Overview on the developments of microbial fuel cells

Microbial fuel cells (MFCs) are a promising technology for electricity production from a variety of materials, such as natural organic matter, complex organic waste or renewable biomass, and can be advantageously combined with applications in wastewater treatment. The problem with MFCs is that they are technically still very far from attaining acceptable levels of power output, since the performance of this type of fuel cells is affected by limitations based on irreversible reactions and processes occurring both on the anode and cathode side. However, in the last years, there has been a growing amount of work on MFCs which managed to increase power outputs by an order of magnitude.The present review article discusses a number of biological and engineering aspects related to improvement of MFC performance including the effect of important parameters, such as pH, temperature, feed rate, shear stress and organic load. The recent progresses on scale-up MFC are summarized and the different modelling approaches to describe the different biological and transport phenomena in MFCs are also provided.     

微生物燃料电池在毒性物质检测中的应用

微生物燃料电池(Microbial fuel cell,MFC)利用微生物整体作为催化剂催化底物将化学能直接转化为电能,是一种极具应用前景的生物电化学技术。微生物在阳极氧化还原有机物产生电子并传递给阳极,电子通过外电路传递至阴极后将电子释放给阴极中的氧化剂,从而产生电流。当有毒物质进入MFC,微生物活性降低,电子传递量变少,电流降低,而电流的产生与微生物活性呈线性关系,据此可检测样品的毒性。本文主要介绍了微生物燃料电池在毒性物质抗生素、重金属离子、有机污染物、酸等方面的研究,并分析了微生物燃料电池存在的问题及未来研究方向,以期不久的将来微生物燃料电池能付之使用。     

Microbial fuel cells as an alternative energy source: current status

Microbial fuel cell (MFC) technology is an emerging area for alternative renewable energy generation and it offers additional opportunities for environmental bioremediation. Recent scientific studies have focused on MFC reactor design as well as reactor operations to increase energy output. The advancement in alternative MFC models and their performance in recent years reflect the interests of scientific community to exploit this technology for wider practical applications and environmental benefit. This is reflected in the diversity of the substrates available for use in MFCs at an economically viable level. This review provides an overview of the commonly used MFC designs and materials along with the basic operating parameters that have been developed in recent years. Still, many limitations and challenges exist for MFC development that needs to be further addressed to make them economically feasible for general use. These include continued improvements in fuel cell design and efficiency as well scale-up with economically practical applications tailored to local needs.     

Electricity generation from carbon monoxide and syngas in a microbial fuel cell

Electricity generation in microbial fuel cells (MFCs) has been a subject of significant research efforts. MFCs employ the ability of electricigenic bacteria to oxidize organic substrates using an electrode as an electron acceptor. While MFC application for electricity production from a variety of organic sources has been demonstrated, very little research on electricity production from carbon monoxide and synthesis gas (syngas) in an MFC has been reported. Although most of the syngas today is produced from non-renewable sources, syngas production from renewable biomass or poorly degradable organic matter makes energy generation from syngas a sustainable process, which combines energy production with the reprocessing of solid wastes. An MFC-based process of syngas conversion to electricity might offer a number of advantages such as high Coulombic efficiency and biocatalytic activity in the presence of carbon monoxide and sulfur components. This paper presents a discussion on microorganisms and reactor designs that can be used for operating an MFC on syngas.     

Microfabricated Microbial Fuel Cell Arrays Reveal Electrochemically Active Microbes

Microbial fuel cells (MFCs) are remarkable “green energy” devices that exploit microbes to generate electricity from organic compounds. MFC devices currently being used and studied do not generate sufficient power to support widespread and cost-effective applications. Hence, research has focused on strategies to enhance the power output of the MFC devices, including exploring more electrochemically active microbes to expand the few already known electricigen families. However, most of the MFC devices are not compatible with high throughput screening for finding microbes with higher electricity generation capabilities. Here, we describe the development of a microfabricated MFC array, a compact and user-friendly platform for the identification and characterization of electrochemically active microbes. The MFC array consists of 24 integrated anode and cathode chambers, which function as 24 independent miniature MFCs and support direct and parallel comparisons of microbial electrochemical activities. The electricity generation profiles of spatially distinct MFC chambers on the array loaded with Shewanella oneidensis MR-1 differed by less than 8%. A screen of environmental microbes using the array identified an isolate that was related to Shewanella putrefaciens IR-1 and Shewanella sp. MR-7, and displayed 2.3-fold higher power output than the S. oneidensis MR-1 reference strain. Therefore, the utility of the MFC array was demonstrated.     

Flow shear stress applied in self-buffered microbial fuel cells

The development of renewable and clean energy has been the priority of the global research field due to the urgent effects of climate change. Microbial fuel cell (MFC) is recognized as a sustainable approach to simultaneously generate power and treat wastewater through the employment of microorganisms as catalyst. The use of buffer solution in the wastewater treatment makes the commercial application of MFCs challenging due to their environmental impact and high costs. This work uses rotational motion to generate the flow stress in the anode chamber of the MFCs to enhance biofilm growth and mass transfer that leads to an overall performance improvement of the system. The effects on pH, chemical oxygen demand (COD), and power density were evaluated under rotational speeds of the magnetic stirrer from 0 to 640 rpm. The influence of the stirrer was then assessed utilizing the same parameters specified for scenarios with and without buffer. The results reveal that at 480 rpm of stirring speed, the pH value was neutral with a maximum COD removal of 82 % for bufferless and 93 % for buffered scenarios. In addition, for bufferless operation at 480 rpm yielded a power density of 402 mWm⁻². The results of the flow stress analysis for bufferless and buffered MFCs are beneficial for the commercialization and future development of the system for wastewater treatment applications.     

Microbial fuel cells: novel biotechnology for energy generation

Microbial fuel cells (MFCs) provide new opportunities for the sustainable production of energy from biodegradable, reduced compounds. MFCs function on different carbohydrates but also on complex substrates present in wastewaters. As yet there is limited information available about the energy metabolism and nature of the bacteria using the anode as electron acceptor; few electron transfer mechanisms have been established unequivocally. To optimize and develop energy production by MFCs fully this knowledge is essential. Depending on the operational parameters of the MFC, different metabolic pathways are used by the bacteria. This determines the selection and performance of specific organisms. Here we discuss how bacteria use an anode as an electron acceptor and to what extent they generate electrical output. The MFC technology is evaluated relative to current alternatives for energy generation.     

Micro-sized microbial fuel cell: A mini-review

This review presents the development of micro-sized microbial fuel cells (including mL-scale and μL-scale setups), with summarization of their advantageous characteristics, fabrication methods, performances, potential applications and possible future directions. The performance of microbial fuel cells (MFCs) is affected by issues such as mass transport, reaction kinetics and ohmic resistance. These factors are manipulated in micro-sized MFCs using specially allocated electrodes constructed with specified materials having physically or chemically modified surfaces. Both two-chamber and air-breathing cathodes are promising configurations for mL-scale MFCs. However, most of the existing μL-scale MFCs generate significantly lower volumetric power density compared with their mL-counterparts because of the high internal resistance. Although μL-scale MFCs have not yet to provide sufficient power for operating conventional equipment, they show great potential in rapid screening of electrochemically microbes and electrode performance. Additional possible applications and future directions are also provided for the development of micro-sized MFCs.     

Assessment of organic removal in series- and parallel-connected microbial fuel cell stacks

Microbial fuel cells (MFCs) degrade organic contaminants in wastewater while simultaneously producing electricity, but must be stacked to yield adequate voltage and current. This study examined the evolution of the chemical oxygen demand (COD) removal rate and efficiency in two identical individual MFCs (i-MFCs) in series- and parallel-connected stacks (sc- and pc-MFCs, respectively) under batch and continuous operation. The stack voltage and current increased in the respective series and parallel connections of the two i-MFCs (MFC unit 1 and MFC unit 2). Voltage reversal was observed in the sc- MFC below an external load of 100 Ω. Regardless of occurrence of the voltage reversal, organic reduction between i-MFCs and sc-MFCs showed no significant difference (gap of < 9% and < 6% in COD removal rate and efficiency, respectively); additionally, organic removals between the two individual MFCs in series indicated differences less than 9% of COD removal rate and 5% of COD removal efficiency in batch mode. Continuous operation also yielded similar organic removals as the MFCs in individual and series connection (voltage reversal occurred) mode, even over 8 days operation. Parallel connection yielded identical organic removals and currents in the two individual MFCs of the pc-MFC, even though the two separate i-MFCs showed different organic removal rates and current productions. This study provides the guide for the application of stacked MFCs for power source and efficient organic pollutant removal in wastewater treatment process.     

微生物燃料电池生物质能利用现状与展望

作为一种新概念的废物处理与能源化技术,微生物燃料电池研究在过去10年里取得了长足的进步和技术突破。本文在简要介绍微生物燃料电池研究现状基础上,系统综述了该技术及与其他技术耦合在生物质能利用方面的最新研究进展,重点分析了其中存在的问题,并展望了该技术在生物质能转化和利用方面的研究前景。