Microbial Fuel Cell Power Research Articles

High-performance bacterium-enhanced dual-compartment microbial fuel cells for simultaneous treatment of food waste oil and copper-containing wastewater

Microbial fuel cells (MFCs) use the metabolic actions of microorganisms in an anode chamber to convert the chemical energy from wastewater into electrical energy. To improve the MFC power generation performance and chemical oxygen demand (COD) removal efficiency, Stenotrophomonas acidaminiphila was added to the anode chamber of a dual-compartment MFC. In this process, Stenotrophomonas acidaminiphila promotes the degradation of macromolecules such as bis(2-ethylhexyl) phthalate in food waste oil. Additionally, the generated electrical energy reduced Cu2+ in the copper-containing wastewater in the cathode chamber to Cu monomers. The maximum power density of the MFC was 49.5 ± 3.5 mW/m2, the maximum removal efficiencies of COD and Cu2+ were 63.5 ± 5.8% and 96.5 ± 1.0%, respectively, and Cu2+ was reduced to brick-red Cu monomers. This study provides insights into the simultaneous implementation of food waste oil treatment and metal resource recovery.

Performance and biotoxicity of electro-Fenton treatment of bisphenol A: Evaluation of copper recovered from microbial fuel cell cathodes for subsequent catalytic applications

A three-tank microbial fuel cell (MFC) is successfully constructed to achieve electromigration and is used in the electro-Fenton process to treat bisphenol A (BPA). The MFC system exhibits excellent mobility and efficiently aggregates Cu+ to the cathode. Under optimal operating conditions, the MFC achieves a maximum power density of 31.4 mW/m2, which is a 3.4-fold increase over that at 0.5 kΩ. Increasing the external resistance increased the MFC power output (ca 1.5 times) and copper ion migration (ca 4.6 times) while reducing the internal resistance of the system (ca 25.3 %). Surface analysis of the cathode carbon cloth shows a 5.5-fold increase in copper content at 1 kΩ over that at 0.5 kΩ. This also increases the oxygen reduction reaction rate, thereby increasing the H2O2 yield by 1.5 times. The recovered copper cathode at 1 kΩ exhibits the best catalytic degradation of BPA, removing 99.7 % of BPA in 180 min, increasing 1.4 and 1.8 times that obtained at 1.5 and 0.5 kΩ, respectively. The optimal operating conditions significantly increased the abundance of electrochemically active bacteria (Azospirillaceae) (3.2 %−41.7 %), indicating that the optimized MFC is favorable for the rapid acclimatization of electrochemically active bacteria.

Asymmetric reactors as an innovative approach for optimum microbial fuel cells performance

Microbial fuel cells (MFCs) exhibit asymmetric overpotentials and redox potentials/rates at the cathode and anode. However, the impact of this asymmetric on power density and anode microbial community remains poorly understood. In this study, asymmetric reactors were designed for H-type MFCs to investigate this configuration. Contrary to the initial expectation of increased MFC power output with larger cathode volumes, it was unexpectedly found that the small-cathode reactor outperformed the large-cathode reactor, achieving a 61 % increase in maximum power density. Electrochemical characterization revealed a slightly lower charge transfer resistance (29.34 Ω) in the small-cathode reactor with carbon-felt anode biofilm in PBS. Moreover, 16S rRNA sequence analysis showed that the small-cathode reactor harbored a higher proportion of anaerobic bacteria (83 %), lower species diversity, and a higher abundance of exoelectrogens. Additionally, higher abundances of key gene modules (top eight), such as quinone oxidoreductase and citrate cycle, were observed in the small-cathode reactor. The anode biofilms in both reactors also synthesized some vitamins, such as menaquinone and thiamine. Furthermore, compared to the large-cathode reactor, each set of the small-cathode reactor saved ¥ 20, 23 g of borosilicate, and 55 mL of cathode electrolytes. This study sheds light on the interplay between reactor conformation and performance, contributing to the development of low-cost, high-performance MFCs for real field conditions.

Tailoring flow straighteners’ architectures through additive manufacturing to enhance power performance and scale-up microbial fuel cell technology

In an aim to scale up the microbial fuel cell (MFC), this research is a first attempt to investigate the impact of two lattice structures flow straighteners: gyroid and X lattice to compare with the conventional honeycomb flow straightener, fabricated via additive manufacturing. The study focused on assessing their effect on the degradation of domestic wastewater and power generation in a dual chamber recirculation MFC. Other than the geometry, structures were also tested at flow rates of 20 mL/min, 60 mL/min, and 100 mL/min. Our study found that MFC equipped with a gyroid structure flow straightener produced the highest power density of 2871.89mWm−2, followed by the X lattice flow straightener of 2626.56 mWm−2 and 2096.03 mWm−2 with honeycomb flow straightener. ANSYS simulations revealed that this increased power density is attributed to the enhanced mixing of wastewater. Traditional honeycomb-based flow straighteners showed straight streamlines, causing bacteria to settle and leading to lower output voltage. The novel X lattice and gyroid lattice designs ensured uniform substrate mixing, addressing the issue of substrate settling and consequently boosting the MFC's power performance. An optimized flow rate of 60 mL/min yielded the best output. Overall, this study successfully introduced two novel lattice structures for flow straighteners, demonstrating their potential in enhancing power performance and the scalability of this technology when produced using additive manufacturing.

Exogenous electric field as a biochemical driving factor for extracellular electron transfer: Increasing power output of microbial fuel cell

Although microbial fuel cells (MFCs) offer a promising avenue for clean power production, they are hindered by inefficient extracellular electron transfer (EET), thereby resulting in a low power output. This study focused on augmenting MFC power by boosting the EET rate using an exogenous electric field (EEF). By leveraging the dual benefits of microbial electrolysis cells (MECs) in organic waste treatment and energy recovery, we developed an MFC–MEC system that utilizes the EEF from MEC as a connecting link. Two configurations, EEF in the same direction (SD-MFC–MEC) and EEF in the reverse direction (RD-MFC–MEC), were used to examine the EET kinetic rate at the MFC anode in the EEF environment using various electrochemical methods for quantitative evaluation. Our findings revealed that EEF significantly enhanced MFC anode biofilm formation and electrochemical activity, leading to a prominent improvement in electrode reaction rates. The EET rate constants in the SD-MFC–MEC and RD-MFC–MEC were more than double those in the control R-MFC, with power density increases of 117.8% and 108.4%, respectively. The formation of electrochemically active sites within the biofilm induced by EEF has emerged as a crucial factor in amplifying the EET rate, and consequently, the MFC power output. Additionally, the variation in EET rate constants between the SD-MFC–MEC and RD-MFC–MEC was minimal, thereby indicating the negligible impact of the EEF orientation on the EET efficiency. This study provides a novel method for quantitatively examining EET rates, opens up new avenues for further facilitating microbe-to-electrode electron transfer, and promotes the application of MFC–MEC systems in energy recovery, CO2 emission reduction, and waste treatment.

Effect of bluff body embedded in flow channel on power performance of microbial fuel cell

The microbial fuel cell (MFC) has emerged as an eco-friendly method for generating clean energy from wastewater. However, its current power performance falls short of meeting commercial application requirements, highlighting the urgent need for power enhancement. To address this, the implementation of bluff bodies within the MFC channel is a proof of concept to enhance nutrient mass transport without the need for external energy input. In this study, fluid simulation was first conducted to analyze the impact of different bluff body designs on flow regimes. The results showing bluff body having spread-out six circles arrays with a height of 0.5 mm (6C_H5) led to a wide velocity distribution within the flow channel, high velocity, and no solute accumulation on the electrode surface, thereby facilitating increased nutrient coverage during transport. Through experimental confirmation, MFC with 6C_H5 achieved an impressive 154 % increase in maximum power density compared to without a bluff body. The outcome can be attributed to sufficient nutrient acquisition for the bacteria to generate more power due to better nutrient transport and a shear environment. The significant finding of the bluff body’s impact on the fluid dynamic aspect has proven the feasibility of enhancing MFC power performance.

Bifunctional polypyrrole/ferroferric oxide as anode material for enhanced electricity generation and energy storage in microbial fuel cell

The microbial fuel cell (MFC) is an electrochemical electricity generation device that uses microorganisms to degrade organic matter to produce electrical energy. However, due to the limited charge generated by microorganisms, the output power of MFC is relatively low. Additionally, as a traditional MFC, it cannot store charge. In this paper, we designed and developed a dual-function capacitive MFC anode, which could generate electricity and store energy simultaneously. The capacitive anode was prepared by the direct growth of polypyrrole and ferric oxide on the carbon felt matrix, and the two materials played a synergistic effect. The power density of MFC equipped with the CF/PPy/Fe3O4-modified anode reached 6.61 W/m3, 29.8% higher than that of the CF/Fe3O4 anode. When in the charging-discharging 45 min test(C45/D45), the total charge Qt released by the CF/PPy/Fe3O4 anode was increased by 1431.74 C/m2 compared with the CF/Fe3O4 anode. In this paper, the method of preparing a dual-function capacitive bioanode could store the electricity generated by microorganisms in the capacitive anode, which greatly improved the current output of MFC and solved its low output power problem.

Enhanced Electricity Generation and Heavy Metal Removal by a Rutile–Biochar Cathode MFC

The issue of heavy metal pollution has gradually emerged as a significant global concern. Microbial fuel cells (MFCs) hold immense potential for clean energy production and pollutant treatment. However, their limited power generation efficiency hampers the large-scale implementation of MFCs. The porous microstructure of biochar and the excellent physical and chemical properties of rutile render both materials promising catalysts with positive potential. In this study, we employed biochar as a carrier for rutile to fabricate a novel rutile–biochar (Rut-B) composite material, investigating its efficacy in enhancing MFC power generation efficiency as a cathode catalyst, as well as its application in heavy metal pollutant degradation. Scanning electron microscopy (SEM) results confirmed the successful preparation of biochar-loaded rutile composites. The MFC achieved maximum current density and power density values of 152.26 mA/m2 and 9.88 mW/m2, respectively—an increase of 102.7% and 224% compared to the control group without the addition of Rut-B. Furthermore, the biochar-loaded rutile MFC exhibited excellent performance in degrading heavy metal pollutants; within 7 h, the Pb2+ degradation rate reached 92.4%, while the Zn2+ degradation rate reached 84%. These rates were significantly higher than those observed in the control group, by factors of 437.2% and 345%, respectively. The cyclic degradation experiments also demonstrated the outstanding stability of the system over multiple cycles. In summary, this study successfully combined natural rutile with biochar to create an efficient electrode catalyst that not only enhances electricity generation performance but also provides an environmentally friendly and cost-effective approach for remediating heavy metal pollution.

Accelerating Electricity Generation and Cr (VI) Removal Using Anatase–Biochar-Modified Cathode Microbial Fuel Cells

Microbial fuel cells (MFC) have considerable potential in the field of energy production and pollutant treatment. However, a low power generation performance remains a significant bottleneck for MFCs. Biochar and anatase are anticipated to emerge as novel cathode catalytic materials due to their distinctive physicochemical properties and functional group architectures. In this study, biochar was utilized as a support for an anatase cathode to investigate the enhancement of the MFC power generation performance and its environmental impact. The results of the SEM and XPS experiments showed that the biochar-supported anatase composites were successfully prepared. Using the new cathode catalyst, the maximum current density and power density of the MFC reached 164 mA/m2 and 10.34 W/m2, respectively, which increased by 133% and 265% compared to a graphite cathode (70.51 mA/m2 and 2.83 W/m2). The degradation efficiency of Cr (VI) was 3.1 times higher in the biochar-supported anatase MFC than in the graphite cathode. The concentration and pH gradient experiments revealed that the degradation efficiency of Cr (VI) was 97.05% at an initial concentration of 10 mg/L, whereas a pH value of two resulted in a degradation efficiency of 94.275%. The biochar-supported anatase composites avoided anatase agglomeration and provided more active sites, thus accelerating the cathode electron transfer. In this study, natural anatase and biochar were ingeniously combined to fabricate a green and efficient electrode catalyst, offering a novel approach for the preparation of high-performance positive catalysts as well as a sustainable, economical, and environmentally friendly method for Cr (VI) removal in aqueous solutions.

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This study investigated the utilization of bamboo leaf waste and two varieties of bacterial sources, chicken manure and effective microorganism, in a microbial fuel cell (MFC) at three substrate concentrations (40 g/liter, 80 g/liter, and 160 g/liter). The primary objective was to investigate the kinetics of bacterial growth at various substrate concentrations in the MFC, as well as the effect of light conditions and pH on MFC power generation. The MFC had dual chambers with graphite electrodes serving as the cathode and anode. Within 72 h, the highest power density of 90.05 mV was attained using the highest substrate concentration of bamboo leaf waste and chicken manure during the logarithmic growth phase, albeit with a shorter duration. The longest sustained phase of bacterial activity was observed during the stationary phase, at the highest substrate concentration of 160 g/liter, followed by 80 g/liter and 40 g/liter. These results indicate that the logarithmic phase is the optimal time for bacterial activity in the MFC. However, attaining long-term stability in power generation in the logarithmic phase requires careful parameter optimization.

Copper recovery from printed circuit boards leaching solution with bioelectricity generation using microbial fuel cell

Recovery of valuable metals via leaching printed circuit boards (PCBs) has gained moment recently. This work studied the Microbial fuel cell (MFC) performances for recovery of Cu from a Cu2+ solution by examining key operating parameters. A dual-chamber MFC with 6cm × 6cm × 7cm dimensions was constructed. Both anode and cathode electrodes were made of a carbon cloth sheet. The anodic and cathodic chambers were separated by a Nafion membrane. The highest Cu recovery efficiency was 99.7% after 240h batch mode operation, yielding 102 mW/m2 MFC power density output using 1g/L Cu2+ solution as the catholyte (initial pH 3) and an anolyte containing 1g/L sodium acetate inoculated with a sludge from a wastewater treatment plant's anaerobic pond, with 2cm distance between the electrodes made of polyacrylonitrile polymer. The highest open circuit voltage, current density (based on cross-section cathode area) and power density with an external load of 1 kΩ was 555mV, 347mA/m2 and 193 mW/m2, respectively. Additionally, recovery of Cu in the leachate of PCBs using sulfuric acid leaching after 48h was performed and the highest Cu recovery was 50% in 48h.

High-performance anode electrocatalyst of MnCo2S4-Co4S3/ bamboo charcoal for stimulating power generation in microbial fuel cell

ABSTRACT Microbial fuel cell (MFC) is a promising technology for recovering energy in wastewater through bacterial metabolism. However, it always suffers from low power density and electron transfer efficiency, restricting the application. This study fabricated the MnCo2S4-Co4S3/bamboo charcoal (MCS-CS/BC) through an easy one-step hydrothermal method, and the material was applied to carbon felt (CF) to form high-performance MFC anode. MCS-CS/BC-CF anode exhibited lower Rct (10.1 Ω) than BC-CF (17.24 Ω) and CF anode (116.1 Ω), exhibiting higher electrochemical activity. MCS-CS/BC-CF anode promoted the electron transfer rate and resulted in enhanced power density, which was 9.27 times higher (980 mW m-2) than the bare CF (105.7 mW m-2). MCS-CS/BC-CF anode showed the best biocompatibility which attracted distinctly larger biomass (146.27 mg/μL) than CF (20 mg/μL) and BC-CF anode (20.1 mg/μL). The typical exoelectrogens (Geobacter and etc.) took dramatically higher proportion on MCS-CS/BC-CF anode (59.78 %) than CF (2.99 %) and BC-CF anode (26.67 %). In addition, MCS-CS/BC stimulated the synergistic effect between exoelectrogens and fermentative bacteria, greatly favoring the extracellular electron transfer rate between bacteria and the anode and the power output. This study presented an efficient way of high-performance anode electrocatalyst fabrication for stimulating MFC power generation, giving suggestions for high-efficient energy recovery from wastewater.

Modeling of microbial fuel cell power generation using machine learning-based super learner algorithms

Electricity generation from microbial fuel cells (MFCs) is a potential environment-friendly technology. This study provides Bayesian Algorithm (BA) based Support Vector Regression (SVR) and Boosted Regression Tree (BRT) as prospective super learner modeling tools (BA-SVR, BA-BRT) for predictions of electricity production from MFCs. The membrane thickness, external resistance, and anode area were considered independent variables, while power generation was taken as a response variable. The key novelties of this study include (i) hybridization of BA with SVR and BRT (separately) for forecasting power generation from fuel cells for the first time, (ii) performance comparison of the developed models (BA-SVR and BA-BRT) with the existing Response Surface Methodology (RSM) based on the coefficient of determination (R2), relative error (RE), mean absolute error (MAE), mean absolute percentage error (MAPE), root mean square error (RMSE), and computing efficiency, and the (iii) analysis of the models’ robustness by utilizing Gaussian white noise. Based on the performance indicators, the proposed super leaner models showed excellent performance compared to the existing M.J. Salar-García et al. RSM model. The BA-SVR model provided the lowest errors (MAE of 2.94, RSME of 7.2926, MAPE of 13.8341) with the highest R2 of 0.9981, compared to the BA-BRT and RSM models. The proposed BA-SVR model showed superior performance to the RSM and BA-BRT models in predicting the MFCs’ power generation, with a performance improvement of more than 90% regarding MAPE, as an example. The future prediction and high robustness of the proposed super learner model would ensure quick estimation for maximization of electricity generation that may lead to reducing massive lab trials and saving resources.

Isolation and Characterization of Bacteria with High Electroactive Potential from Poultry Wastewater.

Natural resources are in short supply, and the ecosystem is being damaged as a result of the overuse of fossil fuels. The creation of novel technology is greatly desired for investigating renewable and sustainable energy sources. Microorganisms have received a lot of interest recently for their potential to transform organic waste into sustainable energy and high-value goods. New exoelectrogens that can transmit electrons to electrodes and remove specific wastewater contaminants are expected to be studied. In this study, we examined three distinct samples (as determined by chemical oxygen demand and pH) that can be used as anolytes to generate power in single-chamber and double-chamber microbial fuel cells using graphite electrodes. Wastewater from poultry farms was studied as an exoelectrogenic anolyte for microbial fuel cell power generation. The study examined 10 different bacterial strains, numbered A1 through A10. Due to their highly anticipated capacity to metabolize organic/inorganic chemicals, the diverse range of microorganisms found in poultry wastewater inspired us to investigate the viability of generating electricity using microbial fuel cells. From the investigated bacterial strains, the highest voltage outputs were produced by strains A1 (Lysinibacillus sphaericus) and A2 (Bacillus cereus), respectively, at 402 mV and 350 mV. Among the 10 different bacterial strains, strain A6 generated the least amount of electricity, measuring 35.03 mV. Furthermore, a maximum power density of 16.16 1.02 mW/m2 was achieved by the microbial fuel cell using strain A1, significantly outperforming the microbial fuel cell using a sterile medium. The strain A2 showed significant current and power densities of 35 1.12 mA/m2 and 12.25 1.05 mW/m2, respectively. Moreover, in the two representative strains, chemical oxygen demand removal and Coulombic efficiency were noted. Samples from the effluent anode chamber were taken in order to gauge the effectiveness of chemical oxygen demand removal. Wastewater had an initial chemical oxygen demand content of 350 mg/L on average. Strains A1 and A2 decomposed 94.28% and 91.71%, respectively, of the organic substrate, according to the chemical oxygen demand removal efficiency values after 72 h. Strains A1 and A2 had electron donor oxidation efficiencies for 72 h of 54.1% and 60.67%, respectively. The Coulombic efficiency increased as the chemical oxygen demand decreased, indicating greater microbial electroactivity. With representative strains A1 and A2, Coulombic efficiencies of 10% and 3.5%, respectively, were obtained in the microbial fuel cell. The findings of this study greatly advance the field as a viable source of power technology for alternative energy in the future, which is important given the depletion of natural resources.

Improving microbial fuel cells power output using internal and external optimized, tailored and totally green supercapacitor

Improving microbial fuel cells power output using internal and external optimized, tailored and totally green supercapacitor

Generation of Electricity by Using Microbial Fuel Cell Prototype Fed by Sewage: Case Study at the University of Dar es Salaam

The access to electricity is still not reliable in Tanzania. Whilst, there are several locations within the country that have wastewater cites that are not economically used to produce electricity. At the University of Dar es Salaam (UDSM), there are main grid power, and few scattered solar panels. This study was intended to bridge the divide between the current increasing power demands of the UDSM by exploiting not so much used sources, such as electric energy from wastewater. This study was undertaken to develop a Microbial Fuel Cell (MFC) prototype fed by sewage in Dar es Salaam, for electricity generation using cost effective materials for the cathode compartment. The collection of samples took place using sewage substrates from the UDSM oxidation ponds. The untreated sewage was collected from oxidation ponds. Preliminary experiments were carried out to identify the cathode and substrate that produced better results in terms of volts and current output. Aluminium produced the most desirable results compared to copper, stainless steel and mild steel in all the substrates. On the other hand, untreated sewage with aluminium/carbon electrodes produced higher voltage and current compared to treated sewage with the same electrodes. Thereafter, a prototype of the MFC was developed by connecting three single chambered cells in series of 628 cm3 volume of untreated sewage with aluminium and carbon electrodes. The prototype generated a stable voltage of 1.73 V and a current of 0.07 mA recorded for a period of one hour. The power generated was enough to light a 6.25 mW LED bulb of 25 mA across a 100 Ω resister. Therefore, untreated sewage produced more power in MFCs with aluminium/carbon electrodes compared to the other tested materials.
 Keywords: Aluminium electrodes, charcoal electrode, alternative energy source, wastewater

Development of peat microbial fuel cells (Peat MFCs) – the green and sustainable generators of electricity

Although deemed unsuitable for construction, Peat soils have remarkable applications in MFCs by generating electric power because of the microbial decomposition of rich organic matter. The demerits such as weak skeleton, high water content, acidic nature, and humus contamination of peat soil for civil engineering applications are considered merits in microbial fuel cell applications. Peat soil-based Microbial Fuel Cells (MFCs), the first of its kind among MFCs, are explored to generate electric power as high as 6 V when six MFCs connected in a series and lighted up an LED for 288 h. The performance of peat MFCs as a function of bamboo waste, fulvic acid, iron winding and surface area of the BC anode has been discussed in this work. The synergistic effect of organic decomposition by microbes and Fe complexation with humic substances (HS) has been detailed to be responsible for the cause of electric power in Peat MFCs. ATP measurement in peat soils after defined time periods confirmed the growth of microbial population, which successfully degraded the organic matter in MFCs. The characterization of BC anode and GAC cathode using FTIR, Raman, SEM with EDS, BET isotherm studies substantiated the structural modification and porous nature of the fresh and the used electrodes. The EIS study was performed to determine the dynamics of internal resistances due to the degradation kinetics in Peat MFCs. The cost effectiveness and the sustainability of Peat MFCs towards green technology are detailed in this paper.

Sustainable microbial fuel cell functionalized with a bio-waste: A feasible route to formaldehyde bioremediation along with bioelectricity generation

Bioelectrochemical systems, especially microbial fuel cell (MFC), are gaining popularity owing to their eco-friendly and energy generation with bioremediation. Due to its unstable electrode material, MFCs have poor electron transportation and production. To increase electron transport and bacterial biocompatibility, better anode materials are needed. Waste palm kernel shell-derived graphene oxide (PKS-GO) and reduced graphene oxide (PKS-rGO) were used to produce the anode electrodes to increase electron transport. The MFC with the PKS-rGO anode generated more energy (24.47 mW/m2) than the PKS-GO anode (13.77 mW/m2). Similarly, the maximum current densities recorded for both anodes were 84.98 mA/m2 for PKS-rGO and 63.74 mA/m2 for PKS-GO. Additionally, the PKS-GO anode showed a 0.00015F/g specific capacitance (Cp) value, whereas the PKS-rGO anode had a Cp value of 0.00021F/g. The enhanced capacitance of the PKS-rGO anode may be due to redox enzymes on microbial cell membranes. The electrochemical impendence spectroscopy also showed a rapid transportation rate of electrons in the case of the PKS-rGO anode. PKS-GO's anode has 1240 ῼ internal resistance, whereas PKS-rGO has 232 ῼ. The secondary use of MFC in wastewater treatment was also taken into account. The PKS-rGO anode (87 %) is more effective in bioremediating formaldehyde (FA) than the PKS-GO anode (81.70 %). The sequence reveals a prominent species of Niallia circulans strain for the PKS-GO anode, and two dominant species for the PKS-rGO anode, Bacillus siamensis strain and Bacillus velezensis strain. A comparative overview shows the effectiveness of the material compared to previous studies. Critical challenges constraining progress in MFC power output enhancement and future perspectives are also included.

Variance-based global sensitivity analysis of a multi-population, single-chamber microbial fuel cell operating in continuous flow mode at steady state

Microbial fuel cells (MFCs) are environmentally friendly devices which are used to convert chemical energy in organic wastes to electrical energy. MFCs have a strong non-linearity that requires a very sophisticated controlling system. Consequently, this makes optimization and performance study of MFCs a difficult process. For better estimation of the constants used for optimization of MFCs, global sensitivity analysis is performed. The global sensitivity method based on Sobol’s indices coupled with Monte Carlo simulations was applied on multi-population, single-chamber MFC operating in a continuous flow at steady state for the first time. In this paper, first-order and total-order sensitivity indices were used to visualize the impacts associated with six main parameters resulted from the maximization of power density using Matlab. Such parameters are maximum anodophilic-specific growth rate, half-rate constant of anodophilics, curve steepness factor, mediator half-rate constant, number of electrons transferred per mole mediator and decay rate constant of anodophilic bacteria. The results showed that the curve steepness factor has almost no impact on the power density of MFC. While all other studied, factors are sensitive parameters that impact the power density of MFC. It is worth mentioning that maximum anodophilic growth rate and the number of electrons transferred per mole of mediator are the most sensitive parameters that affecting the power density production having total indices of 0.74 and 0.624, respectively. While the half-rate constant of anodophilics, mediator half-rate constant and decay rate constant of anodophilics have almost similar impact by having total-order indices of 0.127, 0.144 and 0.192, respectively. The findings herein are critical in understanding and further model improvement of microbial fuel cells as the most impacting parameters on MFC power density can be optimized further to reduce uncertainty associated with the experimental parameters in the model.Graphical abstract

Importance of pyrolysis programs in enhancing the application of microalgae-derived biochar in microbial fuel cells

Nitrogen-doped (N-doped) biochar was prepared by pyrolyzing lipid-extracted microalgae residues under 800 °C for 2 h with different temperature increasing rates (single-segment programs: 3–8 °C/min for room temperature-800 °C; two-segment programs: 5–8 °C/min for room temperature-500 °C and 3 °C/min for 500–800 °C). The obtained biochar was used for oxygen reduction reactions and microbial fuel cell applications. Interestingly, biochar prepared by two-segment programs achieved better performances than those prepared by single-segment programs with higher onset potentials in oxygen reduction reactions and higher maximal power densities in microbial fuel cell. This is likely because the applied two-segment programs improved the porous structure and enhanced the formation of pyridinic N in the biochar. Notably, applying the optimal program (5–8 °C/min for room temperature-500 °C and 3 °C/min for 500–800 °C) obtained biochar with a maximal oxygen reduction reactions onset potential of 0.877 V and a maximal microbial fuel cell power density of 843.6 mW·m−2, both of which are higher than values achieved using Pt/C. This study suggests that simply improving the pyrolysis program for N-rich biomass pyrolysis is promising for producing high-performance N-doped biochar for microbial fuel cells.