Submerged photocatalytic membrane reactor with suspended and immobilized N-doped TiO2 under visible irradiation for diclofenac removal from wastewater

Abstract

A submerged photocatalytic membrane reactor (SPMR) was used with suspended and immobilized N–TiO2 under visible irradiation for diclofenac (DCF) removal from wastewater. The effects of initial N–TiO2 concentrations for the SPMR with suspended N–TiO2 were determined for batch processes. Hydrogen peroxide was also coupled with the photocatalytic process. In continuous conditions, a reverse osmosis (RO) membrane was combined with the SPMR for enhancing effluent quality. DCF removal by the SPMR with suspended and immobilized N–TiO2 at a low N–TiO2 dosage (0.5g/L) was not much different between the two systems, but increased with higher N–TiO2 dosages for the reactor with suspended N–TiO2. Coupling H2O2 with the photocatalytic process under visible irradiation enhanced the DCF removal efficiency. In continuous conditions, DCF concentrations in the photoreactor increased during the reaction time, while those in the effluent (RO permeate) were steady for both systems and both processes. The permeate flux in the reactor with suspended N–TiO2 declined faster than in the reactor with the immobilized N–TiO2. Coupling H2O2 with the photocatalytic process yielded more resistant permeate flux rates. The cake layer formed on the microfiltration membrane of the SPMR with suspended N–TiO2 under visible irradiation was denser than others after completing the process.