Simulated solar photocatalytic ozonation of contaminants of emerging concern and effluent organic matter in secondary effluents by a reusable magnetic catalyst

Abstract A magnetic TiO2/Fe3O4/activated carbon composite was used as a photocatalyst for the removal of contaminants of emerging concern (CECs) and effluent organic matter (EfOM) of real and simulated effluents from municipal wastewater treatment plants (MWWTPs). While the catalyst showed limited activity under simulated solar irradiation in the absence of ozone, the CECs were completely eliminated and dissolved organic carbon (DOC) removal efficiencies reached up to more than 75% by simulated solar photocatalytic ozonation. The effects of EfOM (0-30 mg·L-1 DOC), carbonate/bicarbonate (0-60 mg·L-1 IC) and PO4-P (0-3.5 mg·L-1) concentrations of the secondary effluent on the photocatalytic activity was studied. Both EfOM and carbonate/bicarbonate concentration accelerated the DOC removal in single ozonation experiments (i.e., absence of catalyst and radiation) due to the presence of initiators of the hydroxyl radical chain, the formation of secondary oxidants (i.e., hydrogen peroxide and carbonate radical) and the buffering capacity of the effluent. However, the interaction of EfOM and carbonate/bicarbonate with the catalyst brought about a decrease of its photocatalytic activity. Phosphates, in the concentration range studied, did not influence appreciably the catalytic activity. The reusability of the catalyst was evaluated through eight consecutive simulated solar phototacalytic ozonation runs. Samples of fresh and reused catalysts were examined by bulk composition analysis, N2 adsorption-desorption isotherms, XRD, XPS, SQUID magnetometry and the pHPZC. Despite some changes in the porous structure and the fixation of some oxygen groups on the carbon surface as a result of ozonation, the catalyst showed good stability and the oxidation efficiency was maintained through runs.