Arachidonic acid-rich oil production by Mortierella alpina with different gas distributors

Arachidonic acid (ARA)-rich oil production by Mortierella alpina is a high oxygen demand and shear-sensitive process. In the aerobic fermentation process, oxygen supply is usually a limiting factor owing to the low solubility of oxygen in the fermentation broth. Two kinds of perforated ring gas distributors and a novel microporous ceramic membrane gas distributor were designed and applied to improve oxygen supply. With the decrease of the orifice diameter of perforated ring gas distributors, dry cell weight (DCW), lipids concentration, and ARA content in total fatty acid increased from 17.86 g/L, 7.08 g/L, and 28.08 % to 25.67 g/L, 11.94 g/L, and 36.99 %, respectively. Furthermore, the effect of different dissolved oxygen (DO) on ARA-rich oil production with membrane gas distributor was also studied. The maximum DCW, lipid concentration, and ARA content using membrane gas distributor with DO controlled at 40 % reached 29.67 g/L, 16.74 g/L, and 49.53 %, respectively. The ARA titer increased from 1.99 to 8.29 g/L using the membrane gas distributor to substitute the perforated ring gas distributor. In the further experiment, a novel tubular titanium metal membrane gas distributor was successfully applied in a 7,000 L bioreactor and the results demonstrated that membrane gas distributor was industrially practical.     

Investigation of the structure of two-phase flows. Model media in bubble-column bioreactors

Summary The following two-phase properties were evaluated in bubble column reactors with porous plate (5 m pore diameter) or perforated plate (1 mm and/or 3 mm hole diameter) gas distributors using distilled water or a 1% methanol solution: transverse profiles of the mean and Sauter bubble diameters, local gas holdups, true mean liquid and bubble velocities. Furthermore, swarm bubble velocity distributions were evaluted and compared with calculated values.     

Fairness versus favoritism in children

Children respond positively to individuals who favor them and also to individuals who are fair. The present studies examine the interaction between these two preferences by presenting children with two distributors who share resources with the child participant and another recipient. Children are asked whom they like better: the distributor who was unfair but favored the child participant or the distributor who was fair and showed no (or reduced) favoritism. In Study 1, we find that when fairness and favoritism are in conflict, children are split on whom they prefer. In Study 2, we find that placing children in a competitive context leads to a stronger preference for the distributor who favored the child participant. In Study 3, we examine whether children's preference for favoritism persists when both distributors gave the child the same number of rewards, but one distributor gave the child participant relatively more than the other recipient. In this situation, we find that children prefer the fair distributor. However, we again find that creating a competitive context reduces children's preference for the fair distributor. Finally we find that in a third-party context, children value fairness over generosity. Taken together, these results show how children balance competing concerns for fairness and favoritism.     

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.     

Mass transfer phenomena in an airlift reactor: effects of solids loading and temperature

Gas holdups and volumetric mass transfer coefficients were measured in a concentric tube airlift reactor designed for the microbial desulfurization of coal. The solutions studied were comprised of an acidified basal salts solution containing thirteen different weight percentages (0 to 40) of coal (74 mum Ohio #1) at three different temperatures (30, 50, and 72 degrees C). Gas holdup epsilon(G) decreased with solids loading for the entire range studied. An enhancement in the volumetric mass transfer coefficient K(L)a with respect to that in pure solution was observed from zero to approximately 5 wt % (solids volume fraction epsilon(s) = 0.035), the maximum enhancement occurring at approximately 2 wt % (epsilon(s) = 0.014). At higher solids fractions, the mass transfer coefficient decreased with further solids additions. Gas holdups and the mass transfer coefficients increased with temperature over the studied range. The K(L)a and epsilon(G) were correlated to three process variables separately and the separate correlations combined to yield generalized correlations for the mass transfer coefficient and gas holdup for this system. The correlations may be used for design, operation, and ost estimation of such systems.     

Sparged animal cell bioreactors: mechanism of cell damage and Pluronic F-68 protection.

Pluronic F-68 is a widely used protective agent in sparged animal cell bioreactors. In this study, the attachment-independent Spodoptera frugiperda Sf9 insect cell line was used to explore the mechanism of this protective effect and the nature of cell damage in sparged bioreactors. First, bubble incorporation via cavitation or vortexing was induced by increasing the agitation rate in a surface-aerated bioreactor; insect cells were rapidly killed under these conditions of the absence of polyols. Supplementing the medium with 0.2% (w/v) Pluronic F-68, however, fully protected the cells. Next, cell growth was compared in two airlift bioreactors with similar geometry but different sparger design; one of these bioreactors consisted of a thin membrane distributor, while the other consisted of a porous stainless steel distributor. The flow rates and bubble sizes were comparable in the two bioreactors. Supplementing the medium with 0.2% (w/v) Pluronic F-68 provided full protection to cells growing in the bioreactor with the membrane distributor but provided essentially no protection in the bioreactor with the stainless steel distributor. These results strongly suggest that cell damage can occur in the vicinity of the gas distributor. In addition, these results demonstrate that bubble size and gas flow rate are not the only important considerations of cell damage in sparged bioreactors. A model of cell death in sparged bioreactors is presented.     

氧化铝气体分布器应用小球藻培养的研究

光生物反应器设计中,气体分布器对微藻生长有较大的影响,尤其是在鼓泡式光生物反应器中更为显著。实验考察了采用氧化铝烧制的多孔气体分布器的5L鼓泡式光生物反应器中通气速率、CO₂ 浓度对小球藻LICME002生物量、叶绿素含量、油脂积累的影响。对该气体分布器下的CO₂浓度和通气速率对小球藻的作用机理进行了初步的探讨。结果表明,CO₂浓度为3%时,该株微藻生物量、叶绿素、油脂积累的最佳;CO₂浓度超过6%时各项指标显著下降。通过对0.1vvm,0.4vvm,0.7vvm、1.0vvm的通气速条件下的各项指标的分析,确定最佳通气条件为0.4vvm。结论显示,在最佳通气速率和CO₂浓度下,微藻生物量能达到1.52g/L,油脂含量达到31.5%。     

Membrane technology as a basis for creation of treatment-and-prophylactic equipment for inhalation therapy and normobaric hypoxia]

The principles of membrane technology of gas distribution have been considered, that has a wider adoption in different branches of economy and in medicine. One of the promising trends of membrane technology employment is production of respiratory gas mixtures for hypoxytherapy, non-medicamental method to increase the human organism resistance to numerous pathogenetic environmental factors. Gas distributors and devices with different surface mass exchange and wide range of operating stress using hollow selectively permeable fibers of poly-4-methylpentene-1 are designed and produced under conditions of scientific productions. The technology of hollow fibers formation has been tried out on production spinning machinery of enterprises of chemical fibers in Ukraine. Design of gas distributors permits supplying them as a part of different devices of normobaric hypoxia from individual ones to devices of joint use allowing for customer's demands.     

Hydrodynamics and oxygen transfer in pneumatic bioreactor devices

Gas holdup and oxygen transfer studies in non-Newtonian suspensions of cellulose fibres conducted in two large (0.098 m(3) each) reactors are described. Both reactors-a bubble column and a similar internal loop airlift-were unusual in that they had rectangular cross-sections. In all cases gas holdups and k(L)a(L) declined with increasing solid concentration and, under identical conditions, the bubble column performed better than the airlift. The fluid systems used were carefully selected to represent mould fermentation broths.The behavior of true mass transfer coeffcient k(L) with changes in bubble size is discussed for these systems.     

Mass transfer characteristics of a fermentation broth in a reactor: co-current downflow contacting reactor

Gas holdups, dispersion height, volumetric mass transfer coefficients and k_La of water and a yeast fermentation broth were studied in a co-current downflow contacting reactor. k_La and gas holdup increased with increasing superficial gas velocity and there was a parallelism between k_La and gas holdup. The values of k_La gas holdup, and dispersion height measured in the air/fermentation broth system were all lower than those in air/water system.     

A comparison of some methods of estimating volumetric mass-transfer coefficients in an external-loop airlift fermenter

Volumetric mass-transfer coefficients were measured in an 11-L external-loop airlift fermenter with deionized water, a fermentation medium, and during a fermentation. Both a Mackareth oxygen electrode and a novel rapid-response probe were used. When the conventional step-change dynamic method was used for water, the long, nonlinear response time of the Mackareth electrode made correction of its readings difficult; this problem did not occur when the rapid-response probe was used. A comparison was made with a method of mass-transfer coefficient determination which does not involve any assumptions about the gas residence time distribution. However, this method requires that the liquid phase is well-mixed and this requirement was not met in the airlift fermenter. Comparison of the present results with other K(L) a determinations for airlift fermenters showed that K(L) a in water depends on the active gas holdup, the value of K(L) a/epsilon at 20 degrees C being ca. 0.37 s(-1). Although higher gas holdups were obtained with the fermentation medium than for water, the values of K(L) a/epsilon were lower, ca. 0.22 s(-1) at 20 degrees C.     

Bioreactors configured with distributors and carriers enhance the performance of continuous dark hydrogen fermentation

Anaerobic granular sludge bed (AnGSB) bioreactors were supplemented with activated carbon carriers and combined with distributors (e.g., acrylic resin board, stainless steel net and plastic net) installed at different locations to investigate the effect of distributor/carrier on biohydrogen production efficiency. The results show that plastic net stimulated the substrate/microorganisms contact and sludge granulation, thereby leading to a much better H₂ production performance when compared with those obtained from traditional CSTR. The highest H₂ production rate (7.89 L/h/L) and yield (3.42 mol H₂/mol sucrose) were obtained when two pieces of plastic nets were installed at both 4 cm and 16 cm from the bottom of AnGSB without carrier addition and the bioreactor was operated at a HRT of 0.5 h. For the AnGSB installed with two pieces of plastic net distributors, addition of carriers led to significant improvement on the H₂ production efficiency at a longer HRT (1–4 h) when compared with the carrier-absent system.     

Oxygen transfer to mycelial fermentation broths in an airlift fermentor

Oxygen transfer rates and gas holdups were measured in mycelial fermentation broths of Chaetomium cellulolyticum and Neurospora sitophila, each cultured in a 1300-L pilot-plant-scale airlift fermentor. These cultures exhibited highly non-Newtonian flow behavior coupled with a substantial decrease in oxygen transfer rates. The volumetric mass transfer coefficients in these cultures were found to be 65-70% lower than those in water. The data were compared with the available correlations obtained for simulated fermentation broths. In general, the data for C. cellulolyticum are in satisfactory agreement with the correlations for the model media but the data for N. sitophila are higher than that predicted by the correlations. Model media based correlations are found to be applicable to the fermentation processes if the culture medium does not possess a high yield stress.     

The anomaly of oxygen diffusion in aqueous xanthan solutions

A membrane-covered polarographic oxygen electrode was used to measure oxygen diffusion coefficients in aqueous polyelectrolyte solutions of xanthan gum, sodium alginate, and sodium carboxymethylcellulose (CMC). In sodium alginate solutions, dilute xanthan solutions, and solutions containing more than 0.3 wt % CMC, oxygen diffusion coefficients decrease with increasing polymer concentrations. Interestingly, in dilute CMC solutions and concentrate xanthan solutions containing more than 0.5 wt % xanthan gum, oxygen diffusion coefficients increase with increasing polymer concentrations, and values exceeding that in pure water are generally observed.     

Optimal design of the tubular microporous membrane aerator for shear-sensitive cell cultures.

In this paper, a theoretical analysis of oxygen transport across the tubular microporous membrane is described. This analysis has provided some insight into the optimal design of the membrane aerator. It was found in this study, at fixed inlet pressure, that the overall membrane oxygen transfer rate increases with increased tubing length only up to a certain length, i.e., the "critical length". When a large membrane surface area is required, the fiber should be divided into parallel segments to increase the overall oxygen transfer rate. A manifold or a gas distributor can then be used to distribute gas into segments of tubing. The length of each segment cannot exceed the critical length. In addition, shorter tube segments should give a higher oxygen transfer rate per unit tube length; however, this advantage is counterbalanced by the fact that gas distribution into huge numbers of parallel tubings may not be uniform.     

USE OF POTASSIUM PYROANTIMONATE IN THE LOCALIZATION OF SODIUM IONS IN RAT KIDNEY TISSUE

Potassium pyroantimonate added to fixative solutions has been used in tissue localization of sodium ions. The distribution and specificity of the resulting precipitate in rat kidney is described in this study. Two reproducible patterns of precipitate were obtained in control tissues. The first pattern, which occurred after fixation in solutions containing aldehyde, showed the precipitate to be mainly extracellular. The second pattern, showing the precipitate in both intracellular and extracellular locations, occurred after aldehyde fixation in those experimental situations favoring cellular swelling or after fixation with solutions containing osmium tetroxide. It appeared that sodium ions could move after fixation but that sodium pyroantimonate precipitate could not. Since model systems demonstrated that dense precipitate formed when potassium pyroantimonate was added to solutions containing certain biological amines or some divalent cations, it appeared likely that the reagent did not provide specific tissue localization for sodium ions.     

Hydrodynamic study of an internal airlift reactor for microalgae culture

Internal airlift reactors are closed systems considered today for microalgae cultivation. Several works have studied their hydrodynamics but based on important solid concentrations, not with biomass concentrations usually found in microalgae cultures. In this study, an internal airlift reactor has been built and tested in order to clarify the hydrodynamics of this system, based on microalgae typical concentrations. A model is proposed taking into account the variation of air bubble velocity according to volumetric air flow rate injected into the system. A relationship between riser and downcomer gas holdups is established, which varied slightly with solids concentrations. The repartition of solids along the reactor resulted to be homogenous for the range of concentrations and volumetric air flow rate studied here. Liquid velocities increase with volumetric air flow rate, and they vary slightly when solids are added to the system. Finally, liquid circulation time found in each section of the reactor is in concordance with those employed in microalgae culture.     

A novel parallel distributor for dispensing of IRORItrade mark RF-encoded tags to microkans in 96-well format

A novel parallel radio-frequency (RF) tag distributor has been developed which allows for distribution of RF tags into Irori microkans in 96-well format. The distributor has a holding capacity of approximately 1000 RF tags and distributes RF tags in groups of 12. Using the distributor, a block of 96 microkans can be filled with RF tags in less than 30 sec resulting in significant time savings over one-at-a-time manual RF tag distribution. The distributor may also be of utility as a solid-phase synthesis tool for dispensing resin enclosed in capsules (which have the same shape as RF tags). Copyright 1998 John Wiley & Sons, Inc.     

A radial flow hollow fiber bioreactor for the large-scale culture of mammalian cells

A radial flow hollow fiber bioreactor has been developed that maximizes the utilization of fiber surface for cell growth while eliminating nutrient and metabolic gradients inherent in conventional hollow fiber cartridges. The reactor consists of a central flow distributor tube surrounded by an annular bed of hollow fibers. The central flow distributor tube ensures an axially uniform radial convective flow of nutrients across the fiber bed. Cells attach and proliferate on the outer surface of the fibers. The fibers are pretreated with polylysine to facilitate cell attachment and long-term maintenance of tissuelike densities of cell mass. A mixture of air and CO(2) is fed through the tube side of the hollow fibers, ensuring direct oxygenation of the cells and maintenance of pH. Spent medium diffuses across the cell layer into the tube side of the fibers and is convected away along with the spent gas stream. The bioreactor was run as a recycle reactor to permit maximum utilization of nutrient medium. A bioreactor with a membrane surface area of 1150 cm(2) was developed and H1 cells were grown to a density of 7.3 x 10(6) cells/cm(2).     

Reduction of porphyrins to porphyrinogens with palladium on carbon

Porphyrinogens serve as substrates for three heme biosynthetic enzymes. Porphyrinogens are highly unstable and must be generated as an integral part of enzyme assays. Methods commonly employed to generate porphyrinogens include chemical reduction using sodium amalgam or sodium borohydride and enzymatic generation from porphobilinogen. Chemical reduction yields porphyrinogens in highly alkaline solutions with high ionic strength, whereas enzymatic generation requires purified enzymes, deproteination, and complete buffer replacement. This article describes an improved method for reducing porphyrins to porphyrinogens using palladium on carbon as a catalyst under hydrogen at ambient temperature and pressure in the dark. The palladium catalyst is removed by filtration, the filtrate is blown dry with an inert gas, and the dried porphyrinogen can be dissolved in a buffer compatible with biological studies.