devices and as sensors for detecting toxicity and BOM.

Impact of Ohmic Resistance on Measured Electrode Potentials and Maximum Power Production in Microbial Fuel Cells

Low solution conductivity is known to adversely impact power generation in microbial fuel cells (MFCs), but its impact on measured electrode potentials has often been neglected in the reporting of electrode potentials. While errors in the working electrode (typically the anode) are usually small, larger errors can result in reported counter electrode potentials (typically the cathode) due to large distances between the reference and working electrodes or the use of whole cell voltages to calculate counter electrode potentials. As shown here, inaccurate electrode potentials impact conclusions concerning factors limiting power production in MFCs at higher current densities. To demonstrate how the electrochemical measurements should be adjusted using the solution conductivity, electrode potentials were estimated in MFCs with brush anodes placed close to the cathode (1 cm) or with flat felt anodes placed further from the cathode (3 cm) to avoid oxygen crossover to the anodes. The errors in the cathode potential for MFCs with brush anodes reached 94 mV using acetate in a 50 mM phosphate buffer solution. With a felt anode and acetate, cathode potential errors increased to 394 mV. While brush anode MFCs produced much higher power densities than flat anode MFCs under these conditions, this better performance was shown primarily to result from electrode spacing following correction of electrode potentials. Brush anode potentials corrected for solution conductivity were the same for brushes set 1 or 3 cm from the cathode, although the range of current produced was different due to ohmic losses with the larger distance. These results demonstrate the critical importance of using corrected electrode potentials to understand factors limiting power production in MFCs.

Inhibitory Effect of Furanic and Phenolic Compounds on Exoelectrogenesis in a Microbial Electrolysis Cell Bioanode

The objective of this study was to systematically investigate the inhibitory effect of furfural (FF), 5-hydroxymethylfurfural (HMF), syringic acid (SA), vanillic acid (VA), and 4-hydroxybenzoic acid (HBA), which are problematic lignocellulose-derived byproducts, on exoelectrogenesis in the bioanode of a microbial electrolysis cell. The five compound mixture at an initial total concentration range from 0.8 to 8.0 g/L resulted in an up to 91% current decrease as a result of exoelectrogenesis inhibition; fermentative, nonexoelectrogenic biotransformation pathways of the five compounds were not affected. Furthermore, the parent compounds at a high concentration, as opposed to their biotransformation products, were responsible for the observed inhibition. All five parent compounds contributed to the observed inhibition of the mixture. The IC₅₀ (i.e., concentration resulting in 50% current decrease) of individually tested parent compounds was 2.7 g/L for FF, 3.0 g/L for HMF, 1.9 g/L for SA, 2.1 g/L for VA and 2.0 g/L for HBA. However, the parent compounds, when tested below their respective noninhibitory concentration, jointly resulted in significant inhibition as a mixture. Catechol and phenol, which were persistent biotransformation products, inhibited exoelectrogenesis only at high concentrations, but to a lesser extent than the parent compounds. Exoelectrogenesis recovery from inhibition by all compounds was observed at different rates, with the exception of catechol, which resulted in irreversible inhibition.

Performance evaluation of a continuous-flow bioanode microbial electrolysis cell fed with furanic and phenolic compounds

An MEC bioanode operated under different continuous-flow conditions converts problematic furanic and phenolic compounds to renewable hydrogen.