Simulation And Optimization Study Of Membrane Bioreactor Using Computational Fluid Dynamics

Membrane bioreactor(MBR) is now widely used for wastewater treatment and reuse, as ithas significant benefits over other biological wastewater treatment processes, such as the smallfootprint and good product quality. However, membrane fouling and high energy consumptionremain the major disadvantanges of this technology. However, the hydrodynamics of the systemwas complex and faled to understand, such as the distribution of mixture velocity, cross-flowvelocity and shear stress at the membrane surface. For solving the fluid dynamics problems,Computational Fluid Dynamics(CFD) as a powerful tool was used in the research of MBR. In thisstudy, CFD was implemented to study the hydrodynamic characteristics of MBR, the importantgeometry parameters and aeration intensity were optimized in this thesis. The main conclusionswere as follows:(1)When the membrane distance from the bottom50mm, air content and speed in the inletwere high, at other places gas content and speed were low, the overall gas holdup distribution aswell as the aeration and turbulent kinetic energy was very low, so it was not conducive to flush themembrane module.(2)When the membrane distance from the bottom150mm, air content and speed in the inletwere high, The upper half of the gas content of the membrane module plummeted to very low,after some distance membrane gas scattered locations, turbulent kinetic energy is small anduneven, which is not conducive to a uniform air and water turbulent, the gas-water two-phaseturbulence in the surface and sides of the membrane were less than ideal.(3)When the membrane distance from the bottom100mm, gas content rise by column, andcentered on membrane component distribution is symmetrical, there is a decreasing trend on theleft and right side, in the middle of the membrane module position of gas content and uniformstability, conducive to the mixture of gas water two phase flow, the aeration speed were even, themembrane module wash effect is very good.(4)When the membrane distance from the bottom100mm, aeration intensity0.1m/s, the gascontent is very low, the whole flow field were in very low flow region and uneven, the scour isstrong on the middle of membrane module, weak on both sides of membrane surface, which isvery obvious.(5)When the membrane distance from the bottom100mm, aeration intensity were0.5m/s, gas content and the speed were too big, above the membrane module surface, gas content andspeed were very low, a part of the membranes could not be flushed well, membrane module wasbad to make high effective, speed were too large on both sides of the reactor, and gas water mixedlevel were too high, which was not conducive to evenly mix and the big gas velocity alsocontributed to the formation of small materials that aggravate membrane fouling.(6)When the membrane distance from the bottom100mm, aeration intensity were0.3m/s,gas inside the membrane module and the lateral has a uniform distribution of gas content, themixing of the gas and water was good, especially in the free surface area of the upper membranecomponents, a certain amount of gas content is benefit for the erosion of the membrane module.Highest circulation area is in the middle of the film position which closest to the membranesurface, and the membrane surface was good fluid scouring, reduced the membrane pore blocking,alleviate the membrane fouling.The CFD model and modeling results in this study were successfully validated againstexperimental results. The results would provide technical support for design and development ofMBR with low energy and high efficiency, and the research method provide by this paper could beused as a reference for further hydraulic study on MBRs.