Simulation and optimization of airlift external circulation membrane bioreactor using computational fluid dynamics

Abstract

The airlift external circulation membrane bioreactor (AEC-MBR) is a new MBR consisting of a separated aeration tank and membrane tank with circulating pipes fixed between the two tanks. The circulating pipe is called a H circulating pipe (HCP) because of its shape. With the complex configuration, it was difficult but necessary to master the AEC-MBR's hydraulic characteristics. In this paper, simulation and optimization of the AEC-MBR was performed using computational fluid dynamics. The distance from diffusers to membrane modules, i.e. the height of gas-liquid mixing zone (h m ), and its effect on velocity distribution at membrane surfaces were studied. Additionally, the role of HCP and the effect of HCP's diameter on circulation were simulated and analyzed. The results showed that non-uniformity of cross-flow velocity existed in the flat-plate membrane modules, and the problem could be alleviated by increasing h m to an optimum range (h m /B 0.55; B is total static depth). Also, the low velocity in the boundary layer on the membrane surface was another reason for membrane fouling. The results also suggested that HCP was necessary and it had an optimum diameter to make circulation effective in the AEC-MBR.

Computational fluid dynamics simulation as a tool for optimizing the hydrodynamic performance of membrane bioreactors

“…The ow velocity was higher in the middle of the channel, while a boundary layer with much lower velocity existed near the membrane surface. The nonuniformity of gas-liquid ow in channels between two membranes was also found by Zhang et al 11 Fluid owed through the central member channel of the MBR tted with only one aeration tube, thus indicating that ow velocity distribution between the channels was non-uniform and that signicant velocity gradients were present. However, the gas content in the MBR tted with seven aeration tubes was much higher are more uniformly distributed, indicating a more optimal design.…”

“…Therefore, computational uid dynamic (CFD) calculations provide an opportunity to quantify ow eld distribution values in MBRs that cannot be detected experimentally. [8][9][10][11] Consequently, numerical methods have been developed that enable ow rates in aerated membrane ltration processes to be predicted accurately. [12][13][14][15] Yang et al 16 used CFD model for the cost-effective optimization of MBR and the model further revealed that the high nitrogen removal efficiency (>90%) was achieved due to the high recirculation ratio driven by airli force without destroying the oxygen deprivation and enrichment in the anoxic and oxic zone, respectively.…”

Determination of Sustainable Critical Flux through a Long-Term Membrane Resistance Model

“…A simulation of the 3D flow field between polymer film sheets by the commercial CFD code ANSYS Fluent ® showed that there is non-uniformity of gas–liquid flow in channels between two polymer film elements; the flow velocity is higher in the middle of the channel and that much lower in the boundary layer at the polymer film surface [ 34 ]. According to the simulation, the ratio of boundary velocity to bulk flow velocity is selected at 0.02.…”