Advances in Water Treatment and Enviromental Management

FOULING PHENOMENON IN CROSS-FLOW MICROFILTRATION PROCESSES 177Fig. 4: Particle displacement rulesthe influence of the tangential flow on the behaviour of suspended particles close to the edgeand inside the deposit.3.2 ResultsParticle displacement and adhesion rules, such as those previously defined, can be usedmore generally to simulate the formation of aggregates which have very different structuresallowing the simulation of many different applications. Our concern is the understanding offouling phenomena occuring during drinking water ultrafiltration. Numerical simulations ofdeposits are carried out for a great number of particles entering individually the specifiedfiltration region, it means physically that such aggregates can be compared to real depositswe can observe after a long water cross-flow microfiltration period. The effect of tangentialshear flow on the structure of a solid particle deposit on the porous wall is taken account forin form of a compacity factor which prevents dendrits from being developed by interfaceerosion and also reduces vertical increase of aggregates before complete space filling. Thisphenomenon has been experimentally visualized by HOUI (1989) in a cross-flow microfiltrationmicromodel with video recording of an optical microscop image. Now we specially focus onanalysing capture mechanisms by precising their influence on three morphological depositsproperties: porosity, density and mean thickness. The final objective of these investigations isto determine the two fundamental macroscopic parameters, permeability and thickness,necessar for the description of the working conditions of a hollow fiber module.All simulations are developed for a filter surface considered as a nuclepore membrane of 20% porosity and a pore diameter of 1µm. The size of solid particles is equal to 0.2 µw, thoseFig. 5: Simulation with α=20°, θ i =1°, θ v =1°, N r =4Fig. 6: Simulation with α=20°, θ.=1°, θv=1º, Nr