Modified Bubble Column Research Articles

Mass production of Ajmalicine by bioreactor cultivation of hairy roots of Catharanthus roseus

Catharanthus roseus has been known to produce Ajmalicine which is used for treatment of circulatory disorders. Significantly low content of the drug in the natural plant necessitates development of alternative production protocols. Hairy root propagation was considered as a viable alternative. Mass cultivation of the hairy root culture was attempted in several bioreactor configurations; Bubble column, Rotating drum bioreactor, Modified Bubble column with polypropylene (PP) mesh support and Modified Bubble column with Polyurethane foam (PUF) support. Important factors like medium composition, inoculum density, illumination period and aeration rates were optimized before mass propagation of hairy roots. From the data gleaned, the cultivation in rotating drum bioreactor resulted in ajmalicine content of only 4.6±0.4mg/l. However, the ajmalicine concentration surpassed even that obtained in shake flask (with 34±2.3mg/l) in a customized bioreactor wherein the hairy roots were anchored onto a polyurethane foam, the highest reported in this scale of cultivation.

Optimization of Atropine Extraction Process from Atropa Belladonna by Modified Bubble Column Extractor with Ultrasonic Bath

Modified Bubble Column Extraction with Ultrasonic Bath (BCE-UB) method was used to extract atropine from the stem and leaves of Atropa belladonna. Optimum condition were obtained with Kamada solvent which was chloroform-methanol-ammonia 15:15:1(v/v/v) as extraction solvent, the particle size of less than 350 µm, an extraction time of 23.95 min, a liquor to material ratio of 15.08 mL/g and an air flow of 6.31 mL/min.g. In this state, percent of extracted atropine was calculated which was equal to 6.81%. Percent of extracted atropine was 6.31% that showed a little difference compared to the predicted value. In order to study the effect of bubbles on the extraction rate, the same extraction with the previous method was performed in a stirred tank. Percent of atropine was 5.59%.

Production of Diacylglycerol-enriched Oil by Glycerolysis of Soybean Oil using a Bubble Column Reactor in a Solvent-free System

In this study, diacylglycerol-enriched soybean oil (DESO) was synthesized through Lipozyme 435-catalyzed glycerolysis of soybean oil (SO) in a solvent-free system using a modified bubble column reactor. The effects of enzyme load, mole ratio of glycerol to soybean oil, reaction temperature, gas flow and reaction time on DAG production were investigated. The selected conditions were established as being enzyme load of 4 wt% (mass of substrates), glycerol/soybean oil mole ratio of 20:1, reaction temperature of 80°C, gas flow of 10.6 cm/min, and a reaction time of 2.5 h, obtaining the DAG content of 49.4±0.5 wt%. The reusability of Lipozyme 435 was evaluated by monitoring the contents of DAG, monoacylglycerol (MAG) and triacylglycerol (TAG) in 10 consecutive runs. After purified by one-step molecular distillation, the DAG content of 63.5±0.3 wt% was achieved in DESO. The mole ratio of 1, 3-DAG to 1, 2-DAG was 2:1 and the fatty acid composition had no significant difference from that of soybean oil. However, the thermal properties of DESO and SO had considerable differences. Polymorphic form of DESO were mainly the β form and minor amounts of the β' form. Granular aggregation and round-shaped crystals were detected in DESO.

Production of the Biopesticide Azadirachtin by Hairy Root Cultivation of Azadirachta indica in Liquid-Phase Bioreactors

Batch cultivation of Azadirachta indica hairy roots was carried out in different liquid-phase bioreactor configurations (stirred-tank, bubble column, bubble column with polypropylene basket, and polyurethane foam disc as root supports) to investigate possible scale-up of the A. indica hairy root culture for in vitro production of the biopesticide azadirachtin. The hairy roots failed to grow in the conventional bioreactor designs (stirred tank and bubble column). However, modified bubble column reactor (with polyurethane foam as root support) configuration facilitated high-density culture of A. indica hairy roots with a biomass production of 9.2gl(-1)dry weight and azadirachtin yield of 3.2mgg(-1) leading to a volumetric productivity of azadirachtin as 1.14mgl(-1)day(-1). The antifeedant activity in the hairy roots was also evaluated by no choice feeding tests with known concentrations of the hairy root powder and its solvent extract separately on the desert locust Schistocerca gregaria. The hairy root powder and its solvent extract demonstrated a high level of antifeedant activity (with an antifeedant index of 97% at a concentration of 2% w/v and 83% at a concentration of 0.05% (w/v), respectively, in ethanol).

Elicitation and in situ adsorption enhanced secondary metabolites production of Tripterygium wilfordii Hook. f. adventitious root fragment liquid cultures in shake flask and a modified bubble column bioreactor

The experiments of elicitation and in situ adsorption were conducted in shake flasks and then tested in a modified bubble column bioreactor for enhancing the productions of three active metabolites in Tripterygium wilfordii Hook. f., triptolide, wilforgine and wilforine. Methyl jasmonate was screened out as the elicitor and the non-ionic polymeric ion-exchange resin of Amberlite(®) XAD-7 was used for in situ product removal and protecting the alkaloids from degradation in the medium. In shake flask experiments, 3.55-fold, 49.11-fold, and 10.40-fold of triptolide, wilforgine, and wilforine, respectively, could be recovered from the medium and XAD-7 resin by elicitation and in situ product removal, compared with the control. The modified 10L bubble column bioreactor had similar productions of the three active metabolites but needed a further optimization of parameters for better growth of adventitious roots.

Numerical Simulations for Hydrodynamics of Air-Water External Loop Airlift Reactor Flows With Bubble Break-Up and Coalescence Effects

The external loop airlift reactor (ELALR) is a modified bubble column reactor that is composed of two vertical columns interconnected with two horizontal tubes and is often preferred over traditional bubble column reactors because it can operate over a wider range of conditions. In the present work, the gas-liquid flow dynamics in an ELALR were simulated using an Eulerian–Eulerian ensemble-averaging method with bubble breakup and coalescence effects in a three-dimensional system. The population balance models (PBM) of Luo and Svendsen (1996, “Theoretical Model for Drop and Bubble Breakup in Turbulent Dispersions,” AIChE J., 42, pp. 1225–1233) and Prince and Blanch (1990, “Bubble Coalescence and Breakup in Air-Sparged Bubble Columns,” AIChE J., 36, pp. 1485–1499) were used to simulate the bubble breakup and coalescence effects, respectively. The bubble breakup and coalescence closure models were implemented into CFDLib, a multiphase flow source code developed by Los Alamos National Laboratory, and validated with experiments. The computational fluid dynamics (CFD) simulations were then compared to experimental measurements from a 10.2 cm diameter ELALR for superficial gas velocities ranging from 1 to 20 cm/s. From this work, the 3D PBM simulations of an external loop airlift reactor were generally comparable with the 3D single bubble size simulations. However, the 3D PBM simulations have closer agreement with experimental findings than the single bubble size simulations especially regarding the length of gas bubbles in the downcomer.

Gas Holdup and Frictional Pressure Drop In a Modified Slurry Bubble Column

Abstract This article presents the analysis of gas holdup, pressure drop and bubble size of gas-liquid-solid flow in a modified downflow slurry bubble column. The analysis is done based on the Lockhart-Martinelli principle. The Lockhart-Martinelli model is modified and incorporate to predict the frictional pressure drop and gas holdup of three-phase flow in the modified bubble column. The effects of operating variables such as slurry flow rate, gas flow rate, slurry concentration and particle diameter on frictional pressure drop and gas holdup are investigated. To predict the gas holdup, Sauter mean bubble diameter and pressure drop, correlations have also been developed as function of different dimensionless groups by introducing the operating variables and physical properties. The studies of the pressure drop in the downflow slurry bubble column may give insight into a further understanding and modeling of the three-phase flow characteristics in industrial applications.

A Combined Numerical and Experimental Study of Hydrodynamics for an Air-Water External Loop Airlift Reactor

The external loop airlift reactor (ELALR) is a modified bubble column reactor that is composed of two vertical columns that are interconnected with two horizontal tubes and is often preferred over traditional bubble column reactors because they can operate over a wider range of conditions. In the present work, the gas-liquid flow dynamics in an ELALR was simulated using an Eulerian–Eulerian ensemble-averaging method in two-dimensional (2D) and three-dimensional (3D) coordinate systems. The computational fluid dynamics (CFD) simulations were compared to experimental measurements from a 10.2 cm diameter ELALR for superficial gas velocities ranging from 1 cm/s to 20 cm/s. The effect of specifying a mean bubble diameter to represent the gas phase in the CFD modeling was investigated, and 2D and 3D simulations were found to be in good agreement with the experimental data. The ELALR flow regimes were compared for the reactor operating in bubble column, closed vent, and open vent modes, and the 2D simulations qualitatively predicted the behavior of bubble growth in the downcomer. However, it was found that 3D simulations were necessary to capture the physics of the ELALR for gas holdup, bulk density differences, and riser superficial liquid velocity.

Properties of bacterial cellulose produced in a pilot-scale spherical type bubble column bioreactor

The saccharogenic liquid obtained by the enzymatic saccharification of food wastes was used as a medium for production of bacterial cellulose (BC). The enzymatic saccharification of food wastes (SFW) was carried out by the cultivation supernatant of Trichoderma inhamatum KSJ1. 5.6 g/L of BC was produced in a new modified 50 L bubble column bioreactor by Acetobacter xylinum KJ1. The productivity was similar to that of a modified 10 L bubble column bioreactor (5.8 g/L). When pure oxygen was supplied into the scaled-up culture conditions, 6.8 g/L (12% enhancement) of BC was produced, indicating a very useful method for BC mass production. The oxygen uptake rate (OUR) and q O2 (specific oxygen uptake rate) were 0.214 mg-DO/L·min and 0.257 mg-DO/g-cell·min, respectively. The physical properties, such as morphology, molecular weight, crystallinity, and tensile strength of BCs produced in static culture (A), 10 L (B) and 50 L (C) modified bubble column cultures were investigated. All BCs showed fibrils with highly networking structure. The number average molecular weight of BCs in A, B and C was 2,314,000, 1,878,000, and 1,765,000, respectively. All of the BCs had a form of cellulose I representing pure cellulose. The relative degree of crystallinity showed the range of 79.6–86.0%. Tensile strengths of BC sheet in A, B and C were 1.75, 1.21, and 1.19 kg/mm2, respectively. In conclusion, BC production by the modified bubble column culture mode of 50 L brought more favorable results in terms of the physical properties and its ease of scale-up.

Energy Efficiency of Two‐Phase Mixing in a Modified Bubble Column

AbstractEnergy efficiency for gas liquid mixing in a modified downflow bubble column reactor has been analyzed in this paper. Efficiencies of the different parts of the bubble column have been assessed on the basis of energy dissipation. Prediction of the energy dissipation coefficient as well as energy utilization efficiency due to gas‐liquid mixing as a function of different physical, geometric and dynamic variables of the system has been done by correlation method. The distribution of energy utilization in the different zones of the column has also been analyzed. Experiments were carried out with air‐water and air‐aqueous solutions of carboxy methyl cellulose with different concentrations.

Efficient dispersion in a modified two-phase non-Newtonian downflow bubble column

A comprehensive study of dispersion of gas-non-Newtonian fluid has been made in a modified downflow bubble column. Distribution of gas holdup in axial location has been anticipated from hydrostatic force balance. The experimental gas holdup data in such modified bubble column have been analyzed by slip velocity and drift-flux models. A correlation in terms of various physical, geometric and operating parameters of the present system has also been developed to analyze the gas holdup.

Bubble size distribution and gas–liquid interfacial area in a modified downflow bubble column

Bubble size distribution and the gas–liquid specific interfacial area were measured as a function of axial location, nozzle diameter and superficial liquid and gas velocities in a modified bubble column reactor. The experimental measurements of bubble size and its distribution are analyzed with distribution model to gain insight into the breakup and coalescence mechanisms taking place. Axial profile of bubble number flux was estimated based on size distribution model incorporated with coalescence phenomena. Also correlation for Sauter mean bubble diameter has been developed with operating variables.

The Effect of Partitioning Plates Packed with Particles in a Multistage Bubble Column to the Mass Transfer

Longitudinal concentration distributions have been measured under various conditions for oxygen absorption in standard bubble columns. The disadvantages of standard bubble columns are considerable because of backmixing in the continuous liquid phase and the decrease of interfacial area due to bubble coalescence in the viscous liquids. To overcome these disadvantages, modified bubble columns, such as multistage bubble columns partitioned with perforated plates, have been used. When the catalytic particles suspended in the slurry bubble column are brittle and easily break down, the packing of the brittle particles into a partitioning plate is considered, which is called the multistage bubble column with a partitioning plate packed with particles (PMBC). The aims of this study are to make experimentally and theoretically clear the effect of operating parameters on the mass transfer characteristics of the PMBC, and to elucidate the concentration distributions of dissolved oxygen in the PMBC by a revised back flow model.

Biological treatment of highly foaming pharmaceutical wastewater by modified bubble-column under mechanical foam control

Activated sludge treatment of highly foaming pharmaceutical wastewater was carried out with modified bubble columns equipped with a mechanical foam-breaker (MFRD). The geometry of the bubble column was modified based on the foam breaking mechanism of the MRFD in order to improve the foam breaking capacity and hence to enhance the treatment capacity. Four types of modifications were examined. The activated sludge treatment of the wastewater with the modified columns was successfully carried out with COD removal efficiency about 90% at BOD loading of 4 g/Ld. Little effect of the mechanical foam control on the sludge settling characteristics was observed. The column modification significantly reduced the power required for foam control. The maximum power decrement of 75% was attained. Furthermore, oxygen transfer was found to be facilitated in the modified bubble columns. The results are expected to be helpful for economic and effective treatment of highly foaming organic wastewater.

Suspended rice particles for cultivation of Monascus purpureus in a tower-type bioreactor.

Cultivation of Monascus purpureus (CCRC 31615) for the production of natural pigments was investigated. Traditionally, Monascus species were grown on rice by solid-state culture. For large-scale cultivation, solid-state cultures were associated with some problems such as contamination and scale-up. By using submerged cultures with rice particles, a stirred-tank fermentor was not suitable for submerged cultures as the impeller tended to break the particles into small pieces. A conventional bubble column was also unsuitable as its mixing capability was poor. In the present study, a modified bubble column with wire-mesh draft tubes was employed for the cultivation of M. purpureus. The proposed column had a shorter mixing time and a higher oxygen transfer rate relative to the conventional bubble column. The production of pigments using the proposed column was up to 80% higher than that achieved using the conventional bubble column.

Production of artemisinin by hairy root cultures of Artemisia annua L in bioreactor

Hairy root cultures of Artemisia annua L were cultivated in four different culture systems: a flask, a bubble column, a modified bubble column and a modified inner-loop airlift bioreactor. The artemisinin contents of hairy root cultures in the bubble column and the modified inner-loop airlift bioreactor were higher than that in the modified bubble column. The growth rate and hairy root distribution in the modified inner-loop airlift bioreactor were better than those in other bioreactors, and dry weight and artemisinin production reached to 26.8 g/L and 536 mg/L after 20 days.

Sparged loop reactors

AbstractCirculating bubble columns or loop reactors form one of the important classes of modified bubble columns. The present paper analyses the performance of external loop air lift reactors (EL‐ALR). The EL‐ALR has many advantageous features especially at large scale. These arise from its feature of having controlled liquid circulation which is the key parameter for the design and operation of EL‐ALR contactors. Therefore, a reliable and generalised circulation model has been presented. The reliability of the model depends on the accuracy of the predictive methods for the gas hold‐up and the two‐phase fractional pressure drop. Detailed analysis of these fundamental parameters of gas‐liquid flows has been presented. The effects of design (area ratio of riser to downcomer, height to diameter ratio and volume of reactor) and operating (gas flow rates and sparging locations) parameters on the performance of the EL‐ALR have been analysed in detail. A rational basis has been developed for the estimation of pressure drop, mixing time and mass transfer coefficient. An optimum combination of design and operating parameters has been suggested and a criterion has been developed for the optimum location of spargers. An attempt has been made to provide critical analysis of the published information and to construct a coherent picture of EL‐ALR.

Liquid circulation and mixing in tower fermenters with recirculation loop

Liquid circulation and mixing time studies were carried out in a laboratory bubble column and modified bubble columns. Liquid circulation and mixing time are both strongly dependent on the geometrical configuration of the reactor. Internal recycle loop and external recycle loop shorten the mixing time compared to the bubble column.

Bubble column research in Japan

AbstractMany experimental studies on the bubble column have been reported by Japanese researchers since around 1960. They include studies of bubble behaviour, bubble size distribution, transition from the homogeneous bubbly flow regime to the heterogeneous liquid circulation regime, liquid velocity distribution, longitudinal liquid mixing, hydrodynamic modelling, the gas holdup, and the volumetric coefficient of gas‐liquid mass tranfer kLa. Studies covered various modified bubble columns, such as the airlift reactor with an external or internal loop, the packed bubble column, and others. Performance of three‐phase bubble columns, which deal with suspensions or emulsions, and their use as bioreactors or chemical reactors were also studied.

Mixing in mechanically agitated gas-liquid contactors, bubble columns and modified bubble columns

Mixing time measurements were made in 300 and 1000 mm i.d. mechanically agitated contactors with different types of impellers, located at different heights from the bottom of the vessel. Mixing time measurements were also made in 150, 200, 385 and 1000 mm i.d. bubble columns with varying liquid heights. Transient pH measurement and conductivity measurement were used to measure the mixing times. Impeller speed was varied in the range of 3.33–20 r/sec in the case of mechanically agitated contactors and gas superficial velocity was varied in the range of 10–250 mm/sec in bubble columns. Effect of physical properties of the fluid (surface tension, ionic strength, liquid viscosity) and that of the non-Newtonian behavior on mixing time was studied. Mixing time in the presence of drag reducing agents was also investigated. In the range of variables covered in this work mixing time in mechanically agitated contactors and bubble columns was found to be in the range of 4–6 Mixing time predictions based on the longest loop length and circulation velocity are made in the presence and absence of a gas for mechanically agitat A procedure is given for the prediction of the critical impeller speed for gas phase dispersion in mechanically agitated contactors.