Continuous Acetone-butanol-ethanol Fermentation Research Articles

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.

Kinetic modelling and simulation of batch, continuous and cell-recycling fermentations for acetone-butanol-ethanol production using Clostridium saccharoperbutylacetonicum N1-4

A kinetic model describing acetone-butanol-ethanol (ABE) production applicable to both single substrate fermentations of glucose and xylose as well as co-fermentation of the substrates has been developed. The model accounts for carbon catabolite repression as well as the inhibition of kinetic rates at high substrate concentrations (∼90 g l−1). Model parameters were obtained through kinetic fitting to previously report experimental data. The model was used to study the design and operation of a continuous ABE fermentation process (with and without recycle of biomass). For continuous operation, it was shown that multiple steady-states exist at low dilution rates. For operation with recycle of biomass, the influence of recycle rate on both biomass concentration and ABE productivity were studied. The results indicate that for a range of recycle and dilution rates, ABE productivity can increase to 16 g l−1 h−1 (10 times higher than that without biomass recycling), consistent with experimental results.

Kinetic Study of Acetone-Butanol-Ethanol Fermentation in Continuous Culture.

Acetone-butanol-ethanol (ABE) fermentation by clostridia has shown promise for industrial-scale production of biobutanol. However, the continuous ABE fermentation suffers from low product yield, titer, and productivity. Systems analysis of the continuous ABE fermentation will offer insights into its metabolic pathway as well as into optimal fermentation design and operation. For the ABE fermentation in continuous Clostridium acetobutylicum culture, this paper presents a kinetic model that includes the effects of key metabolic intermediates and enzymes as well as culture pH, product inhibition, and glucose inhibition. The kinetic model is used for elucidating the behavior of the ABE fermentation under the conditions that are most relevant to continuous cultures. To this end, dynamic sensitivity analysis is performed to systematically investigate the effects of culture conditions, reaction kinetics, and enzymes on the dynamics of the ABE production pathway. The analysis provides guidance for future metabolic engineering and fermentation optimization studies.

Economic comparison of a continuous ABE fermentation with and without the integration of an in situ vacuum separation unit

The development of renewable fuels has achieved enormous progress motivated by the rapid decline in petroleum resources and their oscillating price. After a wave of interest in bioethanol and biodiesel, biobutanol has been intensely investigated over the last decade and is considered a suitable renewable fuel. Biobutanol is most often produced through the Acetone‐Butanol‐Ethanol (ABE) bacterial fermentation process. This process is plagued, however, with high recovery costs because of the low final butanol concentration (∼0.01 g/g, 1 wt %) due to product inhibition on the microorganisms. To partly alleviate this problem and increase productivity, in situ butanol recovery techniques from the fermentation broth were proposed. These integrated methods increase the final concentration of butanol, and as a result improve the separation efficiency of the process. This paper compares the economic feasibility of a large‐scale continuous ABE fermentation process with and without integrating a vacuum separation unit. It is illustrated that based on the current market price of butanol, only the integrated fermentation process is economically feasible for discount rates up to ∼45 %. Adding an in situ butanol recovery technique made this process profitable compared to the conventional fermentation process analyzed under two different scenarios: constant fermenter volume and constant butanol production rate. The net present values (NPV) of the conventional process were found to be negative for both scenarios, whereas the integrated vacuum process had a NPV of US$ 87 000 000 at the end of 10 years of operation based on a discount rate of 10 %.

Direct in situ butanol recovery inside the packed bed during continuous acetone-butanol-ethanol (ABE) fermentation.

In this study, the integrated in situ extraction-gas stripping process was coupled with continuous ABE fermentation using immobilized Clostridium acetobutylicum. At the same time, oleyl alcohol was cocurrently flowed into the packed bed reactor with the fresh medium and then recycled back to the packed bed reactor after removing butanol in the stripper. A high glucose consumption of 52g/L and a high butanol productivity of 11g/L/h were achieved, resulting in a high butanol yield of 0.21g-butanol/g-glucose. This can be attributed to both the high bacterial activity for solvent production as well as a threefold increase in the bacterial density inside the packed bed reactor. Also reported is that 64% of the butanol produced can be recovered by the integrated in situ extraction-gas stripping process. A high butanol productivity and a high glucose consumption were simultaneously achieved.

Continuous acetone-butanol-ethanol (ABE) fermentation and gas production under slight pressure in a membrane bioreactor.

Two rounds of acetone-butanol-ethanol (ABE) fermentation under slight pressure were carried out in the continuous and closed-circulating fermentation (CCCF) system. Spores of the clostridium were observed and counted, with the maximum number of 2.1 × 10(8) and 2.3 × 10(8)ml(-1) separately. The fermentation profiles were comparable with that at atmospheric pressure, showing an average butanol productivity of 0.14 and 0.13 g L(-1)h(-1). Moreover, the average gas productivities of 0.28 and 0.27 L L(-1)h(-1) were obtained in two rounds of CCCF, and the cumulative gas production of 52.64 and 25.92 L L(-1) were achieved, with the hydrogen volume fraction of 41.43% and 38.08% respectively. The results suggested that slight pressures have no obvious effect on fermentation performance, and also indicated the significance and feasibility of gas recovery in the continuous ABE fermentation process.

Acetone–butanol–ethanol production with high productivity using Clostridium acetobutylicum BKM19

Conventional acetone-butanol-ethanol (ABE) fermentation is severely limited by low solvent titer and productivities. Thus, this study aims at developing an improved Clostridium acetobutylicum strain possessing enhanced ABE production capability followed by process optimization for high ABE productivity. Random mutagenesis of C. acetobutylicum PJC4BK was performed by screening cells on fluoroacetate plates to isolate a mutant strain, BKM19, which exhibited the total solvent production capability 30.5% higher than the parent strain. The BKM19 produced 32.5 g L(-1) of ABE (17.6 g L(-1) butanol, 10.5 g L(-1) ethanol, and 4.4 g L(-1) acetone) from 85.2 g L(-1) glucose in batch fermentation. A high cell density continuous ABE fermentation of the BKM19 in membrane cell-recycle bioreactor was studied and optimized for improved solvent volumetric productivity. Different dilution rates were examined to find the optimal condition giving highest butanol and ABE productivities. The maximum butanol and ABE productivities of 9.6 and 20.0 g L(-1) h(-1) , respectively, could be achieved at the dilution rate of 0.85 h(-1) . Further cell recycling experiments were carried out with controlled cell-bleeding at two different bleeding rates. The maximum solvent productivities were obtained when the fermenter was operated at a dilution rate of 0.86 h(-1) with the bleeding rate of 0.04 h(-1) . Under the optimal operational condition, butanol and ABE could be produced with the volumetric productivities of 10.7 and 21.1 g L(-1) h(-1) , and the yields of 0.17 and 0.34 g g(-1) , respectively. The obtained butanol and ABE volumetric productivities are the highest reported productivities obtained from all known-processes.

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 8.79g/l using 4-fold diluted SEW liquor supplemented with 35g/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 12g/l was obtained at a dilution rate of 0.21h−1. The maximum solvent productivity (4.86g/lh) with yield of 0.27g/g was obtained at dilution rate of 0.64h−1. Further, to increase the solvent yield, the unutilized sugars were subjected to batch fermentation.

The effects of dilution rate and glucose concentration on continuous acetone–butanol–ethanol fermentation by Clostridium acetobutylicum immobilized on bricks

AbstractBACKGROUND: Owing to the rapid depletion of petroleum fuel, the production of butanol through biological routes has attracted increasing attention. However, low butanol productivity severely impedes its potential industrial production. It is known that the immobilization of whole cells can enhance productivity in the acetone‐butanol‐ethanol (ABE) continuous fermentation process. Therefore, the objective of this study was to develop a low‐cost continuous operation for butanol production.RESULTS: Bricks were chosen as cell support because of their low cost and ease of use for immobilization. The solvent productivity for the bricks with immobilized cells was 0.7 g L−1 h−1, 1.89 times that of free cells (0.37 g L−1 h−1) at a dilution rate of 0.054 h−1. The productivity improvement can contribute to greater retention of biomass inside the reactor due to immobilization. The increase in glucose feed concentration raised total solvent production. However, it resulted in a decrease in yield (grams of solvents produced per gram of glucose introduced). Continuous operation with immobilized cells at a dilution rate of 0.107 h−1 resulted in a solvent productivity of 1.21 g L−1 h−1, 2.1 times that of the operation at 0.027 h−1. However, the yield (butanol produced per glucose consumed) was decreased to 0.19 from 0.29 under the same glucose feeding condition of 60 g L−1.CONCLUSION: The increase in dilution rate and feed glucose concentration enhanced productivity, but decreased the utilization of substrates and the final solvent concentration. Therefore, a balance between productivity and glucose utilization is required to ensure continuous process operation. Copyright © 2011 Society of Chemical Industry

Biodiesel production from crude palm oil and evaluation of butanol extraction and fuel properties

Three principal variables, molar ratio of methanol to oil, amount of catalyst, and reaction temperature, affecting the yield of acid-catalyzed production of methyl ester (biodiesel) from crude palm oil were investigated. The biodiesel was then used as an extractant in batch and continuous acetone–butanol–ethanol fermentation, and its fuel properties and that of the biodiesel–ABE product mix extracted from the batch culture analyzed. The optimized variables, 40:1 methanol/oil (mol/mol) with 5% H 2S0 4 (vol/wt) reacted at 95°C for 9 h, gave a maximum ester yield of 97%. Biodiesel preferentially extracted butanol, and enhanced its production in the batch culture from 10 to 12 g l −1. The fuel properties of biodiesel and the biodiesel–ABE mix were comparable to that of No.2 diesel, but their cetane numbers and the boiling points of the 90% fractions were higher. Therefore, they could serve as efficient No. 2 diesel substitutes. The biodiesel–ABE mixture had the highest cetane number.