Competitive study of homogeneous and heterogeneous Fenton-like flow-through propoxur oxidation in ROC solution

Abstract

Reverse osmosis is used as a tertiary treatment for wastewater reclamation. However, sustainable management of the concentrate (ROC) is challenging, due to the need for treatment and/or disposal. The objective of this research was to investigate the efficiency of homogeneous and heterogeneous Fenton-like oxidation processes in removing propoxur (PR), a micro-pollutant compound, from synthetic ROC solution in a submerged ceramic membrane reactor operated in a continuous mode. A freshly prepared amorphous heterogeneous catalyst was synthesized and characterized, revealing a layered porous structure of 5–16 nm nanoparticles that formed aggregates (33–49 μm) known as ferrihydrite (Fh). The membrane exhibited a rejection of >99.6% for Fh. The homogeneous catalysis (Fe3+) exhibited better catalytic activity than the Fh in terms of PR removal efficiencies. However, by increasing the H2O2 and Fh concentrations at a constant molar ratio, the PR oxidation efficiencies were equal to those catalyzed by the Fe3+. The ionic composition of the ROC solution had an inhibitory effect on the PR oxidation, whereas increased residence time improved it up to 87% at a residence time of 88 min. Overall, the study highlights the potential of heterogeneous Fenton-like processes catalyzed by Fh in a continuous mode of operation. HIGHLIGHTS Propoxur removal from ROC solution in a submerged ceramic membrane reactor was studied.; Homogeneous (Fe3+) and heterogeneous (ferrihydrite) Fenton-like oxidation were compared.; While Fe3+ exhibited better catalytic activity than Fh, increased H2O2 and Fh concentrations led to similar PR removal as Fe3+.; Maximal PR removal of 87% was obtained at a residence time of 88 min.; The composition of the ROC inhibited the PR oxidation.;

Keywords

• ceramic membrane
• ferrihydrite
• micro-pollutants
• reverse osmosis concentrate
• submerged membrane reactor