Photocatalytic membrane reactor performance towards oxytetracycline removal from synthetic and real matrices: Suspended vs immobilized TiO2-P25

Integrated hybrid systems coupling microfiltration (MF) with UVA photolysis (UVA-MF) or TiO2-P25 photocatalysis (UVA/TiO2-MF) were investigated for the removal of oxytetracycline (OTC) from synthetic (ultrapure water-UPW) and real (secondary effluent from an urban wastewater treatment plant-UWW) matrices, both spiked with 5 mg L-1 of OTC. The photocatalytic membrane reactor (PMR) was tested both using the TiO2-P25 nanoparticles in suspension or immobilized on the external surface of the membrane - nano-engineered membrane (NEM). In all cases, reaction occurs only inside the membrane module. The effect of transmembrane pressure (TMP) (1.0-2.0 bar) and of TiO2-P25 loading (0.1-0.4 g L-1) in slurry conditions, on the efficiency of the photocatalytic UVA/TiO2-MF system was investigated. Additionally, OTC oxidation efficiency was evaluated as a function of the amount of TiO2-P25 deposited on the external surface of the ceramic MF membrane. The membrane ensured the retention of TiO2-P25 particles, when using the PMR catalyst slurry system. The higher OTC removal efficiency (> 90% of antibiotic removal after 30 min) as well as the higher permeate flux decline (66% after 5 h) were observed when using the highest TiO2-P25 loading. The NEM contributed to the in-situ OTC and by-products oxidation, improving its antifouling properties, and, consequently, leading to a low permeate flux decline (8% after 5 h) when using UPW as solution matrix. However, a permeate flux decline of 66% was observed for UWW-NEM after the same reaction time. Despite the advantages of NEM, the OTC removal efficiency was higher when using TiO2-P25 slurry due to the higher photocatalyst surface area. Nevertheless, the NEM showed a good stability of the catalyst thin film during 3 consecutive reaction cycles.