The Influence of Sugar Composition and pH Regulation in Batch and Continuous Acetone-Butanol-Ethanol Fermentation

Acetone-butanol-ethanol (ABE) fermentation is influenced by external conditions. This work aimed to study the influence of pH regulation on monosaccharide composition in batch and continuous fermentation processes to determine butanol production and productivity. Batch fermentations with ammonium acetate or calcium carbonate combined with minimum pH control (pH >= 4.8 or 5.1) were assessed with pure xylose and glucose/xylose mixtures (ratios of 1:1 and 3:1). Continuous two-stage fermentation was developed using plastic rings to retain the biomass. Although batch fermentations with pure xylose performed better without active minimum pH control with both buffers, minimum pH control was necessary to metabolize xylose in the presence of glucose. Xylose uptake was favored by the use of calcium carbonate and pH >= 5.1 at a ratio of 1:1, while ammonium acetate and a pH >= 4.8 was the best option for a 3:1 ratio. The best butanol production and productivity values with sugar mixtures in batch reactors were 8.8 g L-1 and 0.61 g L-1 h(-1) with an ammonium acetate pH >= 4.8 (ratio 3:1). The glucose/xylose ratio combined with pH regulation thus modulated xylose metabolism and solvent production in batch modes. Immobilized cells combined with operating at D = 0.333 h(-1) and pH regulation increased butanol productivity almost fourfold up to 2.4 +/- 0.2 g L-1 h(-1).