MFC Systems Research Articles

Comparative Environmental Analysis of Microbial Electrochemical Systems

Role of biobased fuel production takes a special role at international and European level. Microbial electrochemical systems (MEC– microbial electrolysis cell and MFC – microbial fuel cell) have a great energy production potential in combination with organic waste degradation. Energy efficiency of microbial systems and thus a positive effect to the greenhouse gas mitigation has been stated by many authors. However, due to the novelty of the technology and also availability of experimental MFC and MEC systems only, the environmental assessment of the microbial systems is not widely performed.This paper focuses on a comparative environmental analysis of MECs and MFCs based on life cycle inventory data.

Enhancement of electricity production in a mediatorless air-cathode microbial fuel cell using Klebsiella sp. IR21.

A novel dissimilatory iron-reducing bacteria, Klebsiella sp. IR21, was isolated from the anode biofilm of an MFC reactor. Klebsiella sp. IR21 reduced 27.8% of ferric iron to ferrous iron demonstrating that Klebsiella sp. IR21 has electron transfer ability. Additionally, Klebsiella sp. IR21 generated electricity forming a biofilm on the anode surface. When a pure culture of Klebsiella sp. IR21 was supplied into a single chamber, air-cathode MFC fed with a mixture of glucose and acetate (500mgL(-1) COD), 40-60mV of voltage (17-26mAm(-2) of current density) was produced. Klebsiella sp. IR21 was also utilized as a biocatalyst to improve the electrical performance of a conventional MFC reactor. A single chamber, air-cathode MFC was fed with reject wastewater (10,000mgL(-1) COD) from a H2 fermentation reactor. The average voltage, current density, and power density were 142.9±25.74mV, 60.5±11.61mAm(-2), and 8.9±3.65mWm(-2), respectively, in the MFC without inoculation of Klebsiella sp. IR21. However, these electrical performances of the MFC were significantly increased to 204.7±40.24mV, 87.5±17.20mAm(-2), and 18.6±7.23mWm(-2), respectively, with inoculation of Klebsiella sp. IR21. The results indicate that Klebsiella sp. IR21 can be utilized as a biocatalyst for enhancement of electrical performance in MFC systems.

Microbial Fuel Cells: A Source of Bioenergy

The demands of energy in the world continue to accelerate and this triggers the global energy crisis and environmental Pollution. The reliance on fossil fuels (oil and gas) is unsustainable because of its finite, depleting supplies and impact on environment. As a result researchers are focusing on alternative, renewable and carbon neutral energy sources which are necessary for environmental and economic sustainability. MFC is a bioreactor that converts chemical energy present in the organic or inorganic compound substrates to electrical energy through catalytic reactions of microorganisms. Many substrates involve in generating electricity including carbohydrates, proteins, volatile acids, cellulose and wastewaters used as feed in MFC studies. MFC has a wide range of applications, including serving as household electrical generators and powering items such as small portable electronic devices boats, automobiles, electronics in space and self-feeding robots. The construction and analysis of MFCs requires knowledge at both scientific and engineering fields, ranging from microbiology and electrochemistry to materials and environmental engineering. We conclude that for further development of MFC technology a greater focus on the understanding of its components, microbial processes, factors of limitations and designs of the construction the in MFC systems is mandatory, in order to be simplified and large scale system developed; so that it will be cost-effective and to increase electricity production. This paper aimed to review on the current microbiology knowledge in electricity production, the materials and methods used to build the technology and the applications to MFC technology also highlighted.

Pyrolyzed binuclear-cobalt-phthalocyanine as electrocatalyst for oxygen reduction reaction in microbial fuel cells

A novel platinum (Pt)-free cathodic materials binuclear-cobalt-phthalocyanine (Bi-CoPc) pyrolyzed at different temperatures (300–1000°C) were examined as the oxygen reduction reaction (ORR) catalysts, and compared with unpyrolyzed Bi-CoPc/C and Pt cathode in single chamber microbial fuel cells (SCMFCs). The results showed that the pyrolysis process increased the nitrogen abundance on Bi-CoPc and changed the nitrogen types. The Bi-CoPc pyrolyzed at 800°C contained a significant amount of pyrrolic-N, and exhibited a high electrochemical catalytic activity. The power density and current density increased with temperature: Bi-CoPc/C-800>Bi-CoPc/C-1000>Bi-CoPc/C-600>Bi-CoPc/C-300>Bi-CoPc/C. The SCMFC with Bi-CoPc/C-800 cathode had a maximum power density of 604mWm−2. The low cost Bi-CoPc compounds developed in this study showed a potential in air-breathing MFC systems, with the proper pyrolysis temperature being chosen.

Simultaneous electricity generation and microbially-assisted electrosynthesis in ceramic MFCs

To date, the development of microbially assisted synthesis in Bioelectrochemical Systems (BESs) has focused on mechanisms that consume energy in order to drive the electrosynthesis process. This work reports – for the first time – on novel ceramic MFC systems that generate electricity whilst simultaneously driving the electrosynthesis of useful chemical products. A novel, inexpensive and low maintenance MFC demonstrated electrical power production and implementation into a practical application. Terracotta based tubular MFCs were able to produce sufficient power to operate an LED continuously over a 7day period with a concomitant 92% COD reduction. Whilst the MFCs were generating energy, an alkaline solution was produced on the cathode that was directly related to the amount of power generated. The alkaline catholyte was able to fix CO2 into carbonate/bicarbonate salts. This approach implies carbon capture and storage (CCS), effectively capturing CO2 through wet caustic ‘scrubbing’ on the cathode, which ultimately locks carbon dioxide.

In Field Applications of Single Chamber Membraneless Microbial Fuel Cells (SCMFCs) for Wastewater Treatment, Metal Reduction and Nutrients Removal

In this study, prototypes of SCMFCs were applied or are in process to be applied for real world applications. Particularly, several large surface electrodes MFCs are currently operating in the 32 parallel lines wastewater treatment plant of Nosedo (Milan,Italy). Different chemical and biological conditions led to favorable environment for the development of effective bioanodes and biocathodes in MFCs immersed in the anoxic and aerobic tanks, despite low organic load in the wastewater inlet. The influence of carbon electrode surface extent was preliminary evaluated, showing the possibility of scale-up processes.Another preliminary study is currently in progress in the water of a prealpine meromictic lake (Idro Lake, Italy). The possibility of using bio-electrochemical/electrolyses system for remediating a local pollution will be deployed. The typical presence of the net separation between an aerobic and anaerobic area in the water body makes a meromictic lake affine to a massive MFC. A optimized procedure for the electro-sorption of specific oxide/hydroxide transitional metals (e.g. manganese and other metals and nutrients) on cathodes of MFC systems will be developed for the application in field, as a new innovative strategy for metal pollution remediation.Future applications will be also directed in deploying sediment MFC with anode immersed in the sediments and cathode covered by plants. Based on the preliminary results, a “garden island” will be designed for covering a wetland in order to reduce significantly also the organic load in the pool. Prototype of multi–array MFCs, with an impressive design and style of “little floating garden” will be studied and presented at the International Exposition in Milan 2015.Preliminary experimentations are now devoted to develop and validate electrochemically/chemically activated materials and hierarchically catalyzed surfaces, in collaboration with several different specialists, in order to enhance the performance of cathodes and anodes of the SCMFC tested and decrease operating costs.

Membrane filtration biocathode microbial fuel cell for nitrogen removal and electricity generation

Conductive materials with attached biofilms, were used as membrane filtration biocathodes to filter the effluent and supply electrons for denitrification. Stainless steel mesh and carbon felt were employed to fabricate membrane modules, and the two MFC systems were termed as M1 and M2, respectively. High effluent quality was obtained with M1 and M2 in terms of turbidity, COD and ammonium. In M1, no bioelectrochemical denitrification took place, while nitrate decreased from 35.88±4.15 to 27.33±5.32mg-N/L through the membrane in M2, causing a removal efficiency of 23.3±6.5% with respect to cathodic nitrate. The denitrification ceased without electricity. The maximum power densities of M1 and M2 were 121 and 1253mW/m3, respectively. Micrococcus bacteria and rod-shaped bacteria covered the surface of carbon felt and fewer bacteria were found on stainless steel mesh. According to fluorescence in situ hybridization, the putative bacteria affiliated with Paracoccus genus and Pseudomonas spp. dominated in the interior biofilm on carbon felt for denitrification. Results demonstrate that the carbon felt system can perform bioelectrochemical denitrification to polish the effluent.

Comparative Metagenomics of Anode-Associated Microbiomes Developed in Rice Paddy-Field Microbial Fuel Cells

In sediment-type microbial fuel cells (sMFCs) operating in rice paddy fields, rice-root exudates are converted to electricity by anode-associated rhizosphere microbes. Previous studies have shown that members of the family Geobacteraceae are enriched on the anodes of rhizosphere sMFCs. To deepen our understanding of rhizosphere microbes involved in electricity generation in sMFCs, here, we conducted comparative analyses of anode-associated microbiomes in three MFC systems: a rice paddy-field sMFC, and acetate- and glucose-fed MFCs in which pieces of graphite felt that had functioned as anodes in rice paddy-field sMFC were used as rhizosphere microbe-bearing anodes. After electric outputs became stable, microbiomes associated with the anodes of these MFC systems were analyzed by pyrotag sequencing of 16S rRNA gene amplicons and Illumina shotgun metagenomics. Pyrotag sequencing showed that Geobacteraceae bacteria were associated with the anodes of all three systems, but the dominant Geobacter species in each MFC were different. Specifically, species closely related to G. metallireducens comprised 90% of the anode Geobacteraceae in the acetate-fed MFC, but were only relatively minor components of the rhizosphere sMFC and glucose-fed MFC, whereas species closely related to G. psychrophilus were abundantly detected. This trend was confirmed by the phylogenetic assignments of predicted genes in shotgun metagenome sequences of the anode microbiomes. Our findings suggest that G. psychrophilus and its related species preferentially grow on the anodes of rhizosphere sMFCs and generate electricity through syntrophic interactions with organisms that excrete electron donors.

The effect of physico-chemically immobilized methylene blue and neutral red on the anode of microbial fuel cell

A fast and cost effective immobilization of electron carriers, methylene blue (MB) and neutral red (NR) by pH shift was proposed to improve bioanodic performance. The adsorption of mediators onto the carbon cloth anode was verified using cyclic voltammogram (CV) and the effect of the immobilized mediators on acclimation, power density, and acetate removal of MFCs was investigated. A peak power density of Pmax(MB) = 11.3 W/m3 was achieved over days 110 ∼ 120, as compared to Pmax(Control) = 5.4 W/m3 and Pmax(NR) = 3.1 W/m3 for the treated anode after 15 sequential fed-batch operations. The VFA removal rates however were similar for all MFC systems, ranging from 82 to 87%. It could be suggested that the increase in power density for the MB treated electrode resulted from an enhanced electron transport from exo-electrogenic bacteria. MB may also have a selective effect on the bacterial community during the start-up stage, increasing the voltage production and acetate removal from day 1 to 16. However, MFC with NR treated anode produced an initial voltage under 100 mV, with lower coulombic efficiency (CE). NR exhibited less favourable mediator molecule binding to the electrode surface, when subject to pH driven physico-chemical immobilization.

New generation of carbon nanocomposite proton exchange membranes in microbial fuel cell systems

In this study, self-made carbon nanofiber (CNF)/Nafion and activated carbon nanofiber (ACNF)/Nafion nanocomposite membranes are fabricated and tested in a microbial fuel cell. The data are compared with Nafion 117 as a common membrane in MFCs and Nafion 112. The electrospinning method was used for the production of CNFs. This method is chosen because it is simple, highly cost effective, and the most prolific method of all that could be used to produce CNF. Nanocomposite membranes are used because they had higher production power and coulombic efficiency (CE) than Nafion 117 and Nafion 112 in MFC systems. The results reveal that the system is operated by the ACNF/Nafion membrane produce the highest voltage of 57.64mWm−2, while Nafion 112 produces the lowest power density (13.99mWm−2).