Fig. 3.
Maximum CH4 evolution rate (MERmax) values from the DoE fed-batch experiment of M. thermaggregans shown as a function of temperature and pH. MERmax values were calculated via gas outflow correction factor, referred to as rinert (gray bars) or through off-gas measurements by using a drum-type gas meter (colored bars). All DoE fed-batch cultivations were performed within a temperature range from 50 to 70 °C and pH range from 6.2 to 7.8. M. thermaggregans was cultivated within 1.5 L of MM medium and continuously gassed with 1 vvm H2/CO2 (80 Vol.-% H2 in CO2) at atmospheric pressure. In addition, 0.5 mol L−1 Na2S·9H2O was continuously added with a DS of 0.3 mL h−1. Experiments indicated with a yellow (A: 50 °C and 7.0 pH), light blue (F: 60 °C and 6.2 pH), dark blue (O: 60 °C and 7.8 pH), light green (P: 65 °C and 6.2 pH), and violet (W: 70 °C and 7.0 pH) bar were performed once. Experiments illustrated with an orange (B, C: 55 °C and 6.6 pH), red (D, F: 55 °C and 7.4 pH), green (R, S: 65 °C and 6.6 pH), and dark green (U, V: 65 °C and 7.4 pH) bars were performed twice. Experimental results shown with green bars (R, S, T: 65 °C and 6.6 pH) were performed in triplicates. The center point indicated with blue bars (60 °C and 7.0 pH) was examined in octuplicates