Continuous acetone–butanol–ethanol (ABE) fermentation and gas production under slight pressure in a membrane bioreactor

Two rounds of acetone–butanol–ethanol (ABE) fermentation under slight pressure were carried out in the continuous and closed-circulating fermentation (CCCF) system. Spores of the clostridium were observed and counted, with the maximum number of 2.1 × 108 and 2.3 × 108 ml−1 separately. The fermentation profiles were comparable with that at atmospheric pressure, showing an average butanol productivity of 0.14 and 0.13 g L−1 h−1. Moreover, the average gas productivities of 0.28 and 0.27 L L−1 h−1 were obtained in two rounds of CCCF, and the cumulative gas production of 52.64 and 25.92 L L−1 were achieved, with the hydrogen volume fraction of 41.43% and 38.08% respectively. The results suggested that slight pressures have no obvious effect on fermentation performance, and also indicated the significance and feasibility of gas recovery in the continuous ABE fermentation process.