A tubular ceramic membrane coated with TiO2-P25 for radial addition of H2O2 towards AMX removal from synthetic solutions and secondary urban wastewater

Abstract

This work aims to integrate several hydrogen peroxide (H₂O₂) activation mechanisms, photolysis (UVC irradiation), chemical electron transfer (TiO₂-P25 photocatalysis), and reaction with TiO₂-P25 in dark conditions, for reactive oxygen species (ROS) generation towards the removal of contaminants of emerging concern (CECs), in a single unit operated in continuous-flow mode. An H₂O₂ stock solution is fed by the lumen side of a tubular ceramic membrane, delivering the oxidant to the (i) catalyst immobilized in the membrane shell-side and (ii) annular reaction zone (ARZ, space between membrane shell-side and outer quartz tube) where CECs contaminated water flows with a helix trajectory, being activated by UV light provided by four lamps placed symmetrically around the reactor. First, the effect of several parameters in the removal of a CEC target molecule, amoxicillin (AMX), was evaluated using a synthetic solution ([AMX]_inlet = 2.0 mg L^-1): (i) light source (UVA or UVC radiation), (ii) H₂O₂ dose, (iii) H₂O₂ injection method (radial permeation vs. upstream injection), and (iv) number of TiO₂-P25 layers deposited on the membrane. The UVC/H₂O₂/TiO₂ system with radial addition of H₂O₂ (20 mg L^-1) and 9-TiO₂-P25 layers provided the highest AMX removal efficiency (72.2 ± 0.5%) with a UV fluence of 45 mJ cm^-2 (residence time of 4.6 s), due to the synergic effect of four mechanisms: (i) AMX photolysis, (ii) H₂O₂ photocleavage, (iii) TiO₂-P25 photoactivation, and (iv) chemical reactions between H₂O₂ and TiO₂-P25. The urban wastewater matrix showed a negative effect on AMX removal (~44%) due to the presence of ROS scavengers and light-filtering species.

Keywords: Amoxicillin; Hydrogen peroxide; Photocatalysis; Tube-in-tube membrane reactor; UVC/H2O2.