Pulse-width modulated external resistance increases the microbial fuel cell power output

Periodic polarization duty cycle tunes performance and adhesion of anodic electroactive biofilms

Periodic polarization can improve the performance of anodic electroactive biofilms (EABs). The impact of the half-period duration was previously investigated at constant duty cycle (50%), i.e., the proportion of a period during which the electrode is polarized. Here, we cultured eight EABs on glassy carbon electrodes at four different duty cycles (50%, 67%, 80% and 91%) by varying the time interval under open circuit conditions, while keeping the polarization duration at 10 s. The shorter duty cycles slightly slowed initial growth but produced EABs generating higher faradaic currents. The total charge recovery over 38 days increased with decreasing duty cycles from 0.53 kC.cm-2 (duty cycle of 91%) to 1.65 kC.cm-2 (50%). EABs with the shortest duty cycle fully detached twice from the electrode surface, but detachments were quickly followed by the formation of more efficient EABs. We then carried out controlled removal of some aged and low current-producing EABs by applying a 30 s cathodic current (H2 evolution at -15 mA.cm-2) and observed the subsequent rapid development of fresh EABs displaying better electrochemical performance. Our results illustrate that well-chosen dynamic controls of electrode potentials can substantially improve the average current production of EABs, or allow a simple replacement of underperforming EABs.

Model development of bioelectrochemical systems: A critical review from the perspective of physiochemical principles and mathematical methods

Bioelectrochemical systems (BESs) are promising devices for wastewater treatment and bio-energy production. Since various processes are interacted and affect the overall performance of the device, the development of theoretical modeling is an efficient approach to understand the fundamental mechanisms that govern the performance of the BES. This review aims to summarize the physiochemical principle and mathematical method in BES models, which is of great importance for the establishment of an accurate model while has received little attention in previous reviews. In this review, we begin with a classification of existing models including bioelectrochemical models, electronic models, and machine learning models. Subsequently, physiochemical principles and mathematical methods in models are discussed from two aspects: one is the description of methodology how to build a framework for models, and the other is to further review additional methods that can enrich model functions. Finally, the advantages/disadvantages, extended applications, and perspectives of models are discussed. It is expected that this review can provide a viewpoint from methodologies to understand BES models.

Microbial fuel cell soft sensor for real-time toxicity detection and monitoring

Real-time toxicity detection and monitoring using a microbial fuel cell (MFC) is often based on observing current or voltage changes. Other methods of obtaining more information on the internal state of the MFC, such as electrochemical impedance spectroscopy (EIS), are invasive, disruptive, time consuming, and may affect long-term MFC performance. This study proposes a soft sensor approach as a non-invasive real-time method for evaluating the internal state of an MFC biosensor during toxicity monitoring. The proposed soft sensor approach is based on estimating the equivalent circuit model (ECM) parameters in real time. A flow-through MFC biosensor was operated at several combinations of carbon source (acetate) and toxicant (copper) concentrations. The ECM parameters, such as internal resistance, capacitance, and open-circuit voltage, were estimated in real time using a numerical parameter estimation procedure. The soft sensor approach proved to be an adequate replacement for EIS measurements in quantifying changes in the biosensor internal parameters. The approach also provided additional information, which could lead to earlier detection of the toxicity onset.

The influential role of external electrical load in microbial fuel cells and related improvement strategies: A review

The scope of the currentreviewis to discuss and evaluate the role of the external electrical load/resistor (EEL) on the overall behavior and functional properties of microbial fuel cells (MFCs). In this work, a comprehensive analysis is made by considering various levels of MFC architecture, such as electric and energy harvesting efficiency, anode electrode potential shifts, electro-active biofilm formation, cell metabolism and extracellular electron transfer mechanisms, as a function of the EEL and its control strategies. It is outlined that taking the regulation of EEL into account at MFC optimization is highly beneficial, and in order to support this step, in this review, a variety of guidelines are collected and analyzed.

Modeling and optimization strategies towards performance enhancement of microbial fuel cells

Considering the complexity associated with bioelectrochemical processes, the performance of a microbial fuel cell (MFC) is governed by input operating parameters. For scaled-up applications, a MFC system needs to be modeled from engineering perspectives in terms of optimum operating conditions to get higher performance and energy recovery. Several conceptual numerical models to advanced computational simulation approaches have been developed to represent simple-form of a complex MFC system. Application of mathematical and computation models are explored to establish the relationship between operating input-variables and power output. The present review discusses about the complexity of system, modeling strategies used and reality of such modeling for scaling-up applications of MFCs. Additionally, the selection of an appropriate mathematical model reduces the computational duration and provides better understanding of the system process. It also explores the possibility and progress towards commercialization of MFCs and thus the need of development of model-based optimization and process-control approaches.

Harvesting Energy from Multiple Microbial Fuel Cells with a High-Conversion Efficiency Power Management System

Direct electricity production from waste biomass in a microbial fuel cell (MFC) offers the advantage of producing renewable electricity at a high Coulombic efficiency. However, low MFC voltage (below 0.5 V) necessitates the simultaneous operation of multiple MFCs controlled by a power management system (PMS) adapted for operating bioelectrochemical systems with complex nonlinear dynamics. This work describes a novel PMS designed for efficient energy harvesting from multiple MFCs. The PMS includes a switched-capacitor-based converter, which ensures operation of each MFC at its maximum power point (MPP) by regulating the output voltage around half of its open-circuit voltage. The open-circuit voltage of each MFC is estimated online regardless of MFC internal parameter knowledge. The switched-capacitor-based converter is followed by an upconverter, which increases the output voltage to a required level. Advantages of the proposed PMS include online MPP tracking for each MFC and high (up to 85%) power conversion efficiency. Also, the PMS prevents voltage reversal by disconnecting an MFC from the circuit whenever its voltage drops below a predefined threshold. The effectiveness of the proposed PMS is verified through simulations and experimental runs.

Real-Time Performance Optimization and Diagnostics during Long-Term Operation of a Solid Anolyte Microbial Fuel Cell Biobattery

This study describes a novel approach for real-time energy harvesting and performance diagnostics of a solid anolyte microbial fuel cell (SA-MFC) representing a prototype smart biobattery. The biobattery power output was maximized in real time by combining intermittent power generation with a Perturbation-and-Observation algorithm for maximum power point tracking. The proposed approach was validated by operating the biobattery under a broad range of environmental conditions affecting power production, such as temperature (4–25 °C), NaCl concentration (up to 2 g L−1), and carbon source concentration. Real-time biobattery performance diagnostics was achieved by estimating key internal parameters (resistance, capacitance, open circuit voltage) using an equivalent electrical circuit model. The real time optimization approach ensured maximum power production during 388 days of biobattery operation under varying environmental conditions, thus confirming the feasibility of biobattery application for powering small electronic devices in field applications.

Factors Affecting the Effectiveness of Bioelectrochemical System Applications: Data Synthesis and Meta-Analysis

Microbial fuel cells (MFCs) and microbial electrolysis cells (MECs) are promising bioelectrochemical systems (BESs) for simultaneous wastewater treatment and energy/resource recovery. Unlike conventional fuel cells that are based on stable chemical reactions, these BESs are sensitive to environmental and operating conditions, such as temperature, pH, external resistance, etc. Substrate type, electrode material, and reactor configuration are also important factors affecting power generation in MFCs and hydrogen production in MECs. In order to discuss the influence of these above factors on the performance of MFCs and MECs, this study analyzes published data via data synthesis and meta-analysis. The results revealed that domestic wastewater would be more suitable for treatment using MFCs or MECs, due to their lower toxicity for anode biofilms compared to swine wastewater and landfill leachate. The optimal temperature was 25–35 °C, optimal pH was 6–7, and optimal external resistance was 100–1000 Ω. Although systems using carbon cloth as the electrodes demonstrated better performance (due to carbon cloth’s large surface area for microbial growth), the high prices of this material and other existing carbonaceous materials make it inappropriate for practical applications. To scale up and commercialize MFCs and MECs in the future, enhanced system performance and stability are needed, and could be possibly achieved with improved system designs.

Long-term performance of a microbial electrolysis cell operated with periodic disconnection of power supply

This study describes a new approach for achieving stable long-term performance and maximizing removal of chemical oxygen demand (COD) in a Microbial Electrolysis Cell (MEC) by periodic disconnection of the MEC power supply.

Intermittent load implementation in microbial fuel cells improves power performance

This study reports on the response of small-scale MFCs to intermittent loading, in terms of power output over time. The aim was to understand the evolution with time of power output under different duty cycles, in conditions close to practical implementation. Inexpensive ceramic membranes were compared to cation exchange membranes, under continuous flow and with a pre-digester connected. Results show that at the minute-scale, all the duty cycles investigated, produced 78% higher power bursts from the MFCs (500μW) than when under continuous loading (280μW). These results were recorded from MFCs employing ceramic membranes, whereas the difference in performance for MFCs employing commercially available cation-exchange-membranes was insignificant. When normalising to daily energy production, only specific duty cycles produced more power than continuous loading. Furthermore, the introduction of a pre-digester increased the MFC power outputs 10-fold, thus confirming that separating fermentation from electro-active respiration, significantly enhances the system performance.