Accumulation of carbon dioxide (CO2), associated with global temperature rise, and drastically decreasing fossil fuels necessitate the development of improved renewable and sustainable energy production processes. A possible route for CO2 recycling is to employ autotrophic and hydrogenotrophic methanogens for CO2-based biological methane (CH4) production (CO2-BMP). In this study, the physiology and productivity of Methanobacterium thermaggregans was investigated in fed-batch cultivation mode. It is shown that M. thermaggregans can be reproducibly adapted to high agitation speeds for an improved CH4 productivity. Moreover, inoculum size, sulfide feeding, pH, and temperature were optimized. Optimization of growth and CH4 productivity revealed that M. thermaggregans is a slightly alkaliphilic and thermophilic methanogen. Hitherto, it was only possible to grow seven autotrophic, hydrogenotrophic methanogenic strains in fed-batch cultivation mode. Here, we show that after a series of optimization and growth improvement attempts another methanogen, M. thermaggregas could be adapted to be grown in fed-batch cultivation mode to cell densities of up to 1.56 g L⁻¹. Moreover, the CH4 evolution rate (MER) of M. thermaggregans was compared to Methanothermobacter marburgensis, the CO2-BMP model organism. Under optimized cultivation conditions, a maximum MER of 96.1 ± 10.9 mmol L⁻¹ h⁻¹ was obtained with M. thermaggregans—97% of the maximum MER that was obtained utilizing M. marburgensis in a reference experiment. Therefore, M. thermaggregans can be regarded as a CH4 cell factory highly suited to be applicable for CO2-BMP. Electronic supplementary material The online version of this article (10.1007/s00253-018-9183-2) contains supplementary material, which is available to authorized users.
A methane productivity > 25 [kg CH4 m-3 h-1] at >96 Vol.% CH4 in the raw offgas was achieved with the CO2-BMP process using a unique high pressure bioreactor. Experiments have been performed at the gas converting bioprocess development labs of Krajete GmbH in the frame of the H2020 project CELBICON https://www.youtube.com/watch?v=_0tqGBwMtCg More info are available on www.celbicon.org where you can see how biomethanation technology was coupled to bioplastic (PHA) production starting from pressurized syngas.
Over recent years the interest in new biofuel generations, based on converting gaseous substrate(s) such as carbon dioxide (CO2), carbon monoxide (CO) or hydrogen (H2) to gaseous product(s), arose. An example for such a gas converting bioprocess is the biological methane production process using CO2 as sole carbon source (CO2-BMP) . Axenic cultures of Methanothermobacter marburgensis grown in a defined mineral medium already proved that high conversion rates of CO2 and H2 to methane (CH4) can be reached . However, this bioprocess was often described in literature as a gas transfer limited bioprocess . Therefore, the kinetic limitation towards an increased methane productivity cannot be overcome solely by the growth of more biomass during continuous operation. More important is the development of a suitable bioreactor system that allows reaching a high mass transfer of the limiting gaseous substrate (H2) in the liquid phase once an appropriate feeding strategy is applied to maintain sufficient biocatalyst in suspension for converting all the dissolved reactive gases. This work will present development steps , , methods ,  as well as the applied bioprocess control approach  that enabled to construct and operate a custom designed and manufactured high pressure 20 L bioreactor system to overcome the so far existing performance limitations. In this setup, a methane evolution rate (MER) higher than 1.4 molCH4 Lbroth-1 h-1 was reached using an axenic chemostat culture of Methanothermobacter marburgensis grown on a defined mineral medium at pressures up to 16 bar while using solely CO2 as carbon source. The application of this feed forward control strategy enabled to predict and control biomass growth during operation which in return allowed to convert more than 99% of the applied 2.9 vvm [NLgas Lbroth-1 min-1] of H2-CO2 into a high purity bio-CH4 (>95 Vol.% CH4 in the raw wet gas).
The CO2-BMP process uses selected archaea microorganisms as biological catalyst to perform a carbon activation and methanation autocatalytic reaction which converts hydrogen and carbon dioxide directly into methane, water and biomass in continuous or intermittent operations. The integrated modular development workflow consists of studying the biomethanation process from different angles and using different “levels” of pressurized H2 and CO2.The following aspects have been investigated in CELBICON project: pressure tolerance, media demands, feed strategy development for fermentation and validation runs in continuous culture to reach performances above 20 kgCH4 m-3 h-1 (MER > 1250 mmolCH4 Lbroth-1 h-1) in steady state production in order to support process simulation and tecno-economic assessment. Furthermore, the methodologies from the CO2-BMP process development are transferable to other gas converting bioprocess endeavour like performing acetone production from H2 and CO2 as in ENGICOIN project
The process uses archaea microorganisms as biological catalyst to perform a carbon activation and methanation reaction by converting hydrogen and carbon dioxide directly into methane, water and biomass
More and more attention has recently been paid to the electrochemical treatment of wastewater for the degradation of refractory organics, such as phenol and its derivatives. The electrodeposition of different types of manganese oxides (MnOx) over two substrates, namely metallic titanium and titania nanotubes (TiO2-NTs), is reported herein. X-Ray Diffraction (XRD) and X-Ray Photoelectron Spectroscopy (XPS) analyses have confirmed the formation of different oxidation states of the manganese, while Field Emission Scanning Electronic Microscopy (FESEM) analysis has helped to point out the evolutions in the morphology of the samples, which depends on the electrodeposition parameters and calcination conditions. Moreover, cross section FESEM images have demonstrated the penetration of manganese oxides inside the NTs for anodically deposited samples. The electrochemical properties of the electrodes have been investigated by means of cyclic voltammetry (CV) and linear sweep voltammetry (LSV), both of which have shown that both calcination and electrodeposition over TiO2-NTs lead to more stable electrodes, which exhibited a marked increase in the current density. The activity of the proposed nanostructured samples toward phenol degradation has been investigated. The cathodically electrodeposited manganese oxides (α-MnO2) have been found to be the most active phase, with a phenol conversion of 26.8%. The anodically electrodeposited manganese oxides (α-Mn2O3), instead, have shown higher stability, with a final working potential of 2.9 V vs. RHE. The TiO2-NTs interlayer has contributed, in all cases, to a decrease of about 1 − 1.5 V in the final (reached) potential, after a reaction time of 5 h. Electrochemical impedance spectroscopy (EIS) and accelerated life time tests have confirmed the beneficial effect of TiO2-NTs, which contributes by improving both the charge transfer properties (kinetics of reaction) and the adhesion of MnOx films.
Low-cost manganese oxide, MnOx-based electrocatalysts, containing α-MnO2 and mixed α-Mn2O3/α-MnO2 phases, were synthesized by scalable anodic and cathodic electrodeposition methods, respectively. Their morphological and chemical composition were characterized by means of Field Emission Scanning Electronic Microscopy (FESEM), X-Ray Diffraction (XRD) and X-ray Photoelectron Spectroscopy (XPS). These electrodes were tested for the electro-oxidation of a recalcitrant molecule (i.e. phenol) in a lab-scale high temperature and high pressure (HTHP) batch electrocatalytic reactor. Their electrocatalytic activity was compared with that of state-of-the-art anodes for phenol electro-oxidation: antimony-doped tin oxide (SnO2–Sb5+) and ruthenium oxide (RuO2): first, under standard ambient conditions, and then, under the conditions of a Polymeric Electrolyte Membrane (PEM) electrolyzer (i.e. 85 °C and 30 bar) and of mild Catalytic Wet Air Oxidation (CWAO, i.e. 150 °C and 30 bar). Both reaction time and current density were varied to investigate their effect in the performances of the system as well as on the reaction mechanism. Both MnOx electrodes reported enhanced conversion efficiencies, up to ∼75%, at the highest pressure and temperature, and at the lowest applied current density, which influenced the process by improving dissolution of the O2 evolved, the reaction kinetics and thermodynamics, and by minimizing irreversibilities, respectively. The here reported MnOx films achieved conversion and mineralization efficiencies comparable to Sb-SnO2 (that is the more toxic) and RuO2 (that is more expensive) materials, operating under mild CWAO operation conditions, which demonstrate the potential of the electrocatalytic HTHP process as a sustainable advanced oxidation technology for wastewater treatment or electrosynthesis applications. https://authors.elsevier.com/a/1WsqP33-eDRMF
Conversion of surplus electricity to chemical energy is increasingly attracting attention. Thereof, biological energy conversion and storage technologies are one of several viable options. In this work, the inherent challenges faced in analyzing the CO2-based biological methane production (CO2-BMP) process for energy conversion and storage are discussed. A comprehensive assessment of key process parameters on several CO2-BMP process variables was conducted. It was found that literature data often misses important information and/or the required accuracy for resolution of the underlying mechanistic effects, especially when modelling reactor dependent variables. Multivariate dependencies inherently attributable to gas-to-gas conversion bioprocesses are particularly illustrated with respect to CO2-BMP. It is concluded that CO2-BMP process modelling requires the application of process analytical technology. The understanding of the CO2-BMP mechanistic process is discussed to assist with the analysis and modelling of other gas-to-gas conversion processes. The findings presented in this work could aid in establishing a biotechnology-based energy to gas conversion and storage landscape.
The CO2 that comes from the use of fossil fuels accounts for about 65% of the global greenhouse gases emissions, and it plays a critical role in global climate changes. Among the different strategies that have been considered to address the storage and reutilization of CO2, the transformation of CO2 into chemicals or fuels with a high added-value has been considered a winning approach. This transformation is able to reduce the carbon emissions and induce a “fuel switching” that exploits renewable energy sources. The aim of this brief review is to gather and critically analyse the main efforts that have been made and achievements that have been reached in the electrochemical reduction of CO2 for the production of CO. The main focus is on the prospective of exploiting the intrinsic nature of the electrolysis process, in which CO2 reduction and H2 evolution reactions can be combined, into a competitive approach, to produce syngas. Several well-stablished processes already exist for the generation of fuels and fine-chemicals from H2/CO mixtures of different ratios. Hence, the different kinds of electrocatalysts and electrochemical reactors that have been used for the CO and H2 evolution reactions have been analysed, as well as the main factors that influence the performance of the system from the thermodynamic, kinetic and mass transport points of view.