Showing papers in "Biochemical Engineering Journal in 2004"
TL;DR: An extension of the OTR-Device, termed respiration activity monitoring system (RAMOS) is described, which allows additional measurement of the carbon dioxide transfer rate and the respiratory quotient in shaking bioreactors.
Abstract: Online measurement of respiration activity (including oxygen transfer rate (OTR), carbon dioxide transfer rate (CTR), respiratory quotient (RQ)) of microbial cultures in stirred bioreactors with exhaust gas analysis has been state of the art for years. As much more experiments are conducted in shaking bioreactors compared to stirred bioreactors, Anderlei and Buchs [Biochem. Eng. J. 7 (2001) 157] developed a measuring device (OTR-Device) for online determination of the oxygen transfer rate in shake flasks under sterile conditions. In this paper, an extension of the OTR-Device, termed respiration activity monitoring system (RAMOS) is described, which allows additional measurement of the carbon dioxide transfer rate and the respiratory quotient in shaking bioreactors. Fermentations of the yeasts Saccharomyces cerevisiae and Pichia stipitis carried out with RAMOS are presented. These measurements show very clearly the differences in respiration activities between the Crabtree-positive yeast S. cerevisiae and the Crabtree-negative yeast P. stipitis . Furthermore, a fermentation of the bacterium Corynebacterium glutamicum is presented, showing the influence of an oxygen limitation on the metabolic activities of the culture. Also, a fermentation of a hybridoma cell line was carried out with RAMOS to elucidate the measuring sensitivity of the system. The new device provides the most important and characteristic parameters (OTR, CTR, RQ) representing biological cultures online, enabling users to draw conclusions on metabolisms of microorganisms already in shaking bioreactors.
295 citations
TL;DR: In this article, the lead biosorption capacity of a Streptomyces rimosus biomass treated with NaOH (0.1 M) was studied in the batch mode.
Abstract: The lead biosorption capacity of a Streptomyces rimosus biomass treated with NaOH (0.1 M) was studied in the batch mode. After pretreatment of biomass at the ambient temperature, optimum conditions of biosorption were found to be: a biomass particle size between 50 and 160 μm, an average contact time of 3 h, a biomass concentration of 3 g/l and a stirring speed of 250 rpm. The equilibrium data could be fitted by Langmuir isotherm equation. Under these optimal conditions, 135 mg Pb 2+ /g biomass was obtained.
291 citations
TL;DR: In this article, the essential role of hydraulic settling time in the formation of aerobic granules was studied in four column sequencing batch reactors (R1, R4, R3 and R4).
Abstract: The essential role of hydraulic settling time in the formation of aerobic granules was studied in four column sequencing batch reactors (R1–R4). Results showed that aerobic granules were successfully cultivated and became dominant only in the R4 operated at the shortest settling time of 5 min, while a mixture of aerobic granules and suspended sludge was observed in R1–R3 run at settling times of 20, 15 and 10 min, respectively. After the steady state was achieved, the respective settling times of R1–R3 was shortened from 20 to 5 min, from 15 to 2 min and from 10 to 1 min; as the result, aerobic granules completely displaced suspended sludge in these three reactors after two-week operation. It was found that cell surface hydrophobicity was improved significantly at short settling times. Analyses of the polyvalent metals contents in aerobic granules showed that the accumulation of calcium in aerobic granules was related to the settling time, however, the total content of iron, magnesium and aluminium in aerobic granules was much pretty lower than the granule calcium content and almost remained constant. It is obvious that a short settling time favours aerobic granulation, and one may expect to manipulate the formation and characteristics of aerobic granules by controlling settling time.
222 citations
TL;DR: In this paper, two coupled anaerobic sequencing batch reactors (ASBR) operated at mesophilic temperature were used for fruit and vegetable waste anaerobatic digestion, and the effect of increasing loading rates on the acidification step was investigated.
Abstract: The two-phase anaerobic digestion of a mixture of fruit and vegetable wastes (FVW) was studied, using two coupled anaerobic sequencing batch reactors (ASBR) operated at mesophilic temperature. The effect of increasing loading rates on the acidification step was investigated. Results indicated that the hydrolysis yield (81%) stabilized at an OLR of 7.5 g COD/L.d. The volatile fatty acids concentration increased when the loading rate was increased and reached its maximum value (13.3 g/L) at higher loading rate tested (10.1 g COD/L.d). Methanogenic fermentation of the liquefaction acidification products was efficiently performed in the ASBR reactor and high methane productivity was obtained (320 L CH4 per kg of input COD). Total COD in the final effluent from the methanizer was usually below 1500 mg/L, and soluble COD below 400 mg/L. Overall COD removal in the treatment system was 96%. Phase separation with conventional ASBR reactors resulted in high process stability, significant biogas productivity and better effluent quality from fruit and vegetable wastes anaerobic digestion.
217 citations
TL;DR: In this article, a computer aided response surface modeling, optimization and analysis of the age and size of the two-stage inocula was carried out in batch reactor studies and the optimal values were obtained including primary inoculum age and density = 56h and 5.5h, respectively.
Abstract: The inoculum age and density markedly influence the productivity and economics of bioprocesses. Some literature reports demonstrated the use of two-stage inocula for the production of surfactin. However, no systematic studies to elucidate the individual, cumulative and interactive effects of the important twin parameters, inoculum age and size on surfactin production, have been reported. Thus, a computer aided response surface modeling, optimization and analysis of the age and size of the two-stage inocula was carried out in batch reactor studies. The optimal values thus, obtained include primary inoculum age and size = 56 h and 5.5% (v/v), secondary inoculum age and size = 4.5 h and 9.5% (v/v), respectively. At the above optimal conditions, the model predicts a maximum relative surfactin concentration of 58–59 CMC −1 , mainly due to a strong interaction between primary inoculum size and secondary inoculum age. The experimental verifications substantiated the model predictions by showing a maximum relative surfactin concentration of 58 CMC −1 , which was found to be equivalent to about 1.3 g L −1 crude surfactin as estimated gravimetrically, thereby resulting in an improved production.
189 citations
TL;DR: The current article reviews the advances that has been made in both the empirical- and mechanistic-type kinetic models and discusses the insights that have been achieved through the modeling work and the improvements to models that will be necessary in the future.
Abstract: Mathematical models are important tools for optimizing the design and operation of solid-state fermentation (SSF) bioreactors. Such models must describe the kinetics of microbial growth, how this is affected by the environmental conditions and how this growth affects the environmental conditions. This is done at two levels of sophistication. In many bioreactor models the kinetics are described by simple empirical equations. However, other models that address the interaction of growth with intraparticle diffusion of enzymes, hydrolysis products and O2 with the use of mechanistic equations have also been proposed, and give insights into how these microscale processes can potentially limit the overall performance of a bioreactor. The current article reviews the advances that have been made in both the empirical- and mechanistic-type kinetic models and discusses the insights that have been achieved through the modeling work and the improvements to models that will be necessary in the future.
179 citations
TL;DR: This result suggests that S plays a critical role in the mediation of H 2 evolution from P. subcordiformis, and strongly depended upon the duration of anaerobic incubation, deprivation of sulphur (S) from the medium and the medium pH.
Abstract: A marine green alga, Platymonas subcordiformis , was demonstrated to photobiologically evolve hydrogen (H 2 ) after the first stage of photosynthesis, when subjected to a two-phase incubation protocol in a second stage of H 2 production: anaerobic incubation in the dark followed by the exposure to light illumination. The anaerobic incubation induced hydrogenase activity to catalyse H 2 evolution in the following phase of light illumination. H 2 evolution strongly depended upon the duration of anaerobic incubation, deprivation of sulphur (S) from the medium and the medium pH. An optimal anaerobic incubation period of 32 h gave the maximum H 2 evolution in the second phase in the absence of sulphur. Evolution of H 2 was greatly enhanced by 13 times when S was deprived from the medium. This result suggests that S plays a critical role in the mediation of H 2 evolution from P. subcordiformis . A 14-fold increase in H 2 production was obtained when the medium pH increased from 5 to 8; with a sharp decline at pH above eight. H 2 evolution was enhanced by 30–50% when supplementing the optimal concentrations of 25 mM acetate and 37.5 mM glucose.
172 citations
TL;DR: In this paper, the authors investigated the inhibition of free ammonia to the development of aerobic granules for simultaneous organic carbon removal and nitrification in sequencing batch reactors and found that the specific oxygen utilization rates of heterotrophic and nitrifying bacteria were reduced by a factor 5 and 2.5, respectively.
Abstract: This study investigated the inhibition of free ammonia to the development of aerobic granules for simultaneous organic carbon removal and nitrification in sequencing batch reactors. Five column sequencing batch reactors (SBRs) were operated at different N/COD ratios in the range of 5/100 to 30/100. Results showed that aerobic granules formed only when the free ammonia concentration were less than 23.5 mg l −1 , and nitrification was completely inhibited at a free ammonia concentration greater than 10 mg l −1 . It was found that the specific oxygen utilization rates of heterotrophic and nitrifying bacteria were reduced by a factor 5 and 2.5 as the free ammonia concentration increased from 2.5 to 39.6 mg N l −1 . Free ammonia resulted in a significant decrease of cell hydrophobicity, and also repressed the production of cell polysaccharides. These would be responsible for the failure of aerobic granulation at high free ammonia concentrations. This study probably for the first time demonstrated that free ammonia could hinder the formation of aerobic granules through its inhibition to energy metabolism of microorganisms.
159 citations
TL;DR: It is shown how a scale-down reactor system called “TubeSpin” can increase process development speed and efficiency as well as the improvement of volumetric productivity using butyrate and temperature shifts.
Abstract: Process development with mammalian cells is often limited by the lack of resources and assay capacity to deal with the multiplicity and complexity of interrelated parameters in culture technology. Multi-component analysis, an issue in media development and in screening of newly established production cell lines, is subject to the same limitations. We therefore developed a high throughput system for the culture of mammalian cells in suspension. Our scale-down reactor system called “TubeSpin” allows many experiments to be run in parallel with a minimum of resources and labor. Reactor conditions were readily simulated using 50 ml centrifugation tubes as culture vessels mounted on a rotational shaker installed in a warm room. This system was applied to the development work for a number of CHO based processes for the production of a human recombinant IgG. We show here how such a system can increase process development speed and efficiency. The results presented illustrate the improvement of volumetric productivity using butyrate and temperature shifts.
156 citations
TL;DR: In this article, the authors investigated the viability of ozonation and cavitation (hydrodynamic cavitation and ultrasonication) for the disinfection of the heterotropic plate count (HPC) bacteria and indicator microorganisms in bore well water.
Abstract: Ozone is a powerful oxidant, which is used extensively for water disinfection. Although it is claimed to produce less toxic byproducts than chlorine, the mutagenicity of the aldehydes and other compounds produced as byproducts during ozonation cannot be ruled out. Due to this there is a need for additional disinfection processes, which can reduce or eliminate these toxic byproducts by reducing the usage of ozone. Moreover, higher cost of these biocides necessitates its optimum usage. Synergistic processes reduces to half or one-third the required concentration of ozone for disinfection as found in this study. Due to these factors, synergistic processes appear to be promising for water disinfection. In this study, we investigate the viability of ozonation and cavitation (hydrodynamic cavitation and ultrasonication) for the disinfection of the heterotropic plate count (HPC) bacteria and indicator microorganisms (total coliforms, faecal coliforms and faecal streptococci) in bore well water.
153 citations
TL;DR: In this paper, the authors present advances in understanding and modelling the gas-liquid mass transfer in shake flasks at water-like liquid viscosity in flask sizes between 50 and 1000 ml.
Abstract: The gas–liquid mass transfer in 250 ml shake flasks has previously been sucessfully modelled on basis of Higbie’s penetration theory. The current contribution presents advances in understanding and modelling the gas–liquid mass transfer in shake flasks at waterlike liquid viscosity in flask sizes between 50 and 1000 ml. An experimental investigation of the maximum gas–liquid mass transfer capacity OTRmax using the sodium sulphite system was extended to relative filling volumes of 4–16%, shaking diameters of 1.25, 2.5, 5, 7, 10 cm and shaking frequencies of 50–500 rpm for the above flask sizes. Simultaneously, the previous model of the gas–liquid mass transfer was extended to a “two sub-reactor model” to account for different mechanisms of mass transfer in the liquid film on the flask wall and the bulk of the liquid rotating within the flask. The shake flask is for the first time considered to be a two-reactor system consisting of a stirred tank reactor (bulk liquid) and a film reactor (film on flask wall and base). The mass transfer into the film on the flask wall and base at “in-phase” operating conditions is described by Higbie’s penetration theory. Two different mass transfer theories were applied to successfully describe the mass transfer into the bulk liquid: a model by Kawase and Moo-Young and a model by Gnielinski. The agreement between the new modelling approach, which requires absolutely no fitting parameters and the experimental is within ±30%. The applicability of the models to a biological system was shown using a Pichia pastoris culture. This is particularly notable since geometrically non-similar liquid distributions in very different sizes of shaking flasks are covered. A comparable description of the gas–liquid mass transfer in bubble aerated reactors like stirred tanks is absolutely out of reach. A spatially- and time-resolved consideration of the mass transfer in the liquid film on the flask wall and base has shown that the validity of Higbie’s theory sensitively depends on the film thickness and contact time.
TL;DR: A chromatic spectrum of blue and red light was used to enhance the growth and extracellular polysaccharide production due to the characteristics of the photosynthetic process.
Abstract: Blue light and red light can be used to improve the efficiency of photosynthesis and increase the production of extracellular polysaccharide. Growth and extracellular polysaccharide production by Porphyridium cruentum were measured as a function of light wavelength and intensity. Light quality was a key factor for controlling the growth and polysaccharide production. The growth rate of P. cruentum increased with enhanced of light intensity, however a light level beyond the saturation point inhibited the growth of microalgae. A chromatic spectrum of blue and red light was used to enhance the growth and extracellular polysaccharide production due to the characteristics of the photosynthetic process. Efficient light transfer was the most important parameters in optimizing the mass culture of the photosynthetic organism.
TL;DR: The aim of these experiments is to study the oxygen mass transfer rate through the mass transfer coefficient, kla, for a stirred bioreactor and different fermentation broths, using a large domain of operating variables, using MATLAB software.
Abstract: The oxygen mass transfer represents the most important parameter implied on the design and operation of mixing–sparging equipment of the bioreactors. It can be described and analyzed by means of mass transfer coefficient, kla. The kla values are affected by a lot of factors, such as geometrical and operational characteristics of the vessels, media composition, type, concentration and microorganisms morphology, biocatalysts properties. The aim of these experiments is to study the oxygen mass transfer rate through the mass transfer coefficient, for a stirred bioreactor and different fermentation broths, using a large domain of operating variables. For quantifying the effects of the considered factors (concentration and morphology of biomass, specific power input, superficial air velocity) on kla for submerged and surface aeration, the experiments were carried out for non-respiring biomass suspensions of Propionibacterium shermanii, Saccharomyces cerevisiae and Penicillium chrysogenum, mycelial aggregates (pellets) and free mycelia morphological structures. By means of the experimental data and using MATLAB software, some mathematical correlations describing the influences of the considered factors on kla have been proposed for each microbial culture. These equations offer a good agreement with the experiment, the maximum deviation being ±8.4% for submerged aeration, and ±9.1% for surface aeration, respectively.
TL;DR: Promising results with the crude preparation of Penicillium aurantiogriseum lipolytic preparation justify the undertaking of purification studies and the use of the pure enzyme in a more in-depth investigation for its potential in biocatalysis in organic solvents.
Abstract: The effects of various environmental conditions and chemical compounds on the activity and stability of the lipolytic preparation obtained from a wild strain of Penicillium aurantiogriseum were characterized during a preliminary evaluation of its potential for use in biocatalysis. In aqueous solution, the optimum pH for activity was 8.0 and the enzyme was stable between pH 6.0 and pH 9.0. In assays of 1 min duration carried out at pH 8.0, enzyme activities were quite high from 37 to 70 °C, with a maximum at 60 °C. However, thermal stability was rather low at temperatures higher than 28 °C. Hydrolytic activity was enhanced by Mg 2+ , Zn 2+ , Co 2+ and Mn 2+ , but was inhibited by Cu 2+ , Ba 2+ and Hg 2+ , while Ca 2+ had no effect. Sodium azide activated the enzyme. Triton X-100 caused an inhibition of 52%, while Tween 80 and SDS had negligible effects on enzymatic activity. Despite the low ratio of the activity towards p -nitrophenyl palmitate (pNPP) in organic medium to that in aqueous medium ( R O/A =4.3×10 −2 ), the enzyme showed a good stability in organic solvents with high log P values, the best result being in n -heptane (114% residual activity). These promising results with the crude preparation justify the undertaking of purification studies and the use of the pure enzyme in a more in-depth investigation for its potential in biocatalysis in organic solvents.
TL;DR: In this article, the purification results of lactic acid from the fermentation broth with paper sludge as a cellulosic feedstock using weak anion exchanger Amberlite IRA-92 were investigated.
Abstract: Lactic acid promises to be an important commodity chemical in the future as a monomer for the production of biodegradable polylactic acid. With the increase of the lactic acid demand, the need to explore alternative feedstock sources and purification processes that are inexpensive and efficient is becoming more important. This paper first reports the purification results of lactic acid from the fermentation broth with paper sludge as a cellulosic feedstock using weak anion exchanger Amberlite IRA-92. Some factors such as flow rate, sample volume loaded, pH, and column were systematically examined to improve the purity, yield and productivity in lactic acid purification. Adsorption isotherm of standard lactic acid and lactic acid in the fermentation broth by anion exchanger IRA-92 were also investigated. Results indicate that in purification process the increase of pH of the fermentation broth ranging from 5.0 to 6.0 can significantly enhance the recovery yield, purity and productivity. The decrease of flow rate and sample volume loaded can also improve the recovery yield and purity but apparently reduce the productivity. In addition, the scale-up of purification process in laboratory size has little influence on the recovery yield and purity. After optimization, the yield, purity and productivity are found to be about 82.6%, 96.2% and 1.16 g LA/(g-resin day), respectively.
TL;DR: In this paper, an effective approach to a practical high-performance enzymatic hydrolysis of cellulose was investigated using a ultrasonic irradiation as a pretreatment and a combination of cellulases from Trichoderma viride and Aspergillus niger.
Abstract: Effective approaches to a practical high-performance enzymatic hydrolysis of cellulose were investigated using a ultrasonic irradiation as a pretreatment and a combination of cellulases from Trichoderma viride and Aspergillus niger. Their efficacy on enhancement of reactivity was discussed based on the kinetic parameters, i.e. Michaelis constant Km, maximum reaction rate Vmax and initial reaction rate, correlating with ultrasonic conditions and enzyme combination, respectively. A relatively high-weight fraction of A. niger cellulase in the mixed-enzyme system afforded rapid initiation of the hydrolysis reaction, while a kinetic analysis revealed that a T. viride cellulase weight fraction of ca. 0.3 was optimal in enhancing Vmax without increasing Km. Pretreatment of the cellulose fibers with ultrasonic irradiation prior to initiating the enzyme reaction further improved the reaction rate. Enhancement of Vmax by ultrasonication was effective in greater weight fraction of T. viride used system. The correlation between the ultrasonic irradiation time required to obtain a desired initial reaction rate and the irradiation power employed was examined, and it was found that the time needed for effective degradation could be markedly reduced by increasing the irradiation power. This finding is considered to support the possibility of applying ultrasonication pretreatment in a practical cellulose saccharification process.
TL;DR: In this article, the lactic acid extraction by tri-n-octylamine dissolved in decanol and docecane has been studied and a mathematical model of extraction, taking into account formation of acid/amine complexes, has been composed and solved.
Abstract: The paper deals with the lactic acid extraction by tri-n-octylamine dissolved in decanol and docecane. The extraction efficiency depends on the initial lactic acid concentration and the initial pH value of the solution. In case of lactic acid extraction from simulated fermentation broth, the partially loading of extractant with HCl leads to increasing of the distribution coefficient. The extraction equilibrium constants have been determined. The strong influence of diluents on the values of the graphically determined extraction constant and the number of extractant molecules in the acid–amine complex has been shown. A mathematical model of extraction, taking into account formation of (1:1) (2:1) and (1:2) acid/amine complexes, has been composed and solved. The model fits very well the experimental results.
TL;DR: In this article, the authors measured the oxygen transfer rate (OTR) of polypropylene vessels with different sizes in the horizontal plane, using an enzymatic method involving glucose oxidase, horseradish peroxidase (HRP), and 2,2-azino-bis 3-ethybenz-thiazoline-6-sulfonic acid (ABTS).
Abstract: Oxygen transfer rates (OTRs) during orbital shaking were measured for differently sized polypropylene vessels that were either square or round in the horizontal plane, using an enzymatic method involving glucose oxidase, horseradish peroxidase (HRP), and 2,2-azino-bis 3-ethybenz-thiazoline-6-sulfonic acid (ABTS). In comparison to non-shaking conditions (3.2 mmol O2 l−1 h−1), OTRs in 4 mm ×4 mm vessels (corresponding to wells in 384-square deepwell microtiter plates) at a working volume of 0.125 ml could only be significantly enhanced at 300 rpm if a shaking diameter of 50 mm was applied (25 mmol O2 l−1 h−1) instead of 25 mm (6.7 mmol O2 l−1 h−1). Larger square vessels ( 18 mm ×18 mm and 50 mm ×50 mm) yielded high oxygen transfer rates and a regular shaking pattern, demonstrating that vessels in this size range could be a viable, space-efficient, alternative to baffled or unbaffled Erlenmeyer shaking flasks. Round vessels (internal diameter 6.6 mm) resulted in OTRs that were approximately 50% of those measured for square vessels in the same size range.
TL;DR: In this paper, the effects of water content, temperature, substrate concentration and the molar ratio of oleic acid and alcohols on the ester yield were investigated in solvent-free system.
Abstract: Biolubricant was prepared in integrated system by an esterification reaction of fusel oil and oleic acid, where immobilised Novozym 435 lipase enzyme was used as a biocatalyst. Firstly shaken flasks experiments were carried out, and the effects of water content, temperature, substrate concentration and the molar ratio of oleic acid and alcohols on the ester yield were investigated in solvent-free system. To eliminate the negative effect of the water produced in the reaction, integrated system was constructed, and pervaporation was used for water removal. The method was suitable to achieve 99.8% conversion under optimal conditions. The oleochemical ester produced doesn’t have aquatic toxicity and the determined tribologycal, physico-chemical properties of the lubricant proved that it is an environmental friendly product.
TL;DR: The ordered bi–bi mechanism with inhibition by both R(−)-methyl mandelate (substrate) and R( (−)-mandelic acid (product) was found to fit the initial rate data very well and the kinetic constants were determined.
Abstract: Separation of racemic mixtures is a formidable task and various approaches have been suggested. The resolution of R(−)-mandelic acid, which is used as an intermediate in pharmaceutical and drug industry, from a racemic mixture was studied in non-aqueous media via lipase catalyzed hydrolysis of RS(∓)-methyl mandelate. Novozym 435 (component B of the lipase from Candida antartica), lipozyme RM IM (Rhizomucor miehei lipase) and lipozyme TL IM (Thermomyces lanuginosus lipase) were screened for their activity and selectivity to get R(−)-mandelic acid. Novozym 435 was found to be the most effective in hydrolysis of R(−)-methyl mandelate with an optical purity of 78% at the end of 24 h. Effects of various process parameters such as speed of agitation, catalyst loading, substrate concentration, product concentration and temperature were studied. The ordered bi–bi mechanism with inhibition by both R(−)-methyl mandelate (substrate) and R(−)-mandelic acid (product) was found to fit the initial rate data very well and the kinetic constants were determined.
TL;DR: A modified Gompertz equation was able to adequately model the fermentation of cellulose by rumen microorganisms and might provide useful information for the application of rumen cultures for conversion of cellulosic wastes into value-added products.
Abstract: Batch experiments were performed to investigate the anaerobic degradation of crystalline cellulose of 10 g l−1 by rumen microorganisms at pH from 4.8 to 7.3. The degradation efficiency increased with pH and the highest value of about 78% was achieved at pH 6.8 and 7.3. Acetate and propionate were the major aqueous products at all pH values. With increasing pH, the molar percentage of acetate decreased, whereas that of propionate increased. A modified Gompertz equation was able to adequately model the fermentation of cellulose by rumen microorganisms. The results from this study might provide useful information for the application of rumen cultures for conversion of cellulosic wastes into value-added products.
TL;DR: In this paper, the Weibull equation was used to evaluate the susceptibility of disaccharides to the hydrolysis of two glucose residues or of glucose and fructose or galactose residues.
Abstract: The hydrolysis of disaccharides consisting of two glucose residues or of glucose and fructose or galactose residues in subcritical water was measured using a tubular reactor at 10 MPa and 180–260 °C. The relationship between the fraction of remaining disaccharide and the residence time could be expressed by the Weibull equation for all the disaccharides tested at any temperature. The susceptibility to hydrolysis largely depended on the type of disaccharide, and it was found that the electrostatic potential charge of a glucosidic oxygen atom was an indication for the susceptibility of disaccharide to the hydrolysis. It was also shown that the enthalpy–entropy compensation held for the hydrolysis of disaccharides in subcritical water.
TL;DR: To stabilize the lipase activity of Rhizopus oryzae cells as whole-cell biocatalysts, the effect of cell membrane fatty acid composition on biodiesel-fuel production was investigated and both methanolysis activity and enzymatic stability were maintained at significantly elevated levels.
Abstract: To stabilize the lipase activity of Rhizopus oryzae cells as whole-cell biocatalysts, the effect of cell membrane fatty acid composition on biodiesel-fuel production was investigated. The fatty acid composition of the cell membrane was easily controllable by addition of various fatty acids to the culture medium. Oleic or linoleic acid-enriched cells showed higher initial methanolysis activity than saturated fatty acid-enriched cells, among which palmitic acid-enriched cells exhibited significantly greater enzymatic stability than unsaturated fatty acid-enriched cells. It was assumed that fatty acids significantly affect the permeability and rigidity of the cell membrane, and that higher permeability and rigidity lead to increases in methanolysis activity and enzymatic stability, respectively. When the optimal fatty acid ratio of 0.67, indicated by Rf [=oleic acid/(oleic acid + palmitic acid)], was adopted for repeated methanolysis reactions, both methanolysis activity and enzymatic stability were maintained at significantly elevated levels, with methyl ester content of around 55% even in the 10th batch cycles.
TL;DR: Optimization of a fed-batch bioreactor using a cascade recurrent neural network (RNN) model and modified genetic algorithm and modified GA is studied, showing that the algorithm is able to generate a smooth feed rate profile, where the optimality is still maintained.
Abstract: Optimization of a fed-batch bioreactor using a cascade recurrent neural network (RNN) model and modified genetic algorithm (GA) is studied in this paper. The complex nonlinear relationship between the manipulated feed rate and the biomass product is described by two recurrent neural sub-models, in which outputs of one sub-model are fed into another sub-model to provide meaningful information for the biomass prediction. The simulation results show that the error of prediction is less than 8%. Based on the neural network model, a modified GA is employed to determine a smooth optimal feed rate. The evolution of feed rate profiles shows that the algorithm is able to generate a smooth feed rate profile, where the optimality is still maintained. The final biomass quantity that yields from the optimal feed rate profile based on the neural network model reaches 99.8% of the “real” optimal value obtained based on the mechanistic model. An experimental investigation has also been carried out to verify the feasibility of the proposed technique.
TL;DR: In this article, a rotary viscometer was used to determine the relationship between shear rate and shear stress of sludge samples drawn from a submerged membrane bioreactor, including various solid contents.
Abstract: In this work, the main objective was to conduct a study on the flow model of the sludge produced in a submerged membrane bioreactor (sMBR). For this purpose, the sludge samples were drawn from a bioreactor, including various solid contents. The relationship between shear rate and shear stress of the samples was determined by using a rotary viscometer. The effects of temperature and solid concentration on the rheology of the sludge were also investigated. It was found that the best flow model for the samples was the Ostwald de Vaele model. The apparent viscosity decreased logarithmically with an increase in the rotary velocity and increased exponentially with an increase in the solid content of sludge.
TL;DR: A formalism integrating PCA and generalized regression neural networks (GRNNs) is introduced in this paper and the effectiveness of the proposed modeling and monitoring formalism has been successfully demonstrated by conducting two case studies involving penicillin production and protein synthesis.
Abstract: Multivariate statistical methods namely, principal component analysis (PCA) and partial least squares (PLS), which perform dimensionality reduction and regression, respectively, are commonly used in batch process modeling and monitoring. While PCA is used to monitor whether process input variables are behaving normally, the PLS is used for predicting values of the process output variables. A significant drawback of the PLS is that it is a linear regression formalism and thus makes poor predictions when relationships between process inputs and outputs are nonlinear. For overcoming this drawback, a formalism integrating PCA and generalized regression neural networks (GRNNs) is introduced in this paper for conducting batch process modeling and monitoring. The advantages of this PCA-GRNN hybrid methodology are (i) process outputs can be predicted accurately even when input-output relationships are nonlinear, and (ii) unlike other commonly used artificial neural network (ANNs) paradigms (such as the multi-layer perceptron), training of a GRNN is a one-step procedure, which helps in faster development of nonlinear input-output models. A two-module software package has been developed for implementing the PCA-GRNN formalism and the effectiveness of the proposed modeling and monitoring formalism has been successfully demonstrated by conducting two case studies involving penicillin production and protein synthesis.
TL;DR: In this article, the effect of different carbon sources on lactic acid production by Rhizopus oryzae was studied using glucose, sucrose, beet molasses, carob pod and wheat bran as substrate.
Abstract: The effect of different carbon sources on lactic acid production by Rhizopus oryzae was studied using glucose, sucrose, beet molasses, carob pod and wheat bran as substrate. The highest lactic acid concentration was obtained when 150 g/l glucose was present in the medium as the sole carbon source. In that case, the lactic acid yield was approximately 60% by weight based on the amount of glucose consumed. Wheat bran was found to be an unsuitable substrate for this particular fermentation. Pasteurisation of molasses increased lactic acid production rate compared to that of untreated molasses. Likewise, 58 g/l lactic acid was obtained by using the supernatant containing sugars extracted from carob pod. This medium could therefore be considered as an alternative carbon source for lactic acid production.
TL;DR: In this paper, a factorial design was performed with the aim of optimizing the bacteriocin production by Bacillus licheniformis P40, using response surface methodology (RSM).
Abstract: In this work, a 2 3 factorial design was performed with the aim of optimizing the bacteriocin production by Bacillus licheniformis P40, using response surface methodology (RSM). The bacteriocin production was first tested on different byproducts, like feather meal, grape bagasse, an industrial fibrous soybean residue and cheese whey. Cheese whey was the selected medium to test the effect of three variables (temperature, initial pH and whey concentration) by RSM. Statistical analysis of results showed that, in the range studied, the three variables have a significant effect on bacteriocin production. Response-surface data showed maximum bacteriocin production at initial pH between 6.5 and 7.5 and temperature between 26 and 37 °C when the cheese whey concentration was 70 g l −1 . Increasing whey concentration resulted in increase of bacteriocin production, with an activity at the maximum whey concentration tested. It was not possible to determine a relation between bacteriocin production and optimal conditions for bacterial growth.
TL;DR: An adaptation of the state-of-the-art AI-based robust optimization technique, non-dominated sorting genetic algorithm with jumping genes (NSGA-II-JG) is used in finding the Pareto solutions for both the existing as well as SMBR system at the design stage.
Abstract: The isomerization of glucose to fructose is an important industrial process in obtaining high fructose syrup, a sweetener widely used in food industry. In this work, a hybrid simulated moving bed reactor (SMBR) system is optimized using experimentally verified dynamic SMB model to maximize the net productivity of HFS55 using minimum solvent. An adaptation of the state-of-the-art AI-based robust optimization technique, non-dominated sorting genetic algorithm with jumping genes (NSGA-II-JG) is used in finding the Pareto (non-dominated) solutions for both the existing as well as SMBR system at the design stage. Finally, SMBR configuration was modified to further improve the system performance. Systematic multi-objective optimization resulted in significant performance improvement. Moreover, the new optimization technique gives much faster, smoother and larger spread of the Pareto-optimal solutions.
TL;DR: In this paper, different extraction methods including conventional organic solvent, Soxhlet, heat reflux, ultrasound-assisted and microwave-assisted extractions were attempted for efficient extraction of notoginseng saponins from dried cells of Panax notogseng obtained in bioreactor cultures.
Abstract: Different extraction methods including conventional organic solvent, Soxhlet, heat reflux, ultrasound-assisted and microwave-assisted extractions were attempted for efficient extraction of notoginseng saponins from dried cells of Panax notoginseng obtained in bioreactor cultures. The microwave-assisted extraction for 6 min led to a similar saponin yield (based on mg/100 mg cells) compared to other methods that took 2–14 h. To optimize the microwave-assisted extraction conditions, the treatment time, temperature, solid/liquid (w/v) ratio and the number of repeated extraction steps were further studied. The optimal extraction method was microwave-assisted extraction for 4 min of extraction time at 50 °C of extraction temperature (at a radiation power of 125 W) and 1:150 of the solid/liquid (w/v) ratio. The yield of total saponins extracted from P. notoginseng cells was increased with an increase of extraction steps, and it was obtained more with microwave assistance than that without microwave assistance.