Heterogeneous photocatalytic degradation of pharmaceuticals in synthetic and real matrices using a tube-in-tube membrane reactor with radial addition of H2O2.

A tube-in-tube membrane reactor, with radial addition of hydrogen peroxide, was used for the oxidation of four pharmaceuticals, paracetamol (PCT), furosemide (FRS), nimesulide (NMD), and diazepam (DZP), in a continuous-mode operation, using photochemical and photocatalytic processes, driven by UVA or UVC photons. This reactor allows a controlled titration of small H2O2 doses (inside-out mode) to the catalyst particles immobilized in the membrane shell side and to the annular space between the membrane inner tubing and the concentric outer quartz tubing, where water to be treated flows. Tests were performed using synthetic (SWW) and real (urban wastewater after secondary treatment) (UWW) matrices, both spiked with the pharmaceutical mix solution (200 µg L-1 of each). The photochemical and photocatalytic oxidation efficiency was evaluated as a function of H2O2 dose (5-20 mg L-1), oxidant injection mode (radial permeation vs injection upstream from the reactor inlet), light source (UVA vs UVC lamps) and aqueous matrix (synthetic vs real matrix). At steady-state regime, the UVC/H2O2/TiO2 system, with radial H2O2 addition (20 mg L-1), showed the highest pharmaceuticals removal percentage, PCT (27.4%), FRS (35.0%), NMD (24.2%) and DZP (30.0%) in SWW. A substantial decrease in pharmaceuticals elimination was observed for UWW (PCT - 11.5%, FRS - 20.3%, NMD - 8.2% and DZP - 12.6%), in comparison with the SWW matrix. Finally, twelve transformation products (TPs) were identified; most of them showed in their structures hydroxylation in aromatic moiety; all TPs chemical structures were evaluated by BIOWIN software indicating that the TPs are non-biodegradables.