Fig. 1

Concentration profile (a) during a batch experiment with methanol and propionate with the initial pH 7 at 308 K. Initially (day 0–25), acetate is formed via CO₂ elongation with methanol concurrently with a pH drop. Propionate elongation to valerate starts slowly in the beginning; however, after 40 days when the pH is 5.8 it is the most prevalent metabolic activity. The total conversions at the end of the batch experiment are shown as well (b). The error bars represent the minimum and maximum values measured in the duplo experiments