Effect Of Agitation Rate Research Articles

EFFECT OF AGITATION AND AERATION ON THE CITRIC ACID PRODUCTION BY Yarrowia lipolytica GROWN ON GLYCEROL

The effects of agitation rates from 400 to 900 rpm and aeration rates ranging from 0.18 to 0.6 vvm on biomass and citric acid production on glycerol media by acetate-negative mutants of Yarrowia lipolytica, Wratislavia 1.31 and Wratislavia AWG7, in batch culture were studied. The agitation rates of 800 and 900 rpm (at a constant aeration rate of 0.36 vvm) and aeration rates within the range of 0.24–0.48 vvm (at a constant agitation rate of 800 rpm), which generated dissolved oxygen concentration (DO) higher than 40%, were found the best for citric acid biosynthesis from glycerol. An increase in agitation rate (higher than 800 rpm) and aeration rate (higher than 0.36 vvm) had no impact on DO and citric acid production. The highest citric acid concentration (92.8 g/L) and yield (0.63 g/g) were obtained with Wratislavia 1.31 strain at 0.24 vvm. The highest volumetric citric acid production rate (1.15 g/Lh) and specific citric acid production rate (0.071 g/gh) were reached at 0.48 vvm.

The effects of supersaturation, temperature, agitation and seed surface area on the secondary nucleation of paracetamol in ethanol solutions

This work details the estimation of the secondary nucleation kinetics of paracetamol in ethanol solutions for cooling crystallisation processes, by means of isothermal under-seeded batch experiments. A numerical model, incorporating the population balance equation and the method of moments has been developed to describe the seeding process for a typical cooling crystallisation process, accounting for the primary and secondary nucleation and subsequent crystal growth. Primary nucleation and growth kinetics have been previously evaluated from induction time experiments and isothermal seeded batch experiments, respectively, allowing the secondary nucleation rate to be evaluated for a wide range of experimental conditions. The experimental technique involved the utilisation of two in-situ Process Analytical Techniques (PAT), a Focused Beam Reflectance Measurement (FBRM®) utilised to qualitatively indicate the occurrence of secondary nucleation and an Attenuated Total Reflectance — Fourier Transform Infrared (ATR-FTIR) probe employed for the online monitoring of solute concentration. Initial Particle Size Distributions (PSD) were used in conjunction with desupersaturation profiles to determine the secondary nucleation rate as a function of supersaturation, temperature and crystal surface area. Furthermore, the effects of agitation rate on the secondary nucleation rate were also investigated. Experimental data were compared to the model simulation, with the accuracy of the estimated secondary nucleation kinetics validated by means of the final product PSD and solute concentration.

Synthesis of CaCO3 nanoparticles by controlled precipitation of saturated carbonate and calcium nitrate aqueous solutions

AbstractCalcium carbonate nanoparticles (CCNP) were synthesised by precipitation from saturated sodium carbonate and calcium nitrate aqueous solutions. The effect of agitation rate, mixing time, calcium/carbonate ions concentration and temperature on particle size and morphology were investigated. Particles were characterised using X‐ray diffraction (XRD), transmission electron microscopy (TEM) and thermogravimetric analysis (TGA). Increasing the mixing time from 30 to 180 min resulted in a decrease in particles size. Mixing rate variation between 300 and 14 000 rpm decreased the particle size. Temperature increase favoured a significant growth in particle size and in the formation of aragonite beginning from 80°C. Calcium and carbonate ion concentrations are key parameters controlling the CCNP particle size. Calcite is the main polymorph obtained as revealed by XRD analysis. © 2011 Canadian Society for Chemical Engineering

Effect of Agitation Rate on Ethanol Production from Sugar Maple Hemicellulosic Hydrolysate by Pichia stipitis

Concentrated dilute acid hydrolysate was obtained from hot water extracts of Acer saccharum (sugar maple) and was fermented to ethanol by Pichia stipitis in a 1.3-L-benchtop bioreactor. The conditions under which the highest ethanol yield was achieved were when the air flow rate was set to 100 cm(3) and the agitation rate was set to 150 rpm resulting in an overall mass transfer coefficient (K(L)a) of 0.108 min(-1). A maximum ethanol concentration of 29.7 g/L was achieved after 120 h of fermentation; however, after 90 h of fermentation, the ethanol concentration was only slightly lower at 29.1 g/L with a yield of 0.39 g ethanol per gram of sugar consumed. Using the same air flow rate and adjusting the agitation rate resulted in lower ethanol yields of 0.25 g/g at 50 rpm and 0.30 g/g at 300 rpm. The time it takes to reach the maximum ethanol concentration was also affected by the agitation rate. The ethanol concentration continued to increase even after 130 h of fermentation when the agitation rate was set at 50 rpm, whereas the maximum ethanol concentration was reached after only 68.5 h at 300 rpm.

Effect of impeller type and agitation on the performance of pilot scale ASBR and AnSBBR applied to sanitary wastewater treatment

The objective of this work was to assess the effect of agitation rate and impeller type in two mechanically stirred sequencing batch reactors: one containing granulated biomass (denominated ASBR) and the other immobilized biomass on polyurethane foam (denominated AnSBBR). Each configuration, with total volume of 1 m(3), treated 0.65 m(3) sanitary wastewater at ambient temperature in 8-h cycles. Three impeller types were assessed for each reactor configuration: flat-blade turbine impeller, 45 degrees -inclined-blade turbine impeller and helix impeller, as well as two agitation rates: 40 and 80 rpm, resulting in a combination of six experimental conditions. In addition, the ASBR was also operated at 20 rpm with a flat-blade turbine impeller and the AnSBBR was operated with a draft tube and helix impeller at 80 and 120 rpm. To quantify how impeller type and agitation rate relate to substrate consumption rate, results obtained during monitoring at the end of the cycle, as well as the time profiles during a cycle were analyzed. Increasing agitation rate from 40 rpm to 80 rpm in the AnSBBR improved substrate consumption rate whereas in the ASBR this increase destabilized the system, likely due to granule rupture caused by the higher agitation. The AnSBBR showed highest solids and substrate removal, highest kinetic constant and highest alkalinity production when using a helix impeller, 80 rpm, and no draft tube. The best condition for the ASBR was achieved with a flat-blade turbine impeller at 20 rpm. The presence of the draft tube in the AnSBBR did not show significant improvement in reactor efficiency. Furthermore, power consumption studies in these pilot scale reactors showed that power transfer required to improve mass transfer might be technically and economically feasible.

USE OF MIXTURE DESIGN AND FLOW CHARACTERISTICS TO FORMULATE ICE CREAM COMPOUND COATINGS

ABSTRACT Flow properties of three industrial formulas of ice cream compound coatings were studied in the steady state regime with the coaxial geometry. Flow curves showed shear‐thinning thixotropic behavior. As for molten chocolate, the Casson–Steiner equation was used to fit the compound coating rheograms in the shear rate range 380–1,000 s −1 . The effects of agitation rate and time applied during coating preparation were studied. A new formula of coating was realized using a mixture design and, as dependent variables, the apparent viscosities at different shear rates. Results showed that the flow properties of molten compound coatings could be reproduced by this statistical method, but subsequent research on the influence of fat content and nature, and on the rheological parameters controlling the solidification of coatings, should be carried out to improve their formulation. PRACTICAL APPLICATIONSFormulation of food materials using the scientific (and not the traditional) method is essential in predicting the quality of the final product and reducing the period and cost of developing. This method is based on the use of statistical experimental design and needs the understanding of the techno‐functional properties of the food materials (such as physicochemical properties and rheological behavior). The aim of this research was to use this scientific method in developing a new coating formula. This work illustrates the importance of the mixture design and the rheological properties of molten compound coatings in their formulation. In practice, we showed that the dependent variables used in the mixture design would be chosen with great attention, with respect to the fat contained in coatings. The fat nature and content has a great influence on the functional properties of the coatings used in ice cream manufacture, which is the subject of a forthcoming paper.

An Investigation of the Transformation of Carbamazepine from Anhydrate to Hydrate Using in Situ FBRM and PVM

This study investigated the conversion of carbamazepine (CBZ) from polymorph III to carbamazepine dihydrate (CBZH) using the in situ FBRM and PVM. The effects of agitation rate, temperature, the initial crystal size, solvent composition, and seeds were systematically studied. The transient concentration of CBZ in the solution was examined by ultraviolet spectrophotometer at the same that the solid-phase composition was quantified by offline PXRD, and the rate-controlling step for the transformation was identified. The results show that increase of agitation speed can accelerate the transformation of CBZ from polymorph III to CBZH; higher temperature or larger size of initial crystals elongated transformation time of III to CBZH greatly; seeding shortened the transformation time and the addition of ethanol-induced nucleation and accelerated the transformation.

Copper and cadmium adsorption on pellets made from fired coal fly ash

Studies on the utilization of low cost adsorbents for removal of heavy metals from wastewaters are gaining attention. Fired coal fly ash, a solid by-product that is produced in power plants worldwide in million of tonnes, has attracted researchers’ interest. In this work, fly ash was shaped into pellets that have diameter in-between 3–8 mm, high relative porosity and very good mechanical strength. The pellets were used in adsorption experiments for the removal of copper and cadmium ions from aqueous solutions. The effect of agitation rate, equilibration time, pH of solution and initial metal concentration were studied. The adsorption of both cations follows pseudo-second order kinetics reaching equilibrium after an equilibration time of 72 h. The experimental results for copper and cadmium adsorption fit well to a Langmuirian type isotherm. The calculated adsorption capacities of pellets for copper and cadmium were 20.92 and 18.98 mg/g, respectively. Desorption experiments were performed in several extraction media. The results showed that both metals were desorbed substantially from pellets under acidic solutions. For this reason, metal saturated pellets were encapsulated in concrete blocks synthesized from cement and raw pulverized fly ash in order to avoid metal desorption. The heavy metals immobilization after encapsulation in concrete blocks was tested through desorption tests in several aqueous media. The results showed that after 2 months in acidic media with pH 2.88 and 4.98 neither copper nor cadmium were desorbed thus indicating excellent stabilization of heavy metals in the concrete matrix. As a conclusion, the results showed that fly ash shaped into pellets could be considered as a potential adsorbent for the removal of copper and cadmium from wastewaters. Moreover, the paper proposes an efficient and simple stabilization process of the utilized adsorbents thus guarantying their safe disposal in industrial landfills and eliminating the risk of pollution for groundwater and other natural water receivers.

Kinetic study on pressure leaching of high iron sphalerite concentrate

The kinetics of pressure leaching high iron sphalerite concentrate was studied. The effects of agitation rate, temperature, oxygen partial pressure, initial acid concentration, particle size, iron content in the concentrate and concentration of Fe 2- added into the solution on the leaching rate of zinc were examined. The experiment results indicate that if the agitation rate is greater than 600 r/min, its influence on Zn leaching rate is not substantial. A suitable rise in temperature can facilitate the leaching reaction, and the temperature should be controlled at 140–150 °C. The increase trend of Zn leaching rate becomes slow when pressure is greater than 1.2 MPa, so the pressure is controlled at 1.2–1.4 MPa. Under the conditions of this study, Zn leaching rate decreases with a rise in the initial sulfuric acid concentration; and Zn leaching rate increases with a rise of iron content in the concentrate and Fe 2- concentration in the solution. Moreover, the experiment demonstrates that the leaching process follows the surface chemical reaction control kinetic law of “shrinking of unreacted core”. The activation energy for pressure leaching high iron sphalerite concentrate is calculated, and a mathematical model for this pressure leaching is obtained. The model is promising to guide the practical operation of pressure leaching high iron sphalerite concentrate.

Improvement in Production and Quality of Gellan Gum by Sphingomonas paucimobilis Under High Dissolved Oxygen Tension Levels

The effect of agitation rate and dissolved oxygen tension (DOT) on growth and gellan production by Sphingomonas paucimobilis was studied. Higher cell growth of 5.4 g l(-1) was obtained at 700 rpm but maximum gellan (15 g l(-1)) was produced at 500 rpm. DOT levels above 20% had no effect on cell growth but gellan yield was increased to 23 g l(-1 )with increase in DOT level to 100%. Higher DOT levels improved the viscosity and molecular weight of the polymer with change in acetate and glycerate content of the polymer.

Photobiological Hydrogen Production from Synthesis Gas: Carbon Sources, KL a and Kinetics Evaluation

AbstractPhoto‐evolution of hydrogen from synthesis gas using Rhodospirillum rubrum was studied in batch fermentation. Culture of R. rubrum was initially grown on malate, also with various initial concentrations of acetate and synthesis gas. The synthesis gas was a mixture of H2, CO and CO2. It was found that the doubling time of bacterium on 2.5 g/l of malate, and 2.5 g/l and 6 g/l of acetate were 8.4, 31.8, and 68.6 h, respectively. The growth of R. rubrum was not significant at high concentration of acetate. The cell density of microbe was 0.3 g/l on 2.5 g/l malate for incubation period of 5 days. The cell concentrations of 1.4 and 0.41 g/l were obtained in 2.5 and 6 g/l of acetate, respectively for duration of 5 days. Inhibition of substrate was clearly observed on cell yield and hydrogen production with high concentration of acetate. Maximum hydrogen production (1.8 mmol/l) was obtained when R. rubrum was grown on 2.5 g/l of acetate. Effect of agitation rate was carried out and it was found that more hydrogen production (1.8 mmol) was achieved at 250 rpm. Mass transfer and kinetic studies were performed on 2.5 g/l of acetate. Maximum specific growth rate (m̈m) and Monod constant (KH) were obtained at 9.8 h−1 and 0.14 atm, respectively. No substrate inhibition occurred at CO concentration of 0.56 atm.

Effect of particle size and shape of solids on the viability of acidophilic bacteria during mixing in stirred tank reactors

In this study, the effect of agitation rate, particle size, and shape of solids on the viability of a mesophilic culture of acidophilic bacteria was examined in stirred tank reactors (STRs) fitted with the Rushton turbine (RT) and the pitched blade turbine (PBT) impellers. In the absence of solids, the hydrodynamic shear levels generated as a function of impeller type and speed (1.0–3.35 m/s) were found to have a limited adverse effect on the bacterial cells, i.e., only a ≤16% loss in the viability of the bacterial population over a mixing period of 4 h. However, in the presence of solids (20% w/w) and at an agitation rate of 3.35 m/s, an extensive loss in the viability of bacterial population was observed apparently due to the action of solid particles on the bacterial cells. The rate and extent of the deactivation (i.e., loss in viability) of bacterial cells were shown to depend on the impeller type, the size, and shape of solid particles. The RT impellers caused more extensive loss in the viability of bacterial population than the PBT impellers under the same experimental conditions. The first-order deactivation rate of bacterial cells was found to increase with decreasing particle size down to a certain size (−63+45 μm), below which a reverse trend was noted. The findings have also indicated that the spherical particles (ballotini) deactivate the bacterial cells at a faster rate than the irregular particles (quartz) in shape.

Effect of agitation rate on biomass and protease production by a marine bacterium Vibrio harveyi cultured in a fermentor

A marine bacterium Vibrio harveyi was adapted to grow and produce extracellular proteases in a seawater/Zobell-based medium, supplemented with skim milk under different hydrodynamic conditions, namely agitation and aeration rates. The addition of skim milk to Zobell medium enhanced fivefold the extracellular enzyme production. Protease production seemed to take place after maximum luminescence had been produced. Specific growth rate increased as a consequence of increasing agitation rates. The maximum activity of 4.28 units mg−1 protein were formed with 700 rev min−1 and 0.5 v/v/m. Protease activity detected has a molecular weight of 34 kDa. Another minor band of protease activity was found at 40 kDa.

Monitoring milk fat fractionation: Effect of agitation, temperature, and residence time on physical properties

AbstractWith the use of two central composite designs, the effects of agitation rate, fractionation temperature, and residence time on the thermal properties of the stearin and olein milk fat fractions were investigated. The main function of agitation during fat fractionation was suspending the crystal aggregates and enhancing the heat transfer. For the experimental conditions described here, crystal aggregation did not seem to be affected by agitation. The effect of fractionation temperature on the physical properties of the olein fraction was very significant. Triangle diagrams were shown to be a useful tool for monitoring and designing fractionation processes. They illustrate that oleins with similar melting properties can be produced over a range of yields of stearin, which is important from an industrial point of view. Crystallizer residence time, which influences production costs, clearly affects both stearin yield and olein melting properties. For any fractionation temperature, stearin fractions with virtually identical melting properties and yields can be obtained over a range of olein melting properties. Manipulation of both the fractionation temperature and residence time allows the fractionation process to be adapted to meet changing market demands for fractions with different melting properties.

CFD analysis of turbulence non-homogeneity in mixing vessels: A two-compartment model

A two-compartment model has been developed for calculating the droplet/particle size distribution in suspension polymerization reactors by taking into account the large spatial variations of the turbulent kinetic energy and its dissipation rate in the vessel. The two-compartment model comprised two mixing zones, namely an impeller zone of high local energy dissipation rates and a circulation zone of low kinetic energy. Computational fluid dynamics (CFD) was employed for generating the spatial distribution of energy dissipation rates within an unbaffled mixing vessel agitated by a flat two-blade impeller. A general methodology was developed for extracting, from the results of the CFD simulations, the volume ratio of the impeller over the circulation zone, the ratio of the average turbulent dissipation rates in the two zones, and the exchange flow rate between the two compartments. The effect of agitation rate, continuous phase viscosity, impeller diameter, and mixing vessel scale on the two-compartment model parameters was elucidated. The two-compartment model was then applied to a non-homogeneous liquid–liquid dispersion process to calculate the time evolution of the droplet size distribution in the mixing vessel. An excellent agreement was obtained between theoretical and experimental results on droplet size distributions obtained from a laboratory-scale reactor operated over a wide range of experimental conditions.

Study of particle growth by seeded emulsion polymerization accompanied by electrostatic coagulation

Abstract A seeded emulsion polymerization was conducted in order to prepare an emulsion composed of large-sized particles, which was carried out in parallel with the controlled coagulation process induced by the formation of secondary polymers having an opposite charge to the surface charge of the seed particles. As the first part of this study, effects of agitation rate during the seed polymerization, size of the seed polymer particles and controlled pH of the reaction mixture were investigated. The lower agitation rates yielded a stable latex composed of large-sized grown particles, whereas the higher, intensive agitation rates induced undesirable coagulation between the larger particles, forcing them to separate from the latex. It was revealed that the smaller seed particles performed a well-controlled coagulation and yielded a larger particle size. The lower pH (8.0–8.5) reduced the solid content in the latex due to an uncontrollable formation of coagulums. At the higher pH (9.5–10.0), the controlled coagulation was not as effective as those obtained at the intermediate pH (8.75–9.0).

Characterization of a Slurry Process Used to Make a Plastic-Bonded Explosive

The effects of agitation rate, air sweep rate, and reactor temperature in the production of PBX 9501, a plastic-bonded explosive molding powder, were investigated. These variables affected the agglomerate length, the agglomerate shape, and the bulk density of the molding powder, but had very little effect on the properties of pressed pieces made from the molding powder.

Xanthan gum production by Xanthomonas campestris w.t. fermentation from chestnut extract.

Xanthomonas campestris w.t. was used for production of xanthan gum in fermentations with chestnut flour for the first time. Fermentations were carried out with either chestnut flour or its soluble sugars (33.5%) and starch (53.6%), respectively, at 28 degrees C and 200 rpm at initial pH 7.0 in flasks. The effect of agitation rate (at 200, 400, and 600 rpm) on xanthan gum production was also studied in a 2-L batch reactor. It was found that xanthan production reaches a maximum value of 3.3 g/100 mL at 600 rpm and 28 degrees C at 45 h.

Oxygen transfer effects in serine alkaline protease fermentation by Bacillus licheniformis: use of citric acid as the carbon source

The effects of oxygen transfer on serine alkaline protease (SAP) production by Bacillus licheniformis on a defined medium with C c = 9.0 kg m −3 citric acid as sole carbon source were investigated in 3.5 dm 3 batch bioreactor systems. The concentrations of the product (SAP) and by-products, i.e., neutral protease, amylase, amino acids, and organic acids were determined in addition to SAP activities. At Q o/V = 1 vvm air flow rate, the effect of agitation rate on DO concentration, pH, product, and by-product concentrations and SAP activity were investigated at N = 150, 500, and 750 min −1; these are named as low-(LOT), medium-(MOT), and high oxygen transfer (HOT) conditions. LOT conditions favor biomass concentration; however, substrate consumption was highest at HOT conditions. MOT was optimum for maximum SAP activity which was 441 U cm −3 at t = 37 h. The total amino acid concentration was maximum in LOT and minimum in MOT conditions; lysine had the highest concentration under all oxygen transfer conditions. Among organic acids, acetic acid had the highest concentration and its concentration increased with oxygen transfer rate. The oxygen transfer coefficient increases with the agitation rate and the oxygen consumption rate increased almost linearly with the biomass concentration.

Short Communication: Effect of agitation rate on the growth and production of xylanase free of cellulase by Thermomyces lanuginosus MH4 in bioreactor

Cellulase-free xylanase production by T. lanuginosus MH4 was investigated in a 3-litre stirred tank bioreactor under different agitation rates and an aeration rate of 1v/v/m. The cultivation time in the bioreactor was reduced significantly over that in shake culture conditions. A xylanase productivity of 0.1 mkat1−1h−1 was achieved on xylan in the bioreactor. This was nearly double to that obtained in shake culture. The agitation rates influenced both growth and enzyme secretion in the bioreactor. The highest level of biomass concentration and activities of both xylanase and β-xylosidase were obtained at 150 revmin−1