Hybrid Ultrafiltration/Photocatalytic Membranes for Efficient Water Treatment

The development of hybrid materials exhibiting the simultaneous action of photocatalysis and membrane filtration can lead to improved water treatment processes. Photocatalysis has the potential to solve problems related to the fouling of membranes, the generation of toxic condensates, and the existence of very small and harmful organic pollutants in the permeate effluent. On the other hand membranes, especially the ceramic ones, are appropriate supports for the deposition of thin photocatalytic layers due to their high affinity with the photocatalyst (e g, TiO2) and the possibility to further stabilize and activate the deposit with calcination. In addition, membranes exhibit two surfaces that come into contact with the polluted water and can be exploited for the photocatalyst deposition. Thus, with appropriate design of the membrane module it is possible to illuminate both membrane surfaces and develop very efficient photocatalytic ultrafiltration processes. Such processes must involve "double sided active photocatalytic membranes", where the pollutant undergoes two sequential photodegradation steps, the first in contact with the feed surface and the second in contact with the permeate surface of the membrane. Moreover the asymmetric pore structure of ceramic membranes assures proper mixing of the fluid and better contact with the porous photocatalytic layers. In this work double side active photocatalytic ultrafiltration (UF) membranes were developed by means of different chemical vapor deposition (CVD) techniques. Their performance in the 'elimination of methyl orange from water was elucidated by means of a prototype photocatalytic membrane reactor under continuous flow, applying UV irradiation on both membrane surfaces. Important aspects of membrane technology such as the evolution of water permeability and the energy consumption were compared with the standard and highly efficient nanofiltrafion (NF) process and the results indicated the beneficial effects of the hybrid UF/photocatalytic process.