Development of a mathematical model for Bacillus circulans growth and alkaline protease production kinetics

BACKGROUND: An unstructured mathematical model was developed to understand information on the relationship between Bacillus circulans growth and metabolism‐related protease production (using logistic and Luedeking–Piret equations respectively) in a batch reactor with respect to glucose consumption and fermentation time. The objective was to develop an indispensable tool for the optimisation, control, design and analysis of alkaline protease production. RESULTS: Biomass growth and enzyme production titres changed with a change in substrate concentration. Modelling analysis of biomass and enzyme production titres at different substrate concentrations revealed significant accuracy in terms of statistical consistency and robustness with respect to fermentation kinetic profiles. CONCLUSION: With the B. circulans strain used, an economic protease yield (2837 × 10³ U g^?1) with respect to biomass and glucose ratio was achieved at low substrate concentration (10 g L^?1). The developed model could be effectively utilised for designing, controlling and up‐scaling the protease production process in high‐density fermentation in selected bioreactors with statistical consistency. Copyright © 2008 Society of Chemical Industry     

Optimization of media constituents through response surface methodology for improved production of alkaline proteases by Serratia rubidaea

BACKGROUND: Response surface methodology is used to build a predictive model of the combined effects of independent variables (pH, salt concentration starch and casein). The model was validated in a laboratory‐scale bioreactor for extracellular protease production from a newly isolated Serratia rubidaea. RESULTS: Optimum medium conditions obtained from the optimization experiments after 48 h incubation were starch, 8 g L^?1; casein, 4 g L^?1; salt concentration 6.25 g L^?1; and initial pH, 8. A coefficient of determination (R²) value of 0.9305 shows the fitness of the second‐order model for the present studies. Results of model coefficients estimated by multiple linear regressions indicate that linear effects of casein concentration (P < 0.001308) and initial pH (P < 7.91 E‐07) are more significant than similarly interactive effects of starch and casein (P < 0.019153), casein and salt concentration (P < 0.016294), casein and pH (P < 0.039904) and salt concentration and pH (p < 0.017845). The P‐values of quadratic effects of casein, x2 × x2 (P < 0.000171); SC, x3 × x3 (P < 0.009134); initial pH, x4 × x4 (P < 0.000114) are more significant for maximal production. After optimization, protease production was enhanced experimentally by almost 65% in a shake flask and by almost 115% in a bioreactor. CONCLUSION: The alkaline proteases secreted by S. rubidaea were significant from an industrial perspective because of their stability against surfactants, oxidants and solvents. The statistical design is useful in economic protease production in a cost‐effective medium for potential use on an industrial scale. Copyright © 2007 Society of Chemical Industry     

A thermodynamic approach toward defining the limits of biogas production

In this article, the authors present theoretical thermodynamic targets for producing biogas. The research shows the relationship between the mass of substrate used vs the methane produced from a feedstock of glucose and an estimate for that of cellulose. Calculations based on material and energy balances are used to determine the performance target (material and energy limits) of an anaerobic digestion system. These limits cannot be exceeded even if one genetically engineer organisms to increase yield. The results show that all processes that produce methane are feasible from a Gibbs free energy point of view but do not conserve the chemical potential of the feed material. The thermodynamics show that methane production is material and energy limited. The maximum amount of methane that can be formed sustainably is 3 moles per mole of glucose, producing 142 kJ of heat per mole of glucose which needs to be rejected. © 2015 American Institute of Chemical Engineers AIChE J, 61: 4270–4276, 2015     

A small-scale flow alkaline fuel cell for on-site production of hydrogen peroxide

The behavior of a small-scale flow alkaline fuel cell (AFC) built-up for on-site production of HO₂⁻ using commercial gas-diffusion electrodes has been studied. It produces a spontaneous current due to the oxidation of H₂ to H₂O at the H₂-diffusion anode and the reduction of O₂ to HO₂⁻ at the O₂-diffusion cathode, while a fresh 1.0-6.0 mol dm⁻³ KOH electrolyte at 15.0-45.0 °C is injected through it. Under circulation of HO₂⁻+KOH solutions in open circuit, the flow AFC behaves as a two-electron reversible system. When it is shorted with an external load (R_ext), steady cell voltage-current density curves are found. The use of O₂/N₂ mixtures to fed the cathode causes a loss of its performance, being required to supply pure O₂ to yield a maximum HO₂⁻ electrogeneration. The current density and HO₂⁻ productivity increase with raising OH⁻ concentration, temperature and pressure of O₂ fed. At R_ext=0.10 Ω, a current efficiency close to 100% is obtained, and current densities >100 mA cm⁻² are achieved for 1.0 mol dm⁻³ KOH at 45.0 °C and for higher KOH concentrations at 25.0 °C. The flow AFC can work under optimum conditions up to 6.0 mol dm⁻³ KOH and 45.0 °C for possible industrial applications.     

Cross-Recognition of Promoters by the Nine SigB Homologues Present in Streptomyces coelicolor A3(2)

In contrast to Bacillus subtilis, Streptomyces coelicolor A3(2) contains nine homologues of stress response sigma factor SigB with a major role in differentiation and osmotic stress response. The aim of this study was to further characterize these SigB homologues. We previously established a two-plasmid system to identify promoters recognized by sigma factors and used it to identify promoters recognized by the three SigB homologues, SigF, SigG, and SigH from S. coelicolor A3(2). Here, we used this system to identify 14 promoters recognized by SigB. The promoters were verified in vivo in S. coelicolor A3(2) under osmotic stress conditions in sigB and sigH operon mutants, indicating some cross-recognition of these promoters by these two SigB homologues. This two-plasmid system was used to examine the recognition of all identified SigB-, SigF-, SigG-, and SigH-dependent promoters with all nine SigB homologues. The results confirmed this cross-recognition. Almost all 24 investigated promoters were recognized by two or more SigB homologues and data suggested some distinguishing groups of promoters recognized by these sigma factors. However, analysis of the promoters did not reveal any specific sequence characteristics for these recognition groups. All promoters showed high similarity in the -35 and -10 regions. Immunoblot analysis revealed the presence of SigB under osmotic stress conditions and SigH during morphological differentiation. Together with the phenotypic analysis of sigB and sigH operon mutants in S. coelicolor A3(2), the results suggest a dominant role for SigB in the osmotic stress response and a dual role for SigH in the osmotic stress response and morphological differentiation. These data suggest a complex regulation of the osmotic stress response in relation to morphological differentiation in S. coelicolor A3(2).     

聚氯乙烯生产现场的配电设计

阐述了聚氯乙烯生产现场配电设计情况,结合经验对聚氯乙烯生产现场的电气设计及安装提出了设计思路。     

The use of multivariate analysis for the design of selective isolation conditions for mutants of Streptomyces cattleya with improved antibiotic titre

Twenty-three tests which did not include antibiotic production were carried out on ultraviolet-induced mutants of Streptomyces cattleya NRRL 8057. Principal component analysis of the results indicated the taxometric relationships between members of a population consisting of 77 isolates. Highlitre antibiotic producers were then marked on the population distribution diagram and clusters containing high-titre antibiotic producers noted. Discriminant analysis for the high-titre clusters provided a discriminant function which was derived from data from seven of the tests. These were used to formulate a positive selection procedure which was successful in selecting for a population of mutants which contained a significantly higher number of high-titre isolates than a control population.     

Taguchi design of experiments approach to the manufacture of one-step alumina microfilter/membrane supports by the centrifugal casting technique

The Taguchi design of experiments method was implemented for the optimization of the manufacture of sintered one-step alumina microfilter/membrane supports by the centrifugal casting technique for the first time. A 10 wt.% alumina aqueous slip containing Tiron (0.001 g/g alumina) as dispersant and PVA as binder were used. Acceleration (3 levels), slip volume (3 levels), binder content (3 levels) and pH (2 levels) were selected as controlling parameters (saturated L-9 array). The use of three different target functions has been discussed: (1) the product of top-layer surface porosity times the reciprocal of top-layer surface pore diameter; (2) the product of permeability times thickness; and (3) membrane curvature. It is deduced that the first target function is the most appropriate as far as the membrane characteristics of the sintered compact are concerned. Using this target function a distinct optimum configuration for the controlling parameter levels could be obtained.     

A new development of the strain energy function for hyperelastic materials using a logarithmic strain approach

The development of a new strain energy function for hyperelastic solids based on the logarithmic strain measure is the objective of the present article. For all possible types of deformation it was shown that the proposed energy function is based on three independent material parameters. Using available experimental data for rubber‐like materials from the literature, one may determined the materials parameters by a nonlinear fitting. The available domain of the strain energy function can be determined by plotting the third invariant of logarithmic strain vs the second one. The numerical integration of the experimental data of true stress as a function of the logarithmic strain for various types of deformation yields the strain energy function W, for rubber‐like solids. The proposed model involves only one parameter that must be determined by fitting with the experimental data. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 660–672, 2000     

离子膜法制烧碱电解设计有关问题之我见

针对离子膜法电解制烧碱生产中可能遇到的实际问题,提出相关的解决措施,对生产厂家有指导借鉴意义。     

Effect of dissolved oxygen tension and ph on the production of extracellular protease from a new isolate of bacillus subtilis K2, for use in leather processing

Scale‐up of production of an alkaline protease, previously characterised from a new isolate of Bacillus subtilis for use as a bating enzyme in leather processing, is described. Before large‐scale commercial production of the protease is possible, characteristics of the growth of the bacterium and enzyme production in fermenters must be defined. In 2 dm³ fermenters an optimal specific activity of 296×10³ U g ⁻¹ cell dry weight was obtained after 60 h with the dissolved oxygen tension (DOT) kept above 10% and pH left uncontrolled. Culture pH was 6 on inoculation, falling to 5.3 after 12 h before rising steadily to ∽8 at the end of fermentation. DOT was maintained above 10% by agitation in the range 300 to 500 rpm. The same criteria were adopted for scale‐up to 20 dm³ but the increase in activity occurred 24 h later. © 1999 Society of Chemical Industry     

A decomposition approach for the scheduling of a steel plant production

In this paper we present a decomposition strategy for solving large scheduling problems using mathematical programming methods. Instead of formulating one huge and unsolvable MILP problem, we propose a decomposition scheme that generates smaller programs that can often be solved to global optimality. The original problem is split into subproblems in a natural way using the special features of steel making and avoiding the need for expressing the highly complex rules as explicit constraints. We present a small illustrative example problem, and several real-world problems to demonstrate the capabilities of the proposed strategy, and the fact that the solutions typically lie within 1–3% of the global optimum.     

A systematic approach for the design of a spiral mandrel die

An effective design strategy is presented for the determination of optimal flow channel geometry of a spiral mandrel die, which can produce annular, thin, and uniform products of polymer melt. This strategy includes two steps: First, a two-dimensional flow simulation associated with the Taguchi approach is applied to search several sets of die geometric parameters, from which process the flow uniformity is assessed. Second, the optimum one parameter set selected by further considering total pressure drop, mixing degree and residence time distribution (RTD). The strategy is illustrated through the design of a spiral mandrel die with four spirals traveling a full 360°, and the viscosity of polymer melt is assumed to be power law model. The results indicated that the design criteria such as high flow uniformity, low pressure drop, good mixing degree and narrow RTD are difficult to attain simultaneously. For a particular polymer melt, there exists a design window for the geometric parameters; within the window the geometric parameter set may satisfy most of the design criteria.     

A unified lubrication approach for the design of a coat-hanger die

A simple unified lubrication approach has been proposed to design a coat-hanger die that can deliver wide and uniform liquid sheets. This approach requires that the wall stress in the manifold be constant. With this constraint, any inelastic non-Newtonian fluid model can be used to describe the liquid motion inside the die. Fluid models that can represent the pseudoplastic or viscoplastic behavior of polymeric liquids have been selected for illustration. A general equation that can be solved to determine the effect of production variations on flow uniformity inside the die has also been derived.     

Optimizational production of phenyllactic acid by a Lactobacillus buchneri strain via uniform design with overlay sampling methodology

A Lactobacillus buchneri GBS3 strain isolated from the traditional Chinese pickles was used for the production of 3-phenyllactic acid(PLA), an important compound with antimicrobial activities against a wide species of grampositive and gram-negative bacteria and some fungi. The growth performance of this strain in the de Man, Rogosa and Sharpe(MRS) medium, the production of metabolites of valuable organic acids, and the biosynthesis of PLA using this strain as the whole-cell biocatalyst and phenylpyruvic acid(PPA) as the precursor, were investigated experimentally. The uniform design method with overlay sampling was developed for the optimization of the biotransformation conditions. The results showed that although it produced naturally lactic acid with the maximum concentration of 1.84 g·L~(-1) and PLA with the concentration of 0.015 g·L~(-1) after 66 to 72 h cultivation in MRS broth by fermentation, the present strain displayed an effective utilization ability by transforming PPA to PLA. By the uniform design method with overlay sampling for the design and optimization of transformation conditions, a maximum yield of 10.93 g·L~(-1) PLA with the mole conversion ratio of 83.07% from PPA to PLA was achieved under the optimized condition, i.e., 20 g·L~(-1) glucose, 270 g·L~(-1) cells, 13 g·L~(-1) PPA, pH 8.0 and the reaction time of 15 h, indicating that Lactobacillus buchneri GBS3 was an interesting strain for the biosynthesis of PLA via the microbial transformation. The prediction of PLA yield under different conditions was achieved successfully based on the limited information of only a small number of experiments by the uniform design with overlay sampling. Therefore, the present methodology is effective and helpful for the optimization of the biosynthesis processes of PLA.