A completely anoxic microbial fuel cell using a photo-biocathode for cathodic carbon dioxide reduction

<i>Harvesting Energy using Biocatalysts</i>

Influence of NO 3 and SO 4 on power generation from microbial fuel cells

Pig dung was evaluated for electric current and voltage generation using microbial fuel cell (MFC). Pig dung was collected from three different animal farms; FUTA, Air Force and Apatapiti Extension. Isolation and identification of microorganisms from pig dung was carried out before and after electric current and voltage generation using conventional techniques. Physicochemical composition were determined using standard methods. Microbial fuel cells (MFCs) chambers were fabricated. The circuit was completed with electrodes and flexible wires for electron transfer from the anode to the cathode. Pig dung was used as the anolyte while water was used in the cathode as the electron acceptor. Current and voltage were measured in the morning, afternoon and evening for 40 days using the digital multimeter. The result revealed sixteen microorganisms: Enterobacter cloacae, Escherichia coli, Shigella sp , Citrobacter gillenii, Klebsiella singaporensis, Paenibacillus septentrionalis, Bacillus circulans, Salmonella spp , Enterobacter asburiae, Yersinia intermedia , Yersinia enterocolitica, Fusarium sp, Aspergillus flavus, Aspergillus funmigatus, Aspergillus niger, and Penicillium chrysogenum . The highest bacterial and fungal population; 2.71 x 10 5 cfu/g and 1.47 x 10 4 sfu/g were observed from Air Force and FUTA pig dung respectively before current and voltage generation. The highest bacterial and fungal population; 1.35 x 10 5 cfu/g and 1.60 x 10 4 sfu/g were observed from Apatapiti Extension and FUTA pig dung respectively after current and voltage generation. The highest current and voltage; 0.319 ± 0.00 mA and 572.333 ± 3.84 mV were generated from Apatapiti Extension and Air-Force pig dung. Sterilized pig dung (control) generated a low voltage and current affirms the important role of microorganisms in voltage and current generation. In conclusion, pig dung can be used to generate electrical current and voltage owing to microbial activities present in the pig dung. A nuisance causing waste such as pig dung can serve as a renewable source of energy for electricity generation, this will simultaneously help to resolve the problems of environmental toxics that oozes from its disposal and ultimately serve as a way of mitigating global warming in the world. Keywords: Pig dung, Microbial fuel cell (MFC), current, voltage. DOI : 10.7176/JETP/10-1-02 Publication date: January 31 st 2020

Nitric oxide reduction by microbial fuel cell with carbon based gas diffusion cathode for power generation and gas purification

Background. The formation of an exoelectrogenic biofilm in a microbial fuel cell (MFC) is an important stage, because it affects later on current generation by the system. The fermented residue after methanogenesis as an inoculum contains not only exoelectrogenic microorganisms, but also methanogens, which reduce the productivity of MFC. The use of current allows the formation of a biofilm enriched with exoelectrogenic microorganisms. Objective. The purpose of our study was to establish the parameters of MFC under periodic application of external voltage. Methods. A two-chamber H-type MFC with a salt bridge between the chambers was used for the study. The anolyte was stirred with a magnetic stirrer for 4 h a day and a 3V voltage was simultaneously applied to create selective conditions for exoelectrogenic biofilm growth. Results. The application of external voltage stimulated the increase in the current and voltage of the MFC. With the periodic application of an external voltage, the MFC current increased to 788 ± 40 mA for the MFC with a resistor and without load. After disconnection and discharge, the MFC current dropped to 189 ± 10 mA for the MFC without load and to 154 ± 8 mA for the MFC with a resistor, respectively. Under the conditions of MFC operation without applying external voltage, the current was 960 ± 50 mA for MFC with an open circuit and 672 ± 35 mA for MFC with a closed circuit when a resistor is connected. For all MFC, the current gradually decreased over time. MFC demonstrated capacitive behaviour: after accumulating charge for 4 h, a discharge from 622 ± 30 mV to 462 ± 23 mV was observed. Microscopy showed fouling of the anode. Since the fermented residue after methanogenesis is mixed consortium, the anodic biofilm was also mixed consortium enriched with different species of exoelectrogens. Conclusions. Periodic application of external voltage allowed to increase the current by 17% and double the voltage compared to MFC without external voltage supply. However, after disconnecting the external voltage source, the MFC gradually discharged, that is, the current and voltage decreased. The maximum value of the current of the MFC with an open circuit was 22% more than the MFC with a closed circuit.

Over the last couple decades, microbial fuel cells (MFCs) have become a technology of interest for renewable energy production and waste treatment/reclamation. MFCs are flexible with fuel and, for this reason, have garnered interest as biosensors, unit operations in advanced wastewater treatment, and alternative power sources. MFCs oxidize organic matter at the anode where microbes perform anaerobic respiration to convert organic matter into simpler compounds (such as carbon dioxide, methane, etc.); however, the anode electrode serves as the final electron acceptor [1, 2]. The electrons produced at the anode are used at the cathode in oxygen reduction reaction (ORR), a reaction that requires the presence of a catalyst. The system design for MFCs can vary to meet different applications [3], but one of the more popular designs is a membrane less, single chamber, air cathode microbial fuel cell [4], which has the anode submerged in an oxygen-less, nutrient solution and has an air-exposed cathode. Although promising in concept, MFCs have very low power density, making them cost inefficient. A major performance limitation in MFCs has been identified in the cathode. Overall efficiency and power density a strongly influenced by cathode design and catalyst selection for the ORR [4, 5]. Previous modeling efforts have suggested oxygen crossover to the anode, oxygen diffusion to the ORR catalyst, and the catalyst used are major factors for low power density [6-8]. In this work, improved MFC performance is demonstrated using non-platinum group catalyst material. The novel catalyst was benchmarked against a platinum group catalyst. Using the novel non-platinum catalyst results in a modest increase in open circuit potential, and a significant increase in maximum current density and power density. In addition, we have investigated the influence of non-platinum catalyst loading on the overall performance. The novel catalysts used in this work demonstrated stability over months of operation. This suggests that the non-platinum group catalyst used in this work is more efficient than platinum group catalyst, improving the cell performance while simultaneously enabling lower cost. References Jr, L.B.W., C.H. Shaw, and J.F. Castner, Bioelectrochemical fuel cells. Enzyme and Microbial Technology, 1982. 4(3): p. 6.Kim, H.J., et al., A mediator-less microbial fuel cell using a metal reducing bacterium, Shewanella putrefaciens. Enzyme and Microbial Technology, 2002. 30(2): p. 8.He, Z., S.D. Minteer, and L.T. Angenent, Electricity Generation from Artificial Wastewater Using an Upflow Microbial Fuel Cell. Environmental Science and Technology, 2006. 39: p. 6.Liu, H. and B.E. Logan, Electricity Generation Using an Air-Cathode Single Chamber Microbial Fuel Cell in the Presence and Absence of a Proton Exchange Membrane. Environmental Science and Technology, 2004. 38: p. 6.Rismani-Yazdi, H., et al., Cathodic limitations in microbial fuel cells: An overview. Journal of Power Sources, 2008. 180: p. 12.Ou, S., et al., Full cell simulation and the evaluation of the buffer system on air-cathode microbial fuel cell. Journal of Power Sources, 2017. 347: p. 11.Ou, S., et al., Modeling and validation of single-chamber microbial fuel cell cathode biofilm growth and response to oxidant gas composition. Journal of Power Sources, 2016. 328: p. 12.Ou, S., et al., Multi-variable mathematical models for the air-cathode microbial fuel cell system. Journal of Power Sources, 2016. 314: p. 9. Figure 1

Physiological and electrochemical effects of different electron acceptors on bacterial anode respiration in bioelectrochemical systems.

Microbial Fuel Cells (MFCs) are bio-electrochemical transducers that generate electricity as a direct result of microbial metabolism, when breaking down organic matter for continuous growth and maintenance. On the other hand, Microbial Electrolysis Cells (MECs) consume electricity to drive chemical reactions and recover hydrogen or other high value chemicals, at the cathode half-cell [1]. In MFCs, electric current is generated when for every electron donated to the electrode surface, a proton is transferred from the anode to the cathode. Other cations such as Na+ or K+ may be present in significantly higher concentrations and are more likely to be transferred through a cation exchange membrane [2]. This normally results in electro-osmotically dragged water from the anode to the cathode, and often results in a phenomenon known as cathode flooding, which is a problem for MFCs and other chemical fuel cells. To this day, bio-electrosynthesis has not been reported for energy-generating MFCs, since it is associated with energy-consuming MECs. The main aim of this work was therefore to investigate the effects on MFC performance of low-cost catalyst-free electrode materials, in conjunction with cation and water transport to the cathode half-cell, in the context of beneficial water accumulation and recovery of valuable resources. Materials and Methods Twelve dual–chamber MFCs were tested in triplicate groups assembled with carbon veil anode electrodes. Half-cell chambers were 25mL each and activated sewage sludge (Wessex Water) was used as the inoculum. The cathode chambers contained carbon based electrodes mechanically pressed against the CEM separator. The tested cathode electrodes included: Microporous Layer on carbon cloth (MPL), carbon fibre veil (CV), MPL on carbon fibre veil (CV MPL) and activated carbon (AC). Results and Discussion Results showed that the range of Pt-free cathodes including plain carbon fibre veil, activated carbon, and microporous layer (MPL) in dual-chamber MFCs generated electric current with simultaneous catholyte generation in the cathode chamber.During MFC operation, the production of catholyte on the surface of the cathode electrode was a direct result of electricity generation, and power output has been correlated with catholyte volume. Moreover, the pH of the formed catholyte (>13) and conductivity, showed gradual increase with current generation. The MFC system fed with real wastewater supplemented with sodium acetate showed sodium recovery on the cathode in the form of sodium carbonate salts. Similarly, when the anode feedstock was supplemented with potassium acetate, KOH was formed on the cathode half-cell with additional crystallisation of potassium salts.This paper demonstrates an innovative and energy-efficient system that exploits microbially assisted electrosynthesis for the recovery of valuable elements from wastewater, in the form of chemicals (NaOH, KOH) and electricity. Conclusions This approach leads to carbon capture through wet caustic scrubbing on the cathode, which locks the carbon dioxide into carbonate salts. Acknowledgements This work has been supported by the Bill & Melinda Gates Foundation, grant no. OPP1094890, and the UK EPSRC, grant numbers EP/I004653/1 and EP/L002132/1.

One of the most important challenges for our society is providing powerful devices for renewable energy production. Many technologies based on renewable energy sources have been developed, which represent a clean energy sources that have a much lower environmental impact than conventional energy technologies. Nowadays, many researches focus their attention on the development of renewable energy from solar, water, organic matter and biomass, which represent abundant and renewable energy sources. This research is mainly focused on the development of promising electrode materials and their potential application on emerging technologies such as artificial photosynthesis and microbial fuel cell (MFC). According to desired proprieties of functional materials, this research was focused on two main materials: (1) TiO2 for the development of electrodes for the water splitting reaction due to its demonstrated application potential as photocatalyst material and (2) carbon-based materials for the development of electrodes for MFC. In the first part of the investigation, different TiO2 nanostructures have been studied including: synthesis, characterization and test of TiO2-based materials with the aim of improving the limiting factors of the photocatalytic reaction: charge recombination and separation/migration processes. The photo-catalytic properties of different TiO2 nanostructures were evaluated including: TiO2 nanoparticles (NPs) film, TiO2 nanotubes (NTs) and ZnO@TiO2 core-shell structures. Photo-electrochemical activity measurements and electrochemical impedance spectroscopy analysis showed an improvement in charge collection efficiency of 1D-nanostructures, related to a more efficient electron transport in the materials. The efficient application of both the TiO2 NTs and the ZnO@TiO2 core-shell photoanodes opens important perspectives, not only in the water splitting application field, but also for other photo-catalytic applications (e.g. photovoltaic cells, degradation of organic substances), due to their chemical stability, easiness of preparation and improved transport properties. Additionally, in order to improve the photo-catalytic activity of TiO2 NPs, PANI/TiO2 composite film was synthesized. PANI/TiO2 composite film was successfully applied as anode material for the PEC water splitting reaction showing a significant increase in the photocatalytic activity of TiO2 NPs composite film essentially attributed to the efficient separation of the generated electron and hole pairs. To date, no cost-effective materials system satisfies all of the technical requirements for practical hydrogen production under zero-bias conditions. For this propose, to promote the sustainability of the process, the bias require to conduct PEC water splitting reaction could be powered by MFC systems in which many efforts have been done to improve power and electricity generation as is explained below. In this work, different strategies were also applied in order to improve the performance of anode materials for MFCs. The investigation of commercial carbon-based materials demonstrated that these materials, normally used for other ends are suitable electrodes for MFC and their use could reduce MFC costs and improve the energy sustainability of the process. In addition, to enhance power generation in MFC by using low-cost and commercial carbon-based materials, nitric acid activation (C-HNO3) and PANI deposition (C-PANI) were performed on commercial carbon felt (C-FELT) in order to increase the performance of MFC. Electrochemical determinations performed in batch-mode MFC reveled a strong reduction of the activation losses contribution and an important decrease of the internal resistance of the cell using C-HNO3 and C-PANI of about 2.3 and 4.4 times, respectively, with respect to C-FELT. Additionally, with the aim of solvent different MFC operational problems such as: biofouling, low surface area and large-scale MFC, an innovative three-dimensional material effectively developed and used as anode electrode. The conductive carbon-coated Berl saddles (C-SADDLES) were successfully used as anode electrode in batch-mode MFC. Electrochemical results suggested that C-SADDLES offer a low-cost solution to satisfy either electrical or bioreactor requirements, increasing the reliability of the MFC processes, and seems to be a valid candidate for scaled-up systems and for continuous mode application of MFC technology. In addition, the electrochemical performance and continuous energy production of the most promising materials obtained during this work were evaluated under continuous operation MFC in a long-term evaluation test. Remarkable results were obtained for continuous MFCs systems operated with three different anode materials: C-FELT, C-PANI and C-SADDLES. From polarization curves, the maximum power generation was obtained using C-SADDLES (102 mW•m-2) with respect to C-FELT (93 mW•m-2) and C-PANI (65 mW•m-2) after three months of operation. The highest amount of electrical energy was produced by C-PANI (1803 J) with respect to C-FELT (1664 J) and C-SADDLES (1674 J). However, it is worth to note that PANI activity was reduced during time by the operating conditions inside the anode chamber. In order to demonstrate the wide application potential MFC, this work reports on merging heterogeneous contributions and combining the advantages from three separate fields in a system which enables the ultra-low-power monitoring of a microbial fuel cell voltage status and enables pressure monitoring features of the internal conditions of a cell. The solution is conceived to provide an efficient energy source, harvesting wastewater, integrating energy management and health monitoring capabilities to sensor nodes which are not connected to the energy grid. Finally, this work presented a general concept of the integration of both devices into a hybrid device by interfacing PEC and MFC devices (denoted as PEC-MFC), which is proposed to generate electricity and hydrogen using as external bias the potential produce by microbial fuel cell

Long-time enrofloxacin processing with microbial fuel cells and the influence of coexisting heavy metals (Cu and Zn)

Observing continuously increasing demand in the world for water and energy, alternative sources are needed to meet the requirement of a growing population. Microbial Fuel Cell (MFC) represents one sustainable technology that directly converts organic biomass in wastewater into electric current, thus it can be a potential alternative source for energy and water clean-up. Microbial Fuel Cells generate electric current as a direct result of microbial metabolism, where the anodic biofilm is the engine of the process cleaning wastewater and converting chemical energy to electrical energy. MFC technology development into commercial applications has been limited by high cost of materials and low efficiency of energy recovered. Therefore, the successful scale-up process should involve material and design optimisation. With this approach in mind, recent advancements bring the technology closer to the real life implementation thanks to using ceramic for MFC architecture [1] and improved design of multiple units in the system [2]. In addition, it results in electrochemically treated waste and usable electricity levels, for example to power indoor lighting [3]. The main aim of this work was to increase the efficiency of the ceramic based MFCs by compacting the design and exploring the ceramic support as the building block for small scale modular multi-unit systems. The improved energy density would then allow to utilise the energy locked in the feedstock (waste) more efficiently, make MFCs more applicable in industrial and municipal wastewater treatment facilities, and scale-up-ready for real world application. Materials and Methods MFCs were made out of small scale terracotta cylinders (70 mm long, 15 mm diameter) tested in triplicate groups assembled with carbon veil fibre used as anode electrodes. The cathode electrode was made of activated carbon and placed against the ceramic separator inside the hollow cathode chamber. The MFCs were compared against large tubular MFCs (100 mm long, 42 mm diameter) with the same anode to cathode ratio (27:1) and operated in laboratory conditions. Results and Discussion Results showed that the small scale MFCs shown improved power density performance in comparison to the large tubular MFCs. The maximum performance achieved during polarization experiment showed that volumetric density of the small scale MFCs was 21 W/m3 while large MFCs only 8.5 W/m3which is suggests 2.5 improvement of small MFCs. Smaller MFC devices can take the advantage of high surface to volume ratio which in this case was calculated as 2.6 for small MFCs and 1 for large MFCs. During electrochemical MFC operation, the production of catholyte on the surface of the cathode electrode was also observed and driven by generated current. The simplicity of the design is allowing to configure any number of units in parallel configuration and use them in any wastewater tank as ”dip and go” system. This includes MFC use in urinal tanks to power devices in remote locations or in large wastewater treatment plants to lower energy cost. This might also help to solve the electricity and sanitation problem in the Developing World. Efficient utilisation and scale-up allows the technology to come out of the laboratory to field trails to become useful to societies and to the environment. Conclusions This approach leads to more efficient utilization of organic compounds in wastewater including urine and the development of the off-the-grid electrochemical system that allows net generation of usable power and wastewater decontamination. Acknowledgements This work has been supported by the UK EPSRC, grant numbers EP/I004653/1 and EP/L002132/1 and Bill & Melinda Gates Foundation, grant no. OPP1094890.

Environmental pollution and global warming are major threats to life on Earth. These drastic changes are caused by carbon dioxide emission, which has become a very serious problem worldwide. For the generation of useful sustainable and renewable energy in an efficient manner, the production of electricity using solar energy trapped by algae in combination with microbial fuel cells (MFCs) is a very attractive option. The use of different kinds of algae has become a recent research trend, especially because algae have great capacity to utilize carbon dioxide via photosynthesis, with the potential to convert it into a biomass. Integrating algae into MFCs has given rise to a new MFC model, that of photosynthetic MFCs. Algal MFCs play an extensive role in the treatment of organic contaminants that can be converted to bioelectricity and they also efficiently remove various by-products. This chapter provides- detailed descriptions of the basic experimental setup of MFCs, and the electrode materials used for anodes, cathodes, and membranes. Microbial fuel cells employing different types of algae as substrates under various conditions are described in detail. A brief description of special MFC designs that are integrated with PBR is given. Details of MFC models with algae-assisted anodes and cathodes are also supplied. The multiple bioreactor constructions that are employed to yield algal biomasses are discussed, along with the technologies that will have to be developed. Future challenges and perspectives are highlighted, and we describe research work that can be applied for the commercialization of algal MFCs.

Microbial Fuel Cells (MFCs) are innovative environmental engineering systems that harness the metabolic activities of microbial communities to convert chemical energy in waste into electrical energy. However, MFC performance optimization remains challenging due to limited understanding of microbial metabolic mechanisms, particularly with complex substrates under realistic environmental conditions. This study investigated the effects of substrate complexity (acetate vs. starch) and varying mass transfer (stirred vs. non-stirred) on acclimatization rates, substrate degradation, and microbial community dynamics in air-cathode MFCs. Stirring was critical for acclimating to complex substrates, facilitating electrogenic biofilm formation in starch-fed MFCs, while non-stirred MFCs showed limited performance under these conditions. Non-stirred MFCs, however, outperformed stirred systems in current generation and coulombic efficiency (CE), especially with simple substrates (acetate), achieving 66% CE compared to 38% under stirred conditions, likely due to oxygen intrusion in the stirred systems. Starch-fed MFCs exhibited consistently low CE (19%) across all tested conditions due to electron diversion into volatile fatty acids (VFA). Microbial diversity was higher in acetate-fed MFCs but unaffected by stirring, while starch-fed MFCs developed smaller, more specialized communities. Kinetic analysis identified hydrolysis of complex substrates as the rate-limiting step, with rates an order of magnitude slower than acetate consumption. Combined hydrolysis-fermentation rates were unaffected by stirring, but stirring significantly impacted acetate consumption rates, likely due to oxygen-induced competition between facultative aerobes and electrogenic bacteria. These findings highlight the trade-offs between enhanced substrate availability and oxygen-driven competition in MFCs. For real-world applications, initiating reactors with dynamic stirring to accelerate acclimatization, followed by non-stirred operation, may optimize performance. Integrating MFCs with anaerobic digestion could overcome hydrolysis limitations, enhancing the degradation of complex substrates while improving energy recovery. This study introduces novel strategies to address key challenges in scaling up MFCs for wastewater treatment, bridging the gap between fundamental research and practical applications to advance environmental systems.

Granular activated carbon assisted biocathode for effective electrotrophic denitrification in microbial fuel cells

A strategy for power generation from bilgewater using a photosynthetic microalgal fuel cell (MAFC)