Development of a solar-powered microbial fuel cell

Construction of a Conductive Polymer/AuNP/Cyanobacteria-Based Biophotovoltaic Cell Harnessing Solar Energy to Generate Electricity via Photosynthesis and Its Usage as a Photoelectrochemical Pesticide Biosensor: Atrazine as a Case Study

In this research, a cyanobacteria (Leptolyngbia sp.)-based biological photovoltaic cell (BPV) was designed. This clean energy-friendly BPV produced a photocurrent as a result of illuminating the photoanode and cathode electrodes immersed in the aqueous medium with solar energy. For this purpose, both electrodes were first coated with conductive polymers with aniline functional groups on the gold electrodes. In the cell, the photoanode was first coated with a gold-modified poly 4-(2,5-di(thiophen-2-yl)-1H-pyrrol-1-yl)benzamine polymer, P(SNS-Aniline). Thioaniline-functionalized gold nanoparticles were used to provide a cross-link formation with bis-aniline conductive bonds with the conductive polymer using electrochemical techniques. Leptolyngbia sp., one of the cyanobacteria that can convert light energy into chemical energy, was attached to this layered electrode surface. The cathode of the cell was attached to the gold electrode surface with P(SNS-Aniline). Then, the bilirubin oxidase (BOx) enzyme was immobilized on this film surface with glutaraldehyde activation. This cell, which can use light, thanks to cyanobacteria, oxidized and split water, and oxygen was obtained at the photoanode electrode. At the cathode electrode, the oxygen gas was reduced to water by the bioelectrocatalytic method. To obtain a high photocurrent from the BPV, necessary optimizations were made during the design of the system to increase electron transport and strengthen its transfer. While the photocurrent value obtained with the designed BPV in optimum conditions and in the pseudosteady state was 10 mA/m2, the maximum power value obtained was 46.5 mW/m2. In addition to storing the light energy of the system, studies have been carried out on this system as a pesticide biosensor. Atrazine biosensing via the BPV system was analytically characterized between 0.1 and 1.2 μM concentrations for atrazine, and a very low detection limit was found as 0.024 μM. In addition, response time and recovery studies related to pesticide biosensor properties of the BPV were also investigated.

Photo-assisted microbial fuel cell systems: critical review of scientific rationale and recent advances in system development

Bioelectrochemical systems such as microbial fuel cells (MFCs) have gained extensive attention due to their abilities to simultaneously treat wastewater and generate renewable energy resources. Recently, to boost the system performance, the photoelectrode has been incorporated into MFCs for effectively exploiting the synergistic interaction between light and microorganisms, and the resultant device is known as photo-assisted microbial fuel cells (photo-MFCs). Combined with the metabolic reaction of organic compounds by microorganisms, photo-MFCs are capable of simultaneously converting both chemical energy and light energy into electricity. This article aims to systematically review the recent advances in photo-MFCs, including the introduction of specific photosynthetic microorganisms used in photo-MFCs followed by the discussion of the fundamentals and configurations of photo-MFCs. Moreover, the materials used for photoelectrodes and their fabrication approaches are also explored. This review has shown that the innovative strategy of utilizing photoelectrodes in photo-MFCs is promising and further studies are warranted to strengthen the system stability under long-term operation for advancing practical application.

Evaluating application of photosynthetic microbial fuel cell to exhibit efficient carbon sequestration with concomitant value-added product recovery from wastewater: A review

The emission of CO2 from industrial (24%) and different anthropogenic activities, like transportation (27%), electricity production (25%), and agriculture (11%), can lead to global warming, which in the long term can trigger substantial climate changes. In this regard, CO2 sequestration and wastewater treatment in tandem with bioenergy production through photosynthetic microbial fuel cell (PMFC) is an economical and sustainable intervention to address the problem of global warming and elevating energy demands. Therefore, this review focuses on the application of different PMFC as a bio-refinery approach to produce biofuels and power generation accompanied with the holistic treatment of wastewater. Moreover, CO2 bio-fixation and electron transfer mechanism of different photosynthetic microbiota, and factors affecting the performance of PMFC with technical feasibility and drawbacks are also elucidated in this review. Also, low-cost approaches such as utilization of bio-membrane like coconut shell, microbial growth enhancement by extracellular cell signalling mechanisms, and exploitation of genetically engineered strain towards the commercialization of PMFC are highlighted. Thus, the present review intends to guide the budding researchers in developing more cost-effective and sustainable PMFCs, which could lead towards the commercialization of this inventive technology.

Bioelectrochemical systems (BESs) for agro-food waste and wastewater treatment, and sustainable bioenergy-A review

Producing food by farming and subsequent food manufacturing are central to the world's food supply, accounting for more than half of all production. Production is, however, closely related to the creation of large amounts of organic wastes or byproducts (agro-food waste or wastewater) that negatively impact the environment and the climate. Global climate change mitigation is an urgent need that necessitates sustainable development. For that purpose, proper agro-food waste and wastewater management are essential, not only for waste reduction but also for resource optimization. To achieve sustainability in food production, biotechnology is considered as key factor since its continuous development and broad implementation will potentially benefit ecosystems by turning polluting waste into biodegradable materials; this will become more feasible and common as environmentally friendly industrial processes improve. Bioelectrochemical systems are a revitalized, promising biotechnology integrating microorganisms (or enzymes) with multifaceted applications. The technology can efficiently reduce waste and wastewater while recovering energy and chemicals, taking advantage of their biological elements' specific redox processes. In this review, a consolidated description of agro-food waste and wastewater and its remediation possibilities, using different bioelectrochemical-based systems is presented and discussed together with a critical view of the current and future potential applications.

Photosynthetic microbial fuel cells for methanol treatment using graphene electrodes

Photosynthetic microbial fuel cells (pMFC) represent a promising approach for treating methanol (CH₃OH) wastewater. However, their use is constrained by a lack of knowledge on the extracellular electron transfer capabilities of photosynthetic methylotrophs, especially when coupled with metal electrodes. This study assessed the CH₃OH oxidation capabilities of Rhodobacter sphaeroides 2.4.1 in two-compartment pMFCs. A 3D nickel (Ni) foam modified with plasma-grown graphene (Gr) was used as an anode, nitrate mineral salts media (NMS) supplemented with 0.1% CH₃OH as anolyte, carbon brush as cathode, and 50 mM ferricyanide as catholyte. Two simultaneous pMFCs that used bare Ni foam and carbon felt served as controls. The Ni/Gr electrode registered a two-fold lower charge transfer resistance (0.005 kΩ cm²) and correspondingly 16-fold higher power density (141 mW/m²) compared to controls. The underlying reasons for the enhanced performance of R. sphaeroides at the graphene interface were discerned. The real-time polymerase chain reaction (PCR) analysis revealed the upregulation of cytochrome c oxidase, aa3 type, subunit I gene, and Flp pilus assembly protein genes in the sessile cells compared to their planktonic counterparts. The key EET pathways used for sustaining CH₃OH oxidation were discussed.

Blending of microbial inocula: An effective strategy for performance enhancement of clayware Biophotovoltaics microbial fuel cells

Performance of clayware Biophotovoltaics (BPVs) with three variants of inocula namely anoxygenic photosynthetic bacteria (APB) rich Effective microbes (EM), Up-flow anaerobic sludge blanket reactor (UASB) sludge, SUPER-MIX the blend of EM and UASB inoculum were evaluated on the basis of electrical output and pollutant removal. SUPER-MIX inocula with microbial community comprising of 28.42% APB and 71.58% of other microbes resulted in peak power density of 275 mW/m², 69.3 ± 1.74% Coulombic efficiency and 91 ± 3.96% organic matter removal. The higher performance of the SUPER-MIX than EM and UASB inocula was due to the syntrophic associations of the various APBs and other heterogenous microorganisms in perfect blend which improved biocatalytic electron transfer, electro-kinetic activities with higher redox current and bio-capacitance. The promising performance of clayware BPVs with SUPER-MIX inocula indicate the possibility of BPVs to move towards the scale-up process to minimize the investment towards pure culture by effective blending strategies of inocula.

Electricigens in the anode of microbial fuel cells: pure cultures versus mixed communities

Microbial fuel cell (MFC) is an environmentally friendly technology for electricity harvesting from a variety of substrates. Microorganisms used as catalysts in the anodic chamber, which are termed as electricigens, play a major role in the operation of MFCs. This review provides an introduction to the currently identified electricigens on their taxonomical groups and electricity producing abilities. The mechanism of electron transfer from electricigens to electrode is highlighted. The performances of pure culture and mixed communities are compared particularly. It has been proved that the electricity generation capacity and the ability to adapt to the complex environment of MFC systems constructed by pure microbial cultures are less than the systems constructed by miscellaneous consortia. However, pure cultures are useful to clarify the electron transfer mechanism at the microbiological level and further reduce the complexity of mixed communities. Future research trends of electricigens in MFCs should be focused on screening, domestication, modification and optimization of multi-strains to improve their electrochemical activities. Although the MFC techniques have been greatly advanced during the past few years, the present state of this technology still requires to be combined with other processes for cost reduction.

Applications of Emerging Bioelectrochemical Technologies in Agricultural Systems: A Current Review

Background: Bioelectrochemical systems (BESs) are emerging energy-effective and environment-friendly technologies. Different applications of BESs are able to effectively minimize wastes and treat wastewater while simultaneously recovering electricity, biohydrogen and other value-added chemicals via specific redox reactions. Although there are many studies that have greatly advanced the performance of BESs over the last decade, research and reviews on agriculture-relevant applications of BESs are very limited. Considering the increasing demand for food, energy and water due to human population expansion, novel technologies are urgently needed to promote productivity and sustainability in agriculture. Methodology: This review study is based on an extensive literature search regarding agriculture-related BES studies mainly in the last decades (i.e., 2009–2018). The databases used in this review study include Scopus, Google Scholar and Web of Science. The current and future applications of bioelectrochemical technologies in agriculture have been discussed. Findings/Conclusions: BESs have the potential to recover considerable amounts of electric power and energy chemicals from agricultural wastes and wastewater. The recovered energy can be used to reduce the energy input into agricultural systems. Other resources and value-added chemicals such as biofuels, plant nutrients and irrigation water can also be produced in BESs. In addition, BESs may replace unsustainable batteries to power remote sensors or be designed as biosensors for agricultural monitoring. The possible applications to produce food without sunlight and remediate contaminated soils using BESs have also been discussed. At the same time, agricultural wastes can also be processed into construction materials or biochar electrodes/electrocatalysts for reducing the high costs of current BESs. Future studies should evaluate the long-term performance and stability of on-farm BES applications.

New insights in photosynthetic microbial fuel cell using anoxygenic phototrophic bacteria

Anoxygenic phototrophic bacteria (APB) pay a key role in biogeochemical cycles, and it can convert light energy to chemical energy by photosynthesis process. Photosynthetic microbial fuel cell (photo-MFC) is regarded as a promising energy-harvesting technology, which is also applied to environment treatment in recent years. The previous studies show that photo-MFC with APB have higher power putout than other bioelectrochemical systems. However, photo-MFC with APB is not reviewed due to some limited factors in the development process. In this review, photo-MFC with APB is treated according to its electron transfer pathways, the current understanding, APB strains, application, influence of substrates, and economic assessment. Meanwhile, knowledge of photosynthesis components and electron transfer pathways of APB is crucial for developing new energy and easing the serious energy crisis. Moreover, some new insights (the optimization of light source and self-sustaining bioelectricity generation) are proposed for the future explorations.

Photosynthetic Microbial Fuel Cells

This chapter presents the current state of research on bioelectrochemical systems that include phototrophic organisms. First, we describe what is known of how phototrophs transfer electrons from internal metabolism to external substrates. This includes efforts to understand both the source of electrons and transfer pathways within cells. Second, we consider technological progress toward producing bio-photovoltaic devices with phototrophs. Efforts to improve these devices by changing the species included, the electrode surfaces, and chemical mediators are described. Finally, we consider future directions for this research field.

Generating Electric Current by Bioartificial Photosynthesis

Abundant solar energy can be a sustainable source of energy. This chapter highlights recent advancements, challenges, and future scenarios in bioartificial photosynthesis, which is a new subset of bioelectrochemical systems (BESs) and technologies. BES technologies exploit the catalytic interactions between biological moieties and electrodes. At the nexus of BES and photovoltaics, this review focuses on light-harvesting technologies based on bioartificial photosynthesis. Such technologies are promising because electrical energy is generated from sunlight and water without the need for additional organic feedstock. This review focuses on photosynthetic electron generation and transfer and compares the current status of bioartificial photosynthesis with other artificial systems that mimic the chemistry of photosynthetic energy transformation.The fundamental principles and the operation of functional units of bioartificial photosynthesis are addressed. Selected photobioelectrochemical systems employed to obtain light-driven electric currents from photosynthetic organisms are presented. The achievable current output and theoretical maxima are revisited by conceptualizing operational and process window techniques. Factors affecting overall photocurrent efficiency, performance limitations, and scaleup bottlenecks are highlighted in view of enhancing the energy conversion efficiency of photobioelectrochemical systems. To finish, the challenges associated with bioartificial photosynthetic technologies are outlined. Graphical Abstract Operational window for (bio-)artificial photosynthesis. Green circle in the upper right corner: development objective for research and engineering efforts.

An investigation of anode and cathode materials in photomicrobial fuel cells

Photomicrobial fuel cells (p-MFCs) are devices that use photosynthetic organisms (such as cyanobacteria or algae) to turn light energy into electrical energy. In a p-MFC, the anode accepts electrons from microorganisms that are either growing directly on the anode surface (biofilm) or are free floating in solution (planktonic). The nature of both the anode and cathode material is critical for device efficiency. An ideal anode is biocompatible and facilitates direct electron transfer from the microorganisms, with no need for an electron mediator. For a p-MFC, there is the additional requirement that the anode should not prevent light from perfusing through the photosynthetic cells. The cathode should facilitate the rapid reaction of protons and oxygen to form water so as not to rate limit the device. In this paper, we first review the range of anode and cathode materials currently used in p-MFCs. We then present our own data comparing cathode materials in a p-MFC and our first results using porous ceramic anodes in a mediator-free p-MFC.

Oxygen suppresses light-driven anodic current generation by a mixed phototrophic culture

This paper describes the detrimental effect of photosynthetically evolved oxygen on anodic current generation in the presence of riboflavin upon illumination of a mixed phototrophic culture enriched from a freshwater pond at +0.6 V vs standard hydrogen electrode. In the presence of riboflavin, the phototrophic biomass in the anodic compartment produced an electrical current in response to light/dark cycles (12 h/12 h) over 12 months of operation, generating a maximum current density of 17.5 mA x m(-2) during the dark phase, whereas a much lower current of approximately 2 mA x m(-2) was generated during illumination. We found that the low current generation under light exposure was caused by high rates of reoxidation of reduced riboflavin by oxygen produced during photosynthesis. Quantification of biomass by fluorescence in situ hybridization images suggested that green algae were predominant in both the anode-based biofilm (55.1%) and the anolyte suspension (87.9%) with the remaining biovolume accounted for by bacteria. Genus-level sequencing analysis revealed that bacteria were dominated by cyanobacterium Leptolyngbia (∼35%), while the prevailing algae were Dictyosphaerium, Coelastrum, and Auxenochlorella. This study offers a key comprehension of mediator sensitivity to reoxidation by dissolved oxygen for improvement of microbial solar cell performance.

Photoenhanced electrochemical interaction between Shewanella and a hematite nanowire photoanode

Here we report the investigation of interplay between light, a hematite nanowire-arrayed photoelectrode, and Shewanella oneidensis MR-1 in a solar-assisted microbial photoelectrochemical system (solar MPS). Whole cell electrochemistry and microbial fuel cell (MFC) characterization of Shewanella oneidensis strain MR-1 showed that these cells cultured under (semi)anaerobic conditions expressed substantial c-type cytochrome outer membrane proteins, exhibited well-defined redox peaks, and generated bioelectricity in a MFC device. Cyclic voltammogram studies of hematite nanowire electrodes revealed active electron transfer at the hematite/cell interface. Notably, under a positive bias and light illumination, the hematite electrode immersed in a live cell culture was able to produce 150% more photocurrent than that in the abiotic control of medium or dead culture, suggesting a photoenhanced electrochemical interaction between hematite and Shewanella. The enhanced photocurrent was attributed to the additional redox species associated with MR-1 cells that are more thermodynamically favorable to be oxidized than water. Long-term operation of the hematite solar MPS with light on/off cycles showed stable current generation up to 2 weeks. Fluorescent optical microscope and scanning electron microscope imaging revealed that the top of the hematite nanowire arrays were covered by a biofilm, and iron determination colorimetric assay revealed 11% iron loss after a 10-day operation. To our knowledge, this is the first report on interfacing a photoanode directly with electricigens in a MFC system. Such a system could open up new possibilities in solar-microbial device that can harvest solar energy and recycle biomass simultaneously to treat wastewater, produce electricity, and chemical fuels in a self-sustained manner.

Identification of microbial communities in open and closed circuit bioelectrochemical MBRs by high-throughput 454 pyrosequencing

Two bioelectrochemical membrane bioreactors (MBRs) developed by integrating microbial fuel cell and MBR technology were operated under closed-circuit and open-circuit modes, and high-throughput 454 pyrosequencing was used to investigate the effects of the power generation on the microbial community of bio-anode and bio-cathode. Microbes on the anode under open-circuit operation (A_O) were enriched and highly diverse when compared to those on the anode under closed-circuit operation (A_C). However, among the cathodes the closed-circuit mode (C_C) had richer and more diverse microbial community compared to the cathode under open-circuit mode (C_O). On the anodes A_O and A_C, Proteobacteria and Bacteroidetes were the dominant phyla, while Firmicutes was enriched only on A_C. Deltaproteobacteria affiliated to Proteobacteria were also more abundant on A_C than A_O. Furthermore, the relative abundance of Desulfuromonas, which are well-known electrogenic bacteria, were much higher on A_C (10.2%) when compared to A_O (0.11%), indicating that closed-circuit operation was more conducive for the growth of electrogenic bacteria on the anodes. On the cathodes, Protebacteria was robust on C_C while Bacteroidetes was more abundant on C_O. Rhodobacter and Hydrogenophaga were also enriched on C_C than C_O, suggesting that these genera play a role in electron transfer from the cathode surface to the terminal electron acceptors in the bioelectrochemical MBR under closed-circuit operation.

A comprehensive review of microbial electrochemical systems as a platform technology

Microbial electrochemical systems (MESs) use microorganisms to covert the chemical energy stored in biodegradable materials to direct electric current and chemicals. Compared to traditional treatment-focused, energy-intensive environmental technologies, this emerging technology offers a new and transformative solution for integrated waste treatment and energy and resource recovery, because it offers a flexible platform for both oxidation and reduction reaction oriented processes. All MESs share one common principle in the anode chamber, in which biodegradable substrates, such as waste materials, are oxidized and generate electrical current. In contrast, a great variety of applications have been developed by utilizing this in situ current, such as direct power generation (microbial fuel cells, MFCs), chemical production (microbial electrolysis cells, MECs; microbial electrosynthesis, MES), or water desalination (microbial desalination cells, MDCs). Different from previous reviews that either focus on one function or a specific application aspect, this article provides a comprehensive and quantitative review of all the different functions or system constructions with different acronyms developed so far from the MES platform and summarizes nearly 50 corresponding systems to date. It also provides discussions on the future development of this promising yet early-stage technology.

Biological photovoltaics: intra- and extra-cellular electron transport by cyanobacteria

A large variety of new energy-generating technologies are being developed in an effort to reduce global dependence on fossil fuels, and to reduce the carbon footprint of energy generation. The term 'biological photovoltaic system' encompasses a broad range of technologies which all employ biological material that can harness light energy to split water, and then transfer the resulting electrons to an anode for power generation or electrosynthesis. The use of whole cyanobacterial cells is a good compromise between the requirements of the biological material to be simply organized and transfer electrons efficiently to the anode, and also to be robust and able to self-assemble and self-repair. The principle that photosynthetic bacteria can generate and transfer electrons directly or indirectly to an anode has been demonstrated by a number of groups, although the power output obtained from these devices is too low for biological photovoltaic devices to be useful outside the laboratory. Understanding how photosynthetically generated electrons are transferred through and out of the organism is key to improving power output, and investigations on this aspect of the technology are the main focus of the present review.

Mixotrophic operation of photo-bioelectrocatalytic fuel cell under anoxygenic microenvironment enhances the light dependent bioelectrogenic activity

Electrogenic activity of photo-bioelectrocatalytic /photo-biological fuel cell (PhFC) was evaluated in a mixotrophic mode under anoxygenic microenvironment using photosynthetic consortia as biocatalyst. An acetate rich wastewater was used as anolyte for harnessing energy along with additional treatment. Mixotrophic operation facilitated good electrogenic activity and wastewater treatment associated with biomass growth. PhFC operation documented feasible microenvironment for the growth of photosynthetic bacteria compared to algae which was supported by pigment (total chlorophyll and bacteriochlorophyll) and diversity analysis. Pigment data also illustrated the association between bacterial and algal species. The synergistic interaction between anoxygenic and oxygenic photosynthesis was found to be suitable for PhFC operation. Light dependent deposition of electrons at electrode was relatively higher compared to dark dependent electron deposition under anoxygenic condition. PhFC documented for good volatile fatty acids removal by utilizing them as electron donor. Bioelectrochemical behavior of PhFC was evaluated by voltammetric and chronoamperometry analysis.

Rhodobase, a meta-analytical tool for reconstructing gene regulatory networks in a model photosynthetic bacterium

We present Rhodobase, a web-based meta-analytical tool for analysis of transcriptional regulation in a model anoxygenic photosynthetic bacterium, Rhodobacter sphaeroides. The gene association meta-analysis is based on the pooled data from 100 of R. sphaeroides whole-genome DNA microarrays. Gene-centric regulatory networks were visualized using the StarNet approach (Jupiter, D.C., VanBuren, V., 2008. A visual data mining tool that facilitates reconstruction of transcription regulatory networks. PLoS ONE 3, e1717) with several modifications. We developed a means to identify and visualize operons and superoperons. We designed a framework for the cross-genome search for transcription factor binding sites that takes into account high GC-content and oligonucleotide usage profile characteristic of the R. sphaeroides genome. To facilitate reconstruction of directional relationships between co-regulated genes, we screened upstream sequences (-400 to +20bp from start codons) of all genes for putative binding sites of bacterial transcription factors using a self-optimizing search method developed here. To test performance of the meta-analysis tools and transcription factor site predictions, we reconstructed selected nodes of the R. sphaeroides transcription factor-centric regulatory matrix. The test revealed regulatory relationships that correlate well with the experimentally derived data. The database of transcriptional profile correlations, the network visualization engine and the optimized search engine for transcription factor binding sites analysis are available at http://rhodobase.org.

Microbial solar cells: applying photosynthetic and electrochemically active organisms

Microbial solar cells (MSCs) are recently developed technologies that utilize solar energy to produce electricity or chemicals. MSCs use photoautotrophic microorganisms or higher plants to harvest solar energy, and use electrochemically active microorganisms in the bioelectrochemical system to generate electrical current. Here, we review the principles and performance of various MSCs in an effort to identify the most promising systems, as well as the bottlenecks and potential solutions, for "real-life" MSC applications. We present an outlook on future applications based on the intrinsic advantages of MSCs, specifically highlighting how these living energy systems can facilitate the development of an electricity-producing green roof.

A review of the substrates used in microbial fuel cells (MFCs) for sustainable energy production

Microbial fuel cells (MFCs) have gained a lot of attention in recent years as a mode of converting organic waste including low-strength wastewaters and lignocellulosic biomass into electricity. Microbial production of electricity may become an important form of bioenergy in future because MFCs offer the possibility of extracting electric current from a wide range of soluble or dissolved complex organic wastes and renewable biomass. A large number of substrates have been explored as feed. The major substrates that have been tried include various kinds of artificial and real wastewaters and lignocellulosic biomass. Though the current and power yields are relatively low at present, it is expected that with improvements in technology and knowledge about these unique systems, the amount of electric current (and electric power) which can be extracted from these systems will increase tremendously providing a sustainable way of directly converting lignocellulosic biomass or wastewaters to useful energy. This article reviews the various substrates that have been explored in MFCs so far, their resulting performance, limitations as well as future potential substrates.

Photosynthetic microbial fuel cells with positive light response

The current study introduces an aerobic single-chamber photosynthetic microbial fuel cell (PMFC). Evaluation of PMFC performance using naturally growing fresh-water photosynthetic biofilm revealed a weak positive light response, that is, an increase in cell voltage upon illumination. When the PMFC anodes were coated with electrically conductive polymers, the rate of voltage increased and the amplitude of the light response improved significantly. The rapid immediate positive response to light was consistent with a mechanism postulating that the photosynthetic electron-transfer chain is the source of the electrons harvested on the anode surface. This mechanism is fundamentally different from the one exploited in previously designed anaerobic microbial fuel cells (MFCs), sediment MFCs, or anaerobic PMFCs, where the electrons are derived from the respiratory electron-transfer chain. The power densities produced in PMFCs were substantially lower than those that are currently reported for conventional MFC (0.95 mW/m(2) for polyaniline-coated and 1.3 mW/m(2) for polypyrrole-coated anodes). However, the PMFC did not depend on an organic substrate as an energy source and was powered only by light energy. Its operation was CO(2)-neutral and did not require buffers or exogenous electron transfer shuttles.

Self-sustained phototrophic microbial fuel cells based on the synergistic cooperation between photosynthetic microorganisms and heterotrophic bacteria

A sediment-type self-sustained phototrophic microbial fuel cell (MFC) was developed to generate electricity through the synergistic interaction between photosynthetic microorganisms and heterotrophic bacteria. Under illumination, the MFC continuously produced electricity without the external input of exogenous organics or nutrients. The current increased in the dark and decreased with the light on, possibly because of the negative effect of the oxygen produced via photosynthesis. Continuous illumination inhibited the current production while the continuous dark period stimulated the current production. Extended darkness resulted in a decrease of current, probably because of the consumption of the organics accumulated during the light phase. Using color filters or increasing the thickness of the sediment resulted in a reduction of the oxygen-induced inhibition. Molecular taxonomic analysis revealed that photosynthetic microorganisms including cyanobacteria and microalgae predominated in the water phase, adjacent to the cathode and on the surface of the sediment. In contrast, the sediments were dominated by heterotrophic bacteria, becoming less diverse with increasing depth. In addition, results from the air-cathode phototrophic MFC confirmed the light-induced current production while the test with the two-chamber MFC (in the dark) indicated the presence of electricigenic bacteria in the sediment.