On the design and simulation of an airlift loop bioreactor with microbubble generation by fluidic oscillation

Microbubble generation by a novel fluidic oscillator driven approach is analyzed, with a view to identifying the key design elements and their differences from standard approaches to airlift loop bioreactor design. The microbubble generation mechanism has been shown to achieve high mass transfer rates by the decrease of the bubble diameter, by hydrodynamic stabilization that avoids coalescence increasing the bubble diameter, and by longer residence times offsetting slower convection. The fluidic oscillator approach also decreases the friction losses in pipe networks and in nozzles/diffusers due to boundary layer disruption, so there is actually an energetic consumption savings in using this approach over steady flow. These dual advantages make the microbubble generation approach a promising component of a novel airlift loop bioreactor whose design is presented here. The equipment, control system for flow and temperature, and the optimization of the nozzle bank for the gas distribution system are presented. (C) 2009 The Institution of Chemical Engineers. Published by Elsevier B.V All rights reserved

Gas-liquid mass transfer : a comparison of down-and up-pumping axial flow impellers with radial impellers

The performance of a down- and up-pumping pitched blade turbine and A315 for gas-liquid dispersion and mass transfer was evaluated and then compared with that of Rushton and Scaba turbines in a small laboratory scale vessel. The results show that when the axial flow impellers are operated in the up-pumping mode, the overall performance is largely improved compared with the down-pumping configuration. Compared with the radial turbines, the up-pumping A315 has a high gas handling capacity, equivalent to the Scaba turbine and is economically much more efficient in terms of mass transfer than both turbines. On the other hand, the uppumping pitched blade turbine is not as well adapted to such applications. Finally, the axial flow impellers in the down-pumping mode have the lowest performance of all the impellers studied, although the A315 is preferred of the pitched blade turbine

Hydrodynamics of a three-phase external-loop airlift bioreactor

The effect of the distributing plate orifice diameter, airflow rate, solids loading and solids density on the hydrodynamic characteristics - gas holdup, circulation time and liquid velocity - of a three-phase external-loop airlift reactor was characterized. It was observed that the gas distributor has a small effect on riser gas holdup, circulation time and downcomer liquid velocity. On the contrary, the airflow rate, solids loading and solids density significantly affect the hydrodynamic characteristics of the external-loop airlift reactor. A previously described model was used to estimate simultaneously both the riser gas holdup and the downcomer linear liquid velocity. The model simulated with high-accuracy experimental data obtained with three different distributing plate orifice diameters, two solids density and solids loading up to 30% (v/v).Fundação para a Ciência e a Tecnologia (FCT) – PRAXIS/2/2.1/BIO/1061/95.Comunidade Europeia - INCO-COPERNICUS - Contract Nº ERB IC15-CT-98-0904 e Instituto de Biotecnologia e Química Fina (IBQF) - GGP XXI/BD/2937/96

A mathematical model for transfer of O<SUB>2</SUB> and CO<SUB>2</SUB> in a membrane artificial lung

An analysis of oxygen absorption and carbon dioxide desorption in a film of blood through a gas-permeable membrane is presented. The mathematical analysis treats blood as a homogeneous, non-Newtonian fluid, in which the system pO2, pCO2 hemoglobin, pH is always in equilibrium due to the reaction rate in the erythrocites. Influence of flow rate, hematocrit and gas composition on blood saturation are studied, and the possibility of calculating an optimal membrane length is found.Facultad de Ingenierí

Experimental pulse technique for the study of microbial kinetics in continuous culture

A novel technique was developed for studying the growth kinetics of microorganisms in continuous culture. The method is based on following small perturbations of a chemostat culture by on-line measurement of the dynamic response in oxygen consumption rates. A mathematical model, incorporating microbial kinetics and mass transfer between gas and liquid phases, was applied to interpret the data. Facilitating the use of very small disturbances, the technique is non-disruptive as well as fast and accurate. The technique was used to study the growth kinetics of two cultures, Methylosinus trichosporium OB3b growing on methane, both in the presence and in the absence of copper, and Burkholderia (Pseudomonas) cepacia G4 growing on phenol. Using headspace flushes, gas blocks and liquid substrate pulse experiments, estimates for limiting substrate concentrations, maximum conversion rates Vmax and half saturation constants Ks could rapidly be obtained. For M. trichosporium OB3b it was found that it had a far higher affinity for methane when particulate methane monooxygenase (pMMO) was expressed than when the soluble form (sMMO) was expressed under copper limitation. While for B. cepacia G4 the oxygen consumption pattern during a phenol pulse in the chemostat indicated that phenol was transiently converted to an intermediate (4-hydroxy-2-oxovalerate), so that initially less oxygen was used per mole of phenol.

Hydrodynamic considerations on optimal design of a three-phase airlift bioreactor with high solids loading

The hydrodynamic study of a three-phase airlift (TPAL) bioreactor with an enlarged gas–liquid dual separator was carried out. Different lengths and diameters of the draft tube were tested to show how the design of the separator zone affects the hydrodynamic performance of the TPAL reactor. Ca-alginate beads with entrapped yeast biomass at different loadings (0, 7, 14 and 21% v/v) were used in order to mimic the solid phase of conventional high cell density systems, such as those with cells immobilized on carriers or flocculating cells. Important information on multiphase flow and distribution of gas and solid phases in the internal-loop airlift reactor (ALR) with high solids loading was obtained, which can be used for suggesting optimal hydrodynamic conditions in a TPAL bioreactor with high solids loading. It is finally suggested that the ALR with a dual separator and a downcomer to riser cross-sectional area ratio (AD/AR) ranging from 1.2 to 2.0 can be successfully applied to batch/continuous high cell density systems, where the uniform distribution of solid phase, its efficient separation of particles from the liquid phase, and an improved residence time of air bubbles inside the reactor are desirable.European Community - ‘Improving Human Research Potential’ - Marie Curie Fellowship - contract number HPMF-CT-2002-01643

Experiments on gas transfer to a film of blood through a membrane

The result of an increase in mean saturation of blood predicted by two mathematical models was verified by means of a series of experiments using cattle blood flowing in a 1.1 mm thick film, with flow rates ranging between 0.6 and 2.5 cc/min. The use of the equation of O2 transfer without taking into account the coupled CO2 transfer leads to slightly conservative predictions, and experimental data fit the calculated values of saturation within an error of 5%. For very slow flow rates the deviations reach 10%.Facultad de Ingenierí

Liquid-liquid equilibria of UCON + (sodium or potassium) phosphate salt aqueous two-phase systems at 23 °C

Six phase diagrams for UCON−phosphate salt aqueous two-phase systems (ATPSs), at 23 °C, are presented. The ATPSs were obtained combining UCON (a random copolymer of 50 % ethylene oxide and 50 % propylene oxide) and a phosphate salt (KH2PO4, K2HPO4, potassium phosphate buffer pH = 7, NaH2PO4, Na2HPO4, and sodium phosphate buffer pH = 7). Among the salts used, Na2HPO4 proved to be the most effective in ATPS formation, providing the greatest heterogeneous region in the phase diagram. The previous established relation between the anion valence and the concentration needed to form a biphasic system was confirmed: higher valence requires lower concentration. Na+ salts require, in all cases, lower concentration to form ATPSs than the corresponding K+ salts. The size of the heterogeneous region in the phase diagrams increases with an increase of the pH value of the salt used in ATPS preparation.Fundação para a Ciência e a Tecnologia (FCT) - SFRH/BD/43439/2008Fundo Europeu de Desenvolvimento Regional (FEDER) - FEDER/POCI/201

Gas absorption with second-order chemical reaction in a packed column : Effects of contact-time distribution

Absorption of carbon dioxide into aqueous solution of sodium hydroxide was studied in a packed column under conditions such that the accompanying reaction was of the second order. In this case the average or volumetric reaction factor for the packed column, i.e. the ratio of the volumetric coefficients for absorption with and without chemical reaction, is complicated by the non-uniform contact-time distribution. However, the assumption of Porter''s "long, slow flow paths" model for the contact-time distribution led to a successful correlation for the average reaction factor.Facultad de Ingenierí

Photobioreactor Design and Fluid Dynamics

Photobioreactor design is a subject of great relevance for the attainment of a sustained development in modern technology,and has also considerable interest from the basic scientific and technologic point of view.The aim of the present review paper is presenting and comparing some of the recent attempts by the authors of modelling photosynthesis in reactors.A short inspection of the kinetic models proposed for photobioreactor design is done,and some examples of the integration of such kinetic models and bioreactor fluid dynamics in the modelling of photobioreactors are presented