Ultrafiltration enhanced by coagulation in an immersed membrane system

The aim of this study is to determinate optimum conditions, membrane configuration, air flow, coagulation rate, permeate flux, for the ultrafiltration of surface water. Results show how coagulation is a necessary pre-treatment to remove micro-particles in aqueous suspension (i) before a conventional sedimentation, (ii) before a membrane filtration. When membranes are immersed in a contactor, configuration allow to maintain the permeate flow rate at high value (200 L/h/m(2)/bar) mainly because coagulation induces large floc size. However, when the particle concentration of the suspension is very high (2 to 5 g/L), it is important to increase the shear stresses close to the immersed membrane to minimise a deposit set up on the surface. When no high cohesion forces exist between particles, the aeration, even under weak flow rate, allows to avoid this deposit making.