Wenduo Lu, Yuening Song, Chuanqi Liu et al.

Fermentation • 2023

Microbial electrochemical CO2 reduction and in-situ biogas upgrading can effectively reduce the CO2 content in biogas produced during anaerobic digestion, thereby reducing CO2 emissions and achieving carbon reduction. pH is an important indicator in this process as it can significantly change the solubility and forms of CO2 in the aquatic phase. This study comprehensively evaluated the optimal pH value from the perspectives of methane upgrading performance and electron utilization efficiency and observed and analyzed the morphology of the biofilm on the electrode surface and the microbial community in the cathodic region under optimal conditions. The results showed that the optimal pH was 6.5; methane content reached ~88.3% in the biogas; methane production reached a maximum of 22.1 ± 0.1 mmol·d−1, with an increase in methane production compared to the control group reaching a maximum of 1.7 mmol·d−1; and CO2 conversion rate reached ~22.9%. A dense biofilm with a thickness of 51.3 μm formed on the electrode surface, with Methanobacterium being the dominant genus, with a high relative abundance of 69.3%, and Geobacter had a relative abundance of 20.1%. The above findings have important guiding significance for the practical application of methane upgrading.

Zeena Wang, Dunzhu Li, Yunhong Shi et al.

Sensors • 2023

Hydrogel materials have been used extensively in microbial electrochemical technology (MET) and sensor development due to their high biocompatibility and low toxicity. With an increasing demand for sensors across different sectors, it is crucial to understand the current state within the sectors of hydrogel METs and sensors. Surprisingly, a systematic review examining the application of hydrogel-based METs to sensor technologies has not yet been conducted. This review aimed to identify the current research progress surrounding the incorporation of hydrogels within METs and sensors development, with a specific focus on microbial fuel cells (MFCs) and microbial electrolysis cells (MECs). The manufacturing process/cost, operational performance, analysis accuracy and stability of typical hydrogel materials in METs and sensors were summarised and analysed. The current challenges facing the technology as well as potential direction for future research were also discussed. This review will substantially promote the understanding of hydrogel materials used in METs and benefit the development of electrochemical biosensors using hydrogel-based METs.

E. Klein, Melanie T. Knoll, J. Gescher

Microbial Biotechnology • 2023

Microbial electrochemical systems (MESs) are a highly versatile platform technology with a particular focus on power or energy production. Often, they are used in combination with substrate conversion (e.g., wastewater treatment) and production of value‐added compounds via electrode‐assisted fermentation. This rapidly evolving field has seen great improvements both technically and biologically, but this interdisciplinarity sometimes hampers overseeing strategies to increase process efficiency. In this review, we first briefly summarize the terminology of the technology and outline the biological background that is essential for understanding and thus improving MES technology. Thereafter, recent research on improvements at the biofilm–electrode interface will be summarized and discussed, distinguishing between biotic and abiotic approaches. The two approaches are then compared, and resulting future directions are discussed. This mini‐review therefore provides basic knowledge of MES technology and the underlying microbiology in general and reviews recent improvements at the bacteria–electrode interface.

Jie Cheng, Meng Liu, Xin Su et al.

Environmental Science & Technology • 2023

Adding conductive materials to the cathode of a microbial electrochemical system (MES) can alter the route of interspecies electron transfer and the kinetics of reduction reactions. We tested reductive dechlorination of γ-hexachlorocyclohexane (γ-HCH), along with CH4 production, in MES systems whose cathodes were coated with conductive magnetite nanoparticles (NaFe), biochar (BC), magnetic biochar (FeBC), or anti-conductive silica biochar (SiBC). Coating with NaFe enriched electroactive microorganisms, boosted electro-bioreduction, and accelerated γ-HCH dechlorination and CH4 production. In contrast, BC only accelerated dechlorination, while FeBC only accelerated methanogenesis, because of their assemblies of functional taxa that selectively transferred electrons to those electron sinks. SiBC, which decreased electro-bioreduction, yielded the highest CH4 production and increased methanogens and the mcrA gene. This study provides a strategy to selectively control the distribution of electrons between reductive dechlorination and methanogenesis by adding conductive or anti-conductive materials to the MES's cathode. If the goal is to maximize dechlorination and minimize methane generation, then BC is the optimal conductive material. If the goal is to accelerate electro-bioreduction, then the best addition is NaFe. If the goal is to increase the rate of methanogenesis, adding anti-conductive SiBC is the best.

Kartik Aiyer, Lucinda Elizabeth Doyle

Electrochemistry • 2023

Developed as the earliest application of electroactive microorganisms, microbial fuel cells (MFCs) have been intensively researched over the past two decades. The original goal of harnessing microbially-derived electricity for power generation has been partially successful, particularly for low-wattage devices. Beyond this, MFC technology has proven versatile with additional applications including as a research tool for the enrichment and isolation of novel electroactive microorganisms, as early-detection biosensors, for wastewater treatment and (with supply of additional energy) for microbial electrosynthesis. This chapter provides a comprehensive landscape of modern MFC technology. A brief historical perspective is followed by a primer of MFCs for the beginner. Next, a detailed discussed of the current knowledge on microbial electroactivity, best practices for characterisation, and practicalities of MFC operation is presented. The chapter concludes with an examination of present and emerging MFC applications.

Dan-Dan Zhai, Yang-Chun Yong

Chemical Biotechnology and Bioengineering • 2015

Microbial electrochemical systems (MES) are a relatively new electrochemistry research field and hold great potential for various applications by taking advantage of the metabolic diversity of microorganisms and the flexibility of electrochemical techniques. During the past few decades, a large variety of interesting and novel applications such as energy-generating wastewater treatment, bioelectrochemical CO2 fixation and transformation, bioelectrochemical hydrogen synthesis, desalination, and waste heating energy harvesting have been demonstrated. Meanwhile, multidisciplinary research to improve the performance/efficiency of MES is attracting widespread interest. In the light of deeper understanding of MES through chemistry and biology studies, new interdisciplinary chemical biotechnology research taking advantage of both disciplines is emerging and becoming a hot research topic in this area. In this chapter, the great contributions of chemical bioengineering to MES are highlighted. In particular, augmentation of extracellular electron transfer between bacteria and the electrode by chemicals, conductive polymers, and carbon nanomaterials are reviewed. Moreover, other chemical bioengineering approaches to improve MES through manipulation of cell physiology, such as by surfactant and metal ion treatment, quorum sensing signaling modulation, and cell immobilization, are also emphasized. Future directions for chemical bioengineering of MES are also discussed.

Carlos A. Ramírez-Vargas, Amanda Prado, Carlos A. Arias et al.

Preprints.org • 2018

Microbial electrochemical technologies (MET) rely on the presence of the metabolic activity of electroactive bacteria for the use of solid-state electrodes for oxidizing different kind of compound, that could lead to the synthesis of chemicals, bioremediation of polluted matrices, the treatment of contaminants of interest, as well as the recovery of energy. Keeping in mind those possibilities, since the beginning of the present century, there has been a growing interest in the use of electrochemical technologies for wastewater treatment, and if possible with simultaneous power generation. In the last years, there has been a growing interest to explore the possibility of merging MET with constructed wetlands, to offer a new option of intensified wetland system that could keep a high performance with a lower footprint. Based on that interest, this paper explains the general principles of MET, and the different known extracellular electron transfer mechanisms ruling the interaction between electroactive bacteria and potential solid-state electron acceptors. Also, the adoption of those principles for the development of MET set-ups for simultaneous wastewater treatment and power generation, and the challenges that the technology face. Ultimately, the most recent developments in set-ups that merges MET with constructed wetlands are presented and discussed.

Abhimanyu Sharma, Karan Singh, HarKamal Singh et al.

Resource Recovery from Industrial Wastewater through Microbial Electrochemical Technologies • 2024

The high salinity and complicated chemical makeup of industrial effluent create a serious threat to the environment. Traditional treatment procedures are not always successful in eradicating water impurities, whereas desalination operations can be both expensive and requires a lot of energy usage. To deal with that, microbial desalination cell (MDC) technology has emerged as a viable option in recent years for the purification of industrial wastewater. The purpose of this chapter is to introduce readers to MDCs and their potential uses in industrial wastewater treatment by discussing their basic concepts, essential parts, performance evaluation, and potential in the future. In addition, the challenges and prospective strategies for enhancing MDC effectiveness and commercial viability are discussed.

Sudeep Popat, Prathap Parameswaran, César Torres

ECS Meeting Abstracts • 2014

Anode-respiring bacteria (ARB) catalyze the complete oxidation of organic compounds (e.g. acetate, glucose) into electrical current and carbon dioxide. ARB produce a biofilm at the electrode surface, where even cells on the outer part of the biofilm are participating in current production. Our team uses a variety of electrochemical techniques in order to characterize electron transport responses from various ARB. Through these experiments, we have observed a complex response to anode potential that allows ARB, such as G. sulfurreducens , to optimize their efficiency in electron transport. Identifying this complex behavior allows us to better understand and predict the response of ARB to different conditions in microbial electrochemical cells (MXCs). While the topic of electron transport is the focus of most ARB research, ionic transport is the most important factor in determining rate-limiting and potential loss processes. ARB require near-neutral pH in the medium to grow, differing from chemical fuel cells commonly employed, which run under acidic or alkaline conditions. This pH requirement results in a major transport limitation, as H + ions (now in mM range) should be transported from anode to cathode to achieve electron neutrality. In an MXC anode, H + ions accumulate in the ARB biofilm, creating an acidification that limits current generation. We have identified and characterized ARB that work outside the neutral pH range, including Geoalkalibacter ferrihydriticus and Thermoanaerobacter pseudethanolicus , that allow us to operate MXCs at either acidic or basic conditions. Meanwhile, at the cathode, local gradients leading to pH > 12 is typical in MXC operation. As a consequence, the pH gradient results in Nernstian concentration overpotential of > 300 mV. Thus, understanding and controlling ionic transport in MXCs is essential to ensure an efficient operation. I will discuss our current efforts to characterize and overcome ionic transport limitations in order to develop efficient MXC processes.

Felipe Ernesto Torres Rojas

• 2022

Esta tesis interdisciplinaria combina el estudio de los principios fundamentales biológicos, químicos y físicos de los microorganismos reductores de perclorato electroquímicamente activos con el diseño y la ingeniería para desarrollar reactores bioelectroquímicos para el tratamiento sostenible de dos contaminantes emergentes en el agua: perclorato y clorato. Para lograr este objetivo, primero, se evaluaron las capacidades electroactivas de Dechloromonas sp. CS-1, Clostridiodales sp. CS-2, Paenibacillus sp. CS-3 y Oerskovia sp. CS-4. Estas bacterias aisladas de un sitio natural del norte de Chile solo en Dechloromonas sp. CS-1 y Clostridiodales sp. CS-2 exhibieron una respuesta electroactiva por voltamperometría cíclica obteniendo peaks de corriente a -651 mV y -303 mV (vs. Ag / AgCl), respectivamente. Cada bacteria se probó en una BER mediante la realización de una prueba de cronoamperometría a un potencial de -550 mV vs. Ag / AgCl durante seis días. El estudio electroquímico demostró una eficiencia coulómbica (EC) de 93,328% y 45,643% con una tasa de eliminación de 26,721 ± 2,934 mg L-1 día-1 y 17,289 ± 1,032 mg L -1 día-1, respectivamente. Los resultados sugieren una reducción completa de perclorato para CS-1 (es decir, reacción de 8 electrones) y una reducción incompleta para CS-2 (es decir, reacción de 2 electrones). Este trabajo pionero de bioprospección reveló la actividad electroactiva de Dechloromonas sp. CS-1 y Clostridiodales sp. CS-2 sin el uso de transportadores electroquímicos para la reducción de perclorato. En segundo lugar, se demostró la reducción bioelectroquímica del clorato utilizando BER con un voltaje de aplicación de 0,4 Volt. Los BER ensayados se inocularon con D. agitata CKB. Un experimento de 44 días en el modo de flujo ascendente de recirculación reveló una salida de corriente y eliminación de clorato de 1,54 ± 0,26 µA y 251,5 ± 76,1 mg L-1 respectivamente. Luego, las BER se operaron en modo discontinuo durante 71 días, aumentando el rendimiento a 4,49 ± 0,70 µA y 607,3 ± 64,5 mg L-1. La caracterización electroquímica reveló un pico catódico a -550 ± 8 mV vs. Ag / AgCl y un cálculo de 6 electrones involucrados en la reacción de biorreducción del clorato. A través de este estudio, fue posible establecer, por primera vez, el mecanismo bioelectroquímico de reducción de clorato por D. agitata. Finalmente, se llevó a cabo una modificación química en el electrodo de carbono para mejorar el rendimiento de los BERs utilizados para eliminar estos oxianiones. De acuerdo con la espectroscopía de fotoelectrones de rayos X, la espectroscopía RAMAN y la espectroscopía IR, fue posible describir la funcionalización del electrodo de la tela de carbono. Los resultados muestran que la modificación fue principalmente de los grupos carboxilados (-COOH, -C-O-C-) y nitrogenados (-NH3)+. El electrodo modificado se utilizó en un BER inoculado con Dechloromnoas sp. CS-1, demostrando una mejor respuesta que los controles sin tratamiento durante una prueba de cronoamperometría de 17 días, aplicando un potencial de -500 mV vs Ag / AgCl. El BER con el electrodo modificado mostró una EC de 90,794 ± 9,157% y una tasa de reducción de perclorato de 0,345 ± 0,007 mol m-3 día-1 que fue superior a otros informes en la literatura. Por lo tanto, estos resultados muestran la sinergia positiva entre los microorganismos reductores de perclorato electroactivo y los electrodos modificados para mejorar las BER y eliminar los oxianiones del agua. Luego, al combinar estos tres capítulos (artículos), esta tesis tiene el objetvo de introducir o guiar el camino para el desarrollo de nuevas tecnologías electroquímicas microbianas sostenibles destinadas a eliminar el perclorato y el clorato del agua.

Jingyu Wang, Yongchao Xie, Yi Chen et al.

ChemRxiv • 2024

Most microorganisms grow in assemblages with chemical gradients that influence, and are influenced by, metabolism. pH gradient plays an important role in various metabolism processes. Understanding the effects of the pH gradient on metabolism and regulation within microbial assemblages is important for microbial physiology. However, the complexity of the microbial environment makes it hard to decouple the effect of the pH gradient from other species. Therefore, an artificial pH gradient is required to reveal the correlation of the pH gradient and microbial physiology. Here, we demonstrated a controllable pH gradient plate by using electrochemical proton coupled electron transfer reaction based on interdigital electrodes. The morphology design of the interdigital electrodes enables a pH gradient at the level of 10 micrometers, which was demonstrated under confocal microscope with a resolution of 1 micrometer. The electrochemical system also achieved a fast time response of ten seconds. In summary, this platform provided a flexible pH gradient with a high spatial and temporal resolution.

Sharvari Sunil Gadegaonkar, Ülo Mander, Mikk Espenberg

• 2023

Excess nitrogen has caused environmental issues by polluting the air and water. Many different processes help remove nitrogen compounds from contaminated soils and waters, and the presence of oxygen is one of the most decisive factors. Denitrification in anaerobic conditions is considered the main removal processes of excessive nitrogen, although lately discovered anaerobic ammonium oxidation (ANAMMOX) and dissimilatory nitrate reduction to ammonium (DNRA) may also have an important role in nitrogen elimination of different systems. To a lesser extent, also nitrification can contribute to nitrogen elimination in watery systems. All previously pointed out removal mechanisms occur in the constructed wetlands and could even be enhanced with the bio-electrochemical systems (BES). BES exploit the ability of the electroactive microorganisms to reduce the oxides of nitrogen.We analyzed various articles treating nitrate (NO3) polluted water in BES and normalized their NO3 removal efficiencies to a common unit (mg liter−1 day−1). We analyzed the effect of various factors such as electrode materials, working mode, type of inoculum, number of chambers, systems’ capacity and the microbial community structure on the NO3 removal efficiencies. The highest removal efficiencies were displayed by granular carbon and carbon cloth used as cathode and anode material, respectively. The electrode materials and operational parameters, such as working mode and number of chambers, were deemed important by the random forest classification algorithm. Continuous mode of operation, denitrifying microbes as inoculum type, and two chamber systems have displayed optimum NO3 removal efficiencies. Feature selection using random forest classification showed the type of inoculum and capacity of the BES were unimportant factors. Proteobacteria and Firmicute were the prominent phyla observed in BES treating NO3 polluted water. Besides the denitrification (abundance of narG, nirS, nirK, nosZI, and nosZII genes) process in BES, there is evidence of electrochemical support for anaerobic ammonium oxidation (ANAMMOX) (abundance of hzsB or ANAMMOX specific 16S rRNA gene) and dissimilatory NO3 reduction to ammonium (DNRA) (abundance of nrfA gene) processes. The results of this work aid in understanding the prevalent processes in the BES and help to build efficient BES for optimum NO3 removal.

B. Monisha, Veena Gayathri Krishnaswamy

Resource Recovery from Industrial Wastewater through Microbial Electrochemical Technologies • 2024

Water pollution, which appears to be a global concern, is mostly caused by the discharge of several toxic compounds by various industries such as textiles, pulp and paper, and dairy sectors. Dairy wastewaters are difficult to manage because they include a wide range of contaminants. Wastewater treatment is an expensive and energy-intensive method that requires substantial energy to fulfil the energy demands of rising human population. Renewable energy-based wastewater treatment is a feasible option for overcoming these concerns. Microbial fuel cell (MFC) technology has shown promise as a sustainable strategy, combining energy and nutrient recovery to generate bioelectricity. MFCs can be employed in wastewater treatment, green power generation, biohydrogen synthesis, and ecologically friendly sewage treatment processes. This chapter focuses on different types of industrial wastewater and their physical, chemical, and biological treatment methods, as well as MFC technology and its techniques utilized for treating dairy wastewater, providing beneficial knowledge of combining it with currently employed conventional wastewater treatment procedures to achieve the degradation of various dairy contaminants. The chapter also discusses the types, processes, applications, challenges, and future prospects of wastewater treatment-related MFCs, with the goal of industrialization in the near future, leading to greener fuels and a more sustainable environment.

Nyiko Maurice Chauke, Nomvano Mketo

Resource Recovery from Industrial Wastewater through Microbial Electrochemical Technologies • 2024

This chapter discusses the utilization of proton transfer membranes (PTMs) in microbial fuel cells (MFCs) for wastewater treatment and hydrogen generation. Conventional wastewater treatment methods often consume significant energy and generate harmful by-products, but integrated MFCs offer a promising alternative. In MFCs, microorganisms facilitate oxidation and reduction reactions, hydrogen generation, and converting the chemical energy in wastewater into direct electric current. This allows wastewater to be used as a valuable resource for bioelectricity, biofuels, hydrogen, and other valuable by-products. The selection of appropriate microorganisms, electrode materials, designs, PTMs, and process parameters significantly influences the performance of MFCs. Optimal pH and temperature conditions are crucial for promoting bacterial growth and overall efficiency. However, an important challenge in MFCs is the effective separation process. Various types of PTMs, including ion exchange, composite, porous, and ceramic membranes, have been explored. Despite advancements, issues such as high membrane costs, insufficient ion or proton separation, molecule diffusion, substrate crossover, and biofouling still pose challenges. Nevertheless, MFCs offer a promising solution for wastewater treatment by combining efficient treatment processes with the generation of valuable resources. To successfully implement and commercialize MFCs, it is crucial to address challenges related to membrane separation and optimize process parameters. Continued research and development efforts in this field have the potential to revolutionize wastewater treatment practices, enhance resource recovery, and contribute to a more sustainable future.

Riti Thapar Kapoor, Mohd Rafatullah

Resource Recovery from Industrial Wastewater through Microbial Electrochemical Technologies • 2024

A huge amount of wastewater released from industries flow into different water resources such as rivers. Industrial effluents can be regarded as an important resource for water, nutrients and energy. Microbial fuel cell (MFC), a green eco-friendly approach can be applied for the treatment of wastewater with electricity generation concomitantly. It is a novel strategy to generate clean, renewable, safe green energy to maintain a clean environment. MFC technology can be used for effluent treatment, biochemical oxygen demand and chemical oxygen demand elimination, sulphate and removal of toxic metal and denitrification. MFC has an advantage as compared with other wastewater treatment methods because of certain unique properties such as energy and economic benefits, less effect on the environment and high stability. However, the operation of MFCs also has multiple setbacks such as short life span, high cost, membrane fouling and so on. MFC technology shows a pivotal function in solving problems of energy crisis and waste management. This chapter describes current applications of MFC technology for the treatment of industrial effluents with cost-effective energy generation and covers the gap by highlighting key future research areas to improve its performance.

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IWA Publishing eBooks • 2024

There is currently a critical gap in knowledge regarding the application of microbial electrochemical technologies (METs) in industrial wastewater treatment and resource recovery. Resource Recovery from Industrial Wastewater through Microbial Electrochemical Technologies fills this gap by offering a comprehensive guide for researchers, students, and industry professionals interested in the field of microbial electrochemistry and industrial waste management. The book covers recent advancements in METs, focusing on their application in various industries to treat wastewater while recovering valuable resources, thus promoting sustainability. It provides an in-depth exploration of different industrial processes that generate wastewater, detailing the characteristics and quantities of effluents produced. The specifics of METs are also covered, including various configurations, electrode and membrane materials, microbial cultures, and catalysts used in these technologies. Additionally, the valuable resources that can be recovered through METs, such as biofuels, bioelectricity, and other commodity chemicals, are examined. This book serves as a practical guide for implementing METs in industrial settings, offering strategies to enhance the yield of recovered resources. It also offers insights into how these technologies can be integrated into existing industrial processes to achieve both economic and environmental benefits. Resource Recovery from Industrial Wastewater through Microbial Electrochemical Technologies is essential reading for research scholars, postgraduate students, and scientists working in the fields of microbial electrochemistry and industrial waste management. Industry professionals involved in research and development will benefit from the foundational knowledge and practical guidelines needed to implement METs in their industries. By bridging the existing knowledge gap, this book aims to advance the field of industrial wastewater treatment and contribute to more sustainable industrial practices. ISBN: 9781789063806 (paperback) ISBN: 9781789063813 (eBook) ISBN: 9781789063820 (ePub)

Bin Lai

Microbial Biotechnology • 2023

Abstract Microbial electrochemical technology (MET) has proven to be a promising solution to overcome the redox and energy metabolic constraints, enabling high yields of biosynthesis beyond stoichiometric limits. While there is room for improvement in extracellular electron transfer rates and productivity of the target compounds, it is crucial to think in advance about which bioprocess could be electrified and what would face major challenges. In this opinion paper, I presented and addressed interfacial electron transfer capacity of MET, whether built on biofilm or planktonic cells, and also discussed the upper limits of the MET system for biosynthesis of chemicals accordingly. Potential future application scenarios of different MET were also briefly addressed. This opinion paper aims to encourage the community to rethink the design and development of microbial electrochemical technologies for potential future applications in industrial biotechnology.

Himanshi Sen, Monika Sogani, Jayana Rajvanshi et al.

Resource Recovery from Industrial Wastewater through Microbial Electrochemical Technologies • 2024

The escalating environmental degradation resulting from an exponential growth in waste generation and improper disposal practices necessitates immediate consideration and innovative solutions. The concept of a circular economy, which emphasizes the potential of solid wastes to be transformed into valuable raw materials, offers a promising approach to address this pressing issue. In this chapter, we explore the transformation of industrial waste into electrode and membrane materials for microbial electrochemical technologies (METs). Various synthetic techniques have been identified, enabling the conversion of industrial waste into viable materials for METs. The proposed framework encompasses critical aspects, including waste pre-treatment, raw material extraction, fabrication, and characterization processes, as well as the performance evaluation of electrodes and membranes derived from waste sources. We thoroughly examine the advantages and limitations associated with waste-derived electrodes and membranes, providing valuable insights into their potential applications and challenges. By harnessing waste resources for electrode and membrane production, we not only contribute to environmental sustainability but also advance toward greener practices and a more sustainable future. The favorable material properties inherent in waste resources and the availability of suitable processing facilities render this approach particularly promising. This chapter elucidates the vast potential of using industrial waste to synthesize novel electrode and membrane materials for METs. By adopting a circular economy mindset and promoting waste recycling and reutilization, we can achieve significant benefits in terms of environmental preservation and resource optimization. The integration of waste-derived materials into METs paves the way for a more sustainable and efficient approach to address environmental challenges.

Elena Emelyanova

Archives of Microbiology Research • 2023

A reactor microbial sensor device and a membrane microbial sensor device are low-cost and convenient analytical tools, which are useful for assessment of constitutiveness and inducibility of enzyme systems for transport and initial metabolism of substrate in microbial cells. By means of these devices, it was shown for fusaric acid (5-butilpicolinic acid) and Bacillus subtilis cells that an inducible protein-transporter system without enzyme system of initial metabolism of fusaric acid exists in cells of Bacillus subtilis.

Joanne M. Jones, Marianne Walch, Florian B. Mansfeld

CORROSION 1991 • 1991

Abstract SEM studies have shown that all surfaces of 4140 steel with epoxy and nylon coatings were heavily colonized with a diverse assemblage of bacteria. Breaches in these coatings after exposure to mixed communities of marine microorganisms were detected using SEM and EDAX analyses. These mixed communities consisted of anaerobic and facultatively anaerobic marine species (sulfate reducers and non-sulfate reducers). Epoxy, but not nylon coatings were degraded by a non-marine mixed, microbial community isolated from water trapped in the cargo area of a navy aircraft. Some epoxy coatings showed visible signs of coating deterioration (i.e., pinpoint holes, blistering and peeling) after a one month exposure to the mixed communities. EIS was used to assess the properties of the exposed, coated 4140 steel in laboratory testing.

Isha Raval, Upexa Patel, Ekta Patel et al.

Resource Recovery from Industrial Wastewater through Microbial Electrochemical Technologies • 2024

Synthesis of value-added gases using biological systems has been accepted as one of the important scientific endeavors for many decades. The generation of electricity and the production of acetic acid, formic acid, methane, hydrogen, and other value-added products can all be done with the help of recent technological advancements that use wastewater as a raw material. These optimized biosynthesis processes which are environmentally friendly and cost effective can be considered for scale-up level experiments. Microbial electrochemical technology combines microbes, electrochemistry, and material science that can be amalgamated to efficiently convert the chemical energy contained in the organic molecules. The wastewater and sludge effluent from industrial sector can be used as a probable nutrient source for the microbes. Factors such as nutrient availability, toxicity, variation in microbial population, operating parameters, and so on, have great influence on the yield and quality of the gaseous fuel. This chapter summarizes recent updates on microbial electrochemical systems being utilized for gaseous recovery and parameters that influence productivity of gases.

Praveen Rajpurohit, Manaswini Behera

Resource Recovery from Industrial Wastewater through Microbial Electrochemical Technologies • 2024

With the increase in demand for the improvement of microbial electrochemical technologies (METs) for bioelectricity generation and product recovery, light-assisted METs have developed as an option. The use of light helps in the electrohydrogenesis process at the cathode. Various variants of light-assisted METs employ photosynthetic bacteria/algae, anode and photocathode assembly, and so on. Microbial fuel cells (MFCs) using photosynthetic bacteria, bioelectrodes, and hybrids of photoelectrocatalytic cells (PECs) and MFCs show superior performance compared to individual MFCs. The dye-sensitized solar cell coupling of MFCs helps enhance electrohydrogenesis and H2 production. This book chapter deals with all types of light-assisted METs. The effect of the configuration, electrode material, electrolyte, and physical and chemical factors on the performance of light-assisted METs is discussed. The miniaturizing and stacking of reactors in solar-assisted METs is a current approach showing superior performance. The value-added products formed at the cathodic compartment, carbon-based or H2 gas, are discussed and reported literature compared with the enhanced recovery of existing METs.

Md. Nazir, Rajdeep Shaw, Rajib Bandopadhyay

Resource Recovery from Industrial Wastewater through Microbial Electrochemical Technologies • 2024

The global energy crisis due to the diminishing of fossil fuels with an increasing demand for power has a major impact on the environment and the health of humans. On the contrary, waste production has been increasing for many decades. Among wastewaters, industrial wastewater is a challenging threat in today's era. To generate bioenergy as an alternative energy source, wastewater treatment and nutrient recovery by microbial electrochemical technologies (METs) are very efficient. Different METs are being developed, some of them being very efficient; for example, microbial electrolysis cells produce hydrogen or methane from organic matter when electric current is applied. Microbial electrochemical snorkel is a microbial fuel cell which has a short circuit. Geobacter sp. produces 556 mW/m2 power from food wastes. An alga Shewanella sp. produces 50 mW/m2 from dairy wastewater. Therefore, resource recovery technology using desirable microorganisms is very convenient.

Anthony Chukwubuikem, Carola Berger, Ahmed Mady et al.

Microbial Biotechnology • 2021

Summary Pseudomonas aeruginosa produces phenazine‐1‐carboxylic acid (PCA) and pyocyanin (PYO), which aid its anaerobic survival by mediating electron transfer to distant oxygen. These natural secondary metabolites are being explored in biotechnology to mediate electron transfer to the anode of bioelectrochemical systems. A major challenge is that only a small fraction of electrons from microbial substrate conversion is recovered. It remained unclear whether phenazines can re‐enter the cell and thus, if the electrons accessed by the phenazines arise mainly from cytoplasmic or periplasmic pathways. Here, we prove that the periplasmic glucose dehydrogenase (Gcd) of P . aeruginosa and P . putida is involved in the reduction of natural phenazines. PYO displayed a 60‐fold faster enzymatic reduction than PCA; PCA was, however, more stable for long‐term electron shuttling to the anode. Evaluation of a Gcd knockout and overexpression strain showed that up to 9% of the anodic current can be designated to this enzymatic reaction. We further assessed phenazine uptake with the aid of two molecular biosensors, which experimentally confirm the phenazines’ ability to re‐enter the cytoplasm. These findings significantly advance the understanding of the (electro) physiology of phenazines for future tailoring of phenazine electron discharge in biotechnological applications.

Simeng Li, Gang Chen

Batteries • 2018

Microbial fuel cells (MFCs) and microbial electrolysis cells (MECs) are promising bioelectrochemical systems (BESs) for simultaneous wastewater treatment and energy/resource recovery. Unlike conventional fuel cells that are based on stable chemical reactions, these BESs are sensitive to environmental and operating conditions, such as temperature, pH, external resistance, etc. Substrate type, electrode material, and reactor configuration are also important factors affecting power generation in MFCs and hydrogen production in MECs. In order to discuss the influence of these above factors on the performance of MFCs and MECs, this study analyzes published data via data synthesis and meta-analysis. The results revealed that domestic wastewater would be more suitable for treatment using MFCs or MECs, due to their lower toxicity for anode biofilms compared to swine wastewater and landfill leachate. The optimal temperature was 25–35 °C, optimal pH was 6–7, and optimal external resistance was 100–1000 Ω. Although systems using carbon cloth as the electrodes demonstrated better performance (due to carbon cloth’s large surface area for microbial growth), the high prices of this material and other existing carbonaceous materials make it inappropriate for practical applications. To scale up and commercialize MFCs and MECs in the future, enhanced system performance and stability are needed, and could be possibly achieved with improved system designs.

Qiaochu Liang, Takahiro Yamashita, Ryoko Yamamoto-Ikemoto et al.

Sensors • 2018

Biochemical oxygen demand (BOD) is a widely used index of water quality in wastewater treatment; however, conventional measurement methods are time-consuming. In this study, we analyzed a novel flame-oxidized stainless steel anode (FO-SSA) for use as the probe of bioelectrochemical system (BES)-based biosensors to monitor the BOD of treated swine wastewater. A thinner biofilm formed on the FO-SSA compared with that on a common carbon-cloth anode (CCA). The FO-SSA was superior to the CCA in terms of rapid sensing; the response time of the FO-SSA to obtain the value of R2 > 0.8 was 1 h, whereas the CCA required 4 h. These results indicate that the FO-SSA offers better performance than traditional CCAs in BES biosensors and can be used to improve biomonitoring of wastewater.

Theresia Desy Askitosari, Amanda Larasati

E3S Web of Conferences • 2023

The widespread use of pesticides for agricultural purposes results in their presence in the environment. Pesticide occurrence is causing potential negative impacts on human health and environmental deterioration in general. One of the interdisciplinary field to implement a technology for converting and conserving resources is bioelectrochemistry. An integrated system based on bioelectrochemical processes, namely Bioelectrochemical System (BES), has been well developed to date. The application of BES to remove various materials in the bioremediation process has been well established in the combination with diverse technologies. The set up of integrated BES with Granular Activated Carbon (GAC) is one of the promising solutions to enhance the removal of the pesticide in water. The BES in situ has been implemented to remove contaminants in groundwater. This mini-review discusses the recent development of pesticide removal and environmental remediation using bioelectrochemical approaches, offering new insight into the big scope of green technology application.

Xinyu Wang, Defeng Xing, Nanqi Ren

RSC Advances • 2016

The biocathode bioelectrochemical system (bioc-BES) was used for p -nitrophenol (PNP) degradation with sodium bicarbonate as the carbon source.

Nastaran Khodaparastasgarabad, Manon Couture, Jesse Greener

ChemRxiv • 2024

To target development of bioelectrochemical systems, we developed an advanced microfluidic method to identify reaction bottlenecks in the metabolic activity of a pure-culture Geobacter sulfurreducens electroactive biofilm (EAB). The microfluidic system was devised to include perpendicular flow orientation for improved boundary layer uniformity and was combined with an embedded 3-electrode system to accurately apply a constant potential during the entire experimental duration. A 3-sensor temperature control system provided the basis of accurate temperature pulsing, which modified the EAB metabolic activity over short time intervals relative to the bacterial doubling rate. The system, together with the unique ability to control hydrodynamic, electrochemical, and thermal conditions, was used as the basis for an Arrhenius approach to obtain activation energy barrier values at different growth times, acetate concentrations, and flow rates. The results indicated that bottlenecks in the overall metabolic activity after 1 month of growth time were related to electron transfer through extracellular cytochrome c. After the EAB further matured to 4 months old, the bottleneck appeared to switch to enzyme-driven acetate oxidation. Based on this hypothesis, we observed after 4-months, that strong increases in effective enzyme concentration were primarily obtained by increasing flow rate, and secondarily by increasing acetate concentration.

Z. A. Gasieva, A. S. Galushko, Yu. V. Khomyakov et al.

Агрохимия • 2024

The possibility of increasing the electrogenic properties of the root environment through the use of potential electron carriers, humic acids (HA), was studied. For this purpose, a bioelectrochemical cell has been created, including electrode systems introduced into the planters to remove the potential difference formed during the development of plants. Using the example of Typhoon lettuce, it was determined that an increase in the concentration of HA in the root environment by 2 times allowed to increase the voltage by 7–16% of the control variant, depending on the place of their introduction. The best result – a more stable generation of a high potential difference from the early periods of vegetation was typical for the variant with addition of HA to the upper electrode area – the average voltage value for it was 418 ± 29 mV and a specific power of 0.2 MW/m2. A number of physicochemical parameters of near-electrode regions in plant bioelectrochemical systems have been studied: electrical conductivity, pH, concentration of humic acids at the end of the growing season. The potential electroactivity of microorganisms in the root environment of lettuce has been revealed. It is shown that the ability of humic acids to play the role of a redox mediator in a bioelectrochemical system largely depends on the place of their concentration.

Lina María Agudelo-Escobar, Santiago Erazo Cabrera, Claudio Avignone Rossa

Frontiers in Chemical Engineering • 2022

The primary production of coffee involves the extensive use of water resources, since it is not only used for irrigation of coffee plantations, but it is also required in large volumes for the processing of the coffee berry to obtain high quality green beans. It is calculated that for every kg of dry coffee grain produced, up to 40 L of water are consumed, and its disposal represents a significant environmental problem, since most coffee growers are small producers with no access to efficient technologies for wastewater treatment. This situation leads to these liquid wastes to be discarded untreated in natural water sources, generating environmental pollution and public health problems. Bioelectrochemical Systems (BES) have been proposed as an alternative to conventional wastewater treatments, either as a primary bioremediation strategy or for secondary wastewater treatment systems. Among BES, microbial fuel cells (MFCs) are designed to exploit the metabolic capability of andophilic microorganisms to degrade the organic matter present in the waste. Anodophilic microorganisms use electrodes as terminal electron acceptors, generating a flow of electrons that can be used in the generation of electricity. In this work, we evaluated the ability of native microbial communities to degrade the organic matter present in wastewater from the coffee agroindustry and its electrogenic potential for the co-generation of electricity was evaluated using an MFC device developed by the authors. Wastewater samples obtained at different stages of the coffee wet process were used as inoculum and feedstocks. The system was operated in fed-batch, in both open and closed-circuit conditions, for 60 days. The degree of decontamination or bioremediation of the wastewater was assessed by measurements of physicochemical parameters. For the characterization of the native microbial community, microscopic and molecular techniques were used and the electrogenic potential was established by assessing the electrochemical performance of the system. With the proposed bioelectrochemical system, a reduction of up to 70% of the initial content of organic matter of the residual water from the coffee benefit was achieved, and open circuit voltages of up to 400 mV were recorded, comparable to those reported for conventional air breathing cathode MFC.

Shashikanth Gajaraj

• 2014

[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI AT AUTHOR'S REQUEST.] Much attention has been drawn by bioelectrochemical systems (BES) in the past years for wastewater treatment, due to its potential for enhanced wastewater treatment and resource recovery with added advantages in terms of energy generation, environmental footprint, operating stability and economics. This dissertation focuses on the potential to improve treatment efficiency of different wastewater components when assisted by BES. Modified Ludzack-Ettinger (MLE) process and membrane bioreactor (MBR) process assisted by microbial fuel cells (MFC) showed improved the nitrate-nitrogen removal efficiencies by upto 31% and 20% respectively, and reduced sludge produced by 11% and 6% respectively over the control reactors. While the unique design of the cathode significantly reduced physical membrane fouling, all other bioreactor performance was unaffected. Microbial electrolysis cell (MEC) assisted Cr[VI] reduction was faster in 60 days as compared to 69 days with MFC assisted systems and 85 days with the control. The total Cr removal efficiencies in the control system and the MFC or MEC-assisted systems were 20%, 55%, and 65%, respectively, demonstrating the ability of BES in assisting wastewater remediation process. Finally, MECs incorporated into anaerobic digestion resulted in increased production of methane of 9.4 % or 8.5% with both glucose and activated sludge respectively as the substrate. The integration of MEC had no impact on acetoclastic methanogens involved in anaerobic digestion, but significantly increased the populations of hydrogenotrophic methanogens, especially Methanobacteriales. In conclusion, the integration of BES with conventional wastewater treatment and sludge digestion process enhanced the removal of organic matter, nitrate and toxic metals while supporting healthy microbial consortia.

Nastaran Khodaparastasgarabad, Manon Couture, Jesse Greener

ChemCatChem • 2024

Abstract To target development of bioelectrochemical systems, we developed an advanced microfluidic method to identify reaction bottlenecks in the metabolic activity of a pure‐culture Geobacter sulfurreducens electroactive biofilm (EAB). The microfluidic system was devised to include perpendicular flow orientation for improved boundary layer uniformity and was combined with an embedded 3‐electrode system to accurately apply a constant potential during the entire experimental duration which lasted se. A 3‐sensor temperature control system provided the basis of accurate temperature pulsing, which modified the EAB metabolic activity over short time intervals relative to the bacterial doubling rate. The system, together with the unique ability to control hydrodynamic, electrochemical, and thermal conditions, was used as the basis for an Arrhenius approach to obtain activation energy barrier values at different growth times, acetate concentrations, and flow rates. The results indicated that bottlenecks in the overall metabolic activity after 1 month of growth time were related to electron transfer through extracellular cytochrome c. After the EAB further matured to 4 months old, the bottleneck appeared to switch to enzyme‐driven acetate oxidation. Based on this hypothesis, we observed after 4‐months, that strong increases in effective enzyme concentration were primarily obtained by increasing flow rate, and secondarily by increasing acetate concentration

Taiki Adachi, Yuki Kitazumi, Osamu Shirai et al.

ECS Meeting Abstracts • 2020

Modern societies have energy and environmental issues such as fossil fuel depletion and excessive carbon dioxide (CO 2 ) emissions. Therefore, an effective use of renewable energy resources instead of fossil fuels is essential for the development of a sustainable energy economy. Particularly, dihydrogen (H 2 ), formic acid (HCOOH) and sunlight are expected to be new energy sources. These advantages are as follows; H 2 emits no harmful substances in use; HCOOH has a high energy density and is a liquid fuel that can be easily stored and transported; sunlight is universally available on the ground. However, the electrochemical conversion of the above energy has the following problems; a catalyst for H 2 oxidation, platinum, is expensive; byproducts such as carbon monoxide are generated in CO 2 reduction at usual electrodes; solar cell materials are sometimes expensive and environmentally harmful. In order to overcome these problems, we focused on biocatalysts, which are ecofriendly, and have high catalytic performance and selectivity under mild conditions. Furthermore, we constructed two electro-enzymatic energy conversion devices: an H 2 /HCOO - interconversion system and a bio-solar cell. In an H 2 /HCOO - interconversion system, we applied two enzymes which catalyze bidirectional redox reactions: [NiFe]-hydrogenase from Desulfovibrio vulgaris Miyazaki F (H 2 ase; EC 1.12.2.1) and tungsten-containing formate dehydrogenase from Methylobacterium extorquens AM1 (FoDH1; EC 1.2.1.2). H 2 ase and FoDH1 catalyze the H + /H 2 and CO 2 /HCOO - interconversion, respectively, and we attempted to generate HCOO - without external power supply by the coupling of two bioelectrocatalytic reactions: direct electron transfer (DET)-type H 2 oxidation catalyzed by H 2 ase and mediated electron transfer (MET)-type CO 2 reduction catalyzed by FoDH1 using benzyl viologen (BV) as a mediator (H 2 + CO 2 → HCOO - + H + ). H 2 ase was adsorbed on a bioanode functionalized with p -phenylenediamine, which leads to orientations suitable for DET-type bioelectrocatalysis of H 2 ase, while FoDH1 and BV were adsorbed on a biocathode. In addition, gas-diffusion-type electrodes were employed for high-speed supply of gaseous substrates. The two electrodes were short-circuited in a cell, and CO 2 and H 2 gasses were spontaneously supplied from the outside of the biocathode and the bioanode, respectively. The amount of formate in the electrolyte solution increased almost linearly with the reaction time. On the other hand, when the feed gasses were replaced with Ar gas to remove CO 2 and H 2 from the system, the amount of formate decreased with the time. This is due to the reversed reaction: (HCOO - + H + → H 2 + CO 2 ). These results mean that the difference in equilibrium potentials of the H + /H 2 and CO 2 /HCOO - couples determines the driving force of the reaction, which is reversed depending on conditions, and the interconversion between H 2 and HCOO - was experimentally demonstrated. A bio-solar cell is an electric energy device mimicking natural photosynthesis and extracts excited electrons outside the photosynthetic system. In this study, we constructed a bio-solar cell using the thylakoid membrane from spinach as an anodic photo-bioelectrocatalyst which oxidizes water (H 2 O) to dioxygen (O 2 ) and the recombinant bilirubin oxidase (BOD; EC 1.3.3.5) produced by expressing the gene of BOD from Myrothecium verucarria in Pichia pastoris as a cathodic bioelectrocatalyst which reduces O 2 to H 2 O. In addition, we investigated the characteristics of a thylakoid membrane-functionalized bioanode with a mediator of hexaammineruthenium(III/II) ion ([Ru(NH 3 ) 6 ] 3+/2+ ), which has the following characteristics: fast electrode kinetics, high stability and solubility, and somewhat low redox potential. The photo-driven bioanode prepared by applying the mixture of thylakoid membranes and water-dispersed multi-walled carbon nanotubes on a gold-spattered indium tin oxide (ITO) electrode showed the photocurrent caused by MET-type photo-bioelectrocatalytic H 2 O oxidation in a buffer (pH 7.0) containing 5 mM Ru(NH 3 ) 6 Cl 3 under the light condition. The performance of the bioanode (0.2 mA cm - 2 at 0 V vs. Ag|AgCl|sat. KCl) is better than that in the previous report using 1,2-naphthoquinone as a mediator. Then, a bio-solar cell was constructed by combining the bioanode with the BOD-modified gas-diffusion-type biocathode, and O 2 was spontaneously supplied from the outside of the biocathode. The cell exhibited an open-circuit voltage of 0.61 V and a maximum power density of 50 μW cm - 2 at a cell voltage of 0.42 V under quiescent conditions. To the best of our knowledge, the power density of our cell unit is the highest among those reported for the bio-solar cells to date. These works lead to the artificial photosynthetic system, which generates H 2 or HCOO - from sunlight and H 2 O (and CO 2 ), and they might be a breakthrough for the sustainable energy economy.

Deepak Pant, Sandipam Srikanth, Karolien Vanbroekhoven

Qatar Foundation Annual Research Conference Proceedings Volume 2016 Issue 1 • 2016

Industrial revolution, a consequence of the rapid economic growth, has contributed to ever increasing demand for energy and has resulted in about 40% rise in the atmospheric concentration of carbon dioxide, from 280 ppm in 1750 to 400 ppm in 2015. Abundant use of fossil fuels has become a cause of concern due to their adverse effects on the environment, particularly related to the emission of carbon dioxide (CO 2 ), a major contributor of GHG. In this context, CO 2 capture and is storage or transformation gained significance in the recent research scenario. Various matured CO 2 capture technologies such as amine based capture, needs high energy input, especially in desorption process and are also not sustainable in nature. Alternatively, carbonic anhydrase (CA) proved to be more efficient in capturing CO 2 at faster rate and also needs less energy input for desorption process. However, utilization of the captured CO 2 is more important rather than its capture, to close the carbon cycle and recycle it. In this direction, bioelectrochemical system (BES) is presenting an exciting opportunity with a possibility of simultaneous CO 2 capture and biotransformation to value-added products in a sustainable way. Both microbes and enzymes were studied as catalyst in BES, though the application of enzymes is less foreseen. Present study demonstrates the biotransformation of CO 2 to ethanol using a cascade of dehydrogenases [formate dehydrogenase (FateDH), formaldehyde dehydrogenase (FaldDH) and alcohol dehydrogenase (AlcDH)] together on the electrode of BES. Further to that, carbonic anhydrase (CA) was also included in the cascade and found that the product yield increased by 15% contributing to ethanol production rate of ∼0.6 kg/m 3 /h along with current density of ∼2 A/m 2 . When the FaldDH was excluded from the cascade also, there is no reduction in productivity of ethanol. It was surprising to get ethanol instead of methanol but based on literature, it is also possible for the production of ethanol directly from formic acid, which is economically more viable.

Martí Aliaguilla, Daniele Molognoni, Pau Bosch-Jimenez et al.

E3S Web of Conferences • 2022

Industrial activity has resulted in heavy metals anthropogenic contamination of groundwater, especially in industrial or mining areas. Bioelectrochemical systems (BES) can be used for metals removal and recovery from aqueous solutions. In the framework of GREENER project, double-chamber BES have been adopted to treat groundwater from industrial sites containing copper, nickel and zinc (Cu, Ni and Zn), among other contaminants. Two operation modes, (i) short-circuited microbial fuel cell (MFC), and (ii) power supply driven microbial electrolysis cell (MEC, poisoning the cathode at -0.4 V vs. Ag/AgCl), were studied for metals removal at lab-scale. Two control reactors were run to evaluate metals adsorption on cathodes and membranes, and the effect of anolyte composition. Synthetic water containing different concentrations of Cu, Ni and Zn were treated, and metals removal pathways were studied. MEC and MFC performed similarly and the highest removal efficiencies were 97.1±3.6%, 50.7±6% and 74,5% for Cu, Ni and Zn respectively, from initial concentrations in the range of 1.1-1.5 mM.

Jiyun Baek, Changmam Kim, Young Eun Song et al.

Preprints.org • 2018

The conversion of C1 gas feedstock, such as carbon monoxide (CO), into useful platform chemicals has attracted considerable interest in industrial biotechnology. One conversion method is electrode-based electron transfer to microorganisms using bioelectrochemical systems (BESs). In this BES system, acetate is the predominant component of various volatile fatty acids (VFAs). To appropriately separate and concentrate the produced acetate, a BES type electrodialysis cell with an anion exchange membrane was constructed and evaluated under various operational conditions, such as the applied external current. The higher acetate flux of 23.9 mmol/m2∙hr was observed under -15 mA current in an electrodialysis-based bioelectrochemical system. In addition, the initial acetate concentration affects the separation efficiency and transportation rate. The maximum flux appeared at 48.6 mmol/m2∙hr when the acetate concentration was 100mM, whereas the effect of the initial pH of the anolyte was negligible. The acetate flux was 14.9 mmol/m2∙hr when actual fermentation broth from BES based CO fermentation, was used as a catholyte. A comparison of the synthetic medium with the actual fermentation medium suggests that unknown substances and metabolites in the actual medium interfere with electrodialysis in the BES. These results provide information on the separation and optimal concentration for VFAs produced by C1 gas fermentation through electrodialysis, and a combination of a BES and electrodialysis.

André Gemünde, Jonas Gail, Dirk Holtmann

ChemSusChem • 2023

Abstract Vibrio natriegens promises to be a new standard biotechnological working organism since it grows extraordinarily fast, its productivity surpasses E. coli by far, and genomic tools are getting readily available. Recent studies provided insights into its extracellular electron transfer pathway, revealing it to be similar to other well‐known electroactive organisms. Therefore, we aimed to show for the first time that V. natriegens donates electrons from its metabolism to an electrode by direct contact as well as via an artificial redox mediator. Our results demonstrate current densities up to 196 μA cm −2 using an artificial mediator. Via direct electron transfer, 6.6 μA cm −2 were achieved within the first 24 h of cultivation. In the mediated system, mainly formate, acetate, and succinate were produced from glucose. These findings favor V. natriegens over established electroactive organisms due to its superior electron‐transfer capabilities combined with an outstanding metabolism.

Bin Lai, Anh Vu Nguyen, Jens O Krömer

Methods and Protocols • 2019

Industrial fermentation in aerobic processes is plagued by high costs due to gas transfer limitations and substrate oxidation to CO2. It has been a longstanding challenge to engineer an obligate aerobe organism, such as Pseudomonas putida, into an anaerobe to facilitate its industrial application. However, the progress in this field is limited, due to the poor understanding of the constraints restricting its anoxic phenotype. In this paper, we provide a methodological description of a novel cultivation technology for P. putida under anaerobic conditions, using the so-called microbial electrochemical technology within a bioelectrochemical system. By using an electrode as the terminal electron acceptor (mediated via redox chemicals), glucose catabolism could be activated without oxygen present. This (i) provides an anoxic-producing platform for sugar acid production at high yield and (ii) more importantly, enables systematic and quantitative characterizations of the phenotype of P. putida in the absence of molecular oxygen. This unique electrode-based cultivation approach offers a tool to understand and in turn engineer the anoxic phenotype of P. putida and possibly also other obligate aerobes.

Xueming Zhang, Shaohui Zhang, Tao Huang et al.

Research Square • 2021

Abstract Low-grade ores, tailings and solid wastes contain small amounts of valuable heavy metals. Improper disposal of these results in the waste of resources and contamination of soil or groundwater. Accordingly, the treatment and recycling of low-grade ores, tailings and solid wastes attracted much attention recently. Bioelectrochemical system, an innovative technology for the removal and recovery of heavy metals, has been further developed and applied in recent years. In current study, the low-grade chalcopyrite was bioleached with the assistance of microbial fuel cells. Copper extraction along with electricity generation from the low-grade chalcopyrite were achieved in the column bioleaching process assisted by MFCs. Results showed that after 197 days bioleaching of low-grade chalcopyrite, 423.9 mg copper was extracted from 200 g low-grade chalcopyrite and the average coulomb production reached 1.75 C/d. The introduction of MFCs into bioleaching processes promoted the copper extraction efficiency by 2.7 times (3.62% vs. 1.33%), mainly via promoting ferrous oxidation, reducing ORP and stimulating bacterial growth. This work provides a feasible method for the treatment and recycling of low-grade ores, tailings and solid wastes. But balancing energy consumption of aeration and circulation frequency and chemicals consumption of acid to improve the copper extraction efficiency need further investigation.