Improved Performance of a Slurry Photocatalytic Membrane Reactor with a Vertical Filter and an External Membrane

The research in the field of photocatalytic membrane reactors has evidenced, in almost 20 years, that slurry photocatalyst and submerged membrane is a configuration that seems interesting in the mineralization of recalcitrant pollutants in wastewaters [1]. However, submerged membranes are only able to retain the photocatalyst particles and not many types of pollutants [2], so a RO membrane was used in series to the submerged membrane to improve the quality of the treated water [3]. Two membrane systems in series are quite complicated to operate as well as they have high capital and operating costs. A new configuration, based on a vertical filter working under hydrostatic pressure (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. The 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 have been studied. 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 considered. The filter was able to retain the TiO2 particles while assuring higher flux than a submerged membrane (200 vs. 40 L m-2 h-1 average values). 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 external membrane was not exposed to light irradiation, permitted the recycle in the photoreactor of the not-photodegraded pollutant and produced a treated water (permeate) quality better than a submerged membrane. The obtained overall performance was 80% reduction of gemfibrozil concentration but it can be further improved by a fine tuning of the various parameters, as well as the operation can be of continuous type as required by many industrial applications.