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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]

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]