Microbial Fuel Cell Configuration Research Articles

Optimization and Modeling of a Dual-Chamber Microbial Fuel Cell (DCMFC) for Industrial Wastewater Treatment: A Box–Behnken Design Approach

Microbial fuel cells (MFCs) have garnered significant attention due to their capacity to generate electricity using renewable and carbon-neutral energy sources such as wastewater. Extensive experimental work and modeling techniques have been employed to dissect these processes and understand their respective impacts on electricity generation. The driving force is to enhance MFC performance for practical applications commercially. Among the various statistical modeling approaches, one particularly robust tool is the Design of Experiments (DoE). It serves to establish the relationships between different variables that influence MFC performance and allows for the optimization of the MFC configuration and operation for scaled-up performances in terms of bioelectricity generation. This study focused on optimizing microbial fuel cells (MFCs) for bioelectricity production using industrial wastewater treatment, employing the Box–Behnken design (BBD) methodology. Through an analysis of response surface models and ANOVA tests, it was found that a combined approach of reduced quadratic, reduced two-factor interaction, and linear models yielded sound results, particularly in voltage yield, COD removal, and current density. Second-order regression models predicted optimal conditions for various parameters, with surface area, temperature, and catholyte dosage identified as critical input variables for optimization. Under these conditions, conducted by the four-factor and three-level Box–Behnken design methodology in a double-chamber MFC unit considering eight output variables—CCV yield, % COD removal, current density, power density, % TSS removal, % CE, and % PO43−—the optimum values were 700 mV, 54.4%, 54.4 mA/m2, 73.7 mW/m2, 99%, 21.2%, and 100%, respectively. At optimum operating conditions, the results revealed a desirability of 76.6% out of a total of 92 iterations. The paper highlights the effectiveness of statistical ANOVA fit-statistics modeling and optimization in enhancing DCMFC performance, recommending its use as a sustainable bioenergy source. Furthermore, validation results supported the above optimization output response findings and confirmed the viability of biorefinery wastewater as an anolyte for scaling up DCMFC bioelectricity generation.

Sorting Out the Latest Advances in Separators and Pilot-Scale Microbial Electrochemical Systems for Wastewater Treatment: Concomitant Development, Practical Application, and Future Perspective.

To date, dozens of pilot-scale microbial fuel cell (MFC) devices have been successfully developed worldwide for treating various types of wastewater. The availability and configurations of separators are determining factors for the economic feasibility, efficiency, sustainability, and operability of these devices. Thus, the concomitant advances between the separators and pilot-scale MFC configurations deserve further clarification. The analysis of separator configurations has shown that their evolution proceeds as follows: from ion-selective to ion-non-selective, from nonpermeable to permeable, and from abiotic to biotic. Meanwhile, their cost is decreasing and their availability is increasing. Notably, the novel MFCs configured with biotic separators are superior to those configured with abiotic separators in terms of wastewater treatment efficiency and capital cost. Herein, a highly comprehensive review of pilot-scale MFCs (>100 L) has been conducted, and we conclude that the intensive stack of the liquid cathode configuration is more advantageous when wastewater treatment is the highest priority. The use of permeable biotic separators ensures hydrodynamic continuity within the MFCs and simplifies reactor configuration and operation. In addition, a systemic comparison is conducted between pilot-scale MFC devices and conventional decentralized wastewater treatment processes. MFCs showed comparable cost, higher efficiency, long-term stability, and significant superiority in carbon emission reduction. The development of separators has greatly contributed to the availability and usability of MFCs, which will play an important role in various wastewater treatment scenarios in the future.

Bioenergy Production from Tannery Waste via a Single-Chamber Microbial Fuel Cell with Fly Ash Cathodic Electrodes

Microbial Fuel Cells (MFCs) are attracting attention for their application in simultaneous energy production and waste treatment, as innovative biochemical reactors. They usually operate under adiabatic conditions, utilizing microorganisms to treat wastewater compositions using mainly carbon-based electrodes as anodes and cathodes. During the past years, various anodic and cathodic electrodes with plenty of variations were used in MFC configurations. On the anode side metal-based electrodes are used while on the cathode, ceramic electrodes are currently introduced. In this study, a stainless steel anode is used in a single chamber MFC. Ceramic cathodic electrodes are used, coated with Fly Ash (FA). The mixed transition oxides of FA are tested as potential cathodic catalysts in the operation of the MFC. The FA powder was deposited by two methods: an ultrasound-assisted method and a conventional brush coating. Tannery liquid waste is used as the waste/substrate to be treated in the single-chamber MFC. The configuration with ultrasound-assisted Fly-Ash produced cathodic electrodes, led to the highest power output in batch operation modes and a high degree of simultaneous COD decrease of the tannery waste reaching the values of 0.44 mW/gcat and 85.6% COD removal respectively.

Simultaneous naphthalene degradation and electricity production in a biowaste-powered microbial fuel cell

Naphthalene is a very common and hazardous environmental pollutant, and its biodegradation has received serious attention. As demonstrated in this study, naphthalene-contaminated wastewater can be biodegraded using a microbial fuel cell (MFC). Furthermore, the potential of MFC for electricity generation appears to be a promising technology to meet energy demands other than those produced from fossil fuels. Nowadays, efforts are being made to improve the overall performance of MFC by integrating biowaste materials for anode fabrication. In this study, palm kernel shell waste was used to produce palm kernel shell-derived graphene oxide (PKS-GO) and palm kernel shell-derived reduced graphene oxide (PKS-rGO), which were then fabricated into anode electrodes to improve the system's electron mobilization and transport. The MFC configuration with the PKS-rGO anode demonstrated greater energy production potential, with a maximum power density of 35.11 mW/m2 and a current density of 101.76 mA/m2, compared to the PKS-GO anode, which achieved a maximum power density of 17.85 mW/m2 and a current density of 72.56 mA/m2. Furthermore, there is simultaneous naphthalene biodegradation with energy production, where the biodegradation efficiency of naphthalene with PKS-rGO and PKS-GO is 85.5%, and 79.7%, respectively. In addition, the specific capacitance determined from the cyclic voltammetry curve revealed a value for PKS-rGO of 2.23 × 10−4 F/g, which is also higher than the value for PKS-GO (1.57 × 10−4 F/g) on the last day of operation. Anodic microbial analysis shows that electrogens thrive in the MFC process. Finally, a comparison with previous literature and the future prospects of the study are also presented.

Waste treatment and Sustainable Bioelectricity Generation using Microbial fuel cell

In the last decade, great attentions have been paid to microbial fuel cells (MFC) due to the possibility to be the solution for the three bigger world project – energy security, climate changes and waste management. Different from all the conventional wastewater treatment which are energy intensive, MFC can use waste as substrate/fuel to directly generate electricity through microbial reactions in anode and microbial/enzymatic/abiotic electrochemical reactions in cathode. In this sense, the MFC is an emerging technology for treat waste and produce wealth products (energy and some added value substance – organic acids, nutrients). Although, there are a large number of research in new materials and operational conditional to improve the MFC performance, as yet there are practical barriers, such as low power generation, expensive electrode materials and the inability to scale up MFC. Therefore, this work summarizes information about the recent advances in MFC research, focused on MFC configurations, material electrodes, and performances. Limitations and challenges in applying MFC to treat waste are also discussed, moreover future perspective pointed the new hot topics to solve these problems.

Design and Optimization of Microbial Fuel Cells and Evaluation of a New Air-Breathing Cathode Based on Carbon Felt Modified with a Hydrogel—Ion Jelly®

The increased demand for alternative sustainable energy sources has boosted research in the field of fuel cells (FC). Among these, microbial fuel cells (MFC), based on microbial anodes and different types of cathodes, have been the subject of renewed interest due to their ability to simultaneously perform wastewater treatment and bioelectricity generation. Several different MFCs have been proposed in this work using different conditions and configurations, namely cathode materials, membranes, external resistances, and microbial composition, among other factors. This work reports the design and optimization of MFC performance and evaluates a hydrogel (Ion Jelly®) modified air-breathing cathode, with and without an immobilized laccase enzyme. This MFC configuration was also compared with other MFC configuration performances, namely abiotic and biocathodes, concerning wastewater treatment and electricity generation. Similar efficiencies in COD reduction, voltage (375 mV), PD (48 mW/m2), CD (130 mA/m2), and OCP (534 mV) were obtained. The results point out the important role of Ion Jelly® in improving the MFC air-breathing cathode performance as it has the advantage that its electroconductivity properties can be designed before modifying the cathode electrodes. The biofilm on MFC anodic electrodes presented a lower microbial diversity than the wastewater treatment effluent used as inocula, and inclusively Geobacteracea was also identified due to the high microbial selective niches constituted by MFC systems.

Yeast industry wastewater treatment with microbial fuel cells: Effect of electrode materials and reactor configurations

Simultaneous pollutant removal and electricity production using microbial fuel cells is a promising environmental sustainable technology that contributes to the circular economy. Numerous studies have been conducted previously using exogenously adding easily degradable sugars for electricity generation in microbial fuel cells (MFCs). However, in real-world applications involving wastewater, the performance of the process varies according on the source, the microorganisms presented and the electrodes employed. The simultaneous treatment of baker's yeast industrial effluents and electricity generation is investigated in various MFCs using titanium and graphite electrodes. Reduced chemical oxygen demand (COD) is reported to be between 73% and 92% depending on the MFC configuration and electrodes employed. The two-chamber MFC with titanium electrodes and inoculum sludge from upflow anaerobic sludge blanket reactors (UASB) perform better, reaching 51.02 mW/m2 and 12.74 μA/cm2 power and current densities, respectively.

Moisture-Enabled Germination of Heat-Activated Bacillus Endospores for Rapid and Practical Bioelectricity Generation: Toward Portable, Storable Bacteria-Powered Biobatteries.

Small-scale battery-like microbial fuel cells (MFCs) are a promising alternative power source for future low-power electronics. Controllable microbial electrocatalytic activity in a miniaturized MFC with unlimited biodegradable energy resources would enable simple power generation in various environmental settings. However, the short shelf-life of living biocatalysts, few ways to activate the stored biocatalysts, and extremely low electrocatalytic capabilities render the miniature MFCs unsuitable for practical use. Here, heat-activated Bacillus subtilis spores are revolutionarily used as a dormant biocatalyst that can survive storage and rapidly germinate when exposed to special nutrients that are preloaded in the device. A microporous, graphene hydrogel allows the adsorption of moisture from the air, moves the nutrients to the spores, and triggers their germination for power generation. In particular, forming a CuO-hydrogel anode and an Ag2 O-hydrogel cathode promotes superior electrocatalytic activities leading to an exceptionally high electrical performance in the MFC. The battery-type MFC device is readily activated by moisture harvesting, producing a maximum power density of 0.4mW cm-2 and a maximum current density of 2.2mA cm-2 . The MFC configuration is readily stackable in series and a three-MFC pack produces enough power for several low-power applications, demonstrating its practical feasibility as a sole power source.

Using a microbial fuel cell to balance the carbon‑nitrogen mismatch in submerged fixed-bed reactors for the resilient treatment of mariculture wastewater

Two of the main challenges in treating mariculture wastewater are the variable carbon to nitrogen ratio as well as its high sulfur content. Here we developed and tested the ability of a microbial fuel cell (MFC) to balance the mismatch between carbon and nitrogen loads in a submerged fixed-bed bioreactor (SFBBR) treating mariculture wastewater. Three reactors were tested including an SFBBR without an MFC, an SFBBR coupled to an MFC in an open-circuit (OC) arrangement, and an SFBBR-MFC in a closed circuit (CC) arrangement. The latter allows for flow of electric current. Both MFC configuration reduced sulfide yield by 65.6–111.7 g m−2 compared to the SFBBR alone. All reactors presented high nitrogen removal efficiency (> 95 %) when an external carbon source was applied. Results of highthroughput sequencing and the Picrust2 revealed that the mixotrophic denitrification, namely sulfur autotrophic denitrification and heterotrophic denitrification, contributed to the high nitrogen removal efficiency. When external carbon was withheld, however, the SFBBR-MFC-OC and SFBBR-MFC-CC showed a significantly higher nitrogen removal efficiency than the SFBBR, i.e., 79.9 ± 6.3 % or 76.1 ± 6.3 % vs. 56.0 ± 6.0 %. This difference was most likely driven by the presence of reduced sulfur compounds (e.g., S0, SO32−) generated at the first anodes of the MFC reactors which could support continued nitrogen reduction for up to 48 h without carbon addition. Thus the MFC configuration promoted the formation of a “sulfur-pool” that could balance the carbon‑nitrogen mismatch in the SFBBR, allowing for resilient treatment under variable influent characteristics.

A comparison of reactor configuration using a fruit waste fed two-stage anaerobic up-flow leachate reactor microbial fuel cell and a single-stage microbial fuel cell

Food waste generation and its consequent environmental impacts are increasing due to rapid urbanization, the global population, and associated food demand. Microbial fuel cells (MFCs) are a sustainable technology through which this food waste can be treated and used to produce bioelectricity. This study used two MFC configurations, a two-stage anaerobic up-flow leachate reactor MFC and a single-stage MFC, comparing the potential to treat solid fruit waste and fruit waste leachate. The two-stage MFC showed a higher potential to remove substrate at a shorter time compared to single-stage MFC. In 30 days, the two-stage anaerobic up-flow leachate reactor had a power density of 221 mW/m2. It was able to remove more total solids (by 95 %), volatile solids (by 70 %), total chemical oxygen demand (by 83 %), soluble chemical oxygen demand (by 87 %), and carbohydrates (by 33 %) compared to the single-stage MFC. However, the single-stage MFC showed higher coulombic efficiency (by 86.7 %) compared to the two-stage MFC. The efficiency of single-stage MFC improved by adding buffer and maintaining a neutral pH level of the substrate. The results of this study emphasize the importance of reactor design and demonstrate that MFC can be a viable technology to generate bioenergy from food waste.

Modeling and testing the steady-state and transient behaviors of stacked microbial fuel cells under different electrical connection patterns

Microbial fuel cells (MFCs) represent a key solution in the context of sustainable energy development from organic material. Their implementation for real applications is still limited because of economic issues and low power densities. Several efforts have been done both to improve the economic performances by selecting low-cost materials and to increase the power output by realizing stacked configurations.The development of more complex configurations increases the difficulty of predicting the behavior of these bioenergy systems and their performances. In this contest numerical models, supported by the experimental activities, are very useful tools for forecasting the main biological, electrochemical and mass transfer processes occurring within MFCs during their operation in different conditions.In this paper, an electrical transient model, devoted to perform the stacked MFCs voltages and currents on equivalent electric circuits has been developed. The model, that is the superposition of an exponential pattern over a linear trend, is able to define the transient time domain of the voltage and current solutions of a specific electric circuit, enabling the scalability of the estimation of the electrical variables in stacked MFCs systems. The model calibration has been carried out by means of the experimental activities on a single MFC reactor as well as on a stacked MFCs configuration connected in parallel/series.The experimental activities have been performed by using a test bench consisting of the Agilent Digit Multimeters and a Resistance Box. The experimental tests have allowed to assess: i) the steady-state and transient behaviors of a single MFC; ii) the steady-state and transient behaviors of the stacked MFCs configurations.Results have highlighted that the developed model has proved to be an interesting tool for predicting the transient behavior of output currents and voltages after a step perturbation demonstrating how the MFCs evolve towards stable conditions as the load varies.

Microbial fuel cells for waste nutrients minimization: Recent process technologies and inputs of electrochemical active microbial system

Still, in the current period, non-renewable energy sources have contributed to fulfill the current energy requirement and it causes the deficit of available stocks with emission of pollutant byproducts components. In recent years, efforts were made to harness the sustainable/ renewable fuels from renewable sources/ waste, complex organic matters including biomass at global level. Researchers have put attention on harnessing energy from wastewater and MFCs systems. This MFC approach utilizes the wastewater as feed/ carbon sources to generate bioenergy such as bio- hydrogen and electricity in a sustainable and efficient way via completing the wastewater treatment. This approach consists of anode and cathode electrodes with proton exchange membrane (PEM). Microbial fuel cells are utilized with other effective approaches (anaerobic digestion/ fermentation, local demand-based-MFC approach) that are applied to utilize biowastes for microbial cell growth and electron emission. This review discusses the recent and technologically advanced approach such as microbial fuel cells (MFCs). MFCs can apply to fulfill the increasing trends of global energy demand, found with more utilization in home appliances in urban areas, industrial tasks and transportation sectors. Last few decades, there have been recent modifications in MFCs configurations and design that have improved performance of MFCs. Recent design and configuration of MFCs have shown the removal of maximum chemical oxygen demand (up to 94–97%) with generation maximum current output (up to 5.23 mA) from wastewater. This review presents a comprehensive collection of recent information about technologies and design of MFCs with implementation of microbial electrogene with development of wastewater treatment having sustainable fuel/ energy generation at an effective level.

ZrP2O7 as a Cathodic Material in Single-Chamber MFC for Bioenergy Production.

The present work is the first investigation of the electrocatalytic performances of ZrP2O7 as a cathode in a single-chamber Microbial Fuel Cell (MFC) for the conversion of chemical energy from wastewater to bioelectricity. This catalyst was prepared by a coprecipitation method, then characterized by X-ray diffraction analysis (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), ultraviolet–visible–near-infrared spectrophotometry (UV–Vis–NIR), and cyclic voltammetry analyses. The acid–basic characteristics of the surface were probed by using 2-butanol decomposition. The conversion of 2-butanol occurs essentially through the dehydrating reaction, indicating the predominantly acidic character of the solid. The electrochemical test shows that the studied cathode material is electroactive. In addition, the ZrP2O7 in the MFC configuration exhibited high performance in terms of bioelectricity generation, giving a maximum output power density of around 449 mW m−2; moreover, it was active for wastewater treatment, reducing the chemical oxygen demand (COD) charge to 50% after three days of reaction.

Self-contained and integral microbial fuel cells as portable and sustainable energy sources for low-power field devices

BackgroundWith a smaller environmental footprint and longer operation times, Microbial Fuel Cells (MFCs) are now preferred over other renewable technologies for powering small electronic devices in the field. Although with excellent performance in the laboratory, most of MFCs fail for not considering the real field conditions. The purpose of this study is the development of a compact, portable, and self-sustaining format of energy production based on MFC technologies. For this, three MFC configurations, soil MFC, plant MFC and a hybrid-MFC, where a plant and a soil MFC are combined, are assembled in portable power devices and compared. ResultsPlant MFCs provided lower performances (maximum power of 0.6 ± 0.4 µW·cm−2) resulting from a fast and sharp decrease in the anode potential by the flowing of oxygen from the aerenchyma of the plant roots. The performance of soil MFCs was much better (maximum power of 2.0 ± 0.02 µW·cm−2), but not sustained over time (20 days) by the depletion of organic matter. The combination of a soil MFC and a plant in separate compartments of a single container results in a hybrid-MFC with a good performance (maximum power of 2.7 µW·cm−2) which sustained over time for more than 1 month. ConclusionsTherefore, the hybrid self-containing MFCs appears as an ideal alternative for the long-term power supply of low-power field electronic devices, from meteorological sensors or LED lights.How to cite: Uria-Molto N, Costa RD, Nunziata C, et al. Self-contained and integral microbial fuel cells as portable and sustainable energy sources for low-power field devices. Electron J Biotechnol 2022;57. https://doi.org/10.1016/j.ejbt.2022.04.004

Insights on microbial fuel cells for sustainable biological nitrogen removal from wastewater: A review.

Microbial fuel cells (MFCs) have emerged as a promising technology for energy-efficient wastewater treatment. The feasibility of integrating biological nitrogen removal into MFC systems has been reported. However, better pollutant removal efficiency and power production need to be achieved at a lower cost for a sustainable wastewater treatment system. The objective of this paper is to critically review the nitrogen removal process in various MFC configurations, factors that influence this process, and challenges that should be overcome in future studies. Based on the results of the review, shortcut nitrification-autotrophic denitrification in an MFC is an option as it minimizes the aeration energy and C/N ratio requirement; however, it is necessary to evaluate the N2O emission further. Another attractive option is the heterotrophic anodic denitrification process as it demonstrates the potential for free-buffer MFCs, but the nitrogen removal efficiency at low C/N ratios needs improvement. Bacteria population in MFC system also plays an essential role in both contaminant removal and electricity generation. It can be concluded that MFCs can be a low cost, sustainable solution for the treatment of wastewater and removal of nitrogen. Moreover, selection of MFC configuration will depend on the nature of the wastewater.

The Implications of Membranes Used as Separators in Microbial Fuel Cells.

Microbial fuel cells (MFCs) are electrochemical devices focused on bioenergy generation and organic matter removal carried out by microorganisms under anoxic environments. In these types of systems, the anodic oxidation reaction is catalyzed by anaerobic microorganisms, while the cathodic reduction reaction can be carried out biotically or abiotically. Membranes as separators in MFCs are the primary requirements for optimal electrochemical and microbiological performance. MFC configuration and operation are similar to those of proton-exchange membrane fuel cells (PEMFCs)—both having at least one anode and one cathode split by a membrane or separator. The Nafion® 117 (NF-117) membrane, made from perfluorosulfonic acid, is a membrane used as a separator in PEMFCs. By analogy of the operation between electrochemical systems and MFCs, NF-117 membranes have been widely used as separators in MFCs. The main disadvantage of this type of membrane is its high cost; membranes in MFCs can represent up to 60% of the MFC’s total cost. This is one of the challenges in scaling up MFCs: finding alternative membranes or separators with low cost and good electrochemical characteristics. The aim of this work is to critically review state-of-the-art membranes and separators used in MFCs. The scope of this review includes: (i) membrane functions in MFCs, (ii) most-used membranes, (iii) membrane cost and efficiency, and (iv) membrane-less MFCs. Currently, there are at least 20 different membranes or separators proposed and evaluated for MFCs, from basic salt bridges to advanced synthetic polymer-based membranes, including ceramic and unconventional separator materials. Studies focusing on either low cost or the use of natural polymers for proton-exchange membranes (PEM) are still scarce. Alternatively, in some works, MFCs have been operated without membranes; however, significant decrements in Coulombic efficiency were found. As the type of membrane affects the performance and total cost of MFCs, it is recommended that research efforts are increased in order to develop new, more economic membranes that exhibit favorable properties and allow for satisfactory cell performance at the same time. The current state of the art of membranes for MFCs addressed in this review will undoubtedly serve as a key insight for future research related to this topic.

A Critical Review on Microbial Fuel Cells Technology: Perspectives on Wastewater Treatment

Increasing demand for renewable energy in the backdrop of global change calls for waste valorization and circular economy strategies. Public health concerns and demand for clean energy provide impetus to the development of wastewater based MFC. Wastewater treatment and simultaneous generation of bioelectricity offer a myriad of environmental benefits. Nevertheless, it is pertinent to know the challenges with the microbial fuel cell (MFC) technology to upscale the wastewater based MFC. This paper attempts to critically analyse the processes, application, challenges and opportunities of wastewater based MFCs. A literature survey was conducted to find out the advances in the field of wastewater based MFCs and the focus was to decipher the challenges to the implementation of wastewater based MFCs. Recent developments in MFC technology have improved the power output and studies show that a diverse group of organic-rich wastewater can be treated with MFCs. The developments include improvements in MFC configuration, development of biocatalysts and biocathode, anodic biofilm formation, microbial community interactions, and progress in the organic and pollutant removal. Nevertheless, the MFC technology is replete with challenges about the organic removal rate, power density, electrode performance limiting factors, economic viability, high initial and maintenance cost and difficulty to maintain the exoelectrogens activity in a complex wastewater environment. Opportunities exist in scaling up of MFCs, integration with other wastewater treatment methods and measures to minimise the operating costs. MFCs have the potential to increase the resilience capacity of the sustainable wastewater treatment plant.

Enhanced sludge stabilization coupled with microbial fuel cells (MFCs)

This study presents research results on electricity production from waste activated sludge using MFCs during stabilization process. Different MFC configurations equipped with various electrodes were used. Voltage measurements were continuously done during 35 days of MFC operation. Experimental results showed that bioelectricity generation was linked to volatile solids (VS) and protein reductions as a fraction of extracellular polymeric substances (EPS). Double chamber MFC reactor equipped with graphite electrodes had better power and current densities as 312.98 mW/m2 and 39.07 μA/cm2 while single chamber MFC equipped with titanium electrodes revealed better power and current densities as 97.60 mW/m2 and 17.63 μA/cm2, respectively. Molecular results indicated that power outputs of MFCs effected by diverse microbial communities in anode biofilms. Although organic matter degradation is reported as 35%–55% VS reduction for digesters, this research provided a promising approach for sludge stabilization with enhanced degrading of organic matters up to 75% by using MFCs.

Waste to Energy Conversion and Sustainable Recovery of Nutrients from Pee Power - Recent Advancements in Urine-Fed MFCs

Microbial Fuel Cells (MFCs) offer a sustainable solution for alternative energy production by employing microorganisms as catalysts for direct conversion of chemical energy of feedstock into electricity. Electricity from urine (urine-tricity) using MFCs is a promising cost-effective technology capable of serving multipurpose benefits - generation of electricity, waste alleviation, resource recovery and disinfection. As an abundant waste product from human and animal origin with high nutritional values, urine is considered to be a potential source for extraction of alternative energy in the coming days. However, developments to improve power generation from urine-fed MFCs at reasonable scales still face many challenges such as non-availability of sustainable materials, cathodic limitations, and low power density. The aim of this paper was to critically evaluate the state-of-the-art research and developments in urine-fed MFCs over the past decade (2008-2018) in terms of their construction (material selection and configuration), modes of operation (batch, continuous, cascade, etc.) and performance (power generation, nutrient recovery and waste treatment). This review identifies the preference for sources of urine for MFC application from human beings, cows and elephants. Among these, human urine-fed MFCs offer a variety of applications to practice in the real-world scenario. One key observation is that, effective disinfection can be achieved by optimizing the operating conditions and MFC configurations without compromising on performance. In essence, this review demarcates the scope of enhancing the reuse potential of urine for renewable energy generation and simultaneously achieving resource recovery.

Microbial Biocathode Catalyzing Oxygen Reduction and Processing Nitrification

Oxygen biocathodes with electroactive biofilms on graphite electrodes were developed consistently and reproducibly from wastewater inoculum under a high ammonium content selective pressure in a batch microbial fuel cell configuration using ferrocyanide at the anode. The microbial biocathodes process nitrification reactions and catalyse the reduction of molecular oxygen with an onset potential of 0.0 V vs. Ag /AgCl, and a current density at -0.28 V of j = -296 μA/cm2 at pH 7 and 20 °C under oxygen saturation (Cf. Figure).These biofilms also reduce hydrogen peroxide (not shown) at +0.25 V, the potential of an electroactive species in the biofilm (Cf. Figure). The nitrification reactions performed by the biofilm are found to be associated with the catalytic reduction of dioxygen. Nitrification reactions were studied by assaying the nitrogen species (ammonium, nitrite and nitrate) and the effect of adding hydroxylamine, an intermediate of the enzymatic oxidation of ammonium. Metagenomic studies via 16S rRNA gene sequencing of the biofilms onto the colonized electrodes were performed 4 week after inoculation. These studies show that the cathodic biofilms were significantly enriched with Cupriavidus, a proteobacteria genus, that is likely to be responsible for the catalytic properties of the microbial biocathode.The Figure shows the reduction of molecular oxygen by a colonized electrode at pH 7 and 20 °C in a 0.1 M fresh phosphate buffer as recorded with slow scan rate cyclic voltammetry. Scan rate: 1 mV/s. Green: abiotic graphite electrode under oxygen saturation. Black: biocathode under argon saturation. Red: biocathode under air. Blue: biocathode under oxygen saturation. Note also the chemically reversible system found at +0.25 V and assigned to the biofilm. Catalytic hydrogen peroxide reduction (not shown) occurs at the potential of this system. Figure 1