Optimization of glycerol fed-batch fermentation in different reactor states: a variable kinetic parameter approach

To optimize the fed-batch processes of glycerol fermentation in different reactor states, typical bioreactors including 500-mL shaking flask, 600-mL and 15-L airlift loop reactor, and 5-L stirred vessel were investigated. It was found that by reestimating the values of only two variable kinetic parameters associated with physical transport phenomena in a reactor, the macrokinetic model of glycerol fermentation proposed in previous work could describe well the batch processes in different reactor states. This variable kinetic parameter (VKP) approach was further applied to model-based optimization of discrete-pulse feed (DPF) strategies of both glucose and corn steep slurry for glycerol fed-batch fermentation. The experimental results showed that, compared with the feed strategies determined just by limited experimental optimization in previous work, the DPF strategies with VKPs adjusted could improve glycerol productivity at least by 27% in the scale-down and scale-up reactor states. The approach proposed appeared promising for further modeling and optimization of glycerol fermentation or the similar bioprocesses in larger scales.     

Optimization of simulated moving bed plants with low efficient stationary phases: separation of fructose and glucose

An optimization procedure for simulated moving bed (SMB) plants with low efficient stationary phases is presented. The new aspect is that the desorbent consumption can be cut by 70% by running the plant with lower internal liquid flows and a corresponding larger switch time while the productivity is kept constant. This concept was validated by the separation of fructose and glucose in water on a calcium resin with an eight-column SMB plant. The separation can be predicted well by a true moving bed (TMB) and a simulated moving bed simulation. Adsorption isotherms were determined up to 300 kg/m3 for glucose and 500 kg/m3 for fructose from 25 to 80 degrees C. Experimental SMB runs were performed over a wide range of feed concentrations (10-350 kg/m3) and temperatures (25-80 degrees C). The strong influence of the delay volume is pointed out. For an experimental run with high feed concentration a complete set of data is presented. To reduce biological growth separation at 80 degrees C is recommended.     

On the topological features of optimal metabolic pathway regimes

In this work, the stoichiometric metabolic network ofEscherichia coli has been formulated as a comprehensive mathematical programming model, with a view to identifying the optimal redirection of metabolic fluxes so that the yield of particular metabolites is maximized. Computation and analysis has shown that the over-production of a given metabolite at various cell growth rates is only possible for a finite ordered set of metabolic structures which, in addition, are metabolite-specific. Each regime has distinct topological features, although the actual flux values differ. Application of the model to the production of 20 amino acids on four carbon sources (glucose, glycerol, lactate, and citrate) has also indicated that, for fixed cell composition, the maximum amino acid yield decreases linearly with increasing cell growth rate. However, when the cell composition varies with cell growth rate, the amino-acid yield varies in a nonlinear manner. Medium optimization studies have also demonstrated that, of the above substrates, glucose and glycerol are the most efficient from the energetic viewpoint. Finally, model predictions are analyzed in the light of experimental data.     

Optimized Fed-Batch Fermentation of Scheffersomyces stipitis for Efficient Production of Ethanol from Hexoses and Pentoses

Scheffersomyces stipitis was cultivated in an optimized, controlled fed-batch fermentation for production of ethanol from glucose–xylose mixture. Effect of feed medium composition was investigated on sugar utilization and ethanol production. Studying influence of specific cell growth rate on ethanol fermentation performance showed the carbon flow towards ethanol synthesis decreased with increasing cell growth rate. The optimum specific growth rate to achieve efficient ethanol production performance from a glucose-xylose mixture existed at 0.1 h^?1. With these optimized feed medium and cell growth rate, a kinetic model has been utilized to avoid overflow metabolism as well as to ensure a balanced feeding of nutrient substrate in fed-batch system. Fed-batch culture with feeding profile designed based on the model resulted in high titer, yield, and productivity of ethanol compared with batch cultures. The maximal ethanol concentration was 40.7 g/L. The yield and productivity of ethanol production in the optimized fed-batch culture was 1.3 and 2 times higher than those in batch culture. Thus, higher efficiency ethanol production was achieved in this study through fed-batch process optimization. This strategy may contribute to an improvement of ethanol fermentation from lignocellulosic biomass by S. stipitis on the industrial scale.     

Comparison of Glucose and Glycerol as Carbon Sources for ε-Poly-l-Lysine Production by Streptomyces sp. M-Z18

Glucose is widely used in the production of ε-poly-l-lysine (ε-PL); however, glycerol is an emerging carbon source for ε-PL production in recent years. Glycerol is superior to glucose for ε-PL production according to batch and fed-batch fermentations by Streptomyces sp. M-Z18 in this study. To elaborate this difference, physiological metabolism of Streptomyces sp. M-Z18 on glycerol has compared with glucose during batch fermentation. The activities of key enzymes showed that aspartate kinase (ASPK) and ε-PL synthetase (Pls) in glycerol medium was higher than those in glucose, and especially the activity of Pls could enhance by 2.3- and 3.6-fold at 24 and 36 h, respectively. Moreover, metabolism flux analysis demonstrated that a 25 % higher fluxes derived from glycerol are directed into ε-PL synthesis than glucose. As a result, the mechanism of glycerol better than glucose is determined: the activities of ASPK and Pls in glycerol higher than those in glucose, and result in carbon fluxes directed into ε-PL synthesis increased. This study offers a reference to substitute glycerol for conventional glucose as carbon source for ε-PL production.     

Optimization Strategies Based on Sequential Quadratic Programming Applied for a Fermentation Process for Butanol Production

In this work, the mathematical optimization of a continuous flash fermentation process for the production of biobutanol was studied. The process consists of three interconnected units, as follows: fermentor, cell-retention system (tangential microfiltration), and vacuum flash vessel (responsible for the continuous recovery of butanol from the broth). The objective of the optimization was to maximize butanol productivity for a desired substrate conversion. Two strategies were compared for the optimization of the process. In one of them, the process was represented by a deterministic model with kinetic parameters determined experimentally and, in the other, by a statistical model obtained using the factorial design technique combined with simulation. For both strategies, the problem was written as a nonlinear programming problem and was solved with the sequential quadratic programming technique. The results showed that despite the very similar solutions obtained with both strategies, the problems found with the strategy using the deterministic model, such as lack of convergence and high computational time, make the use of the optimization strategy with the statistical model, which showed to be robust and fast, more suitable for the flash fermentation process, being recommended for real-time applications coupling optimization and control.     

毛细管电泳中葡萄糖-羟丙基甲基纤维素体系分离脱氧核糖核酸

葡萄糖作为羟丙基甲基纤维素（Hydroxpropylmethyl cellulose,HPMC)筛分体系的添加剂,可以改善该体系在低浓度时分离脱氧核糖核酸（DNA）的能力。研究了硼酸浓度和pH值对葡萄糖－羟丙基甲基纤维素体系分离性能的影响;并将葡萄糖与其它添加剂如甘油、甘露醇对分离的影响作了比较,葡萄糖特有的环状结构使得其对羟丙基甲基纤维素体系分离能力的提高更为显著。     

Effect of mobile phase composition on the SMB processes efficiency. Stochastic optimization of isocratic and gradient operation

The solvent composition was adjusted in a theoretical study in order to maximize the efficiency of a simulated moving bed (SMB) process. The isocratic realization of the process as well as the solvent gradient mode were considered. The solvent composition and the flow rates were used as decision variables in a random search optimization algorithm known to be a reliable tool for nonlinear programming problems. The results of the optimization indicate that the optimal composition of the mobile phase depends strongly on the feed concentration. The asymmetry of the internal concentration profiles, which has a negative effect on the separation efficiency, can be partly damped by an increase of the solvent strength. In the cases studied the optimal solvent strength determined for concentrated feed streams is higher than that for diluted ones. Moreover, the optimum is strongly influenced by the value of the selectivity factor and its dependency on the mobile phase composition. Different results were obtained for cases, in which the separation factor increases with increasing the modifier concentration, than for cases, in which the separation factor decreases with increasing the modifier concentration. A similar analysis was performed for a solvent gradient SMB process, in which different solvents are used at the two inlet ports: a weak solvent in the feed stream and a strong solvent in the desorbent stream. Again the optimal mobile phase composition was strongly affected by the type of the isotherms and their non-linearity. The potential of a gradient SMB process in terms of increasing the productivity and reducing the eluent consumption is exemplified.     

Production of acetic acid by immobilized whole cells ofClostridium thermoaceticum

Immobilized cells ofClostridium thermoaceticum for acetic acid production has been investigated. Using κ-carrageenan gel as the immobilization-matrix, high cell concentration within the gel could be achieved and thus lead to high volumetric acetic acid productivity. Batch experiments using 3% gel showed that cell concentration up to 65 g (dry cell weight)/L gel could be achieved. These dry weight cell concentrations in the gel through immobilization are typically 10–15 times greater than what can be obtained in free-cell fermentations. The specific growth rate and acetic acid formation rate were similar to those observed for the free cells. Continuous culture experiments using a feed medium containing 20 g/L of glucose were performed where the reactor contained 50% by volume of the carrageenan gel and the pH was controlled at 6.9. Different steady states were acheived at dilution rates ranging from 0.061 to 0.399 h^?1. Cells grew mainly near the surface of the gel and reached maximum concentration within the matrix of approximately 35 g/L. Dilution rates much greater than the maximum specific growth rate were obtained, which resulted in volumetric productivity up to 4.9 g/L-h. This value was significantly greater than that for the conventional continuous culture with free cells. Using a 40 g/L feed glucose concentration, steady states could be achieved between dilution rates of 0.12–0.4 h^?1. The maximum productivity further increased to 6.9 g/L-h at a dilution rate of 0.37 h^?1 and at an acetic acid concentration of 19 g/L. The cell concentration was 60 g (dry weight)/L gel at steady state.     

Enhancement of oxygen transfer by pressure pulsation in aqueous glycerol fermentation

Aeration plays an important role in the production of glycerol by fermentation with yeast. Effective aeration depends on a number of factors, such as amount of air, fineness of air dispersion, rate of agitation, and time of gasliquid contact. This investigation dealt with the effect of periodic variation in gas pressure on oxygen transfer measured by sulfite oxidation and glycerol fermentation in stirred tanks. The oxygen transfer rate measured with the sulfite oxidation method was improved by 20–30% under the condition of pressure pulsation (PP) at 30°C. The yield and productivity of glycerol were increased by about 26 and 6.8%, respectively, in 48 h by employing a glucose concentration of 250 g/L with PP at 30°C.     

Insights into the Role of Glucose and Glycerol as a Mixed Carbon Source in the Improvement of ε-Poly-l-Lysine Productivity

Using glucose–glycerol mixed carbon source has proved to be an effective strategy for ε-poly-l-lysine (ε-PL) production with rapid cell growth and much higher ε-PL productivity. In this study, we attempt to focus on key enzymes and intracellular energy cofactors to reveal the underlying mechanisms involved in such significant improvements. The activities of key enzymes involved in the pentose phosphate pathway, TCA cycle, anaplerotic pathway and the aspartate family amino acid biosynthesis pathway as well as ε-PL synthetase showed overall enhancement with the mixed carbon source, especially in the late stages of fermentation, compared with those in either glucose or glycerol single carbon sources. Moreover, the intracellular cofactors in terms of NADH and ATP kept higher formation and consumption rates in the mixed carbon source, respectively, throughout batch fermentation. As a result, Streptomyces sp. M-Z18 could be accelerated in cell growth and precursor l-lysine biosynthesis in the mixed carbon source, thus finally shortening fermentation time and enhancing ε-PL productivity. Understanding this process will provide information for the rational regulation of the metabolism network of the quantative production of ε-PL by metabolic engineering.     

Statistical Optimization of 1,3-Propanediol (1,3-PD) Production from Crude Glycerol by Considering Four Objectives: 1,3-PD Concentration,Yield, Selectivity,and Productivity

This study investigated the biological conversion of crude glycerol generated from a commercial biodiesel production plant as a by-product to 1,3-propanediol (1,3-PD). Statistical analysis was employed to derive a statistical model for the individual and interactive effects of glycerol, (NH₄)₂SO₄, trace elements, pH, and cultivation time on the four objectives: 1,3-PD concentration, yield, selectivity, and productivity. Optimum conditions for each objective with its maximum value were predicted by statistical optimization, and experiments under the optimum conditions verified the predictions. In addition, by systematic analysis of the values of four objectives, optimum conditions for 1,3-PD concentration (49.8 g/L initial glycerol, 4.0 g/L of (NH₄)₂SO₄, 2.0 mL/L of trace element, pH 7.5, and 11.2 h of cultivation time) were determined to be the global optimum culture conditions for 1,3-PD production. Under these conditions, we could achieve high 1,3-PD yield (47.4%), 1,3-PD selectivity (88.8%), and 1,3-PD productivity (2.1/g/L/h) as well as high 1,3-PD concentration (23.6 g/L).     

Enhanced operation of a wastewater treatment process by periodic forcing input

This paper considers investigating the performance of a wastewater treatment plant consisting of a bioreactor with recycle followed by a clarifier under forced feed circulation. A previously developed dynamic model for the process is used to conduct the performance analysis. The static version of the model was utilized first to determine the optimal productivity conditions for the process. Numerical optimization is used to design the feed periodic function. The parameters of the feed cyclic functions are determined which resulted in improved productivity and substrate consumption. The improvement in productivity is marginal and is satisfactory for substrate conversion compared to that of the optimal condition and to the steady state condition, which corresponds to the average value of the periodic function.     

Continuous potable alcohol production by immobilizedSaccharomyces cerevisiae on mineral kissiris

A biocatalyst prepared by the immobilization of Saccharomyces cerevisiae on the surface of the mineral kissiris was used in the present study for continuous potable-alcohol production. An ethanol productivity (calculated on the basis of liquid volume) of 10.5 g/L/h was obtained at a 0.7/h dilution rate, 121 g/L sucrose content, and 29.6% conversion employing molasse as feed material. Glucose, raisin extracts, and molasse were successively used as feed materials without stopping the operation of the reactor for 6 mo. The ethanol productivity and yield remained constant during the operational-stability study of the reactor, carried out for 44 d. Biomass productivity, yield, and free-cell concentration in glucose, raisin extracts, and molasse were examined. Finally, a system with two continuous reactors joined successively was also studied in the present investigation.     

An Effective and Simplified Fed-Batch Strategy for Improved 2,3-Butanediol Production by <Emphasis Type="BoldItalic">Klebsiella oxytoca</Emphasis>

Substrate concentration in 2,3-butanediol (2,3-BD) fermentation could not be controlled well in traditional feeding strategies, such as constant, impulse, and exponential feeding strategies. In the present study, fermentative 2,3-BD production by Klebsiella oxytoca was investigated under different batch and fed-batch strategies. The glucose-feedback fed-batch strategy was proved to be not effective for economical 2,3-BD production for the inability of timely feeding, leading that the bacteria reused 2,3-BD as carbon source for cell growth. Based on the phenomena that the byproducing acids caused the pH declining and the requirement of maintaining the pH at a proper level for both cell growth and 2,3-BD accumulation, an improved strategy of pH-stat fed-batch culture with glucose and sodium hydrate fed at the same time was established. Thus, the residual glucose concentration could be controlled through the adjustment of pH automatically. At last, efficient 2,3-BD production was fulfilled under this fed-batch strategy, and the highest 2,3-BD concentration, productivity, and yield were 127.9 g/l, 1.78 g/(l•h), and 0.48 g/g (2,3-BD/glucose), respectively, compared to 98.5 g/l, 1.37 g/(l•h), and 0.43 g/g obtained in glucose-feedback fed-batch strategy. This feeding strategy was simple and easy to operate and could be feasible for industrial 2,3-BD production in the future.     

Enhancement of Fumaric Acid Production by Rhizopus oryzae Using a Two-stage Dissolved Oxygen Control Strategy

Batch fermentative production of fumaric acid by Rhizopus oryzae ME-F12 was investigated in a 7-l stirred tank fermentor under different dissolved oxygen (DO) concentrations. High fumaric acid yield on glucose (0.56 g/g) was achieved under high DO concentration (80%), but the glucose consumption rate and fumaric acid productivity were rather low (0.91 and 0.51 g/l/h). Fumaric acid productivity was enhanced under low DO concentration (30%), but the fuamric acid yield on glucose decreased to 0.52 g/g. In order to achieve the high fumaric acid yield and productivity simultaneously, a two-stage dissolved oxygen control strategy was proposed, in which the DO concentration was controlled at 80% in the first 18 h and then switched to 30%. This was experimentally proven to be successful. Relatively high fumaric acid production (56.2 g/l), high fumaric acid yield on glucose (0.54 g/g), and high glucose consumption rate (1.3 g/l/h) were achieved by applying this strategy. The productivity (0.7 g/l/h) was improved by 37%, 21%, and 9%, respectively, compared with fermentations in which DO concentrations were kept constant at 80%, 60%, and 30%.     

Control of microstructural properties in emulsion polymerization systems

Control strategies for the simultaneous control of microstructural properties of copolymer latexes (copolymer composition and molecular weight distribution) are presented. For linear polymers, on-line control strategies based on calorimetric measurements allowed to produce styrene/n-butyl acrylate emulsion polymers of predefined copolymer compositions and MWDs. The strategy failed for nonlinear polymers because the polymer produced at a certain process time might later in the process become active varying its molecular weight. Alternative open-loop control policies were developed for nonlinear polymers. These strategies required a mathematical model of the process that is used in an off-line optimization to determine the trajectories of the manipulated variables (feed flow rates of monomer and CTA) that allow producing the desired copolymers. The implementation of the open-loop control allowed the production of nonlinear MMA/n-BA emulsion copolymers of well-defined copolymer composition and MWD.     

Efficient 1,3-propanediol Production by Fed-Batch Culture of Klebsiella Pneumoniae: The Role of pH Fluctuation

The fermentative production of 1,3-propanediol (1,3-PD) by Klebsiella pneumoniae under different fed-batch strategies was investigated. pH-stat fed-batch strategies proved to be not effective for economical 1,3-PD production for the existence of relatively high concentration of byproducts and residual glycerol at the end of the fermentation. However, in the pH-stat fed-batch strategy, an important phenomenon was observed that the yields of two main byproducts, 2,3-butanediol and lactic acid, were closely related to pH value. The dominant byproduct was 2,3-butanediol at a pH value of 5.0 to 6.5 but changed to be lactic acid at a pH value of 7.1 to 8.0. Based on the analysis of the phenomenon, a self-protection mechanism in K. pneumoniae, namely that the growing K. pneumoniae cells switch the metabolic pathways responding to environmental pH changes, was proposed. Thus a kind of feeding strategy was further applied during which the pH value was fluctuated between 6.3 and 7.3 periodically by feeding glycerol–ammonia mixture and sulphuric acid to make the metabolic pathways of 2,3-butanediol and lactic acid sub-active under the periodical low or high pH stress. At last, efficient 1,3-PD production was fulfilled under this fed-batch strategy, and the best results were achieved leading to 70 g/l 1,3-PD with a yield of 0.70 mol/mol glycerol and productivity of 0.97 g/l/h, while the two main byproducts and residual glycerol were under low concentrations.     

Estimation of monomer reactivity ratios in free‐radical solution copolymerization of lauryl methacrylate–isobutyl methacrylate

Copolymers of isobutyl methacrylate (i‐BMA) and lauryl methacrylate (LMA) were prepared by free‐radical solution copolymerizations at 70 °C with azobisisobutyronitrile (AIBN) as an initiator. The synthesis of these copolymers was investigated over a wide composition range both at low and high conversion levels. Copolymer compositions were determined from the %C, %H, and %O contents of copolymer by elemental analysis. Monomer reactivity ratios were estimated by analyzing composition data with nonlinear least‐squares (NLLS) models based on Marquardt optimization and van Herk methods. The point estimates, 95% individual confidence intervals and 95% joint confidence intervals are obtained from differential and integral approaches. Even though no explicit integral form for penultimate unit model (PUM) is available, a numerical approach is developed for integral estimation of reactivity ratios from PUM. A simulator program was developed which upon coupling of experimental data, NLLS analysis, and D‐optimal criteria calculates the best optimized values of monomer reactivity ratios and monomer feed compositions in a sequential and iterative order for terminal and penultimate unit models. Moreover, the simulator has the capibilities to calculate all features of van Herk method, maximum compositional drift in each monomer feed composition, and data reconciliation. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 112–129, 2004     

Model-based optimization of a preparative ion-exchange step for antibody purification

A method using a model-based approach to design and optimize an ion-exchange step in a protein purification process is proposed for the separation of IgG from a mixture containing IgG, BSA and myoglobin. The method consists of three steps. In the first step, the model is calibrated against carefully designed experiments. The chromatographic model describes the convective and dispersive flow in the column, the diffusion in the adsorbent particles, and the protein adsorption using Langmuir kinetics with mobile phase modulators (MPM). In the second step, the model is validated against a validation experiment and analyzed. In the third and final step, the operating conditions are optimized. In the optimization step, the loading volume and the elution gradient are optimized with regard to the most important costs: the fixed costs and the feed cost. The optimization is achieved by maximizing the objective functions productivity (i.e. the production rate for a given amount of stationary phase) and product yield (i.e. the fraction of IgG recovered in the product stream). All optimization is conducted under the constraint of 99% purity of the IgG. The model calibration and the analysis show that this purification step is determined mainly by the kinetics, although as large a protein as IgG is used in the study. The two different optima resulting from this study are a productivity of 2.7 g IgG/(s m3) stationary phase and a yield of 90%. This model-based approach also gives information of the robustness of the chosen operating conditions. It is shown that the bead diameter could only be increased from 15 microm to 35 microm with maximum productivity and a 99% purity constraint due to increased diffusion hindrance in larger beads.