Investigation Of Membrane Fouling Behavior Based On Partical Force Analysis And Deposition On The Membrane Surface

Membrane fouling was mainly resulted from reversible and irreversible deposition of trapped particles on the membrane surface,or in the membrane pore.As a process affected significantly by forces,particle deposition onto membrane surface from the remote to the short-range is a continuously coherent process,hence,systemic analysis on the particle force is not only the core problem of particle motion,but also the key to understanding membrane fouling mechanisms.In this study,movement and deposition of particles in the cross-flow ultrafiltration and nanofiltration were studied.Through the analysi s of the forces of the particle in the ultrafiltration and nanofiltration process,the main forces and their ranges in the vertical and horizontal directions of the particles were determined.The User Defined Function(UDF)was coupled with the Discrete Phase Modeling(DPM)in Computational Fluid Dynamics(CFD)to determine the simulation parameters and boundary conditions,and the simulation method of the system was successfully established.The experimental and simulation analysis of the membrane flux during ultrafiltration and nanofiltration showed that the flux error values were within 10% and 15%,respectively,indicating that the CFD simulated membrane flux results were reliable.The particle deposition under varied operation conditions was studied.The experimental results were consistent with the simulation results.It was observed that the larger th e transmembrane pressure applied and the smaller the cross-flow velocity kept,there was larger particle deposition probability.The initial deposition of the particles had significant influence on the overall filtration decreasing rate.With the same operation conditions,the probability of particle deposition in the ultrafiltration experiments was ranged from 32% to 42%,and the simulated probability was ranged from 34% to 42%.In the nanofiltration experiments,the probability of particle deposition was ranged from 8% to 15%,and the simulated probability was from 7% to 13%,indicating that the CFD simulation particle deposition results were quite accurate.The Micro-Particle Image Velocimetry(Micro-PIV)visual cross-flow filtration system was allocated to take high-speed photos of the tracer particles scattered in the flow field,and to measure the transient velocity distribution of the flow field and to track the particle trajectory.The analysis of particle velocity and flow field showed that the experimental results of the visualization were in good agreement with the simulation results.The flow field of the CFD simulation system was accurate.Based on the simulation method,the effects of particle properties and operating conditions on particle forces and deposition probability were investigated.The key factors of membrane fouling were identified,and the probability functions of particle surface deposition under different working conditions were investigated.The membrane fouling control strategies were accordingly proposed,including changing the properties of the liquid,op timizing the operation strategy.This study provided a scientific basis for the optimization design of experiments and membrane modules,and played a good guiding role in the research of membrane fouling.