An integrated flow reactor-membrane filtration system for heterogeneous photocatalysis. Part II: Experiments on the ultrafiltration unit and combined operation

A batch-recirculated photoreactor was combined with a hollow-fibre membrane ultrafiltration (UF) unit for heterogeneous photocatalysis applications. This paper focuses on the operation and modelling of the UF process component and on the performance of the integrated photoreactor-UF process assembly. Methylene blue and titanium dioxide (Degussa P-25) were used as the test pollutant and photocatalyst, respectively. The influence of cross-flow velocity, transmembrane pressure, and TiO2 dose on the permeate flux through the hollow fibre membrane is described. These data are modelled on the basis of concentration polarization and gel layer formation at the membrane surface/feed slurry boundary. The operation of the integrated photoreactor-UF assembly over ten repeat cycles is described. Photocatalyst separation was complete as gauged by nephelometric turbidity measurements. However, a systematic degradation in the photocatalyst performance was noted with each repeat cycle. Dynamic laser light scattering data are consistent with agglomeration of the TiO2 particles as a result of the UF process, and suggest a possible factor in the degraded photocatalytic activity. Possible solutions to this problem are finally presented.