Individual Microbial Fuel Cells Research Articles

Resilience and limitations of MFC anodic community when exposed to antibacterial agents

This study evaluates the fate of certain bactericidal agents introduced into microbial fuel cell (MFC) cascades and the response of the microbial community. We tested the response of functioning urine fed MFC cascades using two very different bactericidal agents: a common antibiotic (Ampicillin, 5 g/L) and a disinfectant (Chloroxylenol 4.8 g/L) in concentrations of up to 100 times higher than the usual dose. Results of power generation showed that the established bacteria community was able to withstand high concentrations of ampicillin with good recovery after 24 h of minor decline. However, power generation was adversely affected by the introduction of chloroxylenol, resulting in a 99% loss of power generation. Ampicillin was completely degraded within the MFC cascade (>99.99%), while chloroxylenol remained largely unaffected. Analysis of the microbial community before the addition of the bactericidal agents showed a significant bacterial diversity with at least 35 genera detected within the cascade. Microbial community analysis after ampicillin treatment showed the loss of a small number of bacterial communities and proportional fluctuations of specific strains within the individual MFCs community. On the other hand, there was a significant shift in the bacterial community after chloroxylenol treatment coupled with the loss of at least 13 bacterial genera across the cascade.

Up-scaling microbial fuel cell systems for the treatment of real textile dye wastewater and bioelectricity recovery

ABSTRACT In this work the energy recovery in microbial fuel cell was studied by electrically stacking its three individual units into series and parallel arrangements. The power output was higher in parallel stacking by 2.07 and 14.77 times than series and individual units respectively. The rate of degradation of dye wastewater was in order of individual Microbial Fuel Cell (MFC) < series stack < parallel stack. The corn cob biochar was used as an additive in the MFC to improve the efficiency of the individual MFC unit. The addition of 0.5 g corn cob biochar enhanced the power output to 38.6 mW/m2 from 0.47 mW/m2 in the MFC individual unit without the biochar additive. The simultaneous COD reduction, TDS reduction and decolourisation of dye wastewater achieved are 82.14%, 68% and 74.8% respectively. The current work demonstrates that the dose of biochar and parallel stacking are a framework to achieve enhanced dye removal and bioenergy recovery via microbial fuel cell.

Long-term bio-power of ceramic microbial fuel cells in individual and stacked configurations

In order to improve the potential of Microbial Fuel Cells (MFCs) as an applicable technology, the main challenge is to engineer practical systems for bioenergy production at larger scales and to test how the prototypes withstand the challenges occurring during the prolonged operation under constant feeding regime with real waste stream. This work presents the performance assessment of low-cost ceramic MFCs in the individual, stacked (modular) and modular cascade (3 modules) configurations during long term operation up to 19 months, utilising neat human urine as feedstock. During 1 year, the performance of the individual MFC units reached up to 1.56 mW (22.3 W/m3), exhibiting only 20% power loss on day 350 which was significantly smaller in comparison to conventional proton or cation exchange membranes. The stack module comprising 22 MFCs reached up to 21.4 mW (11.9 W/m3) showing power recovery to the initial output levels after 580 days, whereas the 3-module cascade reached up to 75 mW (13.9 W/m3) of power, showing 20% power loss on day 446. In terms of chemical oxygen demand (COD) removal, the 3-module cascade configuration achieved a cumulative reduction of >92%, which is higher than that observed in the single module (56%).

Assessment of organic removal in series- and parallel-connected microbial fuel cell stacks

Microbial fuel cells (MFCs) degrade organic contaminants in wastewater while simultaneously producing electricity, but must be stacked to yield adequate voltage and current. This study examined the evolution of the chemical oxygen demand (COD) removal rate and efficiency in two identical individual MFCs (i-MFCs) in series- and parallel-connected stacks (sc- and pc-MFCs, respectively) under batch and continuous operation. The stack voltage and current increased in the respective series and parallel connections of the two i-MFCs (MFC unit 1 and MFC unit 2). Voltage reversal was observed in the sc- MFC below an external load of 100 Ω. Regardless of occurrence of the voltage reversal, organic reduction between i-MFCs and sc-MFCs showed no significant difference (gap of < 9% and < 6% in COD removal rate and efficiency, respectively); additionally, organic removals between the two individual MFCs in series indicated differences less than 9% of COD removal rate and 5% of COD removal efficiency in batch mode. Continuous operation also yielded similar organic removals as the MFCs in individual and series connection (voltage reversal occurred) mode, even over 8 days operation. Parallel connection yielded identical organic removals and currents in the two individual MFCs of the pc-MFC, even though the two separate i-MFCs showed different organic removal rates and current productions. This study provides the guide for the application of stacked MFCs for power source and efficient organic pollutant removal in wastewater treatment process.

Performance of air-cathode stacked microbial fuel cells systems for wastewater treatment and electricity production.

Two different air-cathode stacked microbial fuel cell (MFC) configurations were evaluated under continuous flow during the treatment of municipal wastewater and electricity production at a hydraulic retention time (HRT) of 3, 1, and 0.5 d. Stacked MFC 1 was formed by 20 individual air-cathode MFC units. The second stacked MFC (stacked MFC 2) consisted of 40 air-cathode MFC units placed in a shared reactor. The maximum voltages produced at closed circuit (1,000 Ω) were 170 mV for stacked MFC 1 and 94 mV for stacked MFC 2. Different power densities in each MFC unit were obtained due to a potential drop phenomenon and to a change in chemical oxygen demand (COD) concentrations inside reactors. The maximum power densities from individual MFC units were up to 1,107 mW/m2 for stacked MFC 1 and up to 472 mW/m2 for stacked MFC 2. The maximum power densities in stacked MFC 1 and MFC 2 connected in series were 79 mW/m2 and 4 mW/m2, respectively. Electricity generation and COD removal efficiencies were reduced when the HRT was decreased. High removal efficiencies of 84% of COD, 47% of total nitrogen, and 30% of total phosphorus were obtained during municipal wastewater treatment.

Sampled-time control of a microbial fuel cell stack

Abstract Research into microbial fuel cells (MFCs) has reached the point where cubic metre-scale systems and stacks are being built and tested. Apart from performance enhancement through catalysis, materials and design, an important research area for industrial applicability is stack control, which can enhance MFCs stack power output. An MFC stack is controlled using a sampled-time digital control strategy, which has the advantage of intermittent operation with consequent power saving, and when used in a hybrid series stack connectivity, can avoid voltage reversals. A MFC stack comprising four tubular MFCs was operated hydraulically in series. Each MFC was connected to an independent controller and the stack was connected electrically in series, creating a hybrid-series connectivity. The voltage of each MFC in the stack was controlled such that the overall series stack voltage generated was the algebraic sum (1.26 V) of the individual MFC voltages (0.32, 0.32, 0.32 and 0.3). The controllers were able to control the individual voltages to the point where 2.52 mA was drawn from the stack at a load of 499.9 Ω (delivering 3.18 mW). The controllers were able to reject the disturbances and perturbations caused by electrical loading, temperature and substrate concentration.

Effect of growth solution, membrane size and array connection on microbial fuel cell power supply for medical devices.

Implanted biomedical devices typically last a number of years before their batteries are depleted and a surgery is required to replace them. A Microbial Fuel Cell (MFC) is a device which by using bacteria, directly breaks down sugars to generate electricity. Conceptually there is potential to continually power implanted medical devices for the lifetime of a patient. To investigate the practical potential of this technology, H-Cell Dual Chamber MFCs were evaluated with two different growth solutions and measurements recorded for maximum power output both of individual MFCs and connected MFCs. Using Luria-Bertani media and connecting MFCs in a hybrid series and parallel arrangement with larger membrane sizes showed the highest power output and the greatest potential for replacing implanted batteries.

Concurrent Control of Power Overshoot and Voltage Reversal with Series Connection of Parallel‐Connected Microbial Fuel Cells

AbstractOne in four microbial fuel cell (MFC) units suffers from power overshoot. Series connection of the unit to a high‐current‐producing unit showed significant current loss (57 %) due to power overshoot and the resultant voltage reversal. To concurrently control the power overshoot and voltage reversal, the two MFC units in series were converted to parallel connection, and this was then connected in series with another parallel‐connected MFC group. The current loss for series connection of the two parallel‐connected MFCs was as small as 3 % compared to the sum of the maximum current of the four individual MFC units, without power overshoot; the anode potentials in the units were kept low between −0.24 V and −0.10 V at which electrochemically active bacteria can be easily grown. These results show that series connection of parallel‐connected MFCs could be a readily applicable way for concurrently controlling the power overshoot and voltage reversal in MFC systems.

Understanding energy loss in parallelly connected microbial fuel cells: Non-Faradaic current

In this work, the mechanisms of energy loss in parallel connection of microbial fuel cells (MFCs) is explored using two MFC units producing different open circuit voltage (OCV) and current. In open circuit mode, non-Faradaic current flows in low OCV unit, implying energy loss caused by different OCVs in parallelly stacked MFCs. In a stacked MFC in parallel under close circuit mode, it is confirmed that energy loss occurs until the working voltage in high OCV unit becomes identical to the other unit having low OCV. This result indicates that different voltage between individual MFC units can cause energy loss due to both non-Faradic and Faradaic current that flow from high voltage unit to low voltage unit even in parallelly stacked MFCs.

Temperature and Humidity Sensor Powered by an Individual Microbial Fuel Cell in a Power Management System.

Microbial fuel cells (MFCs) are of increasing interest as bioelectrochemical systems for decomposing organic materials and converting chemical energy into electricity. The main challenge for this technology is that the low power and voltage of the devices restricts the use of MFCs in practical applications. In this paper, a power management system (PMS) is developed to store the energy and export an increased voltage. The designed PMS successfully increases the low voltage generated by an individual MFC to a high potential of 5 V, capable of driving a wireless temperature and humidity sensor based on nRF24L01 data transmission modules. With the PMS, MFCs can intermittently power the sensor for data transmission to a remote receiver. It is concluded that even an individual MFC can supply the energy required to power the sensor and telemetry system with the designed PMS. The presented PMS can be widely used for unmanned environmental monitoring such as wild rivers, lakes, and adjacent water areas, and offers promise for further advances in MFC technology.

AC power generation from microbial fuel cells

Microbial fuel cells (MFCs) directly convert biodegradable substrates to electricity and carry good potential for energy-positive wastewater treatment. However, the low and direct current (DC) output from MFC is not usable for general electronics except small sensors, yet commercial DC–AC converters or inverters used in solar systems cannot be directly applied to MFCs. This study presents a new DC–AC converter system for MFCs that can generate alternating voltage in any desired frequency. Results show that AC power can be easily achieved in three different frequencies tested (1, 10, 60 Hz), and no energy storage layer such as capacitors was needed. The DC–AC converter efficiency was higher than 95% when powered by either individual MFCs or simple MFC stacks. Total harmonic distortion (THD) was used to investigate the quality of the energy, and it showed that the energy could be directly usable for linear electronic loads. This study shows that through electrical conversion MFCs can be potentially used in household electronics for decentralized off-grid communities.

Distributed multiple-anodes benthic microbial fuel cell as reliable power source for subsea sensors

A new type distributed benthic microbial fuel cell (MFC) (DBMFC) consisting of 18 MFC arrays was developed to enhance the robustness and stability of the power source for subsea sensor networks. A power management system (PMS) was integrated into the DBMFC system to boost the power output for two temperature sensors. The PMS was specifically designed with 18 charge pumps capable of simultaneously harvesting energy from 6 MFC units (18 anodes total) in the DBMFC system. The pilot scale DBMFC (total sediment volume: 1 m3) with continuous ocean water supply showed that the power outputs of individual MFC units were affected by the organic carbon and nitrogen contents in the sediment pore water. The MFC units with higher power output resulted in faster charging/discharging rate of the PMS supercapacitor. Manual disconnection of anodes from the PMS was conducted to simulate the anode malfunction caused by bioturbation. Fewer functional anodes (e.g. 12 out of 18 anodes were disconnected) slowed the charging/discharging rate of the PMS supercapacitor but still supported the PMS to regularly power two sensors. This scale-up DBMFC/PMS/sensor study demonstrated that multiple MFC units with multiple PMS substantially enhanced the stability and robustness of power supply to subsea sensors.

A novel small scale Microbial Fuel Cell design for increased electricity generation and waste water treatment

Microbial Fuel Cells (MFCs) are a sustainable energy technology with minimal carbon footprint, which is promising for wastewater remediation and generation of useful amounts of electricity. This study focuses on the architecture and rapid prototyping materials used for building MFCs and their effect on overall performance. Three MFC variants of the same design were constructed using ABS, PC-ISO and RC25 materials and were compared with an established MFC design. MFCs were assessed in terms of power production and COD reduction both individually and when connected electrically in parallel. In all cases the new design showed a better power output and COD removal. The order of performance in terms of power production and COD reduction for individual MFCs was PC-ISO, RC25 and ABS. However when triplets of the same materials were joined electrically together, then the order was different with RC25 outperforming ABS and PC-ISO, which was dependent on the materials' properties. It is concluded that the best performing individual MFC may not necessarily result in the best performing stack.

Control of voltage reversal in serially stacked microbial fuel cells through manipulating current: Significance of critical current density

Voltage reversal is a critical issue for serially stacking microbial fuel cells (MFCs). It occurs when current density in stacked MFCs increases over critical current density (jcritical). In this study, we clearly show that no voltage reversal occurs in stacked MFCs if current density is maintained below jcritical where the anode and the cathode potential in an inferior unit become identical, with an external resistance placed between individual MFCs. We define threshold resistance (Rthreshold) that enables current density below jcritical in stacked MFCs, and demonstrate the validity of Rthreshold theoretically and experimentally. Voltage reversal is controlled in the stacked MFC equipped with Rthreshold by which the current density in the stacked MFC is kept below jcritical. In comparison, a stacked MFC without Rthreshold faces voltage reversal over jcritical. Energy loss in Rthreshold is comparable to energy loss with other voltage control methods, such as passive or active methods. However, the Rthreshold approach is a simple, inexpensive way of controlling voltage reversal, especially for small MFCs (<50 mL).

Shift of voltage reversal in stacked microbial fuel cells

We proved that sluggish kinetics on the cathode and the imbalance of cathode kinetics cause voltage reversal in a stacked microbial fuel cell (MFC) equipped with a non-Pt cathode. Catholyte aeration to a unit MFC against passive air diffusion to the cathode in the other unit MFC shifted voltage reversal between the two units, due to improved mass transport and O2 concentration effects in the aerated MFC. The shifted voltage reversal returned to an original status when catholyte aeration was stopped. A Pt-coated cathode increased the rate of oxygen reduction reaction (ORR) by a factor of ∼20, as compared to the non-Pt cathode. As a result, the anodic reaction rate that became slower than the rate on the Pt-cathode limited current density to overpotential in the stacked MFC equipped with the Pt-cathode. This work shows that dominant kinetic bottlenecks, which are the primary cause of voltage reversal, can be shifted between individual MFCs of stacked MFCs or electrodes depending on relative kinetics.

Controlling for peak power extraction from microbial fuel cells can increase stack voltage and avoid cell reversal

Microbial fuel cells (MFCs) are bioelectrochemical systems which can degrade organic materials and are increasingly seen as potential contributors to low carbon technologies, particularly in energy recovery from and treatment of wastewaters. The theoretical maximum open circuit voltage from MFCs lies in the region of 1.1 V, but is reduced substantially by overvoltage losses. Practical use of the power requires stacking or other means to increase voltage. Series stacking of MFCs with typically encountered variability in operating conditions and performance raises the risk of cell reversal, which diminishes overall power performance. A novel strategy of MFC subsystem series connectivity along with maximum power point tracking (MPPT) generates increased power from individual MFCs whilst eliminating cell reversal. MFCs fed with lower concentrations of substrate experienced voltage reversal when connected in normal series connection with one common load, but when MFCs and loads together were connected in series, the underperforming cell is effectively bypassed and maximum power is made available. It is concluded that stack voltage may be increased and cell reversal avoided using the hybrid connectivity along with MPPT. This approach may be suitable for stacked MFC operations in the event that large scale arrays/modules are deployed in treating real wastewaters.

Polarization behavior of microbial fuel cells under stack operation

The polarization behavior of microbial fuel cells (MFCs) was evaluated under different stack operation modes, including series, parallel, series–parallel, and parallel–series. During the stack operation, voltages of individual MFCs, subunit stacks, and overall stacks were recorded as a function of the current. Meanwhile, the potentials of individual MFCs’ anode and cathode were also determined via Ag/AgCl electrodes to study the change in potentials under stack operations. The results demonstrated that the MFCs with relatively low ability to generate current were easier to suffer polarity reversal in the series stack, which was confirmed in the series subunit of the series–parallel stack. MFCs with high electroactivity would be enhanced to generate larger maximum power; however, MFCs with low electroactivity outputted smaller maximum power in a parallel stack. The changes in individual MFCs’ behavior under stack operation mode were determined primarily caused by the influences on the behavior of the anode. Results of the present study provide valuable information for optimization of stack operation of MFCs.

Assessment of bioelectricity production in microbial fuel cells through series and parallel connections

Microbial fuel cell (MFC) units which are connected in series and parallel, may increase MFC performance in forms of voltage and current respectively. In this research three individual MFC units were connected with different concentrations (10, 20 and 30gl−1) of glucose, fructose and sucrose. Generated power and current were analyzed through polarization and voltage curves. Parallel connections of three units, which fed with 10gl−1 of each substrate, resulted in voltage and power densities of 0.65V and 72.77mWm−2, respectively. This configuration produced current density of 191.36mAm−2 which was approximately three times higher than a single unit. By similar configuration but in series, produced voltage was increased to 1.78V, as long as power and current densities were about at the same level of one single unit (52.35mWm−2and 57.6mAm−2). Substrate concentration enhancement to 20 and 30gl−1 resulted in the same magnitude of increase for cell performances compared to the single unit results. Serial connection of 20gl−1 of three substrates (glucose, fructose and sucrose) showed the highest results compared to other understudied substrate concentrations; 109.45mWm−2 of power density, 98.14mAm−2 of current density and 2.042V as voltage. Shift of MFC configuration to parallel connection demonstrated 381.44mAm−2, 128.72mWm−2 and 0.68V as current, power densities and voltage respectively. This configuration corresponds to the lowest calculated internal resistance.

MFC-cascade stacks maximise COD reduction and avoid voltage reversal under adverse conditions

Six continuous-flow Microbial Fuel Cells (MFCs) configured as a vertical cascade and tested under different electrical connections are presented. When in parallel, stable operation and higher power and current densities than individual MFCs were observed, despite substrate imbalances. The cascading dynamic allowed for a cumulative COD reduction of >95% in approximately 5.7h, equivalent to 7.97kgCODm−3d−1. Under a series configuration, the stack exhibited considerable losses until correct fluidic/electrical insulation of the units was applied, upon which the stack also exhibited superior performance. In both electrical configurations, the 6MFC system was systematically starved for up to 15d, with no significant performance degradation. The results from the 14-month trials, demonstrate that cascade-stacking of small units can result in enhanced electricity production (vs single large units) and treatment rates without using expensive catalysts. It is also demonstrated that substrate imbalances and starvation do not necessarily result in cell-voltage reversal.

Capturing power at higher voltages from arrays of microbial fuel cells without voltage reversal

Voltages produced by microbial fuel cells (MFCs) cannot be sustainably increased by linking them in series due to voltage reversal, which substantially reduces stack voltages. It was shown here that MFC voltages can be increased with continuous power production using an electronic circuit containing two sets of multiple capacitors that were alternately charged and discharged (every one second). Capacitors were charged in parallel by the MFCs, but linked in series while discharging to the circuit load (resistor). The parallel charging of the capacitors avoided voltage reversal, while discharging the capacitors in series produced up to 2.5 V with four capacitors. There were negligible energy losses in the circuit compared to 20–40% losses typically obtained with MFCs using DC-DC converters to increase voltage. Coulombic efficiencies were 67% when power was generated via four capacitors, compared to only 38% when individual MFCs were operated with a fixed resistance of 250 Ω. The maximum power produced using the capacitors was not adversely affected by variable performance of the MFCs, showing that power generation can be maintained even if individual MFCs perform differently. Longer capacitor charging and discharging cycles of up to 4 min maintained the average power but increased peak power by up to 2.6 times. These results show that capacitors can be used to easily obtain higher voltages from MFCs, allowing for more useful capture of energy from arrays of MFCs.