Continuous production and supercritical extraction of acetone, butanol and ethanol by Clostridium acetobutylicum fermentation.

A batch and continuous fermentation of Clostridium acetobutylicum ATCC 824 was tested for the production of acetone, butanol and ethanol. It was found that the batch process with a glucose-based medium supplemented with yeast extract grew reliably at 1-L scale at pH 5.0, 37 oC, inoculated with a seed meeting the criteria of pH 4.8 ± 0.7 and a glucose concentration of 9.6 ± 4.9 g/L, and producing 0.5 ±0.1% (w/w) final concentration of butanol. Seeds which do not meet these criteria do not reliably result in growth in production medium. A stable continuous fermentation was developed based on the batch process. The continuous fermentation without cell recycling ran stably at a dilution rate of 0.16 h-1 with a filter-sterilised feed medium, producing oscillating levels of butanol between 0% and 2%, as well as copious amounts of polysaccharide slime. As a solution to the issues faced by the continuous fermentation (incomplete conversion, large amounts of slime, and oscillating solvent production levels), a two-stage reactor is proposed, with potential for a commercial development of this fermentation with multiple stages. Multiple stages will allow the fermentation to run to completion, resolving all issues and producing the maximum yield of solvents. Supercritical extraction has been tested for the extraction of ABE from fermentation broth. It was determined to be unsuitable for solvent extraction at the present time. The extract concentrations reached up to 7.58% with very high variance, which is not sufficiently high to warrant further testing with a view to commercialisation