G. Antonopoulou, Ilias Apostolopoulos, George Bampos et al.

Global NEST International Conference on Environmental Science & Technology • 2022

In the present study two identical two-chamber microbial electrolysis cells (MECs), fed with an acetate synthetic medium, were used for hydrogen production, using different anodic materials, i.e. commercial carbon fiber paper (CP) and graphite granules (GG). The effects of the applied voltage (i.e. 0.7 and 0.9 V) and of the acclimation procedure (direct potentiostatic operation as MEC or galvanostatic as microbial fuel cell, MFC) were assessed and the performance of both MECs was compared in terms of their biochemical and electrochemical characteristics.

Nuzahat Habibul, Y. Hu, Yunkun Wang et al.

Environmental Science & Technology • 2016

Plant-microbial fuel cell (PMFC) is a renewable and sustainable energy technology that generates electricity with living plants. However, little information is available regarding the application of PMFC for the remediation of heavy metal contaminated water or soil. In this study, the potential for the removal of heavy metal Cr(VI) using PMFC was evaluated, and the performance of the PMFC at various initial Cr(VI) contents was investigated. The Cr(VI) removal efficiency could reached 99% under various conditions. Both the Cr(VI) removal rates and the removal efficiencies increased with the increasing initial Cr(VI) concentration. Furthermore, the long-term operation of the PMFC indicated that the system was stable and sustainable for Cr(VI) removal. The mass balance results and XPS analysis results demonstrate that only a small amount of soluble Cr(III) remained in the PMFC and that most Cr(III) precipitated in the form of the Cr(OH)3(s) or was adsorbed onto the electrodes. The PMFC experiments of without acetate addition also show that plants can provide carbon source for MFC through secrete root exudates and bioelectrochemical reduction of Cr(VI) was the main mechanism for the Cr(VI) removal. These results extend the application fields of PMFC and might provide a new insight for Cr(VI) removal from wastewater or soil.

Mirna Valdez-Hernández, L. N. Acquaroli, J. Vázquez-Castillo et al.

Energy Sources, Part A: Recovery, Utilization, and Environmental Effects • 2022

ABSTRACT Plant and soil microbial fuel cells (PMFCs and SMFCs, respectively) are bioelectrochemical systems that produce energy using microorganisms as catalysts. This energy can be harvested; however, its impact on biological activity has seldom been explored. To reveal the main characteristics of this impact, we monitored four experimental designs for 20 days under open-sky conditions. The effect of PMFC/SMFC start-up on metabolism was evaluated by photosynthesis of Codiaeum variegatum and heterotrophic soil respiration to determine the short-term effects. To compare the results, a normalized parameter of power density, which considered the PMFC/SMFC configurations, solar irradiance, and soil temperature, was introduced. The highest energy was obtained for the PMFC configuration. The energy harvesting stimulated the photosynthetic rate of C. variegatum up to two times with respect to its normal values, while the heterotrophic soil respiration decreased 30%. Thus, in the PMFC and SMFC start-up operations, the increase in soil temperature due to energy harvesting suggests that soil temperature is the most relevant parameter influencing plant metabolism and energy generation. These results open a new pathway for understanding the bioregulation of plants/soil when subjected to energy harvesting.

Till Siepenkoetter, Urszula Salaj‐Kosla, Xinxin Xiao et al.

Electroanalysis • 2016

Abstract Nanoporous gold (NPG) fabricated by sputtering is a material of versatile morphology with pores whose size can be tailored to accommodate enzymes. The process of pore formation and the size of the pores in NPG are influenced by the composition of Au and Ag in the alloy used to prepare the electrodes together with the temperature and time period of the dealloying process. On increasing the time from 1 to 60 min and the temperature from 0.5 °C to 60.5 °C in concentrated HNO 3 , significant increases in the average pore diameters from 4.4 to 78 nm were observed with simultaneous decreases in the roughness factor (R f ). The pores of NPG were fully addressable regardless of the diameter, with R f increasing linearly up to an alloy thickness of 500 nm. The influence of the pore size on the bioelectrochemical response of redox proteins was evaluated using cytochrome c as a model system. The highest current densities of ca . 30 µA cm −2 were observed at cytochrome c modified NPG electrodes with an average pore size of ca. 10 nm. The pores in NPG were also tuned for the mediatorless immobilization of Myrothecium verrucaria bilirubin oxidase. High current densities of ca . 65 µA cm −2 were observed at Mv BOD modified NPG electrodes prepared by dealloying at 0.5 °C for 5 min with an average pore size of 8 nm, which is too small to accommodate the enzyme into the pores, indicating that the response was from enzyme adsorbed on the electrode surface.

Daniel D. Leicester, Jaime M. Amezaga, Andrew Moore et al.

Molecules • 2020

Bioelectrochemical systems (BES) have the potential to deliver energy-neutral wastewater treatment. Pilot-scale tests have proven that they can operate at low temperatures with real wastewaters. However, volumetric treatment rates (VTRs) have been low, reducing the ability for this technology to compete with activated sludge (AS). This paper describes a pilot-scale microbial electrolysis cell (MEC) operated in continuous flow for 6 months. The reactor was fed return sludge liquor, the concentrated filtrate of anaerobic digestion sludge that has a high chemical oxygen demand (COD). The use of a wastewater with increased soluble organics, along with optimisation of the hydraulic retention time (HRT), resulted in the highest VTR achieved by a pilot-scale MEC treating real wastewater. Peak HRT was 0.5-days, resulting in an average VTR of 3.82 kgCOD/m3∙day and a 55% COD removal efficiency. Finally, using the data obtained, a direct analysis of the potential savings from the reduced loading on AS was then made. Theoretical calculation of the required tank size, with the estimated costs and savings, indicates that the use of an MEC as a return sludge liquor pre-treatment technique could result in an industrially viable system.

Begüm Şen-Doğan, Meltem Okan, Nilüfer Afşar-Erkal et al.

Micromachines • 2020

Microbial Fuel Cells (MFCs) are biological fuel cells based on the oxidation of fuels by electrogenic bacteria to generate an electric current in electrochemical cells. There are several methods that can be employed to improve their performance. In this study, the effects of gold surface modification with different thiol molecules were investigated for their implementation as anode electrodes in micro-scale MFCs (µMFCs). Several double-chamber µMFCs with 10.4 µL anode and cathode chambers were fabricated using silicon-microelectromechanical systems (MEMS) fabrication technology. µMFC systems assembled with modified gold anodes were operated under anaerobic conditions with the continuous feeding of anolyte and catholyte to compare the effect of different thiol molecules on the biofilm formation of Shewanella oneidensis MR-1. Performances were evaluated using polarization curves, Electrochemical Impedance Spectroscopy (EIS), and Scanning Electron Microcopy (SEM). The results showed that µMFCs modified with thiol self-assembled monolayers (SAMs) (cysteamine and 11-MUA) resulted in more than a 50% reduction in start-up times due to better bacterial attachment on the anode surface. Both 11-MUA and cysteamine modifications resulted in dense biofilms, as observed in SEM images. The power output was found to be similar in cysteamine-modified and bare gold µMFCs. The power and current densities obtained in this study were comparable to those reported in similar studies in the literature.

Jiang-Hao Tian, Rémy Lacroix, Asim Ali Yaqoob et al.

Energies • 2023

Microbial electrochemical technologies now enable microbial electrosynthesis (MES) of organic compounds using microbial electrolysis cells handling waste organic materials. An electrolytic cell with an MES cathode may generate soluble organic molecules at a higher market price than biomethane, thereby satisfying both economic and environmental goals. However, the long-term viability of bioanode activity might become a major concern. In this work, a 15-L MES reactor was designed with specific electrode configurations. An electrochemical model was established to assess the feasibility and possible performance of the design, considering the aging of the bioanode. The reactor was then constructed and tested for performance as well as a bioanode regeneration assay. Biowaste from an industrial deconditioning platform was used as a substrate for bioanode. The chemical oxygen demand (COD) removal rate in the anodic chamber reached 0.83 g day−1 L−1 of anolyte. Acetate was produced with a rate of 0.53 g day−1 L−1 of catholyte, reaching a maximum concentration of 8.3 g L−1. A potential difference (from 0.6 to 1.2 V) was applied between the bioanode and biocathode independent of reference electrodes. The active biocathode was dominated by members of the genus Pseudomonas, rarely reported so far for MES activity.

Reyhaneh Yousefi, Mohammad Mahdi Mardanpour, Soheila Yaghmaei

Scientific Reports • 2021

Abstract This study presented the fabrication of macro and micro-scale microbial fuel cells (MFCs) to generate bioelectricity from oxalate solution and monitor the biodegradation in a micro-scale MFC for the first time. The maximum generated power density of 44.16 W m −3 in the micro-scale MFC elucidated its application as a micro-sized power generator for implantable medical devices (IMDs). It is also worthwhile noting that for the macro-scale MFC, the significant amounts of open circuit voltage, oxalate removal, and coulombic efficiency were about 935 mV, 99%, and 44.2%, respectively. These values compared to previously published studies indicate successful oxalate biodegradation in the macro-scale MFC. Regarding critical challenges to determine the substrate concentration in microfluidic outlets, sample collection in a suitable time and online data reporting, an analogy was made between macro and micro-scale MFCs to elicit correlations defining the output current density as the inlet and the outlet oxalate concentration. Another use of the system as an IMD is to be a platform to identify urolithiasis and hyperoxaluria diseases. As a versatile device for power generation and oxalate biodegradation monitoring, the use of facile and cheap materials (< $1.5 per device) and utilization of human excreta are exceptional features of the manufactured micro-scale MFC.

R. Ivanov, P. Genova

Sustainable Extraction and Processing of Raw Materials • 2023

Sediment microbial fuel cells (SMFCs) are bio-electrochemical systems in which the anode is placed in the anaerobic sediment and the cathode is immersed in the surface layer of water. Natural exoelectrogenic bacteria decompose organic compounds in sediment, producing electrons and protons. The electrons reach the cathode through an external electrical circuit, while the protons pass through the soil layer, which acts as a kind of membrane. Oxygen is in many cases the preferred electron acceptor due to its presence in the cathode region and its high potential. Heavy metal ions and other compounds can also be reduced on the cathode, which will increase the energy generated. Based on the above characteristics, SMFCs would be suitable for application as biosensors for monitoring water pollution with heavy metals. In the present study, the possibility of application of SMFCs as biosensors for water pollution with copper has been studied. A high correlation was found between the concentration of copper ions in the range 0,1 – 100 mg/L and the voltage generated by SMFC. The constructed SMFC based biosensor showed wider detection limits for copper compared to other authors' studies as the coefficient of determination reached 0,9911. Native exoelectrogenic bacteria were represented mainly by Geobacter, Clostridium, Anaeromixobacter and Bacillus.

Yangming Lei, M. Du, P. Kuntke et al.

ACS Sustainable Chemistry & Engineering • 2019

Phosphorus (P) removal and recovery from waste streams is essential for a sustainable world. Here, we updated a previously developed abiotic electrochemical P recovery system to a bioelectrochemical system. The anode was inoculated with electroactive bacteria (electricigens) which are capable of oxidizing soluble organic substrates and releasing electrons. These electrons are then used for the reduction of water at the cathode, resulting in an increase of pH close to the cathode. Hence, phosphate can be removed with coexisting calcium ions as calcium phosphate at the surface of the cathode with a much lower energy input. Depending on the available substrate (sodium acetate) concentration, an average current density from 1.1 ± 0.1 to 6.6 ± 0.4 A/m 2 was achieved. This resulted in a P removal of 20.1 ± 1.5% to 73.9 ± 3.7%, a Ca removal of 10.5 ± 0.6% to 44.3 ± 1.7% and a Mg removal of 2.7 ± 1.9% to 16.3 ± 3.0%. The specific energy consumption and the purity of the solids were limited by the relative low P concentration (0.23 mM) in the domestic wastewater. The relative abundance of calcium phosphate in the recovered product increased from 23% to 66% and the energy consumption for recovery was decreased from 224 ± 7 kWh/kg P to just 56 ± 6 kWh/kg P when treating wastewater with higher P concentration (0.76 mM). An even lower energy demand of 21 ± 2 kWh/kg P was obtained with a platinized cathode. This highlights the promising potential of bioelectrochemical P recovery from P-rich waste streams.

Vibeke B. Karlsen, Carlos Dinamarca

Reviews in Environmental Science and Bio/Technology • 2024

Abstract The increased demand for energy worldwide and the focus on the green shift have raised interest in renewable energy sources such as biogas. During biogas production, sulphide (H 2 S, HS − and S 2− ) is generated as a byproduct. Due to its corrosive, toxic, odorous, and inhibitory nature, sulphide is problematic in various industrial processes. Therefore, several techniques have been developed to remove sulphide from liquid and gaseous streams, including chemical absorption, chemical dosing, bioscrubbers, and biological oxidation. This review aims to elucidate electrochemical and bioelectrochemical sulphide removal methods, which are gaining increasing interest as possible supplements to existing technologies. In these systems, the sulphide oxidation rate is affected by the reactor design and operational parameters, including electrode materials, anodic potential, pH, temperature and conductivity. Anodic and bioanodic materials are highlighted here, focusing on recent material developments and surface modification techniques. Moreover, the review focuses on sulphide generation and inhibition in biogas production processes and introduces the prospect of removing sulphide and producing methane in one single bioelectrochemical reactor. This could introduce BESs for combined biogas upgrading and cleaning, thereby increasing the methane content and removing pollutants such as sulphide and ammonia in one unit.

Honghong Yuan, Yumeng Huang, Ouyuan Jiang et al.

Frontiers in Microbiology • 2022

Arsenate [As(V)] is a toxic metalloid and has been observed at high concentrations in groundwater globally. In this study, a bioelectrochemical system (BES) was used to efficiently remove As(V) from groundwater, and the mechanisms involved were systematically investigated. Our results showed that As(V) can be efficiently removed in the BES cathode chamber. When a constant cell current of 30 mA ( I cell , volume current density = 66.7 A/m 3 ) was applied, 90 ± 3% of total As was removed at neutral pH (7.20–7.50). However, when I cell was absent, the total As in the effluent, mainly As(V), had increased approximately 2–3 times of the As(V) in influent. In the abiotic control reactor, under the same condition, no significant total As or As(V) removal was observed. These results suggest that As(V) removal was mainly ascribed to microbial electrosorption of As(V) in sludge. Moreover, part of As(V) was bioelectrochemically reduced to As(III), and sulfate was also reduced to sulfides [S(–II)] in sludge. The XANES results revealed that the produced As(III) reacted with S(–II) to form As 2 S 3 , and the residual As(III) was microbially electroadsorbed in sludge. This BES-based technology requires no organic or chemical additive and has a high As(V) removal efficiency, making it an environment-friendly technique for the remediation of As-contaminated groundwater.

Jiaqi Ren, Gaoming Wu, Zheng Xia et al.

AIChE Journal • 2021

Abstract Low organic carbon‐to‐nitrogen ratio and existing sulfate (SO 4 2− ) in industrial wastewater limited nitrogen removal. Coupling SO 4 2− reduction with sulfide autotrophic denitrification provides a novel strategy. Herein, bioelectrochemical sulfate reduction was coupled with heterotrophic sulfate reduction to drive sulfide autotrophic denitrification. In this coupled system, total nitrogen (TN) removal efficiency was increased from ~25% to ~85% by inputting −45 mA electricity. With the help of supplying electrons to denitrification through SO 4 2− reduction, coulomb efficiency was improved to 61.5%. Also, bioelectrochemical sulfate reduction could improve sulfur recovery and thus increase TN removal efficiency. Furthermore, through tuning turnover numbers of SO 4 2− , high TN removal efficiency can be obtained at various concentrations of SO 4 2− . Moreover, main functional bacteria in this system were identified. Finally, ~75% TN removal efficiency was achieved with real wastewater in this system. Overall, this work offered a new approach for efficient nitrogen removal from industrial wastewater containing SO 4 2− .

Joanna Rodziewicz, Artur Mielcarek, Kamil Bryszewski et al.

Energies • 2022

An attempt was undertaken to determine indicators of energy consumption in bio-electro reactors (BERs) i.e., an aerobic rotating electrobiological disc contactor (REBDC) and an anaerobic sequencing batch biofilm reactor (SBBR), during contaminant removal from soilless tomato cultivation wastewater having a specific composition, i.e., high nitrate and phosphorus concentrations and low COD. Because of this specificity, the energy consumption during the treatment process was characterized by a cumulative indicator for simultaneous removal of phosphorus and nitrates—EEINUTRIENTSrem (electric energy consumption per unit of removed nutrient load, expressed as kWh/kgNUTRIENTSrem). Four values of direct current density were tested: 0.63, 1.25, 2.5, and 5.0 A/m2. The indicator values were compared at a hydraulic retention time (HRT) of 24 h. The study demonstrated that the values of electric energy consumption per unit of removed nutrient load determined in the anaerobic SBBR ranged from 30 to 464 kWh/kg NUTRIENTSrem and were lower than the values obtained in the aerobic REBCD, i.e., 80–1380 kWh/kg NUTRIENTSrem.

Wenjuan Zhao, YiZhao Gao, Yongli Zhao et al.

Biotechnology and Bioengineering • 2022

Abstract Generally, high bioelectroactivity of anodophilic biofilm favors high power generation of microbial fuel cell (MFC); however, it is not clear whether it can promote denitrification of MFC synchronously. In this study, we studied the impact of anodophilic biofilm bioelectroactivity on the denitrification behavior of air‐cathode MFC (AC‐MFC) in steady state and found that high bioelectroactivity of anodophilic biofilm not only favored high power generation of the AC‐MFC, but also promoted the growth of denitrifers at the anodes and strengthened denitrification. Anodophilic biofilms of AC‐MFC with various bioelectroactivity were acclimated at conditions of open circuit (OC), R ext of 1000 Ω and 20 Ω (denoted as AC‐MFC‐OC, AC‐MFC‐1000Ω, and AC‐MFC‐20Ω, respectively) and performed for over 100 days. Electrochemical tests and microbial analysis results showed that the anode of the AC‐MFC‐20Ω delivered higher current response of both oxidation and denitrification and had higher abundance of electroactive bacteria than the AC‐MFC‐OC, AC‐MFC‐1000Ω, demonstrating a higher bioelectroactivity of the anodophilic biofilms. Moreover, these electroactive bacteria favored the accumulation of denitrifers, like Thauera and Alicycliphilus , probably by consuming trace oxygen through catalyzing oxygen reduction. The AC‐MFC‐20Ω not only delivered a 61.7% higher power than the AC‐MFC‐1000Ω, but also achieved a stable and high denitrification rate constant (k DN ) of 1.9 h −1 , which was 50% and 40% higher than that of the AC‐MFC‐OC and AC‐MFC‐1000Ω, respectively. It could be concluded that the high bioelectroactivity of the anodophilic biofilms not only favored high power generation of the AC‐MFC, but also promoted the enrichment of denitrifers at the anodes and strengthened denitrification. This study provided an effective method for enhancing power generation and denitrification performance of the AC‐MFC synchronously.

Anup Gurung, Bhim Sen Thapa, Seong-Yun Ko et al.

Energies • 2023

Nitrate (NO3−-N) and nitrites (NO2−-N) are common pollutants in various water bodies causing serious threats not only to aquatic, but also to animals and human beings. In this study, we developed a strategy for efficiently reducing nitrates in microbial fuel cells (MFCs) powered by a granular activated carbon (GAC)-biocathode. GAC was developed by acclimatizing and enriching denitrifying bacteria under a redox potential (0.3 V) generated from MFCs. Thus, using the formed GAC-biocathode we continued to study their effect on denitrification with different cathode materials and circulation speeds in MFCs. The GAC-biocathode with its excellent capacitive property can actively reduce nitrate for over thirty days irrespective of the cathode material used. The stirring speed of GAC in the cathode showed a steady growth in potential generation from 0.25 V to 0.33 V. A rapid lag phase was observed when a new carbon cathode was used with enriched GAC. While a slow lag phase was seen when a stainless-steel cathode was replaced. These observations showed that effective storage and supply of electrons to the GAC plays a crucial role in the reduction process in MFCs. Electrochemical analysis of the GAC properties studied using electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), and zeta potential showed distinct properties with different abiotic and biocathode conditions. We found that the enrichment of electrotrophic bacteria on GAC facilitates the direct electron transfer in the cathode chamber for reducing NO3−-N in MFCs as observed by scanning electron microscopy.

Rui He, Lifen Liu, Peng Shi et al.

Journal of Chemical Technology & Biotechnology • 2018

Abstract BACKGROUND To decontaminate sites of pollutants, fuel cell and bio‐electrochemical fuel cell reactors can degrade pollutants and generate electricity simultaneously, potentially decrease cost, energy consumptions and treatment cycle. In this study, a photocatalytic fuel cell (PFC) and PEC‐MFC (integrated photo‐electro‐catalysis with microbial fuel cell) were investigated to decontaminate sand/water polluted by RhB, antibiotics and heavy metal ions. RESULTS In the PFC, paired electrodes with ZnIn 2 S 4 ‐AgAgCl/GO or ZnIn 2 S 4 ‐RGO/MnO 2 , effectively removed pollutants in sand/water. The removal of RhB was 95.6% in 100 min with an external resistance of 1 Ω under aeration. Adding cyclo‐dextrin increased pollutant removals, realized 66% removal of RhB in overlying water, and significant removal in sand after 5 h, and 70% removal of tetracycline in overlying water, but only 60% without cyclodextrin after 4 h. Adding KMnO 4 and NaHSO 3 promoted decontamination of tetracycline from sand/water, tetracycline in water was almost completely degraded in 3.5 h with the addition, but only about 65% without any addition. In the PEC‐MFC, integrating photo‐electro‐catalytic electrode with bio‐anode, Cr(VI) in the cathode chamber was reduced rapidly and the concentration of RhB in sand decreased quickly, nearly complete in 2 h. The Cr(VI) in sand was reduced in several hours, so that, compared with previous reports, the treatment time is significantly shortened. CONCLUSION The PFC and PEC‐MFC systems are successful in decontaminating sand/water in polluted sites and are cost‐effective and sustainable methods. By building an on‐site or off‐site system with washing and cycling of the liquid stream, it could be a convenient remediation method for polluted sites. © 2018 Society of Chemical Industry

Sara Cangussú Bassoli, Matheus Henrique Alcântara de Lima Cardozo, Fabiano Luiz Naves et al.

Fermentation • 2025

Microalgal biomass contributes to the valorization of urban and agro-industrial solid waste via hydrothermal co-liquefaction (co-HTL) for the production of biocrude, a sustainable substitute for petroleum. Tropical and populous countries like Brazil generate a lot of agro-industrial waste, such as sugarcane bagasse and malt bagasse, as well as sludge from sewage treatment plants. Such residues are potential sources of biocrude production via thermochemical conversion. To increase biocrude productivity, microalgal biomass has been successfully used in mixing the co-HTL process feed with different residues. In addition to biocrude, co-HTL generates an aqueous phase that can be used to produce H2 and/or electricity via microbial energy cells. In this sense, this paper aims to present the potential for generating energy from solid waste commonly generated in emerging countries such as Brazil based on a simplified scheme of a conceptual biorefinery employing algal biomass co-HTL together with sugarcane bagasse, malt bagasse, and sludge. The biorefinery model could be integrated into an ethanol production plant, a brewery, or a sewage treatment plant, aiming at the production of biocrude and H2 and/or electricity by bioelectrochemical systems, such as microbial electrolysis cells and microbial fuel cells.

D. Carrillo-Peña, A. Escapa, M. Hijosa-Valsero et al.

Biomass Conversion and Biorefinery • 2024

Abstract A microbial electrolysis cell integrated in an anaerobic digestion system (MEC-AD) is an efficient configuration to produce methane from an exhausted vine shoot fermentation broth (EVS). The cell worked in a single-chamber two-electrode configuration at an applied potential of 1 V with a feeding ratio of 30/70 (30% EVS to 70% synthetic medium). In addition, an identical cell operated in an open circuit was used as a control reactor. Experimental results showed similar behavior in terms of carbon removal (70–76%), while the specific averaged methane production from cycle 7 was more stable and higher in the connected cell (MEC AD ) compared with the unpolarized one (OC AD ) accounting for 403.7 ± 33.6 L CH 4 ·kg VS −1 and 121.3 ± 49.7 L CH 4 ·kg VS −1 , respectively. In addition, electrochemical impedance spectroscopy revealed that the electrical capacitance of the bioanode in MEC AD was twice the capacitance shown by OC AD . The bacterial community in both cells was similar but a clear adaptation of Methanosarcina Archaea was exhibited in MEC AD , which could explain the increased yields in CH 4 production. In summary, the results reported here confirm the advantages of integrating MEC-AD for the treatment of real organic liquid waste instead of traditional AD treatment.

René Cardeña, Iván Moreno‐Andrade, Germán Buitrón

Journal of Chemical Technology & Biotechnology • 2018

Abstract BACKGROUND Food waste is a valuable source of hydrogen by dark fermentation. Dark fermentation effluent contains volatile fatty acids that can be further converted into more hydrogen using microbial electrolysis cells (MECs). In this process, the anodic potential ( E an ) has a significant influence on the MEC performance as well as the effluent composition. The objective of this study was to evaluate the effects of variation of the anode potential and substrate composition (food waste fermentation effluent) on the performance of hydrogen production using two‐chamber MECs. RESULTS Colonization was conducted using an E an of 0.5 V vs Ag/AgCl. After 38 days, the E an had decreased to 0.3 V, resulting in an increase in the hydrogen production rate (from 287 to 482 mL H 2 L ‐1 cat d ‐1 ). A maximum hydrogen production rate of 685 mL H 2 L ‐1 cat d ‐1 was observed when effluent that contained the highest acetate concentration was utilized. Cathodic hydrogen recovery was higher than 93%, and hydrogen yield was greater than 873 mL H 2 g ‐1 COD. CONCLUSION The start‐up strategy in which E an is decreased after the formation of an electroactive biofilm resulted in increased hydrogen production. The composition of the food waste fermented effluent influences the hydrogen production rate. © 2017 Society of Chemical Industry

Noémi N. Horváth-Gönczi, Zoltán Bagi, Márk Szuhaj et al.

Fermentation • 2023

Bioelectrochemical systems (BESs) have great potential in renewable energy production technologies. BES can generate electricity via Microbial Fuel Cell (MFC) or use electric current to synthesize valuable commodities in Microbial Electrolysis Cells (MECs). Various reactor configurations and operational protocols are increasing rapidly, although industrial-scale operation still faces difficulties. This article reviews the recent BES related to literature, with special attention to electrosynthesis and the most promising reactor configurations. We also attempted to clarify the numerous definitions proposed for BESs. The main components of BES are highlighted. Although the comparison of the various fermentation systems is, we collected useful and generally applicable operational parameters to be used for comparative studies. A brief overview links the appropriate microbes to the optimal reactor design.

Néstor Isidro Rincón-Catalán, Abumalé Cruz-Salomón, P.J. Sebastian et al.

Processes • 2022

Banana is the most cultivated fruit plant in the world. It is produced in Latin America, Asia and Africa. India and China are the world’s largest banana producers, with almost 41% of the world’s production. This fruit reaches a total world production of 158.3 million tons per year. However, during their production cycle, the banana agroindustry produces large volumes of solid waste derived from overripe fruit. It contributes between 8–20 percent of the waste (around 100 kg of banana waste for every ton of banana produced). Therefore, the use of overripe banana waste represents a huge opportunity for bioenergy production. This work demonstrates that banana waste can be further used for power generation using a microbial fuel cell (MFC) coupled with anaerobic digestion (AD). First, the maximum methane production (MMP), methane production rate (MPR) and biochemical methane potential (BMP) were measured using an anaerobic batch bioreactor for 64 days of monitoring. Finally, the digestate generated from AD was used in the MFC to determine the polarization curve, maximum voltage, maximum power density (MPD), resistance and current. As a result, the AD generated an MMP of 320.3 mL, BMP of 373.3 mLCH4/gVS and MPR of 18.6 mLCH4/Lb⋅day. The MFC generated 286 mV (maximum voltage), 41.3 mW/m2 (MPD), 580.99 Ω (resistance) and 0.0002867 A (current). Both processes together produced a total bioenergy of 13.38 kJ/gVS. This coupled system showed a suitable and promising use of banana waste for ecofriendly bioenergy generation. Therefore, this feedstock could be taken advantage of for generating sustainable processes and developing a circular economy in the banana agroindustry.

Shixiang Dai, Benjamin Korth, Carsten Vogt et al.

Frontiers in Chemical Engineering • 2021

Hydrothermal carbonization (HTC) is a promising technology for chemical and material synthesis. However, HTC produces not only valuable solid coal-materials but also yields process water (PW) with high chemical oxygen demand (COD) that requires extensive treatment. Anaerobic digestion (AD) has been used for initial treatment of HTC-PW, but the AD effluent is still high in COD and particles. Here, we show that microbial electrochemical technologies (MET) can be applied for COD removal from AD effluent of HTC-PW. Bioelectrochemical systems (BES) treating different shares of AD effluent from HTC-PW exhibited similar trends for current production. Thereby, maximum current densities of 0.24 mA cm −2 and COD removal of 65.4 ± 4.4% were reached ( n = 3). Microbial community analysis showed that the genus Geobacter dominated anode biofilm and liquid phase of all reactors indicating its central role for COD oxidation and current generation.

Qing Zhao, Hairong Yuan, Xiujin Li

Processes • 2025

This study aims to investigate the effect of different applied voltages on the biomethanation performance and microbial community characteristics of corn stover (CS) in a microbial electrolysis cell (MEC)-assisted anaerobic digestion (AD) system (MEC-AD). The results showed that the MEC-AD system operating at 0.8 V achieved the highest methane yield of 192.40 mL CH4/g VS (volatile solids), an increase of 14.98% compared to the conventional AD. The system obtained methane yields of 187.74 to 191.18 mL CH4/g VS at lower voltages (0.4 V and 0.6 V), and 156.11–182.75 mL CH4/g VS at higher voltages (1.0 V and 1.2 V), respectively, suggesting that lower or higher voltages would have adversely impacted the methane yield. Correspondingly, the MEC-AD system operating at 0.4–0.8 V achieved over 71.47% conversion rates of total solids (TS), VS, and cellulose. The microbial community analysis revealed that 0.8 V optimally enriched fermentative acidogenic bacteria (FABs, 24.55%) and electroactive bacteria (13.50%), enhancing both hydrolysis acidification efficiency and direct interspecies electron transfer (DIET). Both Methanosarcina and Methanoculleus demonstrated significant positive correlations with FABs, SOBs, and electroactive bacteria. This study reveals that 0.8 V represents the optimal operating voltage for biomethane production in MEC-AD systems, providing critical insights for agricultural waste valorization.

Nhlanganiso Ivan Madondo, Sudesh Rathilal, Babatunde Femi Bakare et al.

Microorganisms • 2023

In this paper, the application of magnetite-nanoparticles and a microbial fuel cell (MFC) was studied on the anaerobic digestion (AD) of sewage sludge. The experimental set-up included six 1 L biochemical methane potential (BMP) tests with different external resistors: (a) 100 Ω, (b) 300 Ω, (c) 500 Ω, (d) 800 Ω, (e) 1000 Ω, and (f) a control with no external resistor. The BMP tests were carried out using digesters with a working volume of 0.8 L fed with 0.5 L substrate, 0.3 L inoculum, and 0.53 g magnetite-nanoparticles. The results suggested that the ultimate biogas generation reached 692.7 mL/g VSfed in the 500 Ω digester, which was substantially greater than the 102.6 mL/g VSfed of the control. The electrochemical efficiency analysis also demonstrated higher coulombic efficiency (81.2%) and maximum power density (30.17 mW/ m2) for the 500 Ω digester. The digester also revealed a higher maximum voltage generation of 0.431 V, which was approximately 12.7 times the 0.034 V of the lowest-performing MFC (100 Ω digester). In terms of contaminants removed, the best-performing digester was the digester with 500 Ω, which reduced contaminants by more than 89% on COD, TS, VS, TSS and color. In terms of cost-benefit analysis, this digester produced the highest annual energy profit (48.22 ZAR/kWh or 3.45 USD/kWh). This infers the application of magnetite-nanoparticles and MFC on the AD of sewage sludge is very promising for biogas production. The digester with an external resistor of 500 Ω showed a high potential for use in bioelectrochemical biogas generation and contaminant removal for sewage sludge.

Chenglong Xu, Jialei Lu, Zhimiao Zhao et al.

Water • 2020

An aircathode microbial desalination cell (AMDC) was successfully started by inoculating anaerobic sludge into the anode of a microbial desalination cell and then used to study the effects of salinity on performance of AMDC and effect of treatment of coastal saline-alkaline soil-washing water. The results showed that the desalination cycle and rate gradually shorten, but salt removal gradually increased when the salinity was decreased, and the highest salt removal was 98.00 ± 0.12% at a salinity of 5 g/L. COD removal efficiency was increased with the extension of operation cycle and largest removal efficiency difference was not significant, but the average coulomb efficiency had significant differences under the condition of each salinity. This indicates that salinity conditions have significant influence on salt removal and coulomb efficiency under the combined action of osmotic pressure, electric field action, running time and microbial activity, etc. On the contrary, COD removal effect has no significant differences under the condition of inoculation of the same substrate in the anode chamber. The salt removal reached 99.13 ± 2.1% when the AMDC experiment ended under the condition of washing water of coastal saline-alkaline soil was inserted in the desalination chamber. Under the action of osmotic pressure, ion migration, nitrification and denitrification, NH4+-N and NO3−-N in the washing water of the desalination chamber were removed, and this indicates that the microbial desalination cell can be used to treatment the washing water of coastal saline-alkaline soil. The microbial community and function of the anode electrode biofilm and desalination chamber were analyzed through high-throughput sequencing, and the power generation characteristics, organics degradation and migration and transformation pathways of nitrogen of the aircathode microbial desalination cell were further explained.

Yolanda Ruiz, Juan A Baeza, Nuria Montpart et al.

Journal of Chemical Technology & Biotechnology • 2020

Abstract Background Cyclic voltammetry (CV) has become a standard tool in the study of bioelectrochemical systems (BES) because it is a nondestructive technique that provides useful information on the electron transfer capacity of these systems. When applied to the large‐surface electrodes typically found in BES, the scan rate must be severely diminished or otherwise the capacitive current masks the faradaic current. Decreasing the scan rate results in an increase in the duration of the experiments, which can lead to a significant alteration of the initial system conditions. Results The repeatability of low scan rate cyclic voltammetry (LSCV) in air cathode microbial fuel cells (AC‐MFCs) operating in batch mode was examined. Consecutive LSCVs at 0.1 mV s −1 were recorded with and without prior renewal of the culture medium. Significant deviations in CV replicates were observed when the medium was not replaced (as high as 40% of maximum intensity). These deviations decreased (<18%) when the medium was refreshed, indicating that significant changes in the culture medium composition occurred during LSCVs. Additional electrochemical tests showed that the peak in the forward scan was probably the result of an accumulation of charge in the anodic system. Conclusion LSCV can affect the response of AC‐MFCs working in batch mode and cast doubt on the repeatability of these experiments, observing differences as high as 40% in maximum intensity. Renewing the culture medium is recommended to improve the repeatability of LSCV replicates. © 2020 Society of Chemical Industry

Wei-Jhe Ma, Ching-Hsing Luo, Jiun-Ling Lin et al.

Sensors • 2016

This paper presents a portable low-power battery-driven bioelectrochemical signal acquisition system for urea detection. The proposed design has several advantages, including high performance, low cost, low-power consumption, and high portability. A LT1789-1 low-supply-voltage instrumentation amplifier (IA) was used to measure and amplify the open-circuit potential (OCP) between the working and reference electrodes. An MSP430 micro-controller was programmed to process and transduce the signals to the custom-developed software by ZigBee RF module in wireless mode and UART in able mode. The immobilized urease sensor was prepared by embedding urease into the polymer (aniline-co-o-phenylenediamine) polymeric matrix and then coating/depositing it onto a MEMS-fabricated Au working electrode. The linear correlation established between the urea concentration and the potentiometric change is in the urea concentrations range of 3.16 × 10−4 to 3.16 × 10−2 M with a sensitivity of 31.12 mV/log [M] and a precision of 0.995 (R2 = 0.995). This portable device not only detects urea concentrations, but can also operate continuously with a 3.7 V rechargeab-le lithium-ion battery (500 mA·h) for at least four days. Accordingly, its use is feasible and even promising for home-care applications.

Nattawet Sriwichai, Rutrawee Sangcharoen, Treenut Saithong et al.

PLOS ONE • 2024

Microbial fuel cells (MFCs) are innovative eco-friendly technologies that advance a circular economy by enabling the conversion of both organic and inorganic substances in wastewater to electricity. While conceptually promising, there are lingering questions regarding the performance and stability of MFCs in real industrial settings. To address this research gap, we investigated the influence of specific operational settings, regarding the hydraulic retention time (HRT) and organic loading rate (OLR) on the performance of MFCs used for treating sulfide-rich wastewater from a canned pineapple factory. Experiments were performed at varying hydraulic retention times (2 days and 4 days) during both low and high seasonal production. Through optimization, we achieved a current density generation of 47±15 mA/m 2 , a COD removal efficiency of 91±9%, and a sulfide removal efficiency of 86±10%. Microbiome analysis revealed improved MFC performance when there was a substantial presence of electrogenic bacteria, sulfide-oxidizing bacteria, and methanotrophs, alongside a reduced abundance of sulfate-reducing bacteria and methanogens. In conclusion, we recommend the following operational guidelines for applying MFCs in industrial wastewater treatment: (i) Careful selection of the microbial inoculum, as this step significantly influences the composition of the MFC microbial community and its overall performance. (ii) Initiating MFC operation with an appropriate OLR is essential. This helps in establishing an effective and adaptable microbial community within the MFCs, which can be beneficial when facing variations in OLR due to seasonal production changes. (iii) Identifying and maintaining MFC-supporting microbes, including those identified in this study, should be a priority. Keeping these microbes as an integral part of the system’s microbial composition throughout the operation enhances and stabilizes MFC performance.

Zhe Liu, Ping Xiang, Zhuang Duan et al.

RSC Advances • 2019

A three-chamber microbial desalination cell (MDC) was constructed for high-salinity mustard tuber wastewater (MTWW) treatment.

Da Seul Kong, Eun Joo Park, Sakuntala Mutyala et al.

Energies • 2021

Crude glycerol is a major byproduct in the production of biodiesel and contains a large number of impurities. The transformation of crude glycerol into valuable compounds such as 1,3-propanediol (1,3-PDO) using clean and renewable processes, like bioconversion, is an important task for the future of the chemical industry. In this study, 1,3-PDO bioproductions from crude and pure glycerol were estimated as 15.4 ± 0.8 and 11.4 ± 0.1 mmol/L, respectively. Because 1,3-PDO is a reductive metabolite that requires additional reducing energy, external supplements of electron for further improvement of 1,3-PDO biosynthesis were attempted using a bioelectrochemical system (BES) or zero-valent iron (ZVI). The conversions of crude and pure glycerol under electrode and iron-based cultivation were investigated for 1,3-PDO production accompanied by metabolic shift and cell growth. The BES-based conversion produced 32.6 ± 0.6 mmol/L of 1,3-PDO with ZVI implementation.

Na Liu, Lina Qiu, Lijuan Qiu

Coatings • 2024

Microbial metal corrosion has become an important topic in metal research, which is one of the main causes of equipment damage, energy loss, and economic loss. At present, the research on microbial metal corrosion focuses on the characteristics of corrosion products, the environmental conditions affecting corrosion, and the measures and means of corrosion prevention, etc. In contrast, the main microbial taxa involved in metal corrosion, their specific role in the corrosion process, and the electron transfer pathway research are relatively small. This paper summarizes the mechanism of microbial carbon steel corrosion caused by SRB, including the cathodic depolarization theory, acid metabolite corrosion theory, and the biocatalytic cathodic sulfate reduction mechanism. Based on the reversible nature of electron transfer in biofilms and the fact that electrons must pass through the extracellular polymers layer between the solid electrode and the cell, this paper focuses on three types of electrochemical mechanisms and electron transfer modes of extracellular electron transfer occurring in microbial fuel cells, including direct-contact electron transfer, electron transfer by conductive bacterial hair proteins or nanowires, and electron shuttling mediated by the use of soluble electron mediators. Finally, a more complete pathway of electron transfer in microbial carbon steel corrosion due to SRB is presented: an electron goes from the metal anode, through the extracellular polymer layer, the extracellular membrane, the periplasm, and the intracellular membrane, to reach the cytoplasm for sulfate allosteric reduction. This article also focuses on a variety of complex components in the extracellular polymer layer, such as extracellular DNA, quinoline humic acid, iron sulfide (FeSX), Fe3+, etc., which may act as an extracellular electron donor to provide electrons for the SRB intracellular electron transfer chain; the bioinduced mineralization that occurs in the SRB biofilm can inhibit metal corrosion, and it can be used for the development of green corrosion inhibitors. This provides theoretical guidance for the diagnosis, prediction, and prevention of microbial metal corrosion.

Thi Quynh Hoa Kieu, Thi Yen Nguyen, Chi Linh Do

Molecules • 2023

A wastewater treatment system has been established based on sulfate-reducing and sulfide—oxidizing processes for treating organic wastewater containing high sulfate/sulfide. The influence of COD/SO42− ratio and hydraulic retention time (HRT) on removal efficiencies of sulfate, COD, sulfide and electricity generation was investigated. The continuous operation of the treatment system was carried out for 63 days with the optimum COD/SO42− ratio and HRT. The result showed that the COD and sulfate removal efficiencies were stable, reaching 94.8 ± 0.6 and 93.0 ± 1.3% during the operation. A power density level of 18.0 ± 1.6 mW/m2 was obtained with a sulfide removal efficiency of 93.0 ± 1.2%. However, the sulfide removal efficiency and power density decreased gradually after 45 days. The results from scanning electron microscopy (SEM) with an energy dispersive X-ray (EDX) show that sulfur accumulated on the anode, which could explain the decline in sulfide oxidation and electricity generation. This study provides a promising treatment system to scale up for its actual applications in this type of wastewater.

V. Dhundale, Vijayshree M Hemke, D. Desai et al.

Annals of Applied Microbiology & Biotechnology Journal • 2018

Microbial fuel cells (MFCs), which can be use bacterial cultures as biocatalyst for the conversion of chemical energy into the electricity from the biomass. The bacteria that can be able to synthesis [1,2] the electron from biodegradation of organic content and transfer the electron are known as exoelectrogen [3]. Now a days the extensive work is performed on the many exoelectrogen in MFCs which were Gram-negative and most exoelectrogens are cultivated in MFCs under 7 pH such as Klebsiella pneumoniae, Desulfobulbus propionicus, Geobacter sulfurreducens, Rhodoferax ferrireducens, Aeromonas hydrophila and Shewanella putrefaciens [4-9]. The extensive bacterial cultures that have been examined as biocatalyst for the bioelectricity generation in MFC comprise the pure culture of aerobic and anaerobic bacteria and consortial diverse cultures from sea floor sediments [10] and wastewater [11-12]. For direct bio electricity generation in MFC, the ideal bacterial culture must be able to grow aerobically and be electrochemically active, utilizing an anode as an alternative electron acceptor while oxidizing metabolites of various carbon sources. But very less studies have been reported using Gram-positive bacteria as biocatalyst in MFCs like Corynebacterium sp. strain MFC03 [13] Thermincola ferriacetica Z-0001 [14] and Bacillus subtilis [15], Clostridium butyricum EG3 [16], were performed to be enable producing bioelectricity. Electrochemical mechanisms have been used in different fields of biotechnology including biosensors, bioelectrochemical synthesis and biofuel cells [17]. Electricity can be generated directly from sewage sludge with microbial fuel cells (MFCs), combining degradation of organic matter and MFC for the generation of bioelectricity and the degradation of sewage sludgeorganic matter under the alkaline condition studied by Yuan et al. A group of bacteria from the extremophiles that has been tested only to a lower range in MFCs. Extremes such as in pH, salinity, temperature and alkalinity, when combined with materials that perform best under such circumstances would able to result in more graceful MFCs [18]. The search for bacteria that function optimally at higher pH and thereby would have higher catalytic rates was the aim of the present study. Electricity generation by anaerobic bacteria and anoxic sediments from hypersaline soda lakes was studied by Miller and Oremland. The objectives of this Research Article

V. Dhundale, Vijayshree M Hemke, D. Desai et al.

Journal of Applied Biology & Biotechnology • 2020

The present study put forth with the fundamental objective to the exploration of exoelectrogens from the extremophilic environment and to investigate the electricity generation from them. A total of 20 bacterial cultures were isolated, from which BW2(1) was selected for the further investigation of the microbial fuel cell (MFC). The experimental results performed that the strain Bacillus alkalogaya BW2(1) was capable of utilizing organic acids and sugars as electron donors to generate electricity. The MFC was constructed and the electricity generation was measured after various intervals using various parameters and substrates, 937 mV electricity was generated after 1 hour, but after 48 hours the electricity generation dramatically decreases to 570 mV. The effect of pH on MFC was also studied, pH enhanced electricity, indicating the requirement of pH for bacterium BW2(1). This is a valuable information for bioelectricity production and optimization from B. alkalogaya BW2(1) has bright future toward the improvement and production of bioelectricity for entirely new areas of industrial and biotechnological applications.

Xiaofei Wang, Antonin Prévoteau, K. Rabaey

Environmental Science & Technology • 2021

Nitrate contamination is a common problem in groundwater around the world. Nitrate can be cathodically reduced in bioelectrochemical systems using autotrophic denitrifiers with low energy investment and without chemical addition. Successful denitrification was demonstrated in previous studies in both microbial fuel cells and microbial electrolysis cells (MECs) with continuous current flow, whereas the impact of intermittent current supply (e.g., in a fluidized-bed system) on denitrification and particularly the electron-storing capacity of the denitrifying electroactive biofilms (EABs) on the cathodes have not been studied in depth. In this study, two continuously fed MECs were operated in parallel under continuous and periodic polarization modes over 280 days, respectively. Under continuous polarization, the maximum denitrification rate reached 233 g NO3--N/m3/d with 98% nitrate removal (0.6 mg NO3--N/L in the effluent) with negligible intermediate production, while under a 30 s open-circuit/30 s polarization mode, 86% of nitrate was removed at a maximum rate of 205 g NO3--N/m3/d (4.5 mg NO3--N/L in the effluent) with higher N2O production (6.6-9.3 mg N/L in the effluent). Conversely, periodic polarization could be an interesting approach in other bioelectrochemical processes if the generation of chemical intermediates (partially reduced or oxidized) should be favored. Similar microbial communities dominated byGallionellaceaewere found in both MECs; however, swapping the polarization modes and the electrochemical analyses suggested that the periodically polarized EABs probably developed a higher ability for electron storage and transfer, which supported the direct electron transfer pathway in discontinuous operation or fluidized biocathodes.

Eleanor R. Clifford, R. Bradley, L. Wey et al.

Chemical Science • 2021

Bioelectrochemical approaches for energy conversion rely on efficient wiring of natural electron transport chains to electrodes. However, state-of-the-art exogenous electron mediators give rise to significant energy losses and, in the case of living systems, long-term cytotoxicity. Here, we explored new selection criteria for exogenous electron mediation by examining phenazines as novel low-midpoint potential molecules for wiring the photosynthetic electron transport chain of the cyanobacterium Synechocystis sp. PCC 6803 to electrodes. We identified pyocyanin (PYO) as an effective cell-permeable phenazine that can harvest electrons from highly reducing points of photosynthesis. PYO-mediated photocurrents were observed to be 4-fold higher than mediator-free systems with an energetic gain of 200 mV compared to the common high-midpoint potential mediator 2,6-dichloro-1,4-benzoquinone (DCBQ). The low-midpoint potential of PYO led to O2 reduction side-reactions, which competed significantly against photocurrent generation; the tuning of mediator concentration was important for outcompeting the side-reactions whilst avoiding acute cytotoxicity. DCBQ-mediated photocurrents were generally much higher but also decayed rapidly and were non-recoverable with fresh mediator addition. This suggests that the cells can acquire DCBQ-resistance over time. In contrast, PYO gave rise to steadier current enhancement despite the co-generation of undesirable reactive oxygen species, and PYO-exposed cells did not develop acquired resistance. Moreover, we demonstrated that the cyanobacteria can be genetically engineered to produce PYO endogenously to improve long-term prospects. Overall, this study established that energetic gains can be achieved via the use of low-potential phenazines in photosynthetic bioelectrochemical systems, and quantifies the factors and trade-offs that determine efficacious mediation in living bioelectrochemical systems.

Roman N. Perchikov, Maxim Cheliukanov, Yulia V. Plekhanova et al.

Biosensors • 2024

Microbial biofilms present one of the most widespread forms of life on Earth. The formation of microbial communities on various surfaces presents a major challenge in a variety of fields, including medicine, the food industry, shipping, etc. At the same time, this process can also be used for the benefit of humans—in bioremediation, wastewater treatment, and various biotechnological processes. The main direction of using electroactive microbial biofilms is their incorporation into the composition of biosensor and biofuel cells This review examines the fundamental knowledge acquired about the structure and formation of biofilms, the properties they have when used in bioelectrochemical devices, and the characteristics of the formation of these structures on different surfaces. Special attention is given to the potential of applying the latest advances in genetic engineering in order to improve the performance of microbial biofilm-based devices and to regulate the processes that take place within them. Finally, we highlight possible ways of dealing with the drawbacks of using biofilms in the creation of highly efficient biosensors and biofuel cells.

O. Kalashnikova, A. Kashevskii, N. Vardanyan et al.

Proceedings of Universities. Applied Chemistry and Biotechnology • 2021

Acidophilic chemolithotrophic microorganisms are used in biohydrometallurgy for the extraction of metals from sulphide ores. Some types of microorganisms belonging to this group are capable of generating electricity under certain conditions. This circumstance determined a recent upsurge of research interest in their use in biofuel cells. Under a constant supply of the substrate to the bioelectrochemical system, acidophilic chemolithotrophic microorganisms are capable of producing electricity for a prolonged period of time. The use of extremophiles in microbial fuel cells is of particular interest, since these microorganisms can serve as bioelectrocatalysts at extreme pH, salinity and temperature, while the vast majority of microorganisms are unable to survive under these conditions. Therefore, selection of optimal conditions and approaches to controlling the work of acidophilic chemolithotrophic microorganisms in such fuel cells is of particular importance. On this basis, a technology for the simulteneous bioleaching of metals from poor ores and the generation of electricity can be developed. Biofuel cells operating at low pH values using acidophilic chemolithotrophic microorganisms are yet to be investigated. The number of studies on acidophilic electroactive microorganisms is very limited. In this regard, the purpose of this review was to consider the prospects for the use of acidophilic chemolithotrophic microorganisms as bioagents in microbial fuel cells. The reviewed publications demonstrate that chemolithotrophic microorganisms can act as both anodic (metal-reducing, sulphur-oxidizing microorganisms) and cathodic (metal-oxidizing prokaryotes, sulfate reducers) highly efficient bioagents capable of using mining wastes as substrates.

Yuxuan Wan, Zongliang Huang, Lean Zhou et al.

Environmental Science & Technology • 2019

Nitrate-N in wastewaters is hard to be recovered because it is difficult to volatilize with an opposite charge to ammonium. Here, we proved the feasibility of dissimilatory nitrate reduction to ammonia (DNRA) by the easy-acclimated mixed electroactive bacteria, achieving the highest DNRA efficiency of 44 %. It was then coupled with microbial electrolysis to concentrate the ammonium by a factor of 4 in the catholyte for recovery. The abundance of electroactive bacteria in the biofilm before nitrate addition, especially Geobacter spp., was found to determine the DNRA efficiency. As the main competitors of DNRA bacteria, the growth of denitrifiers was more sensitive to C/N ratios. DNRA microbial community contrarily showed a stable and recoverable ammoniation performance over C/N ratios ranging from 0.5 to 8.0. A strong competition of electrode and nitrate on electron donors was observed at the early stage (15 d) of electroactive biofilm formation, which can be weakened when the biofilm was mature on 40 d. Quantitative PCR showed a significant increase in nirS and nrfA transcripts in ammoniation process. nirS was inhibited significantly after nitrate depletion while nrfA was still up-regulated. These findings provided a novel way to recover nitrate-N using the organic wastes as both electron donor and power, which has broader implications on the sustainable wastewater treatment and the ecology of nitrogen cycling.