Microfiltration through an inorganic tubular membrane with high frequency retrofiltration

High frequency backpulsing is a promising technique of flux enhancement tha t could contribute to the development of cross-flow micro-/ultrafiltration in water and wastewater treatment. A systematic study of the influence of t he operational parameters was carried out with three suspensions, bentonite in tap water, biologically treated wastewater and activated sludge. The al umina membranes were tubular (0.02, 0:05 or 0.2 mum), with internal or exte rnal skin, the latter being not suitable. The technique was particularly ef ficient for bentonite; a minimal cross-flow velocity was required to reach a net flux independent of the cross-flow. The results are less good for the biological suspensions since the same fluxes could be reached by an increa se of cross-flow velocity. However, the energy required by high frequency b ackpulsing is lower. The average reverse fluxes, measured by a tracer metho d, are surprisingly high and could hamper the development of the technique. At low Reynolds number (Re = 3500), the net flux increased with the revers e flux, then reached a plateau corresponding to the total penetration of th e laminar layer against the membrane wall by the backwash water. (C) 2001 E lsevier Science B.V. All rights reserved.