Overcoming limitations in photochemical UVC/H2O2 systems using a mili-photoreactor (NETmix): Oxytetracycline oxidation

Abstract This study focuses on the intensification of a photochemical UVC/H 2 O 2 system using a mili-photoreactor (NETmix) for a better and faster elimination of oxytetracycline (OTC) from urban wastewater. This mili-photoreactor comprises a network of small cylindrical chambers and prismatic transport channels sealed by a UVC transparent quartz slab allowing unique properties. Since light has a profound effect on the photochemical process, UVC photons distribution over the reaction medium was investigated using a multiple UVC lamp design (4, 6 or 11 W) allocated in parallel or perpendicular to the solution movement. In addition, the effect of other operating variables, such as oxidant dosage (100–900 mg L −1 ), oxidant feed configuration (single entry or continuous multi-injection) and flow rate (50–100 L h −1 ) was studied. A kinetic model able to describe the OTC oxidation by the UVC/H 2 O 2 photochemical system in the mili-photoreactor was also developed. Moreover, matrix effect was evaluated by spiking OTC in a secondary effluent from an urban WWTP. In this case, OTC degradation was inhibited in about 2 to 3 times due to the presence of organic/inorganic substances (soluble and particulate), inherent to the real matrix, that act as scavenger of oxidant species and as UVC light filter. The NETmix mili-photoreactor presented high photochemical space time yield (PSTY) values when compared with a conventional tubular photoreactor. This highlights the NETmix capacity to enhance UVC/H 2 O 2 processes through an homogeneous light distribution over the entire reaction medium.