HYDRODYNAMIC CONTROL OF BIOPARTICLE DEPOSITION IN A MBR APPLIED TO WASTE-WATER TREATMENT

The study of fouling for tubular ceramic ultrafiltration (MWCO 300 kD) membranes during activated sludge filtration under constant flux cond itions led to the experimental identification of two fouling processes : (1) At low recirculation velocity (0.5 m/s; Re similar to 1200), slu dge flee particles were deposited on the membrane surface and this cak e layer provoked a very quick increase of hydraulic resistance (>10(9) m(-1) s(-1)). (2) However, under the usual recirculation conditions ( 4 m/s; Re similar to 9000), floc was not deposited. Filtration was sta ble for several days even with high fluxes (75-150 l/h m(2)). Progress ive membrane fouling resulted in a linear increase of transmembrane pr essure over a certain time, and could be described by an increase in t he hydraulic resistance, with dR/dt varying between 10(5) and 10(8) m( -1) s(-1) depending on hydrodynamic and biological conditions. Mechani sm models (shear induced diffusion, inertial lift, surface transport) led to a very good qualitative description of these results, and revea led the major role of convective backtransport phenomena in fouling pr ocesses. (C) 1998 Published by Elsevier Science B.V. All rights reserv ed.