Microbial Fuel Cell Sensor Research Articles

Low temperature acclimation of electroactive microorganisms may be an effective strategy to enhance the toxicity sensing performance of microbial fuel cell sensors

Microbial fuel cell (MFC) sensing is a promising method for real-time detection of water biotoxicity, however, the low sensing sensitivity limits its application. This study adopted low temperature acclimation as a strategy to enhance the toxicity sensing performance of MFC biosensor. Two types of MFC biosensors were started up at low (10 °C) or warm (25 °C) temperature, denoted as MFC-Ls and MFC-Ws respectively, using Pb2+ as the toxic substance. MFC-Ls exhibited superior sensing sensitivities towards Pb2+ compared with MFC-Ws at both low (10 °C) and warm (25 °C) operation temperatures. For example, the inhibition rate of voltage of MFC-Ls was 22.81 % with 1 mg/L Pb2+ shock at 10 °C, while that of MFC-Ws was only 5.9 %. The morphological observation showed the anode biofilm of MFC-Ls had appropriate amount of extracellular polymer substances, thinner thickness (28.95 μm for MFC-Ls and 41.58 μm for MFC-Ws) and higher proportion of living cells (90.65 % for MFC-Ls and 86.01 % for MFC-Ws) compared to that of MFC-Ws. Microbial analysis indicated the enrichment of psychrophilic electroactive microorganisms and cold-active enzymes as well as their sensitivity to Pb2+ shock was the foundation for the effective operation and good performance of MFC-Ls biosensors. In conclusion, low temperature acclimation of electroactive microorganisms enhanced not only the sensitivity but also the temperature adaptability of MFC biosensors.

Distinct voltage signals of sediment microbial fuel cell sensors in sensing various contaminants

AbstractThe sediment microbial fuel cell (SMFC) sensors using cathode as sensing element exhibited attractive prospects for online and in‐situ monitoring. However, the sensing performance of SMFC sensors to different types of contaminants was seldom reported. In this study, SMFCs were constructed in stimulated wetland to sense five types of contaminants, including oxidative heavy metals (Cu2+ and Cr6+), non‐oxidative heavy metals (Ni2+ and Zn2+), salt (NaCl), acid (HCl), and alkali (NaOH). The addition of Cu2+, Cr6+ or H+ triggered voltage peaks whereas the voltage dropped immediately following the addition of OH−. The addition of Ni2+ and Zn2+ did not trigger any obvious peaks. The NaCl solutions caused slight voltage peaks which were not increased with increasing concentrations. X‐ray photoelectron spectroscopy (XPS) illustrated the reduction of Cu2+ and Cr6+ to elemental Cu and Cr3+ on the cathodic surface, indicating the contaminants that promote or inhibit electron consumption on cathode would cause voltage peaks or drops. The addition of heavy metals, OH− and NaCl significantly increased Simpson's diversity whereas Cu2+, Cr6+ and OH− significantly decreased the abundance of exoelectrogenic bacteria‐associated genera in the top‐layer soil. However, the influence of the contaminants on the abundance and diversity was attenuated in the middle and bottom layers, indicating that the exoelectrogenic bacteria could to some extent withstand these contaminants and guarantee the operation of the SMFC sensors.

Biotoxicity monitoring of Bisphenol A using microbial fuel cell sensors: Optimizing the response of sensor’s voltage changes to toxicity and assessing the impact on the application to river water monitoring

The voltage variation (ΔV) of a microbial fuel cell (MFC) sensor that is used to monitor the concentration of bisphenol A (BPA) in wastewater fluctuates with the chemical oxygen demand (COD) concentration of wastewater, destabilizing a sensor that is used for this purpose. The results obtained by the response surface method reveal that the ΔV of the MFC sensor was significantly influenced by the BPA and COD concentrations, with an R2 of 0.981. Biotoxicity analysis revealed that the response of Vibrio fischeri to toxicity was consistent with the sensor’s output, indicating that the sensor was highly sensitive to toxicity. The developed MFC sensor provides a high ΔV even in long-term toxicity detection. The voltage output of the MFC sensor did not significantly vary in the detection of river water containing BPA at concentrations higher than 60 mg L−1. This indicates that the toxic effect of high BPA concentration is outweighed by the interference of chemical substances in the river water, demonstrating the potential of the MFC sensor for detecting river water with a BPA concentration above 60 mg L−1. With its simplicity, rapid detection, and long-term operability, the MFC sensor has the potential for practical use.

Sensitivity and reusability of a simple microbial fuel cell-based sensor for detecting bisphenol A in wastewater

Polycarbonate plastic processing wastewater contains high concentrations of bisphenol A (BPA), requiring a real-time technology to monitor wastewater containing BPA. Since the activity of electrogenic microorganisms on the anode surface of the microbial fuel cell (MFC) sensor is inhibited by exposure to contaminants, the toxicity of contaminants in wastewater can be determined by observing the variation in voltage output from the MFC sensor. The simple MFC sensor that is developed in this work exhibited a significant decrease in voltage output in BPA-containing wastewater concentration of 5–100 mg/L. Sensitivity analysis revealed that the voltage change (ΔV) was strongly correlated with the BPA concentration, with R2 as high as 0.97. This study was the first to investigate the number of repeated uses of the MFC sensor, using sodium acetate as the regeneration solution for the MFC sensor, leading to a successful recovery of detection performance. However, as the number of uses increased (up to the third or fourth use), the ΔV of the MFC sensor for BPA gradually decreased and the sensitivity decreased significantly from 0.238 mV/mg/L to 0.027 mV/mg/L. In the low BPA concentration range (≦20 mg/L), the MFC sensor can be reused up to 5 times, demonstrating that the proposed MFC sensor can be reused. Microorganisms contribute to the power generation of the MFC sensor, which can be exploited in the detection of pollutants, enabling the determination of wastewater toxicity and providing early warnings of thereof. Conventional MFC sensors are complex and lack the ability to explore repeated use, so they are not easily applied to actual wastewater detection. The proposed MFC sensor has many advantages such as simplicity, rapid detection, and reusability, solving the problem of the high cost of using disposable MFC sensors and making them feasible for practical use.

A low-cost microbial fuel cell based sensor for in-situ monitoring of dissolved oxygen for over half a year

In order to address the need for long-term, in-situ and inexpensive monitoring of dissolved oxygen (DO), a chitin-carrying microbial fuel cell (MFC) based DO sensor was developed using sediment anolyte, which had an extremely low cost of US$12.17 and comparable performance to certain commercial sensors. The MFC based DO sensor had a long lifetime of over half a year with chitin as the fuel, attributed to the syntrophic interactions between fermentative and exoelectrogenic microbes that were well developed for chitin degradation in anaerobic condition with sediment filling in the anode chamber. The use of sediment anolyte introduced hindered diffusion in the porous media, enabling the use of glass fiber as the separator to replace the ion exchange membrane and thus resulting in a much lower cost. Field tests of this MFC based DO sensor were conducted in fresh and saline waters respectively. Excellent performance was achieved with average deviations of <4.5% to three commercial methods of fiber optic sensor (HQ40d, HACH company, USA), Clark type sensor (Pro20i, YSI company, USA) and iodometry. This low-cost MFC sensor also showed a high reliability, with the same response of current generation to different DO levels in random 17-times tests, indicating its great market potentials for in-situ DO monitoring.

Higher performances of open vs. closed circuit microbial fuel cell sensor for nitrate monitoring in water

Microbial fuel cell (MFC) sensor exhibits attractive prospects for real-time monitoring of nitrate (NO3-) in water, with unique advantages of self-powering and simple structure; but its stability and sensitivity are unsatisfactory. In an attempt to address the limitations, here we employed an open-circuit MFC (O-MFC) sensor for real-time monitoring of NO3- in water, compared to a conventional closed-circuit MFC (C-MFC) sensor. The stability of the O-MFC sensor was confirmed when subject to the continuous fluctuation of interfering substances including organic matter (acetate, 2–20 mM), SO42- (250–400 mg/L) and Fe3+ (0.3–0.6 mg/L). For one-time and continuous monitoring of NO3- at a concentration of 1–40 mg/L, the O-MFC sensor both achieved higher sensitivity than that of the C-MFC sensor; especially at a low NO3- concentration of 1 mg/L, the changes of electrical signal (∆E) reached 10.0 ± 1.00 mV and 7.0 ± 0.85 mV respectively. In contrast, the C-MFC sensor failed to monitor at low NO3- concentrations of 1 and 5 mg/L. Moreover, good linear correlation between ∆E and NO3- concentration (R2 = 0.907 and 0.981) was obtained from the O-MFC sensor. However, owing to the highly activity of EAB that mainly grows in the outer layer of biofilm, the response time of the O-MFC sensor is too long. Microbial community analysis further revealed that the open-circuit condition is more suitable for NO3- monitoring in water, providing a new way to improve the performance of MFC sensors.

A critical review on early-warning electrochemical system on microbial fuel cell-based biosensor for on-site water quality monitoring

The microbial fuel cell (MFC) sensor is a very promising self-powered self-sustainable system for early warning water quality detection. These sensors are cost-effective, biodegradable, compact in design, and portable in nature are favorable for real-time in situ water quality monitoring. This review represents the mechanism action behind the toxicity detection, optimization strategies, process parameters, role of biofilm, the role of external resistance, hydrodynamic study, and mathematical modeling for improving the performance of the sensor. Additionally, the techno-economic prospect of this MFC-based sensor and its challenges, limitations are addressed to make it economically more favorable for commercial use. The future direction is also explored based on the sensor's disadvantages and limitations. Comprehensively, this review covered all the possible directions of MFC sensor fabrication, their application, recent advancement, prospects challenges, and their possible solutions.

On-line monitoring of minor oil spills in natural waters using sediment microbial fuel cell sensors equipped with vertical floating cathodes

Oil spills near natural water bodies pose considerable threats to aquatic ecosystem and drinking water system. Various detection techniques have been developed to identify the oil pollution in natural waters. These techniques mainly focus on large and major oil spills involving significant changes in environmental characteristics. However, monitoring of minor oil spills (from seepage and dripping) in waters remains a bottleneck, allowing inconspicuous and persistent oil contamination. To overcome this drawback, a sediment microbial fuel cell (SMFC) sensor equipped with a vertical floating cathode is developed for on-line and in-situ monitoring of minor oil spills in natural waters. The vertical floating cathode was intended for recognizing oil on water surface. Oil on the cathode will trigger current drop. Two kinds of natural sediments were adopted in two sensors (SMFC1 from a lake and SMFC2 from an urban stream) for comparison. Both showed linear relationship between net steady-state current decrease and oil dose (30.78 and 27.29 μA/mL of sensitivity, respectively). The current change process was fitted well to a pseudo-first order kinetic equation. A one-point/two-point dynamic identification methods were derived from the kinetic equation. Therefore, the detection time was shortened from 10 h to 10/30 min. The triggered current decrease was mainly attributed to the increase in internal resistance related to charge and mass transfer. Despite the power loss after oil contamination, results implied SMFC sensor could still achieve self-sustainability. This study shows that the SMFC sensor with vertical floating cathodes is applicable to monitoring the unnoticeable minor oil pollutions in natural waters.

Microbial fuel cells for in-field water quality monitoring.

The need for water security pushes for the development of sensing technologies that allow online and real-time assessments and are capable of autonomous and stable long-term operation in the field. In this context, Microbial Fuel Cell (MFC) based biosensors have shown great potential due to cost-effectiveness, simplicity of operation, robustness and the possibility of self-powered applications. This review focuses on the progress of the technology in real scenarios and in-field applications and discusses the technological bottlenecks that must be overcome for its success. An overview of the most relevant findings and challenges of MFC sensors for practical implementation is provided. First, performance indicators for in-field applications, which may diverge from lab-based only studies, are defined. Progress on MFC designs for off-grid monitoring of water quality is then presented with a focus on solutions that enhance robustness and long-term stability. Finally, calibration methods and detection algorithms for applications in real scenarios are discussed.

The evaluation of long term performance of microbial fuel cell based Pb toxicity shock sensor

Microbial fuel cell (MFC) sensor exhibits attractive prospects for online monitoring of water toxicity as an early warning device. However, the accumulation of dead cells in anode biofilm might decrease the sensing sensitivity of MFC during long term operation. In addition, with repeated exposure to toxins, the microbial community of anode biofilm would also adjust to build up higher endurance to environmental toxicity. In this study, the long term sensing sensitivity of MFC sensor and the microbial community changes were characterized with Pb2+ as the target toxin. The results show that newly formed biofilm with higher live/dead cell ratio exhibited higher sensitivity than mature biofilm. Modification of anodic biofilm via high current stimulation was applied to increase the ratio of live cells, which led to enhanced sensing sensitivity of MFC with mature anode biofilm. However, the enhancement was relatively limited for biofilm that was previously exposed to repeated Pb2+ shocks. Microbial community analysis revealed that the proportions of microbial species possessing higher environmental robustness, such as Hyphomicrobiaceae and Cloacibacillus, significantly increased in the anode biofilm after long term repeated Pb2+ shocks.

Enhancing sensitivity of microbial fuel cell sensors for low concentration biodegradable organic matter detection: Regulation of substrate concentration, anode area and external resistance

The relatively low sensitivity is an important reason for restricting the microbial fuel cell (MFC) sensors’ application in low concentration biodegradable organic matter (BOM) detection. The startup parameters, including substrate concentration, anode area and external resistance, were regulated to enhance the sensitivity of MFC sensors. The results demonstrated that both the substrate concentration and anode area were positively correlated with the sensitivity of MFC sensors, and an external resistance of 210 Ω was found to be optimal in terms of sensitivity of MFC sensors. Optimized MFC sensors had lower detection limit (1 mg/L) and higher sensitivity (Slope value of the linear regression curve was 1.02), which effectively overcome the limitation of low concentration BOM detection. The essential reason is that optimized MFC sensors had higher coulombic efficiency, which was beneficial to improve the sensitivity of MFC sensors. The main impact of the substrate concentration and anode area was to regulate the proportion between electrogens and nonelectrogens, biomass and living cells of the anode biofilm. The external resistance mainly affected the morphology structure and the proportion of living cells of the anode. This study demonstrated an effective way to improve the sensitivity of MFC sensors for low concentration BOM detection.

Portable, Disposable, Paper-Based Microbial Fuel Cell Sensor Utilizing Freeze-Dried Bacteria for In Situ Water Quality Monitoring.

Water quality monitoring is becoming an essential part of our lives as increasing human activities continue to spill unknown and unexpected contaminants into our water systems. To ensure the provision of safe and clean water to the public and the ecosystem, the development of rapid and sensitive in situ early warning systems for water toxicity monitoring is crucial. In this work, an entirely paper-based microbial fuel cell sensor utilizing freeze-dried bacteria is demonstrated as a portable and disposable water toxicity sensor. The bacterial cells were preinoculated on the anode reservoir of the device, and they were freeze-dried, making their on-site and on-demand applications possible. Upon rehydration of the bacteria with the water samples, current readings were obtained, and inhibition ratios (IRs) were calculated for different concentrations of formaldehyde as a model toxin. For 0.001, 0.01, and 0.02% of formaldehyde, IRs of 7.88, 16.08, and 23.14% were obtained, respectively. These IRs showed a very good linearity with the formaldehyde concentrations at R2 = 0.995. Additionally, the shelf life of the freeze-dried microbial fuel cell sensor was investigated. Even after 14 days of storage in the desiccator, at 4, and at −20 °C, the performance outputs compared to the new device were all at 96%.

Rapid detection of biodegradable organic matter in polluted water with microbial fuel cell sensor: Method of partial coulombic yield

The quantification of biodegradable organic matter (BOM) in polluted water plays an essential role for biodegradation-based processing of wastewater and management of water environment. Compared with the traditional detection of five-day biochemical oxygen demand (BOD5), microbial fuel cell (MFC) sensors have shown an advantage for rapid and more accurate BOM assessment in several hours using coulombic yield of MFC as the signal. In this study, we propose a new calculation method that relies on the partial coulombic yield (P-CY) to further shorten the duration of the measurement. The P-CY is the cumulative coulomb at the point at which the voltage acquisition reaches a maximum voltage drop rate. The detection results with the standard GGA solution (a mixture of glucose and glutamic acid) show an enhanced linear relationship ranging from 37.5 mg L−1 to 375 mg L−1 in comparison to conventional methods. Notably, the response time for P-CY is remarkably shortened (0.99 ± 0.18–18.08 ± 0.58 h). The cutoff point for P-CY has more stable electrochemical characteristics, which enhances the accuracy of BOM detection. Furthermore, the validity of our determination of the cutoff point for P-CY is demonstrated by a mathematical model based on the Michaelis-Menten equation. Thus, the P-CY method is viable for the rapid detection of BOM in polluted water.

A microbial fuel cell sensor for unambiguous measurement of organic loading and definitive identification of toxic influents

Multi-stage microbial fuel cells can distinguish toxic shock events from BOD decreases, both of which result in decreased current output.

A Portable, Single-Use, Paper-Based Microbial Fuel Cell Sensor for Rapid, On-Site Water Quality Monitoring.

Human access to safe water has become a major problem in many parts of the world as increasing human activities continue to spill contaminants into our water systems. To guarantee the protection of the public as well as the environment, a rapid and sensitive way to detect contaminants is required. In this work, a paper-based microbial fuel cell was developed to act as a portable, single-use, on-site water quality sensor. The sensor was fabricated by combining two layers of paper for a simple, low-cost, and disposable design. To facilitate the use of the sensor for on-site applications, the bacterial cells were pre-inoculated onto the device by air-drying. To eliminate any variations, the voltage generated by the microorganism before and after the air-drying process was measured and calculated as an inhibition ratio. Upon the addition of different formaldehyde concentrations (0%, 0.001%, 0.005%, and 0.02%), the inhibition ratios obtained were 5.9 ± 0.7%, 6.9 ± 0.7%, 8.2 ± 0.6%, and 10.6 ± 0.2%, respectively. The inhibition ratio showed a good linearity with the formaldehyde concentrations at R2 = 0.931. Our new sensor holds great promise in monitoring water quality as a portable, low-cost, and on-site sensor.

Application of a microbial fuel cell-based biosensor for the energy-saving operation of macrophyte residues bioreactor with low concentration of dissolved organic carbon in effluents

The increasing application of plant residues bioreactor for aquatic environment remediation may release numerous dissolved organic carbon (DOC) into aquatic ecosystems. In this study, a microbial fuel cell (MFC) sensor was integrated with a macrophyte residues bioreactor (MRBR) to provide an energy-saving way for reduction of DOC concentrations in the effluent. Through re-utilization of macrophyte residues as solid carbon source, DOC concentrations in the effluent of MRBR increased to the maximum on day 5 and then dropped down rapidly to a low value, while the ratio of bioavailable DOC decreased gradually. Interestingly, it was found that there existed a linear relationship between DOC concentrations in initial residue leachate and the voltage from MFC biosensor (R2 = 0.9852). Accordingly, aerobic biofilm through aeration were applied in the upper part of MRBR to enhance the degradation of DOC prior to discharge to aquatic systems, and aeration rate was adjusted based on MFC sensor signal. Further experiments demonstrated that when voltage decreased from 0.18 V to 0.09 V, a half of aeration rate (7.5 L min−1) could still lead to a high DOC degradation efficiency (above 50%) and a low DOC concentration (∼10 mg L−1) in the reactor effluent. Thus, the integrated MFC signal could be used to regulate the aeration rate in order to obtain a low DOC concentration in effluents under an energy-saving way.

A comparison of microbial fuel cell and microbial electrolysis cell biosensors for real-time environmental monitoring

This study compares the biosensing performance of a microbial fuel cell (MFC) and a microbial electrolysis cell (MEC). Initial tests provided a qualitative comparison of MFC and MEC currents after the anode compartment liquid (anolyte) was spiked with acetate, or sulphates of NH4+, Na+, Mg2+, Fe2+, or a fertilizer solution. Current measurements showed that the MFC sensor had a faster response time, higher sensitivity, and faster recovery time after the spike. Following the spike tests, the MFC and MEC were operated in a continuous flow mode at several influent concentrations of acetate, and sulphates of NH4+, Na+, and Fe2+. The continuous flow tests confirmed the better performance of the MFC sensor, which was selected for further experiments. Two MFC sensors were used for real-time (on-line) COD measurements of brewery wastewater. Regression analysis showed a strong correlation between the MFC power output and COD concentrations in the anode compartment with a coefficient of determination (R2) of 0.97. Overall, results of this study suggest that an MFC-based sensor can be successfully used as a simple and cost-efficient real-time monitoring tool.

Open external circuit for microbial fuel cell sensor to monitor the nitrate in aquatic environment

This study employed an open external circuit, rather than a closed circuit applied in previous studies, to operate an microbial fuel cell (MFC) sensor for real-time nitrate monitoring, and achieved surprisingly greater sensitivity (4.42 ± 0.3–6.66 ± 0.4 mV/(mg/L)) when the nitrate was at a concentration of 10–40 mg/L, compared to that of the MFC sensor with a closed circuit (0.8 ± 0.05–1.6 ± 0.1 mV/(mg/L)). The MFC sensor operated in open circuit (O-MFC sensor) delivered much more stable performance than that operated in closed circuit (C-MFC sensor) when affected by organic matter (NaAc). The sensitivity of O-MFC sensor was twice that of C-MFC sensor at a low background concentration of organic matter. When organic matter reached a high concentration, the sensitivity of O-MFC sensor remained at an acceptable level, while that of C-MFC sensor dropped to almost zero. Challenged by a combined shock of organic matter and nitrate, O-MFC sensor delivered evident electrical signals for nitrate warning, while C-MFC failed. Another novel feature of this study lies in a new mathematical model to examine the bioanode process of nitrate monitoring. It revealed that lower capacitance of the bioanode in O-MFC was the major contributor to the improved sensitivity of the device.

A novel microbial fuel cell sensor with a gas diffusion biocathode sensing element for water and air quality monitoring

Toxicity monitoring is essential for the protection of public health and ecological safety. Microbial fuel cell (MFC) sensors demonstrated good potential in toxicity monitoring, but current MFC sensors can only be used for anaerobic water monitoring. In this study, a novel gas diffusion (GD)-biocathode sensing element was fabricated using a simple method. The GD-biocathode MFC sensor can directly be used for formaldehyde detection (from 0.0005% to 0.005%) in both aerobic and anaerobic water bodies. Electrochemical analysis indicated that the response by the sensor was caused by the toxic inhibition to the microbial activity for the oxygen reduction reaction (ORR). This study for the first time demonstrated that the GD-biocathode MFC sensor has a detection limit of 20 ppm for formaldehyde and can be used to monitor air pollution. Selective sensitivity to formaldehyde was not achieved as the result of using a mixed-culture, which confirms that it can serve as a generic biosensor for monitoring gaseous pollutants. This study expands the realm of knowledge for MFC sensor applications.

Enhancing the robustness of microbial fuel cell sensor for continuous copper(II) detection against organic strength fluctuations by acetate and glucose addition

Microbial fuel cell sensors have shown great promise for continuous monitoring of toxic substances in wastewater, but a persistent problem is the signal interferences due to fluctuations in organic strength. An approach to eliminate the interferences is to saturate the sensor with an added organic substrate. In this study, signal stabilization using acetate and glucose addition (150, 300 and 500 mg COD/L) to domestic wastewater was examined. Addition of acetate (500 mg COD/L) gave the best performance, increasing the robustness of the sensor by reducing signal interference (decrease in baseline current) from 65% to 15% for a sudden 75% decrease in organic strength. The sensor sensitivity remained unchanged at current drop of 0.16%/(mg/L Cu(II)) for a toxicity event (300 mg/L Cu(II)). Addition of acetate (300 mg COD/L) and glucose (150, 300 and 500 mg COD/L) also resulted in increased robustness but led to a reduced sensitivity to Cu(II).