Simulation study on the influence of aeration on the gas-liquid flow regime in membrane bioreactors
In this study,the flow patterns of membrane bioreactor(MBR)under different aeration models were simulated.Porous media model was adopted to simulate permeable separation membrane and multi-sized bubble flow within MBR was predicted by Population Balance Model(PBM).The effects of permeate side-suction,bubble diameter and aeration velocity on the flow regime,and the impact of near-membrane bubble flow on the membrane surface scouring effect were systematically analyzed.The results show that,for bubble flows distanced from the membrane surface,smaller bubbles promote the mixing of gas and liquid phases within membrane reactor.Under the permeate side-suction pressure of-2 000 Pa,the void fraction decreased by 16％with increasing bubble diameter from 0.1 to 3.0 mm,while the void fraction peak value increased by 12％with increasing aeration velocity from 0.5 to 1.5 m/s.The circulation center of liquid flow gradually moves closer to membrane surface when the aeration orifice approaches membrane surface.For bubble flows near membrane surface,the membrane shear stress increases from 1.92 to 4.87 Pa when the bubble diameter decreases from 3.0 to 1.0 mm under the suction pressure of 0 Pa.The membrane shear velocity and stress increase from 0.02 to 0.22 m/s and 1.97 to 3.83 Pa,respectively,when the aeration velocity increasing from 0.5 to 1.5 m/s.The average membrane shear stress under the suction pressure of-3 000 Pa is 1.85 times as high as that under 0 Pa under the aeration velocity of 0.5 m/s.High suction negative pressure with high-speed aeration of small bubbles is beneficial for enhanced membrane shear stress.The research results will provide guide and basis for the design and optimization of aeration processes in MBR.
万方数据
维普
