Experimental And Numerical Simulation Study On Flow Field Characteristics Near The Membrane Surface In SMBR

Submerged Membrane Bioreactor (Submerged be Bioreactor, SMBR) as a waterpollution control and water reuse technology is widely used in the current, but membranefouling and high energy consumption is a key factor of restricting its development.Through economic and effective method to reduce membrane pollution, increase thepermeation flux has become an important research topic in the field of home and abroad.This paper for the purpose of research gas-liquid two-phase flow field of hollow fibermembrane surface in SMBR, strengthen the mass transfer and reduce the membranefouling at the membrane surface, based on the PIV technology and CFD three-dimensionalunsteady numerical simulation research on the closed surface gas liquid two phase flowfluid mechanics characteristics, got the optimal aeration conditions in this experiment, andimproved experiment and the simulation method in the small scale experiment.In this paper, main conclusions are as follows:(1) Though the PIV for gas liquid two phase flow images visually observed1mm,2mm,3mm the formation process of bubbles under aeration aperture, the analysis resultsshown: aeration intensity of2.5m3/h, the bubble size increases with aeration aperture,bubbles from globular to elliptic ball, a ball cap again. With the increase of bubble size, itswake zone also expanded. But the aerator bubble size, oxygen transfer efficiency is low, sothis experiment1.5m when the effective depth of2mm is the best aeration aperture.(2) On the analysis of3cm from the membrane surface section A and B under threekinds of aeration aperture area the distribution of tangential stress, learned that tangentialstress with aeration increase with the increase of the aperture, but too much shear damagenear the membrane surface of the activated sludge flocculation structure, affect the normalgrowth of microorganisms.2mm diameter tangential stress distribution of the axialdirection under a3mm diameter uniformity.(3) Reactor liquid phase in each region of the axial velocity vector distribution reflectsthe formation process of bubble plume: A region for the plume area formation, B and Cregion for plume formed after area; D region as the surface of the bubble plume flow area.At the same time get the membrane surface liquid velocity with the increase of the aerationintensity show increased before they are stable. The three dimensional unsteady numerical simulation results are in good agreement with those obtained with the experiment.(4) Through the combination of theoretical and experimental analysis of the masstransfer coefficient at the membrane surface and the shear stress, along with the change ofaeration intensity analysis: A, B, C three regions of the membrane surface mass transfercoefficients increase gradually with the increase of aeration intensity, but D region inaeration intensity is6.5m3/h when the performance is lower, explains the membranemodule appears at the top of the reactor in the actual operation adsorption film increasedpollution phenomenon. Considering energy consumption and the conditions of the growthof microorganisms, to determine the experiment2mm aperture corresponding optimalaeration intensity is5.5m3/h, simulation for gas liquid phase velocity near the maximumconcentration at the top of the membrane module, is advantageous to the shedding ofpollutants, and slow the membrane fouling of membrane component at the top.(5) Numerical simulation shows that the distribution of the membrane surface gasholdup, the result showed that with the increase of aeration intensity, membrane surfacealso gradually increase, local gas holdup and gas liquid contact area to expand tend to bemore uniform. But too much oxygen can destroy the activated sludge floc structure, makethe sludge particles become smaller, easier to deposit in the membrane surface and filmhole. So within a certain range increased oxygen can improve the efficiency of wastewaterbiochemical treatment. Another, simulation observed at the bottom of the reactor flowregion and the lower local gas holdup, dead zone, not conducive to the growth ofmicroorganisms, through optimizing the structure of aeration system and the reactorimproved.(6) Small scale experiment improved the experiment and numerical simulationmethod, used the advanced PIV method, fluorescent particles with high pass filter in frontof the camera and narrowband filter to realize for gas liquid two phase flow field at themembrane surface at the same time, optical fiber replaced the membrane fiber, applicationSize-Shape-Analysis module for bubble velocity and equivalent diameter. The VOF modelwas used in the calculation could well capture the dynamics of bubbles.