Development of a simultaneous bioreactor system for characterization of gas production kinetics of methanogenic archaea at high pressure

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.

Keywords: closed batch; high pressure; methanogens; microbiological physiology; parallel bioreactor.

Figure 1

Piping and instrumentation diagram (DIN EN ISO 10628) of the SBRS. Each vessel (R1‐R4) is equipped with instrumentations such as pressure sensors (S01‐S04), heating jackets (S05‐S08), and gas lines including valves

Figure 2

Pressure curves obtained during the gas conversion experiments with MM10 in the SBRS

Figure 3

Pressure curves obtained during the gas conversion experiments with MP10

Figure 4

Pressure curves obtained during the gas conversion experiments with MTa10

Figure 5

Pressure curves of MTa50 and the corresponding calculated MER and k values over time, where MER_max and k_min are determined by the peak maxima and peak minima respectively. Data is not shown for the replicate M. thermaggregans 8, because no pressure drop was detected)