The present study focused on the influence of both hydrodynamic conditions and suspension characteristics on changes in a filtering medium. The results obtained demonstrate (i) airflow increased local turbulence leading to a decrease in the rate of change of TMP, (ii) less biomass was jammed in the lowest fiber density module, that presented systematically the highest fouling rate, (iii) high concentrations of soluble bacterial products in the suspension favored a irreversible marked change in TMP, (iv) the presence of accumulated biomass on the membrane wall appeared to have a beneficial effect, acting like a dynamic membrane in pre-retaining soluble matter. (c) 2006 Elsevier B.V. All rights reserved.