Continuous acetone–butanol–ethanol fermentation using SO2–ethanol–water spent liquor from spruce

SO2–ethanol–water (SEW) spent liquor from spruce chips was successfully used for batch and continuous production of acetone, butanol and ethanol (ABE). Initially, batch experiments were performed using spent liquor to check the suitability for production of ABE. Maximum concentration of total ABE was found to be 8.79 g/l using 4-fold diluted SEW liquor supplemented with 35 g/l of glucose. The effect of dilution rate on solvent production, productivity and yield was studied in column reactor consisting of immobilized Clostridium acetobutylicum DSM 792 on wood pulp. Total solvent concentration of 12 g/l was obtained at a dilution rate of 0.21 h−1. The maximum solvent productivity (4.86 g/l h) with yield of 0.27 g/g was obtained at dilution rate of 0.64 h−1. Further, to increase the solvent yield, the unutilized sugars were subjected to batch fermentation.