Upgrade of a slurry photocatalytic membrane reactor based on a vertical filter and an external membrane and testing in the photodegradation of a model pollutant in water

Submerged slurry photocatalytic membrane reactors have been widely investigated in literature to combine photocatalysis and membrane separation in the mineralization of recalcitrant pollutants in wastewaters. However, submerged membranes are only able to retain the photocatalyst particles and not many types of pollutants. An upgraded configuration, based on a vertical filter (able to retain the photocatalyst) and an external nanofiltration (NF) membrane (able to retain pollutants in the photoreaction zone), has been designed, built and tested. To our knowledge, this novel configuration has never been proposed. The proof-of-concept on the working and behavior of the vertical filter in presence of the photocatalyst and the photocatalytic performance of the overall system, in a batch configuration, in the photodegradation of gemfibrozil as a model pollutant are reported. The filter was able to retain the TiO2 particles while ensuring greater flux compared to the submerged membrane (200 vs 40 L m-2h−1 average values). The external membrane is not exposed to light irradiation, permits the recycle in the photoreactor of the not-photodegraded pollutants and produce a quality of the treated water (permeate) better than a submerged membrane. Some parameters (e.g.: TiO2 amount, pH, light intensity and wavelength, air and oxygen, membrane rejection) that influence the performance of this integrated system (photoreactor, filter and membrane) have been studied and discussed. Indeed, a pH 8.0 (giving 40–50 % rejection of the Fortilife NF membrane) was chosen against pH 9.7 (giving 90 % rejection), to avoid filter plugging. The obtained overall performance (80 % reduction of gemfibrozil concentration) can be further improved by a fine tuning of the various parameters.