Submerged membrane photocatalytic reactor for advanced treatment of p-nitrophenol wastewater through visible-light-driven photo-Fenton reactions

Abstract

A submerged membrane photocatalytic reactor (SMPR) was constructed for the advanced treatment of p-nitrophenol (PNP) wastewater and rapid recycling of powdery catalyst, including a suspended photocatalytic system and a submerged microfiltration (MF) membrane system. To evaluate the performance of the SMPR, a visible-light responsive Fe(III)-ZnS/g-C3N4 photo-Fenton catalyst was successfully synthesized by the microwave hydrothermal method, and several techniques were used to characterize the resulting catalyst. The key operation factors on the wastewater treatment efficiency were successively optimized. When the influent PNP concentration was 10 mg·L−1, initial pH was 5, catalyst dosage was 1.0 g·L−1, H2O2 concentration was 170 mg·L−1, aeration rate was 0.50 m3·h−1, and operation time was 4 h, the PNP removal rate was 91.6% by the SMPR under simulated solar light irradiation. The rejection rate of the catalyst by the MF membrane was 100%, which realized the rapid separation and recycling of the suspended catalyst powders and avoided the catalyst loss and secondary pollution. The toxicity calculation results of PNP and its possible degradation products indicated that the toxicity of PNP wastewater decreased overall after the visible-light-driven photo-Fenton reactions. This study provided a combined photocatalysis-membrane filtration process that had a high treatment efficiency of refractory wastewater and solved the problem about the separation and recycling of the powdery catalyst synchronously.