Hydrodynamics and mass transfer in a tubular airlift photobioreactor

In photobioreactors, which are usually operated under light limitation,sufficient dissolved inorganic carbon must be provided to avoid carbonlimitation. Efficient mass transfer of CO₂ into the culture mediumisdesirable since undissolved CO₂ is lost by outgassing. Mass transferof O₂ out of the system is also an important consideration, due tothe need to remove photosynthetically-derived O₂ before it reachesinhibitory concentrations. Hydrodynamics (mixing characteristics) are afunctionof reactor geometry and operating conditions (e.g. gas and liquid flow rates),and are a principal determinant of the light regime experienced by the culture.This in turn affects photosynthetic efficiency, productivity, and cellcomposition. This paper describes the mass transfer and hydrodynamics within anear-horizontal tubular photobioreactor. The volume, shape and velocity ofbubbles, gas hold-up, liquid velocity, slip velocity, axial dispersion,Reynoldsnumber, mixing time, and mass transfer coefficients were determined intapwater,seawater, and algal culture medium. Gas hold-up values resembled those ofvertical bubble columns, and the hydraulic regime could be characterized asplug-flow with medium dispersion. The maximum oxygen mass transfer coefficientis approximately 7 h^–1. A regime analysisindicated that there are mass transfer limitations in this type ofphotobioreactor. A methodology is described to determine the mass transfercoefficients for O₂ stripping and CO₂ dissolution whichwould be required to achieve a desired biomass productivity. This procedure canassist in determining design modifications to achieve the desired mass transfercoefficient.     

Influence of sparger on energy dissipation, shear rate, and mass transfer to sea water in a concentric-tube airlift bioreactor

Data on volumetric mass-transfer coefficient, K_La_L, in a 12 × 10⁻³ m³ airlift bioreactor are reported. Measurements were made in sea water. The superficial gas velocity ranged up to 0.21 m/s. Four cylindrical spargers (60–1000 μm pore size) were tested. In bubbly flow, the sparger pore size strongly influenced the K_La_L; the highest K_La_L values were obtained with the smallest pore size. In contrast, in the transition and heterogeneous flow regimes, the pore size had little influence on K_La_L. The best correlation of the mass transfer data was obtained when both gas holdup and liquid superficial velocity were taken as independent variables. Shear rates were estimated in the different zones of the reactor. The highest values were found in the bottom zone of the reactor and in the gas-liquid separator. The penetration and isotropic turbulence models were used to develop a semi-theoretical equation relating the volumetric mass-transfer coefficient to shear rate; hence providing a better understanding of how the operational variables may be manipulated to attain a moderate shear rate and an appropriate level of mass transfer, two extremely important parameters for the growth of sensible microorganisms as those used in marine biotechnology.     

Biotransformation of glucose to gluconic acid by Aspergillus niger—study of mass transfer in an airlift bioreactor

A glucose–gluconic acid biotransformation system was suggested for the experimental study of oxygen transfer in bioreactors. This biosystem was used for the investigation of the effect of the flow rate and biomass concentration on the volumetric oxygen transfer coefficient k_La in a 10 dm³ internal-loop airlift bioreactor. For this purpose, the fermentation broth of the mycelial strain Aspergillus niger was employed, representing a three-phase system, where bubbles come into contact with dense rigid pellets. The results showed that the presented biotransformation system can be successfully utilised for the determination of the oxygen transfer rate in airlift bioreactors. The experiments showed a strong positive influence of the air flow rate on the rate (r_Glu), specific rate of gluconic acid production (k_Glu/X) as well as on the volumetric oxygen transfer coefficient (k_La). This confirmed an expected limitation of production rate by the oxygen transport from the gas to the liquid phase in the whole range of air flow rates applied. Moreover, consistent curves of the production rate r_Glu and k_La values vs. biomass concentration c_X (amount of enzymes) were observed. These exhibited a local maximum for c_X equal to 6.68 g dm⁻³. On the other hand, the specific production rate monotonously decreased with increasing biomass concentration. A decline of k_La values at higher c_X values was attributed to a bubble coalescence promoting effect of mycelial pellets.     

A multikinetic model approach to predict gluconic acid production in an airlift bioreactor

This paper uses a multikinetic approach to predict gluconic acid (GA) production performance in a 4.5 L airlift bioreactor (ALBR). The mathematical model consists of a set of simultaneous firstorder ordinary differential equations obtained from material balances of cell biomass, GA, glucose, and dissolved oxygen. Multikinetic models, namely, logistic and contois equations constitute kinetic part of the main model. The main model also takes into account the hydrodynamic and mass transfer parameters. These equations were solved using ODE solver of MATLAB v6.5 software. The mathematical model was validated with the experimental data available in the literature and is used to predict the effect of change in initial biomass and air sparging rate on the GA production. It is concluded that the mathematical model incorporated with multikinetic approach would be more efficient to predict the change in operating parameters on overall bioprocess of GA production in an ALBR.     

Improvement of mixing time,mass transfer,and power consumption in an external loop airlift photobioreactor for microalgae cultures

Longer mixing times and higher power consumption are common problems in the design of photobioreactors. In this study, a vertical triangular external airlift loop photobioreactor was designed, constructed and operated for microalgae production studies. Gas feeding was performed by two spargers: one at the bottom of the hypotenuse (downcomer) and another at the bottom of the vertical side (riser). This configuration provided more effective countercurrent liquid–gas flow in the hypotenuse. The mass transfer coefficient, gas hold-up, mixing time, circulation time, dimensionless mixing time, bubble size, and volumetric power consumption were measured and optimized using response surface methodology. Investigations were carried out on the performance of the riser (the vertical side), downcomer (the hypotenuse), and separator. The countercurrent flow in the hypotenuse provided sufficient contact between gas and liquid phases, and increased mixing and mass transfer rates, in contrast to the results of previous studies. The promising results of this geometry were shorter mixing time and a significant decrease in volumetric power consumption in comparison with other configurations for photobioreactors.     

Hydrodynamics and mass transfer of CO2 in water in a tubular photobioreactor

Microalgae cultivation has received growing importance because of its potential applications in CO₂ bio‐fixation, wastewater treatment and biofuel production. In this regard, proper design of photobioreactors is crucial for large‐scale commercial applications. The hydrodynamics of a photobioreactor has great influence on the transfer of CO₂ from gas phase to liquid phase. Considering the facts, the present research focused on studying the gas holdups and mass transfer from the gas to liquid phase in a tubular photobioreactor at various superficial liquid velocities ranging from 8.4 to 22.4 cm/s and superficial gas velocities ranging from 3.66 to 8.1 cm/s. It was found that the gas holdups were radially distributed. The highest gas holdups were observed at the center zone while the lowest holdups are found near the reactor wall. CO₂ mass transfer coefficient in the photobioreactor was also estimated under different superficial liquid velocities (0.206, 0.355 and 0.485 cm/s) and gas velocities (0.67, 1.16 and 1.37 cm/s). The overall mass transfer coefficient was estimated by fitting the experimental data and comparing results with an unsteady state differential mole balance equation solved by Runge‐Kutta‐Gill method. Model predictions were comparable to experimental results.     

Hydrodynamics and mass transfer in an airlift loop fermentor

Summary The hydrodynamics and mass transfer behaviour of an airlift fermentor with an external loop (height 10m) has been investigated by measuring gas and liquid velocities, gas hold-up, liquid mixing and oxygen transfer coefficients. Liquid phase properties, i.e., ionic strength, viscosity and surface tension have been varied by altering the fermentation media. Results are compared with those from bubble column experiments performed in the same unit. It is shown, that more uniform two-phase flow in the airlift leads to advantages in scale-up and operation.Nomenclature a Specific interfacial area per volume of dispersion (m²/m³) - c Local concentration of tracer (kmol/m³) - c Concentration of tracer at infinite time (kmol/m³) - C_L Concentration of oxygen in the liquid bulk (kmol/m³) - C_L ^* Concentration of oxygen in the interface (kmol/m³) - D_ax Axial dispersion coefficient (cm²/s) - I Ionic strength (kmol/m³) - i Inhomogeneity [defined in Eq. (2)] - Rate of oxygen transfer (kmol/s) - t_c Circulation time (s) - t_M Mixing time (s) - V_R Volume of gas-liquid dispersion (m³) - V_SG Superficial gas velocity in up-flow column (m/s) Greek letter symbols _L Oxygen transfer coefficient (m/s) - Dynamic viscosity (m Pa s) - Surface tension (m N/m) Presented at the First European Congress on Biotechnology, Interlaken, September 25–29, 1978     

Improved algal oil production from Botryococcus braunii by feeding nitrate and phosphate in an airlift bioreactor

To improve biomass and microalgal oil production of Botryococcus braunii, fed‐batch culture was investigated in an airlift photobioreactor. The optimal feeding time of the fed‐batch culture was after 15 days of cultivation, where 1.82 g/L of the microalgal biomass was obtained in the batch culture. Nitrate nutrient was the restrictive factor for the fed‐batch cultivation while phosphate nutrient with high concentration did not affect the microalgal growth. The optimal mole ratio of nitrate to phosphate was 34.7:1, where nitrate concentration reached the initial level and phosphate concentration was one quarter of its initial level. With one feeding, the biomass of B. braunii reached 2.56 g/L after 18 days. Two feedings in 2‐day interval enhanced the biomass production up to 2.87 g/L after 19 days of cultivation. The hydrocarbon content in dry biomass of B. braunii kept at high level of 64.3% w/w. Compared with the batch culture, biomass production and hydrocarbon productivity of B. braunii were greatly improved by the strategic fed‐batch cultivation.     

Cultivation of Aspergillus niger in a pilot plant external-loop air-lift bioreactor

Abstract: Changes of the main hydrodynamic and oxygen transfer parameters during Aspergillus niger cultivation in an external-loop air-lift bioreactor of 200 dm³ operating capacity were investigated. The final average concentrations of biomass and citric acid obtained in batch fermentations were about 17 g 1^-1 and 90 g 1^-1, respectively. Significant influence of the increasing biomass concentration on the rheological properties of the broth and operating parameters was found. Volumetric oxygen transfer coefficient. k ^L a , was found to be dependent on the apparent viscosity of the broth with an exponent of -0.984.     

Models for gibberellic acid transport and enzyme production and transport in the aleurone layer of barley

Gibberellins are growth hormones produced in the embryo of grain released during germination. They promote growth through the production of enzymes in the aleurone layer surrounding the endosperm. These enzymes then diffuse into the endosperm and produce the sugars required by the growing acrospire. Here we model the transport of gibberellins into and along the aleurone layer, the consequent production of enzymes, and their transport into the endosperm. Simple approximate solutions of the governing equations are obtained which suggest that the enzymes are released immediately behind a gibberellin front which travels with almost constant speed along the aleurone layer. The model also suggests that this propagation speed is determined primarily by conditions near the scutellum-aleurone junction, which may enable the embryo to actively control the germination process.     

Analysis of petroleum biodesulfurization in an airlift bioreactor using response surface methodology

For the first time, growing cells of Gordonia alkanivorans RIPI90A were used for biodesulfurization (BDS) of diesel. This process was carried out in an internal airlift bioreactor. BDS parameters (oil/water phase ratio and initial sulfur concentration) were optimized in flasks using response surface methodology. Predicted results were found to be in good agreement with experimental results. Initial sulfur concentration had a remarkable effect on BDS process. Maximum removal of sulfur (21 mg/l) can be achieved at oil/water phase ratio of 25% (v/v) and initial sulfur concentration of 28 mg/l. Moreover, effect of superficial gas velocity (Ug) and working volume (v) on volumetric gas liquid mass transfer coefficient was studied in an airlift bioreactor for BDS of diesel. The best results were achieved at Ug and v of 2.5l/min and 6.6l, respectively. Subsequently, BDS of diesel was investigated in an airlift bioreactor under optimized conditions. Sulfur reduction after 30 h was 14 mg/l.     

Effects of rheological properties and mass transfer on plant cell bioreactor performance: production of tropane alkaloids

Volumetric mass transfer coefficients, K(L)a were measured over an aeration rate range from 0.1 to 1.0 vvm in a 1.2-L draft-tube-type airlift bioreactor for different Datura stramonium cell concentrations and correlated with superficial air velocity and rheological properties of the cell suspension. The measured K(L)a values (17-40 h(-1)) for a cell volume fraction of 0.2 (v/v) were approximately 2 times higher than those for the highest cell concentrations tested (cell volume fraction 0.7-0.8 v/v). Cell suspensions exhibited yield stress and pseudoplastic behavior. This behavior was described by the Casson model. The estimated yield stress values depended upon cell concentration with an exponent of 4.0. An empirical correlation based on the data for plant cell suspensions exhibiting yield stress was developed in order to determine aeration strategy for the plant cell cultivation in draft-tube-type airlift bioreactors: \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm K}_{\rm L} {\rm a} = {\rm A}({\rm U}_{{\rm gr}});{0.3} ({\rm \eta }_{{\rm eff}});{ - 0.4} $$\end{document} Aeration rates above 1.0 vvm caused a significant drop in cell yield and product content. Maximum growth and production were obtained at 0.6 vvm aeration. The cell and product yields obtained at 1.7 vvm were 2.8 times lower than the maximum values (25 g cell DW/L and 73.8 mg tropane alkaloid/L). The effects of the increased aeration rates on cell yield were also evaluated in terms of Reynolds stress. It was found that there was a relation between cell damage and the estimated Reynolds stress. The Reynolds stress estimated for the same aeration rate decreased with increasing cell concentration, suggesting that cells in the cultures at low cell concentrations are subjected to hydrodynamic damage. In the experiments with the cell cultures having a cell concentration of 0.3 (v/v), approximately 70% reduction in cell concentration was observed when the Reynolds stress was increased from 10 to 50 dyn/cm(2). (c) 1993 John Wiley & Sons, Inc.     

Large-scale cultivation of adventitious roots of Echinacea purpurea in airlift bioreactors for the production of chichoric acid, chlorogenic acid and caftaric acid

Adventitious roots of Echinacea purpurea were cultured in airlift bioreactors (20 l, 500 l balloon-type, bubble bioreactors and 1,000 l drum-type bubble bioreactor) using Murashige and Skoog (MS) medium with 2 mg indole butyric acid l⁻¹ and 50 g sucrose l⁻¹ for the production of chichoric acid, chlorogenic acid and caftaric acid. In the 20 l bioreactor (containing 14 l MS medium) a maximum yield of 11 g dry biomass l⁻¹ was achieved after 60 days. However, the amount of total phenolics (57 mg g⁻¹ DW), flavonoids (34 mg g⁻¹ DW) and caffeic acid derivatives (38 mg g⁻¹ DW) were highest after 50 days. Based on these studies, pilot-scale cultures were established and 3.6 kg and 5.1 kg dry biomass were achieved in the 500 l and 1,000 l bioreactors, respectively. The accumulation of 5 mg chlorogenic acid g⁻¹ DW, 22 mg chichoric acid g⁻¹ DW and 4 mg caftaric acids g⁻¹ DW were achieved with adventitious roots grown in 1,000 l bioreactors.     

Growth and development of fern gametophytes in an airlift fermenter

Spores of the fernsPteridium aquilinum andAnemia phyllitidis were grown in an airlift fermenter and subsequent growth and development of gametophytes was monitored. Both species produced greater biomass than that generated in any other solid- or liquid-based culture system tested.Pteridium generated more tissue thanAnemia in every system. The morphology of airlift-grown gametophytes was similar to that of soil-grown plants; fewer gametophytes with perturbed development were observed in airlift cultures than in the other liquid-based systems. No attempt was made to optimise airlift conditions for the species and tissue employed, so it is concluded that airlift cultivation is a promising system for the bulk production of fern gametophytic tissue.     

Effect of melatonin and gibberellic acid foliar application on the yield and quality of Jumbo blackberry species

Not many chemical hormone studies does exist in our country especially in berry fruits. Foliar application of melatonin and gibberellic acid hormones was performed in 2016 and 2017 in order to analyze the effects of different doses of hormone applications on fruit quality and yield. Pheonologic, pomological and some bioactive content analyses of these hormones were studied. According to the research results, while M?+?GA10 ppm (240.50; 3.9) and M?+?GA 5?ppm (226.50; 3.6) applications have the highest fruit number and weight (g), the highest fruit size was obtained from GA 5?ppm (21.21?mm fruit length, 16.56?mm fruit width) and M 10?ppm (21.10?mm fruit length, 16.20?mm fruit width) chemical applications in Jumbo blackberry species. The highest values in Ph, soluble solid content (SSC) and titratable acidity averages were obtained from GA 5?ppm (3.69; 10.80; 2.42) and GA 10?ppm (3.68; 10.70; 2.40) applications; the highest total antioxidant activity in bioactive characteristics averages was found in G 10?ppm 143.21?mg/g, the highest total phenolics was identified in G 5?ppm 72.68?ppm/GAE and the highest total flavonoids was determined in G 10?ppm 4925.75?ppm/QE.     

Use of glycerol for producing 1,3-dihydroxyacetone by Gluconobacter oxydans in an airlift bioreactor

1,3-Dihydroxyacetone can be produced by biotransformation of glycerol with glycerol dehydrogenase from Gluconobacter oxydans cells. Firstly, improvement the activity of glycerol dehydrogenase was carried out by medium optimization. The optimal medium for cell cultivation was composed of 5.6 g/l yeast extract, 4.7 g/l glycerol, 42.1 g/l mannitol, 0.5 g/l K₂HPO₄, 0.5 g/l KH₂PO₄, 0.1 g/l MgSO₄·7H₂O, and 2.0 g/l CaCO₃ with the initial pH of 4.9. Secondly, an internal loop airlift bioreactor was applied for DHA production from glycerol by resting cells of G. oxydans ZJB09113. Furthermore, the effects of pH, aeration rate and cell content on DHA production and glycerol feeding strategy were investigated. 156.3 ± 7.8 g/l of maximal DHA concentration with 89.8 ± 2.4% of conversion rate of glycerol to DHA was achieved after 72 h of biotransformation using 10 g/l resting cells at 30 °C, pH 5.0 and 1.5 vvm of aeration rate.     

Elicitation of secondary metabolism in Echinacea purpurea L. by gibberellic acid and triazoles

In vitro bioreactor production of Echinacea purpurea L. was used to facilitate the screening of compounds capable of eliciting increased secondary metabolite production. Based on previous experience with various bioreactors, the Southern Sun Liquid Lab Rocker was selected for this study as it produces healthy, vigorous, whole plants. The focus of the present study was to quantify the concentration of the medicinally important secondary metabolites caftaric acid and cichoric acid and to study the effect of growth regulators on the production of these compounds in this system. Both marker compounds were produced at levels that compared favorably to field grown plants. Application of gibberellic acid (GA₃), paclobutrazol, uniconazole and a combined treatment of GA₃ with paclobutrazol to the in vitro plants generally increased the concentration of caftaric acid in the roots with little effect on the concentration in the shoots. The concentration of cichoric acid was higher in the roots of treated plants than in the roots of control plants, but lower in corresponding shoots. The present study highlights the use of in vitro production of whole plants as a model system for studying the regulation of plant secondary metabolism in a controlled environment.     

Application of an airlift bioreactor system for the production of adventitious root biomass and caffeic acid derivatives of Echinacea purpurea

In this study, we evaluated the feasibility of using mass cultivation of the adventitious roots of Echinacea purpurea in balloon type bubble (air-lift) bioreactors to produce caffeic acid derivatives, which have pharmaceutical and therapeutic values. An approximately 10 fold increase in biomass and secondary compounds was observed after 4 weeks of culture in balloon type bubble bioreactors (5 L capacity containing 4 L of half strength MS medium). In addition, a linear relationship was observed between the concentration of biomass and the sucrose and ion consumption rate. Furthermore, the concentration of biomass in the bioreactor culture was found to increase as the conductivity decreased. An inoculum density of 7 g/L FW and an aeration rate of 0.1 vvm were found to be suitable for inducing the accumulation of biomass and secondary metabolites. Of the three caffeic acid derivatives evaluated (caftaric acid, chlorogenic acid, and cichoric acid), the concentration of cichoric acid was the highest (26.64 mg/g DW).     

粳稻矮秆品种苗期和成株期对赤霉素反应的研究

本试验对28个粳稻矮秆品种对GA3的反应进行了研究,结果表明粳稻矮秆品种对GA3反应较为复杂,苗期与成株期反应,大多数品种表现为趋势基本一致,但也存在着其它种类型表现;在粳稻中,对GA3反应敏感的矮秆品种并不一定携带含有sd-1等位基因,但含有sd-1基因的品种表现为敏感,不含有sd-1基因的表现为低敏感或不敏感,据此可以初步确定矮4和紫叶矮含有与sd-1非等位的矮秆基因,是一种新的矮源;GA3对株高构成因素的影响表现因品种不同而异,但以基部一、二节间为主.