Fig. 5.
Comparison of cumulative CH4 production (cum. CH4 production), max. CH4 evolution rate (MERmax), max. biomass production rate (r(x),max), and maximum biomass concentration (xmax) of M. thermaggregans and M. marburgensis. The gray bars indicate the performance of M. marburgensis at 65 °C, a pH of 7.0, and with exponential feed. The black bars show M. thermaggregans cultivated at 60 °C, a pH of 7.0, and with exponential feed. Both strains were cultivated within 1.5 L of MM medium and continuously gassed with H2/CO2 (80 Vol.-% H2 in CO2) at atmospheric pressure. H2/CO2 and DS were exponentially fed to the suspension. The exponential feeding experiments were performed in triplicates. Striped bars show the results from M. thermaggregans, observed at the following conditions (optimal DoE runs): cum. CH4 production (G–N: 60 °C and 7.0 pH), MERmax (U, V: 65 °C and 7.4 pH), and r(x),max and xmax (O: 60 °C and 7.8 pH)