Abstract
Membrane fouling in a cross-flow ultrafiltration (UF) is investigated using a tubular membrane for three different feed solutions containing oil droplets and particles. The initial build-up of a highly concentrated fouled cake layer on the membrane surface results in sharp flux decline which acting as secondary filtration layer over the membrane surface. In the present work, the fouled cake layer resistance is quantified in terms of specific cake resistance (a), which depends strongly on the operating parameters. Cake resistance, a, calculated from experimental data using different models, is used as an operational indicator to quantify membrane fouling. Two sets of experiments are performed, first by operating tubular membrane as it is, and later by introducing a static helical turbulence promoter. Results showed that the influence of pressure and feed concentration on a is more important than that of feed temperature and cross-flow velocity. Oil droplets sizes, which vary mainly with temperature, play an important role in the interpretation of results. Droplets coalescence and flocculation of suspended particles and the aggregation of droplets on particles explain these variations. The cake layer is significantly reduced by using a novel static helical type turbulence promoter inside the tubular membrane module allowing operation at low pressure and low cross-flow velocity, thus, aid in reducing membrane fouling without significantly increasing energy consumption. Computational Fluid Dynamics (CFD) calculations of full Navier-Stokes equations are also performed to gain insight into flow hydrodynamics and for estimating shear stresses when the turbulent promoter is deployed. The result indicates that roughly 4-5 times higher shear stress on the membrane surface is generated depending on the applied cross-flow velocity. It potentially explains significant cake layer alteration with variations in specific resistance and corresponding flux enhancement as observed in experiments.