Studies on various reactor configurations for coupling photocatalysis and membrane processes in water purification

General aspects and perspectives of heterogeneous photocatalysis for the treatment of polluted aqueous effluents are presented. Some experimental results obtained by using various configurations of photocatalytic membrane reactors (PMRs) are reported. The configurations studied were: (i) irradiation of the cell containing the membrane, with three sub-cases: (i(1)) catalyst deposited on the membrane; (i(2)) catalyst in suspension, confined by means of the membrane; (i(3)) entrapment of the photocatalyst in a PSF membrane; (ii) irradiation of the re-circulation tank and catalyst in suspension confined by means of the membrane. In the case "(i)", a preliminary investigation of membrane stability under UV irradiation was carried out. PMR characterization in photodegradation tests was mainly carried out in a recycle batch membrane reactor and, in some cases, in a continuous membrane reactor. The comparison between the first set of results, where the membrane was used only as a support for the photocatalyst, and the newest ones, where the adsorption of the pollutant on the membrane and membrane rejection play an important role in the global reactor performance, showed interesting perspectives and synergy for coupling photocatalysis and membranes. Furthermore, the configuration where the re-circulation tank was irradiated and the catalyst was used in suspension, appeared to be the most interesting for industrial applications. For example, in reactor optimization, high irradiation efficiency, high membrane permeate flowrate and selectivity can be obtained by sizing separately the "photocatalytic system" and the "membrane system" and taking advantage of all the best research results for each system. (C) 2002 Elsevier Science B.V. All rights reserved.