Combined energy storage and methane bioelectrosynthesis from carbon dioxide in a microbial electrosynthesis system

Impact of cathodic pH and bioaugmentation on acetate and CH4 production in a microbial electrosynthesis cell

This study compares carbon dioxide conversion in carbonate-fed microbial electrosynthesis (MES) cells operated at low (5.3), neutral (7) and high (8) pH levels and inoculated either with wild-type or bioaugmented mixed microbial populations. Two 100 mL (cathode volume) MES cells inoculated with anaerobic digester sludge were operated with a continuous supply of carbonate solution (5 g L-1 as CO3 2-). Acetate production was highest at low pH, however CH4 production still persisted, possibly due to pH gradients within the cathodic biofilm, resulting in acetate and CH4 volumetric (per cathode compartment volume) production rates of 1.0 ± 0.1 g (Lc d)-1 and 0.84 ± 0.05 L (Lc d)-1, respectively. To enhance production of carboxylic acids, four strains of acetogenic bacteria (Clostridium carboxidivorans, Clostridium ljungdahlii, Clostridium autoethanogenum, and Eubacterium limosum) were added to both MES cells. In the bioaugmented MES cells, acetate production increased to 2.0 g (Lc d)-1. However, production of other carboxylic acids such as butyrate and caproate was insignificant. Furthermore, 16S rRNA gene sequencing of cathodic biofilm and suspended biomass suggested a low density of introduced acetogenic bacteria implying that selective pressure rather than bioaugmentation led to improved acetate production.

Enhancing CH4 production in microbial electrolysis cells: Optimizing electric field via carbon cathode resistivity

Microbial electrolysis cells (MECs) are increasingly recognized as a promising technology for converting CO2 to CH4, offering the dual benefits of energy recovery from organic wastewater and CO2 emission reduction. A critical aspect of this technology is the enhancement of the electron-accepting capacity of the methanogenic biocathode to improve CH4 production efficiency. This study demonstrates that adjusting the cathode resistivity is an effective way to control the electric field intensity, thereby enhancing the electron accepting capacity and CH4 production. By maintaining the electric field intensity within approximately 8.50-10.83 mV·cm-1, the CH4 yield was observed to increase by up to two-fold. The improvement in CH4 production under optimized electric field conditions was attributed to the enhancement of the direct accepting capacity of the biocathode. This enhancement was primarily due to an increase in the relative abundance of Methanosaeta by approximately 10 % and an up to 83.78 % rise in the electron-accepting capacity of the extracellular polymeric substance. These insights offer a new perspective on the operation of methanogenic biocathodes and propose a novel biocathode construction methodology based on these findings, thus contributing to the enhancement of MEC efficiency.

The Effect of Bismuth and Tin on Methane and Acetate Production in a Microbial Electrosynthesis Cell Fed with Carbon Dioxide

This study investigates the impacts of bismuth and tin on the production of CH4 and volatile fatty acids in a microbial electrosynthesis cell with a continuous CO2 supply. First, the impact of several transition metal ions (Ni2+, Fe2+, Cu2+, Sn2+, Mn2+, MoO42-, and Bi3+) on hydrogenotrophic and acetoclastic methanogenic microbial activity was evaluated in a series of batch bottle tests incubated with anaerobic sludge and a pre-defined concentration of dissolved transition metals. While Cu is considered a promising catalyst for the electrocatalytic conversion of CO2 to short chain fatty acids such as acetate, its presence as a Cu2+ ion was demonstrated to significantly inhibit the microbial production of CH4 and acetate. At the same time, CH4 production increased in the presence of Bi3+ (0.1 g L-1) and remained unchanged at the same concentration of Sn2+. Since Sn is of interest due to its catalytic properties in the electrochemical CO2 conversion, Bi and Sn were added to the cathode compartment of a laboratory-scale microbial electrosynthesis cell (MESC) to achieve an initial concentration of 0.1 g L-1. While an initial increase in CH4 (and acetate for Sn2+) production was observed after the first injection of the metal ions, after the second injection, CH4 production declined. Acetate accumulation was indicative of the reduced activity of acetoclastic methanogens, likely due to the high partial pressure of H2. The modification of a carbon-felt electrode by the electrodeposition of Sn metal on its surface prior to cathode inoculation with anaerobic sludge showed a doubling of CH4 production in the MESC and a lower concentration of acetate, while the electrodeposition of Bi resulted in a decreased CH4 production.

A closer look at bio-hydrogen strategy in post-carbon age and its prospect in Egypt

The necessity of achieving climate goals has become more pressing during the past two years. Discussions on implementing and achieving these goals have taken place in addition to the tightening of the climate targets and the desire for net-zero attainment by as early as 2050. Along with the capacity of biomass to supply the energy needs of society today being quite significant, hydrogen may be the best choice to replace fossil fuels as a clean energy source. Therefore, this study presents a high-level overview of the bio-hydrogen technical pathways, as well as socioeconomic and ecological aspects of bio-hydrogen, and an analysis of the global hydrogen development. A focus on Egypt, as a prominent spot on the global energy map, could instruct other emerging countries and help policymakers of the national hydrogen agenda to prioritize developing a new legal framework to regulate hydrogen production projects, offering financial incentives to energy-intensive companies to switch to using green hydrogen, and providing transparency and certainty regarding future hydrogen demand possibilities.

Comparison of in-situ and ex-situ electrolytic H2 supply for microbial methane production from CO2

Both in-situ and ex-situ electrolytic H2 supply have been used for biomethane production from CO2. However, the pros and cons of them have not been systematically compared. The present study makes this comparison using a 20 L continuous stirred-tank reactor equipped with external and internal electrolyzers. Compared to the ex-situ H2 supply, the in-situ electrolytic H2 bubbles were one order of magnitude smaller, which resulted in improved H2 mass transfer and biomass growth. Consequently, the methane production rate and the coulombic efficiency of the in-situ H2 supply (0.51 L·L-1·d-1, 96%) were higher than those of the ex-situ H2 supply (0.30 L·L-1·d-1, 56%). However, due to high internal resistance, the energy consumption for the in-situ electrolysis was 2.54 times higher than the ex-situ electrolysis. Therefore, the in-situ electrolytic H2 supply appears to be more promising, but reducing energy consumption is the key to the success of this technology.

A comprehensive analysis of key factors influencing methane production from CO2 using microbial methanogenesis cells

With increasing attention on carbon capture and utilization (CCU) technologies for the conversion of CO2 into chemical products, microbial methanogenesis cells (MMCs) have been extensively studied over the past few decades for biomethane production. Using rapidly accumulating data for MMCs with varying configurations and operating conditions, a comprehensive analysis was conducted here to investigate the critical factors that influence methane production rates (MPR) in these systems. A comparison of MPR and set potentials or current densities showed weak linear relationships (R2 < 0.6, p < 0.05), indicating the significant contributions of other important factors impacting methane production. A non-quantitative analysis of these additional parameters indicated the potential importance of using metal catalysts for anode materials where oxygen evolution reaction occurs, while most previous MMC research focused more on cathode materials where the biocatalytic reaction occurs. The use of undefined mixed anaerobic cultures as inocula was found to be sufficient for producing high MPRs, as the electrochemical environment at the cathode provides a strong selective pressure to converge on desirable methanogenic cultures. Other operational parameters, such as catholyte pH control and CO2 supply methods, were also important factors impacting MPR in MMCs, indicating the cumulative impact of these various factors will require careful consideration in future research.

Microbial electrosynthesis of methane and acetate—comparison of pure and mixed cultures

Abstract

The electrochemical process of microbial electrosynthesis (MES) is used to drive the metabolism of electroactive microorganisms for the production of valuable chemicals and fuels. MES combines the advantages of electrochemistry, engineering, and microbiology and offers alternative production processes based on renewable raw materials and regenerative energies. In addition to the reactor concept and electrode design, the biocatalysts used have a significant influence on the performance of MES. Thus, pure and mixed cultures can be used as biocatalysts. By using mixed cultures, interactions between organisms, such as the direct interspecies electron transfer (DIET) or syntrophic interactions, influence the performance in terms of productivity and the product range of MES. This review focuses on the comparison of pure and mixed cultures in microbial electrosynthesis. The performance indicators, such as productivities and coulombic efficiencies (CEs), for both procedural methods are discussed. Typical products in MES are methane and acetate, therefore these processes are the focus of this review. In general, most studies used mixed cultures as biocatalyst, as more advanced performance of mixed cultures has been seen for both products. When comparing pure and mixed cultures in equivalent experimental setups a 3-fold higher methane and a nearly 2-fold higher acetate production rate can be achieved in mixed cultures. However, studies of pure culture MES for methane production have shown some improvement through reactor optimization and operational mode reaching similar performance indicators as mixed culture MES. Overall, the review gives an overview of the advantages and disadvantages of using pure or mixed cultures in MES.

Key points

• Undefined mixed cultures dominate as inoculums for the MES of methane and acetate, which comprise a high potential of improvement

• Under similar conditions, mixed cultures outperform pure cultures in MES

• Understanding the role of single species in mixed culture MES is essential for future industrial applications

A review of recent advances in engineering bacteria for enhanced CO2 capture and utilization

Carbon dioxide (CO₂) is emitted into the atmosphere due to some anthropogenic activities, such as the combustion of fossil fuels and industrial output. As a result, fears about catastrophic global warming and climate change have intensified. In the face of these challenges, conventional CO₂ capture technologies are typically ineffective, dangerous, and contribute to secondary pollution in the environment. Biological systems for CO₂ conversion, on the other hand, provide a potential path forward owing to its high application selectivity and adaptability. Moreover, many bacteria can use CO₂ as their only source of carbon and turn it into value-added products. The purpose of this review is to discuss recent significant breakthroughs in engineering bacteria to utilize CO₂ and other one-carbon compounds as substrate. In the same token, the paper also summarizes and presents aspects such as microbial CO₂ fixation pathways, engineered bacteria involved in CO₂ fixation, up-to-date genetic and metabolic engineering approaches for CO₂ fixation, and promising research directions for the production of value-added products from CO₂. This review's findings imply that using biological systems like modified bacteria to manage CO₂ has the added benefit of generating useful industrial byproducts like biofuels, pharmaceutical compounds, and bioplastics. The major downside, from an economic standpoint, thus far has been related to methods of cultivation. However, thanks to genetic engineering approaches, this can be addressed by large production yields. As a result, this review aids in the knowledge of various biological systems that can be used to construct a long-term CO₂ mitigation technology at an industrial scale, in this instance bacteria-based CO₂capture/utilization technology.

Biological methane production coupled with sulfur oxidation in a microbial electrosynthesis system without organic substrates

Methane is produced in a microbial electrosynthesis system (MES) without organic substrates. However, a relatively high applied voltage is required for the bioelectrical reactions. In this study, we demonstrated that electrotrophic methane production at the biocathode was achieved even at a very low voltage of 0.1 V in an MES, in which abiotic HS^- oxidized to SO₄^2- at the anodic carbon-cloth surface coated with platinum powder. In addition, microbial community analysis revealed the most probable pathway for methane production from electrons. First, electrotrophic H₂ was produced by syntrophic bacteria, such as Syntrophorhabdus, Syntrophobacter, Syntrophus, Leptolinea, and Aminicenantales, with the direct acceptance of electrons at the biocathode. Subsequently, most of the produced H₂ was converted to acetate by homoacetogens, such as Clostridium and Spirochaeta 2. In conclusion, the majority of the methane was indirectly produced by a large population of acetoclastic methanogens, namely Methanosaeta, via acetate. Further, hydrogenotrophic methanogens, including Methanobacterium and Methanolinea, produced methane via H₂.

Microbial fuel cell soft sensor for real-time toxicity detection and monitoring

Real-time toxicity detection and monitoring using a microbial fuel cell (MFC) is often based on observing current or voltage changes. Other methods of obtaining more information on the internal state of the MFC, such as electrochemical impedance spectroscopy (EIS), are invasive, disruptive, time consuming, and may affect long-term MFC performance. This study proposes a soft sensor approach as a non-invasive real-time method for evaluating the internal state of an MFC biosensor during toxicity monitoring. The proposed soft sensor approach is based on estimating the equivalent circuit model (ECM) parameters in real time. A flow-through MFC biosensor was operated at several combinations of carbon source (acetate) and toxicant (copper) concentrations. The ECM parameters, such as internal resistance, capacitance, and open-circuit voltage, were estimated in real time using a numerical parameter estimation procedure. The soft sensor approach proved to be an adequate replacement for EIS measurements in quantifying changes in the biosensor internal parameters. The approach also provided additional information, which could lead to earlier detection of the toxicity onset.