Iron effect on acetone-butanol fermentation

WhenClostridium acetobutylicum was grown in batch culture under iron limitation (0.2 mg·l^–1) at a pH of 4.8, glucose was fermented, to butanol as the major fermentation end product, and small quantities of acetic acid were produced. The final conversion yield of glucose into butanol could be increased from 20% to 30% by iron limitation. The acetonebutanol ratio was changed from 3.7 (control) to 11.8. Hydrogenase specific activity was decreased by 40% and acetoacetate decarboxylase specific activity by 25% under iron limitation. Thus, iron limitation affects carbon and electron flow in addition to hydrogenase.     

Importance of agitation in acetone-butanol fermentation

The specific rates of anaerobic solvent production by Clostridium acetobutylicum increased with increasing fermentor impeller speed from 190 to 340 rpm (N(Re) = 3.93 x 10(4)). The maximum values were 5.54, 3.85, and 0.8 mmol/h . g cell for butanol, acetone, and ethanol, respectively. Corresponding rates for respective gases produced were 11.60 and 15.88 mmol/h . g cell for H(2) and CO(2). Further increases in agitation speed resulted in generally decreasing specific production rates to the point of inactive fermentation at 560 rpm. A competition observed between the cellular subsystems for butanol + butyric acid and biomass biosynthesis was evaluated through expressing the energetic yield coefficients. An imbalance between the production and outflux of the former metabolites is apparently further enhanced by a mechanical damage of the cells at high shear rates. A correlation was developed between the production of gases and solvents pointing at both H(2)-to-solvent as well as CO(2)-to-solvent ratios following the same pattern, peaking at 410 rpm.     

Updated model of the batch acetone-butanol fermentation

Summary The recent models of the Acetone-Butanol fermentation did not adequately describe the culture inhibition by the accumulating metabolites and were unable to simulate the acidogenic culture dynamics at elevated pH levels. The present updated modification of the model features a generalised inhibition term and a pH dependent terms for intracellular conversion of undissociated acids into solvent products. The culture dynamics predictions by the developed model compared well with experimental results from an unconventional acidogenic fermentation ofC. acetobutylicum.Nomenclature A acetone concentration in the fermentation broth, [g/L] - AA total concentration of dissociated and undissociated acetic acid, [g/L] - AA _undiss concentration of undissociated acetic acid, [g/L] - APS Absolute Parameter Sensitivity - AT acetoin concentration in the fermentation broth, [g/L] - B butanol concentration in the fermentation broth, [g/L] - BA total concentration of dissociated and undissociated butyric acid, [g/L] - BA _undiss concentration of undissociated butyric acid, [g/L] - E ethanol concentration in the fermentation broth, [g/L] - f(T) inhibition function as defined in Equation (2) - k ₁ constant in Equation (4), [g substrate/g biomass] - k ₂ constant in Equation (4), [g substrate/(g biomass.h)] - k ₁ constant in Equation (5), [g substrate/(g biomass] - k ₂ constant in Equation (5), [g substrate/(g biomass.h)] - k ₃ constant in Equation (6), [g butyric acid/g substrate] - k ₄ constant in Equation (6), [g butyric acid/(g biomass.h)] - k ₅ constant in Equation (7), [g butanol/g substrate] - k ₆ constant in Equation (8), [g acetic acid/g substrate] - k ₇ constant in Equation (8), [g acetic acid/(g biomass.h)] - k ₈ constant in Equation (9), [g acetone/g substrate] - k ₉ constant in Equation (10), [g ethanol/g substrate] - k ₁₀ constant in Equation (11), [g acetoin/g substrate] - k ₁₁ constant in Equation (12), [g lactic acid/g substrate] - K _I Inhibition constant, [g inhibitory products/L] - ke maintenance energy requirement for the cell, [g substrate/(g biomass.h)] - K _AA acetic acid saturation constant, [g acetic acid/L] - K _BA butyric acid saturation constant, [g butyric acid/L] - K _S Monod's saturation constant, [g substrate/L] - LA lactic acid concentration in the fermentation broth, [g/L] - m _i ,n _i constants in Equation (14) - n empirical constant, dependent on degree of inhibition. - P concentration of inhibitory products (B+BA+AA), [g/L] - P _max maximum value of product concentration to inhibit the fermentation, [g/L] - pK_a equilibrium constant - r _A rate of acetone production, [g acetone/L.h] - r _AA rate of acetic acid production, [g acetic acid/L.h] - r _AT rate of acetoin production, [g acetoin/L.h] - r _B rate of butanol production, [g butanol/L.h] - r _BA rate of butyric acid production, [g butyric acid/L.h] - r _E rate of ethanol production, [g ethanol/L.h] - RPS Relative Parameter Sensitivity - r _LA rate of lactic acid production, [g lactic acid/L.h] - r _S dS/dt=total substrate consumption rate, [g substrate/L.h] - r _S substrate utilization rate, [g substrate/L.h] - S substrate concentration in the fermentation broth, [g substrate/L] - S ₀ initial substrate concentration, [substrate/L] - t time, [h] - X biomass concentration, [g/L] - Y _X yield of biomass with respect to substrate, [g biomass/g substrate] - Y _{P i} yield of metabolic product with respect to substrate, [g product/g substrate] Derivatives dX/dt rate of biomass production, [g biomass/L.h] - dP _i /dt rate of product formation, [g product/L.h] Greek letters specific growth rate of the culture, [h^–1] - I specific growth rate of the culture in the presence of the inhibitory products, [h^–1] - µ_max maximum specific growth rate of the culture, [h^–1]     

Agitation and pressure effects on acetone-butanol fermentation

Batch fermentations were run at varying agitation rates and were either pressurized to 1 bar (15.2 psig) or nonpressurized. Agitation and pressure both affect the level of dissolved hydrogen gas in the media, which in turn influences solvent production. In nonpressurized fermentations volumetric productivity of butanol increased as the agitation rate decreased. While agitation had no significant effect on butanol productivity under pressurized conditions, overall butanol productivity was increased over that obtained in the nonpressurized runs. Maximum butyric acid productivity, however, was found to occur earlier and increased as agitation increased. Peak hydrogen productivity occurred simultaneously with peak butyric acid productivity. The proporation of reducing equivalents used in forming the above products was determined using a redox balance based on the fermentation stoichiometry. An inverse relationship between the final concentrations of acetone and acetoin was found in all fermentations studied. The results show that agitation and pressure are important parameters for solvent productivity in acetone-butanol fermentation.     

Mathematical model of a batch acetone-butanol fermentation

A mathematical model for the batch culture of Clostridium acetobutylicum was formulated using experimental data for anaerobic solvent production. The model summarizes biochemical as well as physiological aspects of growth and metabolite synthesis by the production strain. The key fermentation rates are expressed and evaluated with regard to substrate consumption and butanol end-product inhibitory effects. Parametric sensitivity analysis of the batch process model was carried out, indicating the importance of the key process parameters.     

Inhibitory factors involved in acetone-butanol fermentation byClostridium saccharoperbutylacetonicum

Studies carried out onClostridium saccharoperbutylacetonicum (ATCC 27022) reveal that intracellular and extracellular inhibitors, including metabolic end-products, caused the inhibition of cell growth and solvent production. Butanol at the level of 13.0 g/liter was completely inhibitory to the growth of cells, whereas butyric acid totally inhibited the cell growth at a concentration of 8.7 g/liter. Investigations carried out on the effect of addition of culture filtrate concentrate and cell-free extract concentrate indicate that nonvolatile inhibitors produced by cells were also inhibitory for bioconversion. The butanol production was found to be reduced by 15%–20% on addition of cell-free extract concentrate. Inhibition by concentrates was enhanced in the presence of butanol. Addition of heat-sterilized concentrates resulted in a reduction of inhibition.     

The acetone-butanol fermentation in pilot plant and pre-industrial scale

A summary of literature data concerning pilot or preindustrial scale trials of the acetone-butanol fermentation throughout its history is given. The recent pilot plant trials in Austria are also described for the first time. Some aspects of the current development of the acetone-butanol fermentation in general, especially from a technical point of view are also discussed.     

Systems analysis of the culture physiology in acetone-butanol fermentation

The Pronounced differences in performance of a strain of Clostridium acetobutylicum ATCC 824 were analyzed by the method of systems analysis. The mechanism for cellular transport of substrate (glucose), solvents, and acids was studied and mathematically formulated. The systems analysis approach in the treatment of data from culture experiments pointed out the cell membrane malfunction indicated by its altered permeability and reflected in the altered number of active sugar transport sites. Experimental results obtained from the study of the cell uptake of 3-0-methyl glucose (0.7mM) by the "normal culture" and the "retarded culture" confirmed the theoretical predictions regarding a slower transport in the retarded culture. The initial uptake rate and the accumulation coefficient of the sugar in the normal culture were 15.0 and 4.1 times higher, respectively, than those for the retardedculture. Adjustment of the culture pH resulted in further increases in these parameters by factors of 3.0 and 3.5, respectively.     

Adsorbents for extractive bioconversion applied to the acetone-butanol fermentation

Summary Four different polymeric resins were tested as adsorbents in extractive bioconversion applied to the fermentative production of acetone and butanol by Clostridium acetobutylicum. The polymers were tested for their ability to adsorb butanol from pure solutions, and fermentation broths. Furthermore, the effect on the fermentability of the media was tested. The pH was increased to prevent adsorption of intermediates such as acetic and butyric acids. Bonopore, the polymer giving the best adsorption pattern with no undesirable effects, was tested in repeated batch cultures with C. acetobutylicum.     

生物柴油耦联丙酮丁醇发酵的初步研究

以4种生物柴油(原料为地沟油、菜籽油、棕榈油和废肯德基油)作为萃取剂,开展了丙酮丁醇静态萃取发酵。通过分析发酵过程中的产气量及发酵40 h后油水两相中的溶剂浓度,发现生物柴油对丙丁梭菌有毒性。另外,静置条件下丁醇在不同油水两相中的液液平衡系数大致相同。在发酵24 h时加入棕榈生物柴油(油水体积比为0.4∶1),丁醇发酵强度达到最大值0.213 g.(L.h)-1、比对照(传统发酵)提高10.9%,且生物柴油中的丁醇质量浓度达到6.44 g.L-1。     

The economics of acetone-butanol fermentation: theoretical and market considerations

Acetone-butanol (AB) fermentation was once run commercially in many countries until these chemicals could be made more cheaply from fossil oil sources. Research into the revitalisation of the process has shown that the process could once again be run economically in niche markets if run in a relatively small industrial scale processing low-grade agricultural products. The following analysis is intended to help identify suitable niche markets.     

Metabolism analysis and on-line physiological state diagnosis of acetone-butanol fermentation

Fermentation equations for acetone-butanol (AB) were applied in a metabolic analysis of the reaction network under various conditions; that is, at different pHs and a high NADH2 turnover rate using methyl viologen, in a Clostridium acetobutylicum culture. The results disclosed variations in the pattern of rate changes that reflected changes in the physiological state. A linear relationship was found to exist between NADH2 generation and butanol production rate. By coupling an automated measurement system with the fermentation model, on-line estimation of the culture state was accomplished. Based on the AB fermentation model, new parameters were defined for on-line diagnosis of the physiological state and determination of the best timing for amplifying NADH2 generation by the addition of methyl viologen to obtain a high level of butanol productivity. A potential means of achieving optimal control for a high level of solvent production, involving the correlation of certain rates, is proposed.     

Process analysis of the acetone-butanol fermentation by quadrupole mass spectrometry

Summary Mass spectrometric process analysis of the ABE fermentation can be performed. However, the constraints imposed by the conditions at the inlet system do not allow quantifications based on single compound calibrations. Calibrations can be performed with mixtures typical for the process.     

Production of acetone-butanol by extractive fermentation using dibutylphthalate as extractant

Extractive fermentation of glucose, glucose-xylose mixtures and hydrolysates of lignocellulosics to acetone-butanol solvents were studied and compared with similar fermentations in the absence of extractant. The extractant selected for this research was dibutylphthalate which, in addition to having satisfactory physical properties for this purpose, is non-toxic and mildly stimulating to the growth of the organism used, Clostridium acetobutylicum P262. Sugar concentrations mainly in the range of 80 to 100 g/l resulted in solvent concentrations of 28 to 30 g/l in 24 h extractive fermentations, compared to 18 to 20 g/l for non-extractive control fermentations. Conversion factors of 0.33 to 0.37 g solvents/g sugar consumed were obtained. Rapid fermentation was achieved by high cell concentrations and cell recycle from each 24 h fermentation to the succeeding similar 24 h fermentation. Somewhat higher nutrients were also helpful. By this means, 255 l of acetone-butanol solvents were obtained per tonne of aspen wood, 298 l per tonne of pine and 283 l per tonne of corn stover. Such high product yields from inexpensive substrates offer the prospect of economic viability for the process.     

Direct bioconversion of alkali-pretreated straw using simultanesous enzymatic hydrolysis and acetone-butanol fermentation

Summary Conversion of alkali-pretreated wheat straw into butanol and acetone by Clostridium acetobutylicum has been achieved in a one-step hydrolysis and fermentation process involving the use of cellulase from Trichoderma reesei. In the conditions adopted, the results obtained for solvent concentration (17.3 g.l^-1) solvent yield (18.3% with respect to pretreated wheat straw) and overall conversion time (36 h) demonstrate an improved performance over the separate hydrolysis and fermentation operation.     

Continuous acetone-butanol fermentation with high productivity by cell ultrafiltration and recycling

To increase the productivity of the acetone-butanol fermentation, a hollow-fiber ultrafilter is used to separate and recycle cells in a continuous fermentation ofClostridium acetobutylicum. Under partial cell recycling and at a dilution rate of 0.5 hr^–1, a cellular concentration of 20 g/l and a solvent productivity of 6.5 g/l.hr is maintained for several days at a total solvent concentration of 13 g/l.     

On-line monitoring and control of acetone-butanol fermentation by membrane-sensor mass spectrometry

A mass spectrometry (MS) membrane sensor was developed and applied to on-line product measurement in acetone-butanol fermentation. The sensor facilitated the monitoring of acetone, butanol, ethanol, H₂ and CO₂, and single-compound calibration curves for both acetone and butanol showed a linear relationship between the product concentration and the MS response. However, when an actual fermentation was monitored, the product concentration calculated from the MS response was smaller than the concentration determined by gas chromatography, and the relationship between the response and the product concentration was nonlinear. It was found that large amounts of gases (H₂, CO₂) entering the MS analyzation chamber were causing a ‘space charge effect’, which resulted in an MS response ceiling. The problem could be resolved by reducing the surface area of the sensor membrane. Under some fermentation conditions, a by-product, n-butyl butyrate, was produced, and this interfered with the measurement of butanol due to a peak overlapping effect. However, it was found that this could be compensated for by using an empirical equation. Application of the MS membrane sensor in a fed batch culture of acetone-butanol fermentation resulted in successful control of the butanol concentration.     

Changes inClostridium acetobutylicum during acetone-butanol fermentation detected by measurement of electrophoretic mobility

Summary Changes inClostridium acetobutylicum during acetone-butanol fermentation have been detected by measurement of electrophoretic mobility using a laser doppler particle electrophoresis instrument. These results are shown to correspond to the two stages of the fermentation and to agree with other observations of flocculation and changes in morphology of the microorganisms.