Tube-in-tube membrane photoreactor as a new technology to boost sulfate radical advanced oxidation processes

This work proposes a tube-in-tube membrane photoreactor, operated in a continuous-mode, to boost the efficiency of peroxydisulfate (PDS), through the photolytic (UV-C radiation) and photocatalytic (TiO₂-P25) processes. This new technology can efficiently facilitate the transportation of PDS to the catalyst surface and water to be treated. The ultrafiltration tubular ceramic membrane was used as support for the TiO₂-P25 and oxidant-catalyst/water contactor. Tests were performed using a synthetic solution and a municipal secondary effluent, both spiked with a pharmaceutical mix solution (paracetamol (PCT), furosemide (FRS), nimesulide (NMD), and diazepam (DZP); 200 μg L^-1 of each). At steady-state regime, the UVC/S₂O₈^2-/TiO₂ system, with radial PDS addition, showed the highest removal of pharmaceuticals in both matrices. Furthermore, twenty-two transformation products (TPs) were identified by applying LC-QTOF MS technique. Hence, the transformation pathways including hydroxylation in aromatic moiety by an electrophilic attack, electron transfer reactions, cleavage of C-O, C-N bond, H-abstraction and ring opening were proposed. TPs chemical structures were evaluated by in silico (Q)SAR approach using TOXTREE and EPI Suite™ software.