Comparison of Lactic Acid Productivities at High Substrate Conversions in a Continuous Two-stage Fermenter With Cell Recycle Using Different Kinetic Models

The steady-state performance of a two-stage recycle fermenter with two different types (I and II) of configurations for staging was investigated numerically for the continuous production of lactic acid. In Type I the bleed broth withdrawn from the first stage is supplied to the second fermenter, and in Type II both filtrate and bleed broth from the first stage are introduced to the second stage. Using four different kinetic models taken from the literature, the effects of operating parameters on the overall lactic acid productivities and the overall substrate conversions are examined. At moderate conversions, productivities for Type I operation are found to be higher than those for Type II and for the single-stage system. In the case of high conversions close to complete consumption, Type II operation is more efficient than the Type I and single-stage systems. For 99% conversion and 40 kg m^-3 substrate feed concentration, productivities for Type II are predicted to be 14-74% higher compared to those for the single-stage system at the same bleed ratios.     

Analysis of acetic acid productivity in a continuous two‐stage bioreactor with cell recycling

The performance of a two‐stage system with cell recycling and fresh feed at each stage is studied numerically for continuous acetic acid production. In this system, both filtrate and bleed broth from the first stage are supplied to the second fermenter. At high substrate conversions, this configuration is found to provide higher acetic acid productivities than either a previous configuration where only the first‐stage bleed broth is fed to the second stage or a single recycle chemostat at the same bleed ratios. Copyright © 2005 Society of Chemical Industry     

Operating Conditions for High Production Rates of Ethanol in a Continuous Two‐Stage Fermenter with Cell Recycle

A continuous two‐stage fermenter with cell recycle at each stage is studied numerically for efficient production of ethanol. In this system, both filtrate and bleed from the first stage are provided to the second fermenter. Using a product‐inhibition kinetic model with different saturation constants, operating conditions giving the maximum ethanol productivity attainable at high substrate conversions are examined. For high substrate conversions close to complete consumption, the ethanol productivities predicted for this system are found to be higher than those for a single‐stage system and a previous two‐stage configuration at the same bleed ratios.     

Strategies to improve the bioconversion of processed wood into lactic acid by simultaneous saccharification and fermentation

In the one‐step conversion of wood into lactic acid by Simultaneous Saccharification and Fermentation (SSF), inhibition effects caused by hydrolysis‐ and fermentation‐derived compounds on both enzymatic activity and fermentative ability of microorganisms appear when the operation is carried out under conditions leading to high productivities. The main effects inhibiting SSF have been assessed, and the results obtained in fed‐batch experiments allowed the definition of strategies for improving the overall bioconversion process. As cellobiose caused significant inhibition of cellulases, the supplementation of media with β‐glucosidase resulted in improved kinetics and yields. The inhibition of both enzymatic activity and microbial metabolism by lactic acid was confirmed. Intermittent removal of lactic acid by passing the fermentation media through an anion‐exchange resin column resulted in increased productivities and yields. Improved conversion of pretreated wood into lactic acid (67% conversion of cellulose into lactic acid, with maximum lactic acid concentration of 108 g dm^?3 and a productivity of 0.94 g dm^?3 h^?1) was achieved combining multiple substrate addition, supplementation with fresh nutrients and enzymes and removal of lactic acid. © 2001 Society of Chemical Industry     

Effect of Cell Purge on the Stability of Microfiltration Cell Recycle Fermentation Systems

Fermentation with complete cell recycle on microfiltration tubular membranes was studied and its effect upon broth rheology evaluated. The increase in cell concentration was found to be responsible for a continuous rise in viscosity leading to changes of broth rheology and consequent operating problems. A strategy to control the broth rheological behaviour with the aim of achieving long-term stable fermentations is proposed. This strategy involves the use of a cell purge in order to maintain cell concentration at a manageable level. The results obtained show that the total cell concentration in the fermenter can be stabilised if the cell bleed rate is calculated to remove exactly the amount of cells produced. To obtain long-term stable fermentations, the time to initiate the bleeding procedure and the cell bleed rate need to be determined and optimised. © 1997 SCI.     

ANALYSIS OF A TWO-STAGE FERMENTOR WITH RECYCLE FOR CONTINUOUS ETHANOL PRODUCTION

The performance of a recycle two-stage fermentor with cell separators after each stage is analyzed numerically for the continuous production of ethanol. In this system, the bleed withdrawn from the first stage is introduced to the second tank in order to reuse the cells in the bleed. Kinetic expressions and parametric values are taken from the literature. The effects of operating parameters on the concentrations in the stages are examined. Also investigated are the critical dilution rate for washout, the ethanol productivity and the substrate conversion. In addition, the influences of the saturation constant and the equilibrium partition coefficient of ethanol are examined. With respect to the overall productivity and conversion, it is found that the present two-stage system is more efficient than either a recycle chemostat or a recycle two-stage fermentor with a single separator after the final stage.     

透明质酸生产中生物发酵工艺过程

本文介绍了透明质酸产品的实际用途及其生产中生物发酵的过程。主要阐述了生产过程中的发酵工艺流程,及发酵液在种子培养罐,种子发酵罐,主发酵罐,混料罐以及补料罐中的物理、化学变化和具体操作过程。     

Performance evaluation of batch and unsteady state fed‐batch reactor operations for the production of a marine microbial surfactant

BACKGROUND: Biosurfactants are microbially derived surface‐active and amphipathic molecules produced by various microorganisms. These versatile biomolecules can find potential applications in food, cosmetics, petroleum recovery and biopharmaceutical industries. However, their commercial use is impeded by low yields and productivities in fermentation processes. Thus, an attempt was made to enhance product yield and process productivity by designing a fed‐batch mode reactor strategy. RESULTS: Biosurfactant (BS) production by a marine bacterium was performed in batch and fed‐batch modes of reactor operation in a 3.7 L fermenter. BS concentration of 4.61 ± 0.07 g L^?1 was achieved in batch mode after 22 h with minimum power input of 33.87 × 10³ W, resulting in maximum mixing efficiency. The volumetric oxygen flow rate (K_La) of the marine culture was about 0.08 s^?1. BS production was growth‐associated, as evident from fitting growth kinetics data into the Luedeking‐Piret model. An unsteady state fed batch (USFB) strategy was employed to enhance BS production. Glucose feeding was done at different flow rates ranging from 3.7 mL min^?1 (USFB‐I) to 10 mL min^?1 (USFB‐II). USFB‐I strategy resulted in a maximum biosurfactant yield of 6.2 g l^?1 with an increment of 35% of batch data. The kinetic parameters of USFB‐I were better than those from batch and USFB‐II. CONCLUSION: Comparative performance evaluation of batch and semi‐continuous reactor operations was accomplished. USFB‐I operation improved biosurfactant production by about 35% over batch mode. USFB‐I strategy was more kinetically favorable than batch and USFB‐II. © 2012 Society of Chemical Industry     

Overall Energy Requisite and Quality Feature of Industrial Paddy Drying

Energy consumption and rice quality are the main concerns of millers and must be assessed to ascertain suitable industrial drying strategy. In this article, industrial paddy drying methods as usually practiced in the BERNAS paddy drying complexes of Malaysia have been evaluated. The analysis showed that the specific electrical and thermal energy consumption varied between 16.19 kWh to 22.07 kWh and 787.22 MJ to 1015.32 MJ, respectively, in single-stage paddy drying (SSPD) using an inclined bed dryer (IBD) to dry each tonne of freshly harvested paddy with average moisture content of 23.35 ± 0.86% wb. On the other hand, the energy consumptions for two-stage paddy drying (TSPD) with a fluidized bed dryer (FBD) followed by IBD were 21.37 kWh/t to 30.69 kWh/t and 666.81 MJ/t to 1083.42 MJ/t, respectively. SSPD at 35–39°C and TSPD using FBD at 120°C as the first stage, followed by IBD as the second stage at lower temperature of 35–39°C yielded 2–3.6% higher head rice yield than paddy-dried by a single stage with IBD using comparatively higher temperature of 40–44°C. Therefore, IBD is recommended to be operated using a temperature of 35–39°C both in single-stage drying and second-stage drying of paddy after fluidized bed drying to obtain quality rice.     

Steady states of a biotechnological process for producing lactic acid at a given substrate concentration in the inlet stream

Relationships are derived that form the domain in which the multiplicity of steady states exists for the continuous process of lactic acid production in a fermenter with stirring. Algorithms are described for estimating the technological characteristics of the process under the conditions of multiplicity. Methods and results of calculations are presented for different variants of specifying the concentration of a substrate in the inlet stream, and examples of numerical calculations are given.     

Production of bacterial cellulose in static conditions by a simple fed-batch cultivation strategy

The current study investigated fed-batch cultivation for the increased productivity of bacterial cellulose (BC) sheets by Gluconacetobacter hansenii PJK in static conditions using chemically defined medium and waste from beer fermentation broth. Fermentations were carried out in a 3 L jar fermenter without any impeller for 30 days. In the proposed fed-batch cultivation, 500 mL of the medium was initially inoculated with pre-culture in a jar fermenter while a fresh medium was fed periodically. BC production was also done by using batch cultivation which was used as a control for comparison. The results obtained revealed an overall of 2–3 times increase in BC production in fed-batch cultivation compared to batch cultivation after 30 days of cultivation. During these experiments, it was found that waste from beer fermentation broth is a superior medium for the BC production using fed-batch cultivation. The production of water soluble oligosaccharides as useful by-products was also monitored during these investigations. Fed-batch cultivation and waste from beer fermentation was also found superior for the production of these by-products. According to literature search and to the best of our knowledge, it is the first report of using fed-batch cultivation for BC production in static conditions.     

Lactic acid recovery from fermentation broth using one‐stage electrodialysis

One‐stage electrodialysis (ED) for lactic acid recovery with two‐ and three‐compartment water‐splitting ED (WSED) was investigated using various ion‐exchange membranes in order to overcome the inefficiency of two‐stage ED, which consists of desalting ED for recovery and partial purification and subsequent WSED for acidification. The two‐compartment WSED had a low current efficiency and high energy consumption in spite of a simple stack configuration. A three‐compartment WSED successfully converted sodium lactate in the fermentation broth into lactic acid and sodium hydroxide with average yields of 96% and 93%, respectively. In relation to lactic acid purification, of the membranes tested in this study, the highest glucose rejection, 98.3%, was achieved using a PC 100D membrane. The CMS membrane rejected magnesium and calcium at levels as high as 81.7% and 78.5%, respectively. We concluded that the three‐compartment WSED with properly chosen membranes, enabled lactic acid to be recovered directly from the fermentation broth. © 2001 Society of Chemical Industry     

Moisture Adsorption Isotherms of Watermelon Seed and Kernels

The moisture adsorption isotherms of watermelon seeds and kernels from Citrullus lanatus Cv Mateera and Citrullus vulgaris Cv Sugar baby were obtained using standard static method with saturated salt solutions over a range of water activities from 0.113 to 0.92 at 20–60°C. The adsorption capacity of seeds decreased with the increase in temperature at constant water activity. Sorption models were used to explain the adsorption behavior involving water activity and moisture content (Type I) and also temperature (Type II). Oswin's models gave best fit among Type I with coefficient of determination of 0.953–0.995, standard error of 0.031–0.0571, mean relative error of 0.071–0.152, and scattered residual plots. Modified Oswin was the best fit model among Type II for the seeds and kernels of both the cultivars with coefficient of determination of 0.997–0.999, standard error of 0.151–0.255, mean relative error of 0.018–0.244, and scattered residual plots. The net isoelectric heat of adsorption, estimated from Clausius-Clapeyron decreased from about 27.0 to 0.5 kJ/mol in kernels and 18.0 to 0.5 kJ/mol in seeds of both the cultivars as the moisture content increased from 5 to 25% (dry basis).     

Observer-based non-linear control of a fed-batch autoinductive fermentation process

Optimal regulatory control of an autoinductive recombinant culture in a fed-batch reactor is considered. End point optimization results in a three-stage process: biomass growth, inducer synthesis and product synthesis. It is shown that in the last stage the substrate concentration should be maintained constant. This is achieved using an input—output linearizing controller accompanied by a novel non-linear state observer for the estimation of unmeasured state variables on the basis of on-line off-gas carbon dioxide concentration measurements. Experimental runs of luminous recombinant E. coli strain in a laboratory fermenter demonstrate the rapid convergence of the observer estimates as well as the effectiveness and robustness of the overall control system.     

Enhanced biosurfactant production by <Emphasis Type="Italic">Corynebacterium alkanolyticum</Emphasis> ATCC 21511 using self-cycling fermentation

Enhanced biosurfactant production by Corynebacterium alkanolyticum ATCC 21511 was accomplished in a self-cycling fermenter (SCF) on a hexadecane substrate. The phospholipid biosurfactant produced during each cycle could be monitored rapidly using fluorescence spectroscopy. By optimizing the cycling pattern of the SCF, significantly better yields of biosurfactant were obtained than previously reported for this microorganism. It was also possible to virtually eliminate the hydrocarbon residue in the product. Harvest concentrations of 1.9 g L⁻¹ were obtained by using a two-stage fermentation. The first step was the growth of C. alkanolyticum in an SCF to yield a harvest of synchronous cells. These cells were transferred to a second vessel for the production stage. The concentration of biosurfactant could be further increased to 2.7 g L⁻¹ by the addition of more hexadecane at the beginning of the second stage.     

发酵液中乳酸的电渗析法分离

采用电渗法分离发酵液中低浓度乳酸,考察了电渗析器的操作条件对极限电流密度和乳酸电年速率的影响,并分别用修正的Ｗｉｌｓｏｎ公式和乳酸电渗析速率方程描述了它们之间的关系。     

Examination of selected synthesis parameters for typical wood adhesive‐type urea–formaldehyde resins by 13C‐NMR spectroscopy. II

A particleboard adhesive‐type urea–formaldehyde (UF) resin was made at a formaldehyde ratio of 2.10 and added with a second urea at low temperature to the typical final formaldehyde/urea ratio of 1.15. Time samples taken during heat treatments of the resin sample up to 70°C over a period of 250 min showed decreases in Type II/IIi hydroxymethyl group content, accompanied with decreases in resin sample viscosity and increases in formaldehyde emission of bonded particleboards. The results indicate that various hydroxymethyl groups of polymeric UF resin components migrate to the second urea to form Type I hydroxymethyl groups. Time samples taken during the room‐temperature storage of the resin sample over a period of 1 month behaved similarly initially, but in the later stage, some polymerization progressed, shown by increases in viscosity and methylene and methylene–ether group contents. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 1243–1254, 2000     

Combined Dyeing and Resin Finishing of Wool/Viscose and Cotton/Wool Blends

The objective of this study is to establish a single-stage process for anionic dyeing and easy-care finishing of wool/viscose (60/40) and cotton/wool (70/30) blended fabrics. Optimum conditions for maximizing dyeability and achieving high resiliency are: Fixapret® ECO (50 g/L), triethanolamine hydrochloride (20 g/L), ammonium persulfate (7.5 g/L) at 160°C for 3 min. The extent of improvement in both the depth of shade and easy-care properties is determined by the nature of substrate and follows the descending order wool/viscose > cotton/wool. On the other hand, the extent of dye fixation and the change in fastness properties of the obtained dyeings are determined by the class of dyestuff.     

Effect of operating parameters on precipitation for recovery of lactic acid from calcium lactate fermentation broth

Precipitation is a simple, efficient method for separating and recovering lactic acid in the form of calcium lactate from fermentation broth by adding sulfuric acid. Major operating parameters of the recovery step as well as the temperature of concentration of the recovered lactic acid solution and the type and amount of adsorbent used for pigment (color) removal were optimized. When the molar ratio of calcium lactate to sulfuric acid was 1: 1 and the pH was increased to a value greater than the pKa (3.86), calcium sulfate was precipitated and could be removed more effectively, allowing for more efficient separation and recovery of supernatant lactic acid. Precipitation could be facilitated by adding calcium lactate solution with mixing (up to 220 rpm) and was completed in over 18 h. The optimal temperature for the concentration of lactic acid recovered from the supernatant after removing the precipitated calcium sulfate was found to be 90 °C in terms of the time required for concentration and the stability of the product. Activated carbon (SX-PLUS, 9 g/L) was most effective as an adsorbent for color removal from the recovered lactic acid. Under the optimized precipitation conditions, an overall yield of 92% of lactic acid from fermentation broth could be achieved.     

Aqueous Two-Phase Extraction of Lactic Acid: Optimization by Response Surface Methodology

In this study a suitable alcohol/salt aqueous two-phase (ATP) system was selected for the recovery of lactic acid from an aqueous solution. From the different ATP systems studied, the ethanol/dipotassium hydrogen phosphate ATP system appeared to be favorable. To examine the potential of this ATP system, the extraction yield of lactic acid in aqueous solutions was optimized with the response surface methodology. The parameters studied were concentrations of ethanol (22.00–38.80%, w/w), dipotassium hydrogen phosphate (15.00–31.80%, w/w) and lactic acid (26.36–93.64 g/L). The optimum conditions were found to be 30.23% w/w ethanol, 18.40% w/w dipotassium hydrogen phosphate, and 80 g/L lactic acid. Under these conditions, a favorable extraction yield of lactic acid was obtained. The maximum partition coefficient of lactic acid and extraction yield was determined as 2.26 and 87%, respectively. The optimum extraction conditions were then used to guide the recovery of lactic acid from a real fermentation broth. As a result, the partition coefficient and extraction yield of lactic acid reached 2.06–80%, respectively.