Extractive acetonobutylic fermentation by coupling ultrafiltration and distillation

An extractive acetonobutylic fermentation process is developed by integrating bioproduction, Ultrafiltration, and distillation, providing simultaneous retention of biomass, selective removal of inhibitors from the permeate, as well as separation and purification of acetone-butanol-ethanol solvents. Successive batch fermentations were performed with normal pressure distillation (98 degrees C), which permitted prolonging and enhancing (by a factor of 3) solvent production, with very few volume exchanges of medium (average dilution rate ws 0.002 h(-1)), and recovering on-line concentrated solvents. Different operating conditions were also tested in order to study the presence of extracellular autolytic enzymes as inhibition factors: It was shown that, (1) extracellular autolytic activity remains low during the larger part of fermentations, even without enzyme-inactivating thermotreatment in the distillation boiler, and (2) high-temperature distillation causes deleterious effects to the culture medium for long duration treatments. Progressive improvements of the process were achieved, first, by managing continuous runs, providing a minimum renewal of the culture medium and, mainly, by decreasing temperature and pressure of distilation. Solvent productivity then reached 2.6 g/L h for a 0.036 h(-1) average dilution rate, corresponding to a feed concentration of 156 g/L glucose actually consumed.