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Membranebioreactors (MBRs) are becoming more suitable alternativesfor conventional wastewater treatment devices. The performance ofa pressure-driven MBR is dominantly affected by the hydrodynamic conditionsof the system. This study was conducted to investigate various hydrodynamiccharacteristics including shear stress, cross-flow velocity, and membranefouling resistance, using computational fluid dynamics (CFD). Simulationof two- and three-phase flow for a flat-sheet submerged membrane modulewas carried out, and the results were compared with the experimentaldata. The CFD simulation was implemented to analyze the fluid-flowpattern, shear stress on membrane surfaces, and cross-flow velocitybetween membranes at various mixed liquor suspended solid concentrationsin the bioreactor. It was shown that the cross-flow velocity playsan important role in the membrane fouling and determination of thecritical particle diameter. To achieve an optimal operating condition,the critical particle diameter was calculated at different air flowrates and permeate fluxes. The CFD results showed that the outermostmembranes are more prone to fouling because of the lower shear stresson their surface as well as the lower cross-flow velocity betweenthem and the module wall. Moreover, the effect of the air bubble diameteron the air and liquid shear stress was investigated to determine anoptimal bubble size. [ABSTRACT FROM AUTHOR]

ABSTRACT In the present study, bubble size distribution (BSD) within a bubble column reactor was modeled using an artificial neural network (ANN). The fluids tested in the bubble column consisted of 11 different oil mixtures, each containing two different oils. Pure water was also tested. BSD was determined for various superficial gas velocities by photographing the state of the fluid. It was found that bubble size as well as distribution depended on parameters, such as gas flow rate, liquid properties, sparger pore diameter and distance from the sparger in the column. The proposed ANN model is based on more than 4500 data points collected for BSD estimation. Through statistical testing, it was found that the model has a correlation coefficient greater than 70% and upon experimental testing was found to better predict BSD than currently used correlations found in the literature. Copyright © 2011 Curtin University of Technology and John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract: Gas hold-up (ɛ g), sauter mean bubble diameter (d 32) and oxygen transfer coefficient (k L a) were evaluated at four different alkane concentrations (0.05, 0.1, 0.3 and 0.5vol.%) in water over the range of superficial gas velocity (u g) of (1.18–23.52)×10−3 m/s at 25°C in a laboratory-scale bubble column bioreactor. Immiscible hydrocarbons (n-decane, n-tridecane and n-hexadecane) were utilized in the experiments as impurity. A type of anionic surfactant was also employed in order to investigate the effect of addition of surfactant to organic-aqueous systems on sauter mean bubble diameter, gas hold-up and oxygen transfer coefficient. Influence of addition of alkanes on oxygen transfer coefficient and gas hold-up, was shown to be dependent on the superficial gas velocity. At superficial gas velocity below 0.5×10−3 m/s, addition of alkane in air–water medium has low influence on oxygen transfer coefficient and also gas hold-up, whereas; at higher gas velocities slight addition of alkane increases oxygen transfer coefficient and also gas hold-up. Increase in concentration of alkane resulted in increase in oxygen transfer coefficient and gas hold-up and roughly decrease in sauter mean bubble diameter, which was attributed to an increase in the coalescence-inhibiting tendency in the presence of surface contaminant molecules. Bubbles tend to become smaller with decreasing surface tension of hydrocarbon, thus, oxygen transfer coefficient increases due to increasing of specific gas–liquid interfacial area (a). Empirical correlations were proposed for evaluating gas hold-up as a function of sauter mean bubble diameter, superficial gas velocity and interfacial surface tension as well as evaluating Sherwood number as a function of Schmidt, Reynolds and Bond numbers. [Copyright &y& Elsevier]

Oxidation of glucose by homogeneous glucose oxidase was performed in rectangular bubble column reactor at 40 °C, ambient pressure and pH of 5.5 while superficial gas (oxygen) velocity was varied in the homogeneous and transition regime in the range of 0.0014-0.0112 m s-1. Effect of superficial gas (oxygen) velocity on the apparent reaction rate and its parameters was determined and it was observed that the apparent reaction rate on the basis of volume of the liquid increased with increasing the superficial gas (oxygen) velocity. The apparent reaction rate was assumed to be in the form of Michaelis-Menten equation and its apparent kinetic parameters were evaluated by the nonlinear regression method. [ABSTRACT FROM AUTHOR]

Bioconversion of glucose to gluconic acid with glucoseoxidaseas enzyme was considered to occur in a bubble column reactor at 40°C, atmospheric pressure, and pH 5.5 while oxygen gas velocitywas varied in the homogeneous and transition regime in the range of0.0014–0.0112 m s–1. It was found that thesuperficial gas velocity has a positive effect on gas holdup, meanbubble size, and volumetric mass transfer coefficient, while the glucoseconcentration has a negative influence on these hydrodynamic parameters.The modeling of bubble column by considering the complete bubble sizedistribution in the governing equations was carried out in this work.The model was also solved by considering the single and double sizesof bubbles instead of complete bubble size distribution. It was shownthat the results of the model, considering the complete bubble sizedistribution, is in a good agreement with the experimental data, whilethe considered single and double bubble sizes cannot predict the experimentaldata of oxygen concentration in the reactor properly. It was alsofound that the superficial gas velocity has a positive influence onoxygen concentration while glucose concentration has negative influenceat low superficial gas velocity and positive influence at high gasvelocity. [ABSTRACT FROM AUTHOR]

Abstract: Determinations of pertinent hydrodynamic and mass transfer parameters were carried out inside draft tube internal loop airlift bioreactor (DTAB) containing water in diesel (W/D) microemulsions with water to diesel volume ratio (φ) in the range 2.5–40%. For comparative purposes, data for diesel and water was also obtained. Increase in φ of the microemulsion systems up to 40% or increase in the amount of surfactant used to make the microemulsions resulted in a decrease in the values of ɛ g and k L a, which was attributed to the increase in the viscosity of the microemulsions. This viscosity was found to be a more suitable correlating parameter than φ. Increase in the value of φ of the W/D microemulsion resulted in a decrease in the values of liquid velocity for u gr up to 0.032m/s. At higher gas velocities, similar values were obtained for all the microemulsions. On the other hand, increase in φ of the W/D microemulsion resulted in increase in both the circulation time and mixing time values obtained inside the DTAB, although the difference was more pronounced at lower values of u gr. Suitable empirical correlations relating ɛ g , k L a, , circulation time and mixing time to riser superficial gas velocity (u gr) and kinematic viscosity were presented. The downcomer holdup data for diesel and W/D microemulsions was related to the riser holdup data using a single correlation. [Copyright &y& Elsevier]