A new combination of a membrane and a photocatalytic reactor for the depollution of turbid water

This paper describes the combination of a dialysis membrane and a photocatalytic reactor into an original membrane photoreactor (MPR) to mineralize organic compounds contained in artificial turbid waters which are obtained by using natural clay named bentonite. Various systems have been described in the literature, combining photocatalysis with pressure-driven membrane techniques, such as nanofiltration (NF) and ultrafiltration (UF), but these systems can lead to membrane fouling. Only the combination of photocatalysis and membrane distillation avoids this problem, but it needs energy to reach pervaporation phenomena. The MPR system presented here works at ambient temperature, with the membrane used as a barrier for particles and to extract the organic compounds from the turbid water without transmembrane pressure. Thus, we were able to separate the polluted turbid water from the photoreactor compartment and to separate TiO2 continuously from the treated water. The photocatalytic reaction and dialysis were studied separately before the MPR process was developed. A model pollutant, 2,4-dihydroxybenzoic acid (2,4-DHBA), was mineralized from turbid waters by photocatalysis. By means of the membrane, the TiO2 remained in the photoreactor compartment without filtration and bentonite was kept away from the photoreactor.A mathematical model, based on diffusion through the membrane, with zero-order reaction in the reactor, is in good agreement with the experimental data.