Study On The Hydrodynamics And Its Optimization Of Membrane Tank In Membrane Bioreactor Based On Computational Fluid Dynamics

Membrane bioreactor?MBR?has been accepted as a promising water treatment technology for its superiority in steady high quality effluent,small footprint et al.However,high energy consumption of aerators in membrane tanks has always been an obstacle for large-scale application of this technology.In this study,based on evaluation of hydraulic condition of a full-scale MBR plant,computational fluid dynamics?CFD?was utilized to study the hydrodynamics of MBRs.The geometry property of MBR?baffle location,baffle size,tank size,membrane module location in tanks?were thoroughly optimized to create a better hydraulic condition for membrane fouling control,thus to increase aeration efficiency and save energy.The overall hydraulic condition of a full-scale MBR was evaluated by a tracer experiment.The overall plant was found to have 8.02%of dead zones,the membrane tanks were neither close to completely mixed conditions,which indicated requirements of optimization in the hydrodynamics.In this case,a CFD model was developed to study the hydrodynamics in MBR.A bench-scale MBR was manufactured to validate the model.The water velocity profiles derived from experimental measurement showed a satisfying agreement with CFD simulated data?relative error of 1.4%?,indicating a reliability of the CFD model.The validated CFD model was firstly used on a bench-scale MBR,by optimizing the baffle location,baffle size and reactor size.The optimized baffle(surrounded baffles,O_Du=5%,O_Dd=20)was found to have an elevation of 10%-30%for average membrane surface shear stress under different aeration intensity.In the process of reactor size optimization of an unbaffled MBR,the membrane surface shear stress was found to by elevated by 74%with an extra downcomer added,and with a final optimizaiton in reactor size,the favored MBR was found to have elevation of 21.3%-94.1%for membrane surface shear stress under different aeration intensity.Finally,the CFD model was coupled to porous media model and Non-Newtonian model to simulated the hydrodynamics in the membrane tank of a full-scale MBR.A concept of risk velocity(v_0.05)was proposed to judge the membrane fouling potential.Five indexes(water surface–module distance index i_Lu,module–aeration pipe distance index i_La,aeration pipe–tank bottom distance index i_Lb,module–module interval index i _Lint,module–tank lateral wall distance index i_Lw)were used to indicate the module location,and each of them was discussed for their individual impact on the risk water velocity(v_0.05)in the membrane module region.An optimized location of membrane modules in the tank(i _Lu=0.6,i_La=0.6,i_Lb=0.6,i _Lw=0.6,i_Lint=0.6)was proposed,and was found to have an elevation of 146.9%for the risk velocity compared with the currently applied origin design,and had erased all the risk zones in the membrane module in the original design.