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.

BACKGROUND: This study describes the operation of continuous packed‐bed reactors containing Clostridium beijerinckii DSM 6422 attached to granular activated carbon to improve butanol productivity and sugar consumption from rice straw hydrolysate.RESULTS: A single‐stage fermenter, which was evaluated at dilution rates ranging from 0.3 to 1.8 h⁻¹, achieved a maximum butanol productivity of 4.44 g L⁻¹ h⁻¹ at a dilution rate of 1.2 h⁻¹, corresponding to a sugar consumption of 40%. The performance of the two‐stage fermentation plant with in‐line gas stripping and effluent recycling was studied at a dilution rate of 1.2 h⁻¹ for each bioreactor, resulting in a butanol productivity of 4.16 g L⁻¹ h⁻¹ in the first stage and 0.98 g L⁻¹ h⁻¹ in the second. Nutrient supplementation was identified as an effective method of enhancing butanol productivity by up to 50% in the second stage. The overall sugar consumption of the two‐stage packed‐bed reactor with in‐line gas stripping was 69%.CONCLUSION: These findings show considerable promise for the future development of lignocellulosic biorefineries, as they demonstrate a potential to achieve economically profitable butanol production. © 2024 The Author(s). Journal of Chemical Technology and Biotechnology published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry (SCI).

This study evaluates the feasibility of valorizing the starch fraction of thermoplastic starch-based bioplastics (TPS-BPs) by converting it into lactic acid (LA) through microbial fermentation. To enhance the accessibility of the starch fraction within the bioplastic matrix, microwave-assisted pretreatments were evaluated using a 2⁴⁻¹ fractional factorial design. The best pretreatment conditions within the tested design were identified as 150 °C with 0.1% H₂SO₄ for 30 min, which enabled the release of 17.5 g L⁻¹ glucose within 24 h of saccharification. Among the evaluated strains, Heyndrickxia coagulans showed the best kinetic performance in the preliminary comparison at pH 6.0, with a maximum volumetric productivity of 8.25 g L⁻¹ h⁻¹ and a yield of 0.91 g g⁻¹, and was selected for subsequent experiments. To enhance carbon availability and overcome the low starch content (≈20%) of commercial TPS-BP, a co-fermentation strategy with rice straw was implemented. While separate hydrolysis and fermentation (SHF) was limited by carbon catabolite repression, simultaneous saccharification and fermentation (SSF) intensified production. By utilizing TPS-BP pretreatment slurry as the liquid phase for rice straw saccharification, a final LA concentration of 55.1 ± 0.7 g L⁻¹ was achieved. This co-valorization strategy demonstrates a feasible route for integrating the starch fraction of bioplastic waste into circular biorefineries, which could mitigate the seasonal availability of agricultural residues.