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The hydrogen gas-to-liquid mass transfer is the limiting factor in biological methanation. In trickle-bed reactors, mass transfer can be increased by high flow velocities in the liquid phase, by adding a packing material with high liquid hold-up or by using methanogenic archaea with a high methane productivity. This study developed a polyphasic approach to address all methods at once. Various methanogenic strains and packings were investigated from a microbial and hydrodynamic perspective. Analyzing the ability to produce high-quality methane and to form biofilms, pure cultures of Methanothermobacter performed better than those of the genus Methanothermococcus. Liquid and static hold-up of a packing material and its capability to facilitate attachment was not attributable to a single property. Consequently, it is recommended to carefully match organism and packing for optimized performance of trickle-bed reactors. The ideal combination for the ORBIT system was identified as Methanothermobacter thermoautotrophicus IM5 and DuraTop (R).
he hydrogen gas-to-liquid mass transfer is the limiting factor in biological methanation. In a trickle-bed reactor, mass transfer can be increased by high flow velocities in the liquid phase, by adding a packing material with high liquid hold-up, or by choosing methanogenic archaea with a high methane productivity. This study analyzed various packings and methanogenic strains from a hydrodynamic and microbial perspective. By analyzing twelve pure cultures of thermophilic methanogens for their ability to produce high quality methane and to form biofilms on different packings, strains of Methanothermobacter were found to perform better than thus of the genus Methanothermococcus. Best methane production and adherence was observed on DuraTop®, Bioflow 9, and filter foam. DuraTop® and Bioflow 9 had also a high dynamic liquid hold-up, but the maximum hold-up was determined for expanded clay. The ideal combination for use in the ORBIT-trickle-bed reactor was identified as Methanothermobacter thermoautotrophicus IM5 and DuraTop®.
Power-to-Methane as one part of Power-to-Gas has been recognized globally as one of the key elements for the transition towards a sustainable energy system. While plants that produce methane catalytically have been in operation for a long time, biological methanation has just reached industrial pilot scale and near-term commercial application. The growing importance of the biological method is reflected by an increasing number of scientific articles describing novel approaches to improve this technology. However, these studies are difficult to compare because they lack a coherent nomenclature. In this article, we present a comprehensive set of parameters allowing the characterization and comparison of various biological methanation processes. To identify relevant parameters needed for a proper description of this technology, we summarized existing literature and defined system boundaries for Power-to-Methane process steps. On this basis, we derive system parameters providing information on the methanation system, its performance, the biology and cost aspects. As a result, three different standards are provided as a blueprint matrix for use in academia and industry applicable to both, biological and catalytic methanation. Hence, this review attempts to set the standards for a comprehensive description of biological and chemical methanation processes.
In this study, a fully automated process converting hydrogen and carbon dioxide to methane in a high temperature trickle-bed reactor was developed from lab scale to field test level. The reactor design and system performance was optimized to yield high methane content in the product gas for direct feed-in to the gas grid. The reaction was catalyzed by a pure culture of Methanothermobacter thermoautotrophicus IM5, which formed a biofilm on ceramic packing elements.
During 600 h in continuous and semi-continuous operation in countercurrent flow, the 0.05 m3 reactor produced up to 95.3 % of methane at a methane production rate of 0.35 mCH43mR-3h-1. Adding nitrogen as carrier gas during startup, foam control and dosing of ammonium and sodium sulfide as nitrogen and sulfur source were important factors for process automation.