Cometabolic degradation of trichloroethylene in a bubble column bioscrubber

A bubble column bioreactor was used as bioscrubber to carry out a feasibility study for the cometabolic degradation of trichloroethylene (TCE). Phenol was used as cosubstrate and inducer. The bioreactor was operated like a conventional chemostat with regard to the cosubstrate and low dilution rates were used to minimize the liquid outflow. TCE degradation measurements were carried out using superficial gas velocities between 0.47and 4.07 cm s(-1) and TCE gas phase loads between 0.07 and 0.40 mg L(-1) Depending on the superficial gas velocity used, degrees of conversion between 30% and 80% were obtained. A simplified reactor model using plug flow for the gas phase, mixed flow for the liquid phase, and pseudo first order reaction kinetics for the conversionof TCE was established. The model is able to give a reasonable approximation of the experimental data. TCE degradation at the used experimental conditions is mainly limited by reaction rate rather than by mass transfer rate. The model can be used to calculate the reactor volume and the biomass concentration for a required conversion. (c) 1995 John Wiley & Sons Inc.     

Extrinsic control parameters for ozone inactivation of Escherichia coli using a bubble column

Aims:  To investigate the effect of extrinsic control parameters for ozone inactivation of E. coli in a bubble column.
Methods and Results:  Ozone inactivation of Escherichia coli ATCC 25922 in Tryptic Soya Broth was examined. The parameters studied included temperature (ambient, 20, 25 and 30°C), exposure time (up to 30 min), gas flow rate (0·03, 0·06, 0·12, 0·25, 0·5 and 0·75 l min⁻¹) and concentration level (five different levels). The efficacy of ozone treatment was a function of the parameters investigated and optimum control parameters of flow rate (0·12 l min⁻¹), temperature (ambient) and ozone concentration (75  μ g ml⁻¹) resulted in a t _d5 (time required to achieve 5 log reduction) of 20 min.
Conclusions:  Optimum control parameters of gas flow rate, ozone concentration and temperature are reported for E. coli inactivation within a bubble column.
Significance and Impact of the Study:  In 2001, the FDA approved use of ozone as a direct additive to food and in 2004, issued guidelines for the use of ozone in liquid systems. However, these guidelines highlighted gaps in the literature for ozonation of liquid foods. This study provides useful information regarding optimum extrinsic control parameters for E. coli inactivation in liquid media using a bubble column to ensure microbiological safety.     

Xanthan production in bubble column and air-lift reactors

A bubble column (0.05 m(3)) and an air-lift fermentor (1.2 m(3)) were used for the production of the exocellular microbial polysaccharide xanthan with Xanthomonas campestris in a synthetic medium. Upon oxygen depletion in the liquid, the xanthan production rate dropped sharply and then became a linear function of the oxygen transfer rate. The volumetric mass transfer coefficients for oxygen conformed to the correlation of Suh et al. Using this correlation in combination with the model for xanthan batch fermentation suggested by Peters et al., the xanthan fermentations in the bubble column were well described. The model also correctly predicted the time course of the molecular weight of the polysaccharide even when a complex medium was used. In the air-lift fermentor, however, the xanthan production rate and the xanthan yields with respect to oxygen and glucose were lower than expected at the overall oxygen transfer rate. The poor performance of the air lift was traced back to the lack of any oxygen supply in the downcomer.     

Airlift column photobioreactors for Porphyridium sp. culturing: Part II. verification of dynamic growth rate model for reactor performance evaluation

Dynamic growth rate model has been developed to quantify the impact of hydrodynamics on the growth of photosynthetic microorganisms and to predict the photobioreactor performance. Rigorous verification of such reactor models, however, is rare in the literature. In this part of work, verification of a dynamic growth rate model developed in Luo and Al-Dahhan (2004) [Biotech Bioeng 85(4): 382-393] was attempted using the experimental results reported in Part I of this work and results from literature. The irradiance distribution inside the studied reactor was also measured at different optical densities and successfully correlated by the Lambert-Beer Law. When reliable hydrodynamic data were used, the dynamic growth rate model successfully predicted the algae's growth rate obtained in the experiments in both low and high irradiance regime indicating the robustness of this model. The simulation results also indicate the hydrodynamics is significantly different between the real algae culturing system and an air-water system that signifies the importance in using reliable data input for the growth rate model.     

Characterization of factors influencing the growth of Anabaena variabilis in a bubble column reactor

The combined effect of superficial gas velocity, pH, initial phosphate concentration, and light intensity on cell growth was investigated for the mass production of cyanobacterial cells. The light intensity was manipulated to maintain a specific irradiation rate (q(i)) at a constant level for high cell density culture. The optimum condition for the batch culture was achieved at a superficial gas velocity of 2.0 cm/s, pH 7.0, and an initial phosphate concentration of 55 mg/l when the specific irradiation rate was controlled above 11.5 micromol/s/g dry cell. In this condition, the specific growth rate and cell productivity were 1.47 day(-1) and 0.98 g dry cell/l/day, respectively.     

Synergistically applying 1‐D modeling and CFD for designing industrial scale bubble column syngas bioreactors

The reduction of greenhouse gas emissions and future perspectives of circular economy ask for new solutions to produce commodities and fine chemicals. Large‐scale bubble columns operated by gaseous substrates such as CO, CO₂, and H₂ to feed acetogens for product formations could be promising approaches. Valid in silico predictions of large‐scale performance are needed to dimension bioreactors properly taking into account biological constraints, too. This contribution deals with the trade‐off between sophisticated spatiotemporally resolved large‐scale simulations using computationally intensive Euler–Euler and Euler–Lagrange approaches and coarse‐grained 1‐D models enabling fast performance evaluations. It is shown that proper consideration of gas hold‐up is key to predict biological performance. Intrinsic bias of 1‐D models can be compensated by reconsideration of Sauter diameters derived from uniquely performed Euler–Lagrange computational fluid dynamics.     

Semicontinuous system for the production of recombinant mCherry protein in Chlamydomonas reinhardtii

Biotechnology advances have allowed bacteria, yeasts, plants, mammalian and insect cells to function as heterologous protein expression systems. Recently, microalgae have gained attention as an innovative platform for recombinant protein production, due to low culture media cost, compared to traditional systems, as well as the fact that microalgae such as Chlamydomonas reinhardtii are considered safe (GRAS) by the Food and Drug Administration (FDA). Previous studies showed that recombinant protein production in traditional platforms by semicontinuous process increased biomass and bio product productivity, when compared to batch process. As there is a lack of studies on semicontinuous process for recombinant protein production in microalgae, the production of recombinant mCherry fluorescent protein was evaluated by semicontinuous cultivation of Chlamydomonas reinhardtii in bubble column photobioreactor. This semicontinuous cultivation process was evaluated in the following conditions: 20%, 40%, and 60% culture portion withdrawal. The highest culture withdrawal percentage (60%) provided the best results, as an up to 161% increase in mCherry productivity (454.5 RFU h⁻¹ – Relative Fluorescence Unit h⁻¹), in comparison to batch cultivation (174.0 RFU h⁻¹) of the same strain. All cultivations were carried out for 13 days, at pH 7, temperature 25°C and, by semicontinuous process, two culture withdrawals were taken during the cultivations. Throughout the production cycles, it was possible to obtain biomass concentration up to 1.36 g L⁻¹.     

Carotene production from waste cooking oil by Blakeslea trispora in a bubble column reactor: The role of oxidative stress

The oxidative stress induced by hydroperoxides and reactive oxygen species (ROS) during carotene production from waste cooking oil (WCO) and corn steep liquor (CSL) by the fungus Blakeslea trispora in a bubble column reactor was investigated. The specific activities of the intracellular enzymes superoxide dismutase (SOD) and catalase (CAT) as well as the micromorphology of the fungus were measured in order to study the response of the fungus to oxidative stress. The changes of the morphology of microorganism leaded to pellets formation and documented using a computerized image analysis system. As a consequence of the mild oxidative stress induced by hydroperoxides of WCO and ROS a significant increase in carotene production was obtained. The highest carotene concentration (980.0 mg/l or 51.5 mg/g dry biomass) was achieved in a medium consisted of CSL (80.0 g/L) and WCO (50.0 g/L) at an aeration rate of 5 vvm after 6 days of fermentation. In this case the carotenes produced consisted of β‐carotene (71%), γ‐carotene (26%), and lycopene (3%). The strong oxidative stress in the fungus caused a significant increase of γ‐carotene concentration. Bubble column reactor is a useful fermentation system for carotene production in industrial scale.     

Influence of power supply in the feasibility of Phaeodactylum tricornutum cultures

The influence of fluid-dynamic conditions on the yield of Phaeodactylum tricornutum microalgal cultures was analyzed in two stages: first, the influence of air flow rate; second, the influence of using fluid-moving pumps for recirculating the culture. With respect to the air flow rate, the yield of the cultures increased with the aeration rate up to values of 2.0 v/v/min, then stress was observed and the yield of the cultures decreased. With respect to the influence of mechanical power supply for liquid impulsion, three different types of pumps--centrifugal, pulse, and peristaltic--were essayed at different power supplies. The cultures were stressed for the three types of pumps essayed. For each pump, the higher the power supply the lower was the Fv/Fm value and the higher was the stress at which cells were exposed. The highest measured stress was when the culture was moved with the centrifugal pump. Despite measured stress, for all the experiments stable steady states were reached, thus indicating that cells reduced their yield but did not die, as was verified by cell viability measurements. It was observed that the increase of the power supply improved the frequency of light exposition thus enhancing the yield of the cultures. However, the higher the power supply, the lower the microeddy length scale; therefore, stress could appear. Data demonstrated that the microeddy length scale was always much higher than cell size and therefore the turbulence was not responsible for stress. Also, the mass transfer was discarded as responsible for yield reduction. It was concluded that the shear rate was the factor determining the existence of stress phenomena. The evaluation of these shear rates demonstrated that values above 30-80 s(-1) damaged the cells strongly. These data were verified in an outdoor pilot-scale tubular photobioreactor that was implemented with the same type of pumps, thus demonstrating the necessity to take into account this factor in the design and scale-up of microalgal photobioreactors.     

In sito galanthamine extraction during the cultivation of Leucojum aestivum L. shoot culture in two‐phase bubble column cultivation system

Two‐phase bioreactor cultivation system was developed and applied for in sito recovery of extracellular galanthamine during the cultivation of Leucojum aestivum L. shoot culture in a modified column bioreactor system. The inclusion of an external circulation column with adsorbent resin Amberlite XAD‐4 as a second phase, on the 21st day of the beginning of cultivation resulted in 1.25 folds increase in biomass accumulation and maximal amounts of accumulated galanthamine of 6 mg/L (3.1 mg/L intracellular and 2.9 mg/L extracellular). It was demonstrated that the inclusion of a second phase at the cultivation of the L. aestivum shoot culture in a bubble column bioreactor with internal sections redirected the alkaloid metabolism to galanthamine synthesis and inhibits the synthesis of hemanthamine and lycorine type alkaloids. Our research demonstrated that the application of the two‐phase cultivation systems could be an important tool to increase the yields of valuable secondary metabolites in plant tissue culture‐based bioprocess.     

Bubble bed reactor: A reactor design to minimize the damage of bubble aeration on animal cells

A new bubble aeration system was designed to minimize cell killing and cellular damage due to sparging. The residence time of the bubbles in the developed bubble bed reactor was prolonged dramatically by floating them in a countercurrent produced by an impeller. The performance of the new reactor bubble aeration system, implemented in a laboratory reactor, was tested in dynamic aeration experiments with an without cells. An efficiency up to 95% in oxygen transfer could be achieved, which enables a much lower gas flow rate compared with conventional bubble aeration reactors. The low gas flow rate is important to keep cell damage by bubbles as low as possible. A laser light sheet technique used to find the optimal flow pattern in the reactor. The specific power dissipation of the impeller is a good measure to predict cell damage in a turbulent flow. Typical values for the power dissipation measured in the bubble bed reactor were in the range of 0.002 to 0.013 W/kg, which is far below the critical limit for animal cells. The growth of a hybridoma cell line was studied in cell cultivation experiments. A protein-free medium without supplements such as serum or Pluronic F68 was used to exclude any effect of cell-protecting factors, No difference in the specific growth rate and the yield of the antibodies was observed in cell grown in the bubble free surface aeration in the spinner flask. In contrast to the spinner flask, however, the bubble bed reactor design could be scaled up. (c) 1994 John Wiley & Sons, Inc.     

Data-based dynamic compartment model: Modeling of E. coli fed-batch fermentation in a 600 m3 bubble column

Mathematical modeling is a powerful and inexpensive approach to provide a quantitative basis for improvements that minimize the negative effects of bioreactor heterogeneity. For a model to accurately represent a heterogeneous system, a flow model that describes how mass is channeled between different zones of the bioreactor volume is necessary. In this study, a previously developed compartment model approach based on data from flow-following sensor devices was further developed to account for dynamic changes in volume and flow rates and thus enabling simulation of the widely used fed-batch process. The application of the dynamic compartment model was demonstrated in a study of an industrial fermentation process in a 600 m³ bubble column bioreactor. The flow model was used to evaluate the mixing performance by means of tracer simulations and was coupled with reaction kinetics to simulate concentration gradients in the process. The simulations showed that despite the presence of long mixing times and significant substrate gradients early in the process, improving the heterogeneity did not lead to overall improvements in the process. Improvements could, however, be achieved by modifying the dextrose feeding profile.     

A parallel bubble column system for the cultivation of phototrophic microorganisms

An incubator with up to 16 parallel bubble columns was equipped with artificial light sources assuring a light supply with a homogenous light spectrum directly above the bioreactors. Cylindrical light reflecting tubes were positioned around every single bubble column to avoid light scattering effects and to redirect the light from the top onto the cylindrical outer glass surface of each bubble column. The light reflecting tubes were equipped with light intensity filters to control the total light intensity for every single photo-bioreactor. Parallel cultivations of the unicellular obligate phototrophic cyanobacterium, Synechococcus PCC7942, were studied under different constant light intensities ranging from 20 to 102 microE m(-2)s(-1) at a constant humidified air flow rate supplemented with CO(2).     

Quantitative measurement of cell-bubble attachment in bubble columns using foam flotation techniques

A simple and convenient system for quantitatively measuring the number of adsorbed animal cells per unit of bubble surface area (, unit: cells/cm2) was developed. The system was successfully applied to recombinant Chinese hamster ovary (r-CHO) suspension cultures to investigate the dynamic cell-bubble attachment in a bubble column. In serum-free medium, values increased with bubble rising height (H) and cell concentration (C) and then became constant (about 1750 cells/cm2) when H and C were sufficiently high. In medium containing protective additives, the trends of values with H were similar to that in serum-free medium. Compared with serum-free medium, polyvinyl-pyrrolidone (PVP) increased the values to 1941 cell/cm2 whereas other tested additives decreased the values of in some different degree.     

Polyamine and methyl jasmonate-influenced enhancement of betalaine production in hairy root cultures of Beta vulgaris grown in a bubble column reactor and studies on efflux of pigments

Hairy root cultures of red beet (Beta vulgaris) were grown in 3 l bubble column reactor for studying growth and pigment production under the influence of polyamines (PA) and elicitor treatment. Earlier studies with shake flask cultures had shown that combined feeding of spermidine (spd) and putrescine (put) (each 0.75 mM) significantly enhanced betalaine productivity in hairy root cultures of red beet. The present study has been focused on betalaine production in 3 l bubble column bioreactor where the growth pattern and betalaine synthesis under the influence of similar levels of polyamines were followed. A combination of spermidine and putrescine fed to the roots each at levels of 0.75 mM efficiently increased growth and pigment production resulting in 1.23-fold higher biomass (39.2 g FW l⁻¹) and 1.27-fold higher betalaine content (32.9 mg g⁻¹ DW) than control. Treatments with various levels of elicitor-methyl jasmonate (MJ), though progressively retarded biomass, at 40 μM level resulted in a significant increase in betalaine content resulting in 36.13 mg g⁻¹ DW which was 1.4-fold higher than the control. Further higher concentrations of methyl jasmonate treatments supported high as well as rapid accumulation of betalaines, the overall betalaine productivity was hampered mainly because of the inhibitory action on biomass. Pigment release studies with cetyl trimethyl ammonium bromide (CTAB) resulted in optimization of concentration for better efflux of betalaines without showing any inhibitory effect on hairy root viability. These studies on product enhancement and on-line extraction of pigment are useful for developing a bioreactor system for betalaine production using B. vulgaris hairy root cultures. In particular the use of elicitors and efflux studies provide an insight for integrating unit operations and developing a process for continuous operation and higher production of phytochemicals.     

Analyzing and modeling of photobioreactors by combining first principles of physiology and hydrodynamics

Mixing in photobioreactors is known to enhance biomass productivity considerably, and flow dynamics play a significant role in the reactor's performance, as they determine the mixing and the cells' movement. In this work we focus on analyzing the effects of mixing and flow dynamics on the photobioreactor performance. Based on hydrodynamic findings from the CARPT(Computer Automated Radioactive Particle Tracking) technique, a possible mechanism for the interaction between the mixing and the physiology of photosynthesis is presented, and the effects of flow dynamics on light availability and light intensity fluctuation are discussed and quantitatively characterized. Furthermore, a dynamic modeling approach is developed for photobioreactor performance evaluation, which integrates first principles of photosynthesis, hydrodynamics, and irradiance distribution within the reactor. The results demonstrate the reliability and the possible applicability of this approach to commercially interesting microalgae/cyanobacteria culture systems.     

Modeling of photobioreactors: Application to bubble column simulation

Photobioreactors using algae, plant cells, or photosynthetic bacteria have received considerable attention from biochemical engineers. Industry is presently engaged in developing new products and testing a new generation of algal-derived natural products such as natural dyes, polyunsaturated fatty acids and polysaccharides. The present paper is a review of some of the recent findings of the authors in the field. A mathematical representation of the growth of a photosynthetic system in an alternating light-dark regime is presented. This model integrates fluid dynamics and maintenance into the three-state "Photosynthetic Factories" model by Eilers and Peeters. The model was solved analytically and the constants were fitted to experimental data obtained in a thin film tubular reactor. The theoretical prediction that the introduction of light-dark cycles may enhance the growth was confirmed by the experimental results. The model allows predicting the collapse of cultures in photobioreactors either under light-deficit or light-excess conditions, as well as the influence of mixing on these critical phenomena. This paper presents an approach to modeling the kinetics of photosynthetic systems for photobioreactor design. Under conditions of simultaneous occurrence of photoinhibition in one region of the reactor, and photo-limitation in another, it takes into account the movement of the cells from one region to the other. The model was applied to the mathematical modeling of a 13-liter bubble column photobioreactor. Experimental data were satisfactorily fit, using the kinetic data obtained independently in the thin-film experiments. The model was extended to simulate a "farm" of photobioreactors and the results presented defining Ground Productivity, which expresses the rate of biomass production of a farm of relatively small photobioreactors per area of ground required for the installation.     

Mechanical control of foaming in a bubble column

This study was performed to evaluate the effects of the air sparge rate, working liquid volume, liquid feed rate onto the disk, and disk diameter on the foam-breaking performance of foam-breaking apparatus with a rotating disk (FARD) installed in the bubble column. Experimental results showed that the smaller the air sparge rate and working liquid volume were, and the larger the liquid feed rate and disk diameter, the lower the critical disk rotational speed required for reduced foam-breaking. The presence of the effective ranges of the disk diameter and liquid feed rate for foam breaking was also confirmed. Furthermore, the quantitative predictions of the upper limits of the liquid feed rate, foam-breaking regions, and the required foam-breaking power were carried out, based on the results obtained above. Comparison of the FARD with two conventional mechanical foam-breaking spray-type apparati also demonstrated the highest level of the FARD in respect not only to foam-breaking performance but also to power requirements.