Microbial Electrosynthesis System Research Articles

Enhancing bio-alcohol production from volatile fatty acids by suppressing methanogenic activity in single chamber microbial electrosynthesis cells (SCMECs)

This study explored alcohol production from volatile fatty acids (VFAs) in single-chambered microbial electrosynthesis systems (MES) under continuous pH control (≤pH 5.5) for methanogen inhibition. MES with 2 g-COD/l VFA could produce highest current of 5.3 mA followed by 3.6 mA in 6 g-COD/l and 0.44 mA in 8 g-COD/l, implying active bioelectrochemical reactions of microorganisms on the electrodes. Ethanol, methanol and propanol were detected as fermented bio-alcohols without methane production, and ethanol was the main product with a cumulative recovery of 7.14 mM in 2 g-COD/l, 13.6 mM in 6 g-COD/l and 17.9 mM in 8 g-COD/l. Maximum bio-alcohol yield of 0.71 g-CODAlcohols/g-CODVFAs with a recovery efficiency of 35% was obtained from MES under 2.0 g-COD/l, followed by 6 and 8 g-COD/l. The results demonstrate that pH adjustment method is an effective strategy to suppress methanogens for improved bioelectrochemical performance of alcohol production from VFAs in MES.

Impact Mechanisms of Carboxyl Group Modified Cathode on Acetate Production in Microbial Electrosynthesis Systems

Microbial electrosynthesis systems (MESs) can convert carbon dioxide into added value compounds using microorganisms as catalyst, which is expected to help achieve conversion of greenhouse gases into resources. However, the synthetic efficiency of MESs is far behind the industry requirements. In this study, carbon cloth surfaces were bonded with carboxyl groups by electrochemical reduction of aryl diazonium salts and then used as a cathode in MESs reactors. The results showed that the hydrophilicity of the carbon cloth surfaces improved after the carboxyl groups were modified. However, weaker current of cyclic voltammetry was obtained in the modified cathode. Significant differences were observed between modified (CA-H, CA-M, CA-L) and non-modified cathode (CK) during the start-up period. After 48h, the hydrogen production rate of CA-H, CA-M, CA-L was 21.45, 28.60, and 22.75 times higher than CK. After 120h, the acetate accumulation concentration of CA-H, CA-M, CA-L was 2.01, 2.43, and 1.44 times higher than CK. After 324h, there was little difference in the electrochemical activity of cathodic biofilm and protein content (about 0.47 mg·cm-2) in all groups. The analysis of the community structure of cathodic biofilm showed that, in the genus level, Acetobacterium, Norank_p_Saccharibacteria, and Thioclava were the dominant species, accounting for 59.6% to 82.1%. There was little difference in the relative abundance of Acetobacterium in all groups (31.3% to 40.1%). However, the relative abundance of norank_p_Saccharibacteria in CA-H, CA-M, CA-L, and CK were 16.1%, 24.6%, 31.1%, and 37.5%, respectively. The carboxyl modified cathode had a great influence on the start-up stage of MESs, which could be a new idea for the rapid start-up of MESs.

Engineering an electroactive Escherichia coli for the microbial electrosynthesis of succinate by increasing the intracellular FAD pool

In this study, the FAD synthesis pathway was manipulated to increase its cellular concentration and thereby improve the electroactivity of E. coli. In a microbial electrosynthesis (MES) system with neutral red as electron carrier and fumarate as the sole electron acceptor, the engineered strains derived from three E. coli lines displayed increased electric current in the reaction system, indicating improved electroactivity. Furthermore, the production of succinate from fumarate increased by around 60% compared with that of the parent strains, confirming the improvement of E. coli electroactivity by manipulating the FAD synthesis pathway. An MES reaction was performed with engineered E. coli 8739, and an altered metabolic profile with more reductive fermentation products was obtained. When the electroactive succinate-producing strain E. coli T110 was used in the MES, a yield of 0.97 ± 0.02 mol/mol glucose was achieved, which corresponds to an approximately 1.4-fold increase compared with the fermentation with no electricity supply or non-electroactive T110. In addition, a carbon concentration mechanism (CCM) was employed to further improve succinate production and yield in the MES, which produced a succinate yield of 1.16 mol/mol glucose, a 1.7-fold increase compared with that of the parent strain T110, indicating that the electroactive E. coli could be used in MES to produce specific fermentation products with improved yield.

Bioelectrochemical CO2 Reduction to Methane: MES Integration in Biogas Production Processes

Anaerobic digestion (AD) is a widely used technique to treat organic waste and produce biogas. This article presents a practical approach to increase biogas yield of an AD system using a microbial electrosynthesis system (MES). The biocathode in MES reduces carbon dioxide with the supplied electrons and protons (H+) to form methane. We demonstrate that the MES is able to produce biogas with over 90% methane when fed with reject water obtained from a local wastewater treatment plant. The optimised cathode potential was observed in the range of −0.70 V to −0.60 V and optimised feed pH was around 7.0. With autoclaved feed, these conditions allowed methane yields of about 9.05 mmol/L(reactor)-day. A control experiment was then carried out to make a comparison between open circuit and MES methanogenesis. The highest methane yield of about 22.1 mmol/L(reactor)-day was obtained during MES operation that performed 10–15% better than the open circuit mode of operation. We suggest and describe an integrated AD-MES system, by installing MES in the reject water loop, as a novel approach to improve the efficiency and productivity of existing waste/wastewater treatment plants.

Electrosynthesis of acetate from inorganic carbon (HCO3-) with simultaneous hydrogen production and Cd(II) removal in multifunctional microbial electrosynthesis systems (MES).

The simultaneous production of acetate from bicarbonate (from CO2 sequestration) and hydrogen gas, with concomitant removal of Cd(II) heavy metal in water is demonstrated in multifunctional metallurgical microbial electrosynthesis systems (MES) incorporating Cd(II) tolerant electrochemically active bacteria (EAB) (Ochrobactrum sp. X1, Pseudomonas sp. X3, Pseudomonas delhiensis X5, and Ochrobactrum anthropi X7). Strain X5 favored the production of acetate, while X7 preferred the production of hydrogen. The rate of Cd(II) removal by all EAB (1.20-1.32 mg/L/h), and the rates of acetate production by X5 (29.4 mg/L/d) and hydrogen evolution by X7 (0.0187 m3/m3/d) increased in the presence of a circuital current. The production of acetate and hydrogen was regulated by the release of extracellular polymeric substances (EPS), which also exhibited invariable catalytic activity toward the reduction of Cd(II) to Cd(0). The intracellular activities of glutathione (GSH), catalase (CAT), superoxide dismutase (SOD) and dehydrogenase were altered by the circuital current and Cd(II) concentration, and these regulated the products distribution. Such understanding enables the targeted manipulation of the MES operational conditions that favor the production of acetate from CO2 sequestration with simultaneous hydrogen production and removal/recovery of Cd(II) from metal-contaminated and organics-barren waters.

Reduction of Cu(II) and simultaneous production of acetate from inorganic carbon by Serratia Marcescens biofilms and plankton cells in microbial electrosynthesis systems

Simultaneous Cu(II) reduction (6.42 ± 0.02 mg/L/h), acetate production (1.13 ± 0.02 mg/L/h) from inorganic carbon (i.e., CO2 sequestration), and hydrogen evolution (0.0315 ± 0.0005 m3/m3/d) were achieved in a Serratia marcescens Q1 catalyzed microbial electrosynthesis system (MES). The biofilms released increasing amounts of extracellular polymeric substances (EPS) with a higher compositional diversity and stronger Cu(II) complexation, compared to the plankton cells, at higher Cu(II) concentrations (up to 80 mg/L) and circuital currents (cathodic potential of −900 mV vs. standard hydrogen electrode (SHE)). Moreover, the biofilms reduced Cu(II) to Cu(0) more effectively than the plankton cells. At Cu(II) concentrations below 80 mg/L, the dehydrogenase activity in the biofilms was higher than in the plankton cells, and increased with circuital current, which was converse to the lower activities of catalase (CAT), superoxide dismutase (SOD) and antioxidative glutathione (GSH) in the biofilms than the plankton cells, although all these physiological activities were positively correlated with the concentration of Cu(II). This is the first study that evaluates the EPS constituents and the physiological activities of the biofilms and the plankton cells in the MESs, that favors the production of acetate from CO2 sequestration and the simultaneous reduction of Cu(II) from organics-barren waters contaminated with heavy metals.

Engineering an electroactive Escherichia coli for the microbial electrosynthesis of succinate from glucose and CO2

BackgroundElectrochemical energy is a key factor of biosynthesis, and is necessary for the reduction or assimilation of substrates such as CO2. Previous microbial electrosynthesis (MES) research mainly utilized naturally electroactive microbes to generate non-specific products.ResultsIn this research, an electroactive succinate-producing cell factory was engineered in E. coli T110(pMtrABC, pFccA-CymA) by expressing mtrABC, fccA and cymA from Shewanella oneidensis MR-1, which can utilize electricity to reduce fumarate. The electroactive T110 strain was further improved by incorporating a carbon concentration mechanism (CCM). This strain was fermented in an MES system with neutral red as the electron carrier and supplemented with HCO3+, which produced a succinate yield of 1.10 mol/mol glucose—a 1.6-fold improvement over the parent strain T110.ConclusionsThe strain T110(pMtrABC, pFccA-CymA, pBTCA) is to our best knowledge the first electroactive microbial cell factory engineered to directly utilize electricity for the production of a specific product. Due to the versatility of the E. coli platform, this pioneering research opens the possibility of engineering various other cell factories to utilize electricity for bioproduction.

Microbial electrosynthesis system with dual biocathode arrangement for simultaneous acetogenesis, solventogenesis and carbon chain elongation.

A microbial electrosynthesis cell comprising two biological cathode chambers sharing the same anode compartment is used to promote the production of C2-C4 carboxylic acids and alcohols from carbon dioxide. Each cathode chamber provides ideal pH conditions to favor acetogenesis/carbon chain elongation (pH = 6.9), and solventogenesis (pH = 4.9), respectively, without the requirement of external acid/base dosing.

Understanding the interdependence of operating parameters in microbial electrosynthesis: a numerical investigation.

This study describes and evaluates a dynamic computational model for a two chamber microbial electrosynthesis (MES) system. The analysis is based on redox mediators and a two population model, describing bioelectrochemical kinetics at both anode and cathode. Mass transfer rates of the substrate and bacteria in the two chambers are combined with the kinetics and Ohm's law to derive an expression for the cell current density. The effect of operational parameters such as initial substrate concentration at the anode and cathode and the operation cycle time on MES performance is evaluated in terms of product formation rate, substrate consumption and coulombic efficiency (CE). For a fixed operation cycle time of 3 or 4 days, the anode and cathode initial substrate concentrations show linear relationship with product formation rate; however MES operation with a 2 day cycle time shows a more complex behaviour, with acetic acid production rates reaching a plateau and even a slight decrease at higher concentrations of the two substrates. It is also shown that there is a trade-off between product formation rate and substrate consumption and CE. MES performance for operation with cycle time being controlled by substrate consumption is also described. Results from the analysis demonstrate the interdependence of the system parameters and highlight the importance of multi-objective system optimization based on targeted end-use.

Electrode material properties for designing effective microbial electrosynthesis systems

(a) Pictograph and (b) schematic representation of the placement of multiple working electrodes with a single counter electrode and reference electrode using an N'Stat setup and (c) the schematic of the potentiostat interface connection with the electrochemical cell.

Effect of the electric supply interruption on a microbial electrosynthesis system converting inorganic carbon into acetate

Microbial electrosynthesis (MES) technology relies on the direct use of electrons to convert CO2 into long chain organic chemicals. Therefore, MES has been proposed to be coupled to the renewable electricity supply, mainly from solar and wind sources. However, those energies suffer fluctuations and interruptions of variable duration, which can have an adverse effect on MES performance. Such effects on MES has been evaluated for the first time under different interruptions time. H-cell-MES reactors were disconnected from power supply during 4, 6, 8, 16, 32 and 64 h. Interruptions affected the acetate production rate, causing a decrease of until 77% after 64 h off. However, after all the interruptions, the acetate production was restored, taking between 7 and 16 h for the reduction current to turn steady. Therefore, microbial community on MES proved to be resilient and able to recover the electro-autotrophic activity despite the duration of current supply interruptions.

Electrochemically mediated CO2 reduction for bio-methane production: a review

A number of methods for carbon capture, more specifically, CO2 capture have been researched in the past few years. One such method is electrochemical CO2 reduction to biomethane which also serves the purpose of biogas upgradation using microbial electrosynthesis systems. This technology is also known as Power to Gas technology and the review starts with the importance and requirement of PtG in the modern world by studying energy production and consumption patterns in Europe, with a focus on Norway. The paper summarises the recent works and concepts in the field of bioelectrochemical systems with a focus on electron transfer mechanisms, biocatalysts and reactor designs. Works and gaps in the studies of direct interspecies electron transfer and biocathode developments are discussed in detail. This is followed by a discussion explaining various reactor designs, the advantages of single chambered microbial reactors and the importance of reactors that combine anaerobic digestion with microbial electrolysis cells.

Nanoscale membranes that chemically isolate and electronically wire up the abiotic/biotic interface

By electrochemically coupling microbial and abiotic catalysts, bioelectrochemical systems such as microbial electrolysis cells and microbial electrosynthesis systems synthesize energy-rich chemicals from energy-poor precursors with unmatched efficiency. However, to circumvent chemical incompatibilities between the microbial cells and inorganic materials that result in toxicity, corrosion, fouling, and efficiency-degrading cross-reactions between oxidation and reduction environments, bioelectrochemical systems physically separate the microbial and inorganic catalysts by macroscopic distances, thus introducing ohmic losses, rendering these systems impractical at scale. Here we electrochemically couple an inorganic catalyst, a SnO2 anode, with a microbial catalyst, Shewanella oneidensis, via a 2-nm-thick silica membrane containing -CN and -NO2 functionalized p-oligo(phenylene vinylene) molecular wires. This membrane enables electron flow at 0.51 μA cm−2 from microbial catalysts to the inorganic anode, while blocking small molecule transport. Thus the modular architecture avoids chemical incompatibilities without ohmic losses and introduces an immense design space for scale up of bioelectrochemical systems.

Enzyme-Assisted Microbial Electrosynthesis of Poly(3-hydroxybutyrate) via CO2 Bioreduction by Engineered Ralstonia eutropha

Microbial electrosynthesis (MES) is a promising technology to reduce carbon dioxide using inward electron transfer mechanisms to synthesize value-added chemicals with microorganisms as electrocatalysts and electrons from cathodes as reducing equivalents. To enhance CO2 assimilation in Ralstonia eutropha, a formate dehydrogenase (FDH) assisted MES system was constructed, in which FDH catalyzed the reduction of CO2 to formate in the cathodic chamber. Formate served as the electron carrier to transfer electrons derived from cathodes into R. eutropha. To enable efficient formation of formate from CO2, neutral red (NR) was used to facilitate the extracellular regeneration of NADH, the cofactor of FDH. Meanwhile, NR also played an essential role as electron shuttle to directly deliver electrons from cathodes into R. eutropha to increase the level of intracellular reducing equivalents, thus facilitating the efficiency of MES. On the other hand, the Calvin–Benson–Bassham (CBB) cycle was further engineered by the ...

Microbial electrosynthesis of organic chemicals from CO2 by Clostridium scatologenes ATCC 25775T

BackgroundThe conversion of CO2 into high value-added products has a very important environmental and economic significance. Microbial electrosynthesis (MES) is a promising technology, which adopts a bioelectrochemical system to transform CO2 into organic chemicals.ResultsIn this study, Clostridium scatologenes ATCC 25775T, an anaerobic acetogenic bacterium, demonstrated its utility as a biocatalyst in a MES system, for the first time. With the cathodic potential of the MES system decreased from − 0.6 to − 1.2 V (vs. Ag/AgCl), the current density of the MES, and the production of organic chemicals, increased. Combining the genetic analysis and the results of the wet lab experiments, we believe C. scatologenes may accept electrons directly from the cathode to reduce CO2 into organic compounds at a potential of − 0.6 V. The acetic and butyric acid reached a maximum value of 0.03 and 0.01 g/L, respectively, and the maximum value of total coulombic efficiency was about 84%, at the potential of − 0.6 V. With the decrease in cathodic potentials, both direct electron transfer and exogenous electron shuttle, H2 might be adopted for the C. scatologenes MES system. At a potential of − 1.2 V, acetic acid, butyric acid and ethanol were detected in the cathodic chamber, with their maximum values increasing to 0.44, 0.085 and 0.015 g/L, respectively. However, due to the low H2 utilization rate by the C. scatologenes planktonic cell, the total coulombic efficiency of the MES system dropped to 37.8%.ConclusionClostridium scatologenes is an acetogenic bacterium which may fix CO2 through the Wood–Ljungdahl pathway. Under H2 fermentation, C. scatologenes may reduce CO2 to acetic acid, butyric acid and ethanol. It can also be used as the biocatalyst in MES systems.

Enhanced electrosynthesis performance of Moorella thermoautotrophica by improving cell permeability

Microbial electrosynthesis systems (MES) are promising devices in which microbes obtain electrons from electrodes to produce extracellular multicarbon compounds. This study investigates whether improvement in cell permeability can enhance electrosynthesis performance of Gram-positive Moorella thermoautotrophica in MES. Results showed that when ≤30mg/L penicillin was added, the cell permeability was doubled, and the electron uptake per biomass (including both cathode-associated biomass and suspended biomass) was 1.84 times that of the control, while formate and acetate production rates per biomass were 1.96 and 2.23 times those of the control, respectively. Enhanced cell permeability caused higher redox activities of outmost cytochrome C and increased release of redox electron shuttles, both of which were beneficial to extracellular electron uptake. Coulombic efficiencies increased from 73%±3% to 88%±3% with better cell permeability, demonstrating that higher proportion of electrical energy recovered in the chemical-production reaction. This research demonstrates that making a moderate decrease in peptidoglycan of cell walls to improve cell permeability can enhance electron uptakes and chemical production rates of Gram-positive microbes in MES, which would serve as a base for the future genetic modification study of superior electrosynthesis strains.

Metagenome-Assembled Genome Sequences of Acetobacterium sp. Strain MES1 and Desulfovibrio sp. Strain MES5 from a Cathode-Associated Acetogenic Microbial Community.

ABSTRACTDraft genome sequences of Acetobacterium sp. strain MES1 and Desulfovibrio sp. strain MES5 were obtained from the metagenome of a cathode-associated community enriched within a microbial electrosynthesis system (MES). The draft genome sequences provide insight into the functional potential of these microorganisms within an MES and a foundation for future comparative analyses.

Metabolic Reconstruction and Modeling Microbial Electrosynthesis

Microbial electrosynthesis is a renewable energy and chemical production platform that relies on microbial cells to capture electrons from a cathode and fix carbon. Yet despite the promise of this technology, the metabolic capacity of the microbes that inhabit the electrode surface and catalyze electron transfer in these systems remains largely unknown. We assembled thirteen draft genomes from a microbial electrosynthesis system producing primarily acetate from carbon dioxide, and their transcriptional activity was mapped to genomes from cells on the electrode surface and in the supernatant. This allowed us to create a metabolic model of the predominant community members belonging to Acetobacterium, Sulfurospirillum, and Desulfovibrio. According to the model, the Acetobacterium was the primary carbon fixer, and a keystone member of the community. Transcripts of soluble hydrogenases and ferredoxins from Acetobacterium and hydrogenases, formate dehydrogenase, and cytochromes of Desulfovibrio were found in high abundance near the electrode surface. Cytochrome c oxidases of facultative members of the community were highly expressed in the supernatant despite completely sealed reactors and constant flushing with anaerobic gases. These molecular discoveries and metabolic modeling now serve as a foundation for future examination and development of electrosynthetic microbial communities.

Acetate production and electron utilization facilitated by sulfate-reducing bacteria in a microbial electrosynthesis system

The aim of this study is to investigate the effect of sulfate-reducing bacteria on performance of a mixed culture microbial electrosynthesis system (MES). The two-chamber MESs were operated under different cathode potentials (−0.5, −0.6, −0.7, and −0.8V) with or without addition of 6mM sulfate. At −0.7V, acetate production and electrons harvesting in the MES with the sulfate addition were 31.81mM and 5152C, respectively, which improved by 2.7 and 2.4times compared to that without sulfate. With sulfate, the biomass, proportion of live cells, and electrochemical activity of cathode biofilm were enhanced at all the potentials. At −0.7V, the relative abundance of Acetobacterium and Desulfovibrionaceae was 14.2% and 36.7% with sulfate, respectively, compared to 17.4% and 7.3% without sulfate. At −0.7 and −0.8V, the sulfate-reducing bacteria can promote the electron transfer of cathode biofilm and enhance the acetate production.

Energy Efficiency and Productivity Enhancement of Microbial Electrosynthesis of Acetate.

It was hypothesized that a lack of acetogenic biomass (biocatalyst) at the cathode of a microbial electrosynthesis system, due to electron and nutrient limitations, has prevented further improvement in acetate productivity and efficiency. In order to increase the biomass at the cathode and thereby performance, a bioelectrochemical system with this acetogenic community was operated under galvanostatic control and continuous media flow through a reticulated vitreous carbon (RVC) foam cathode. The combination of galvanostatic control and the high surface area cathode reduced the electron limitation and the continuous flow overcame the nutrient limitation while avoiding the accumulation of products and potential inhibitors. These conditions were set with the intention of operating the biocathode through the production of H2. Biofilm growth occurred on and within the unmodified RVC foam regardless of vigorous H2 generation on the cathode surface. A maximum volumetric rate or space time yield for acetate production of 0.78 g/Lcatholyte/h was achieved with 8 A/Lcatholyte (83.3 A/m2projected surface area of cathode) supplied to the continuous flow/culture bioelectrochemical reactors. The total Coulombic efficiency in H2 and acetate ranged from approximately 80–100%, with a maximum of 35% in acetate. The overall energy efficiency ranged from approximately 35–42% with a maximum to acetate of 12%.