Abstract
Cultivation of methanogens under high pressure offers a great opportunity in biotechnological processes, one of which is the improvement of the gas‐liquid transfer of substrate gases into the medium broth. This article describes a newly developed simultaneous bioreactor system consisting of four identical cultivation vessels suitable for investigation of microbial activity at pressures up to 50 bar and temperatures up to 145°C. Initial pressure studies at 10 and 50 bar of the autotrophic and hydrogenotrophic methanogens Methanothermobacter marburgensis, Methanobacterium palustre, and Methanobacterium thermaggregans were performed to evaluate the reproducibility of the system as well as to test the productivity of these strains. The strains were compared with respect to gas conversion (%), methane evolution rate (MER) (mmol L‐1 h−1), turnover rate (h−1), and maximum conversion rate (k min) (bar h−1). A pressure drop that can be explained by the reaction stoichiometry showed that all tested strains were active under pressurized conditions. Our study sheds light on the production kinetics of methanogenic strains under high‐pressure conditions. In addition, the simultaneous bioreactor system is a suitable first step screening system for analyzing the substrate uptake and/or production kinetics of gas conversion and/or gas production processes for barophilic or barotolerant microbes.
Highlights
Recent developments in the field of renewable biofuel production have raised interest in finding new bioprocessing routes as an alternative to fossil fuels
The lag phases for M. marburgensis clearly varied (Figure 2), whereas M. palustre (Figure 3), and M. thermaggregans (Figure 4) showed reproducible gas conversion results when considering the length of the respective lag phases
According to the results of this study, the newly developed simultaneous bioreactor system (SBRS) is a suitable system for the rapid screening of barophilic or barotolerant CO2-type hydrogenotrophic methanogens at hyperbaric pressures of 10 and 50 bar
Summary
Recent developments in the field of renewable biofuel production have raised interest in finding new bioprocessing routes as an alternative to fossil fuels. One of the ideas behind this concept is the re-evaluation of off-gas streams that contain CO2 and H2, the latter being obtained from processes using excess CO2-type hydrogenotrophic methanogens from the domain of archaea utilize H2 and CO2 as a carbon and energy source to autocatalytically produce CH4, water (H2O), and biomass X (g L−1) according to Equation (1). In this case, the methanogenic archaea act as a biocatalyst. Formation of biomass during this process is dependent of the volumetric biomass production rate (r(X)) [8]
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