Application of a micro-meso-structured reactor (NETmix) to promote photochemical UVC/H2O2 processes – oxidation of As(iii) to As(v)

Abstract

A micro-meso-structured reactor (NETmix) was used for the first time to promote photochemical UVC/H₂O₂ processes. The NETmix photoreactor consists of a network of chambers and channels, where the liquid flows, sealed with a quartz slab with high UVC transparency. Due to the small size of channels and chambers, the NETmix presents a uniform irradiance through the entire reactor depth, short molecular diffusion distances and large specific interfacial areas, maximizing the pollutant/oxidant contact. In this study, the NETmix photoreactor was evaluated for As(III) oxidation to As(V) using a photochemical UVC/H₂O₂ system. The effect of the UVC lamp power (4, 6 or 11 W), the number of UVC lamps (2 or 3 lamps) and the UVC lamp layout (parallel or perpendicular to the flow direction) was evaluated, in order to ensure uniform irradiation of the entire reaction mixture. The optimum H₂O₂ concentration for each light distribution system was also evaluated. At the best configuration, 3 lamps of 11 W positioned parallel to the flow direction, total As(III) oxidation ([As(III)]₀ = 1.33 × 10⁻² mM) was achieved in 15 min with an absorbed photon flux density of 1.9 × 10⁻¹ einstein per m³ per s. Significant differences were highlighted between the photon flux actually received in the photoreactor and the radiant power emitted by the lamp. A kinetic model able to represent the As(III) oxidation employing UVC radiation and H₂O₂ in a micro-meso-structured reactor was presented. The photochemical space time yield (PSTY) values obtained for the micro-meso-structured reactor are higher than for conventional batch reactors, showing that the NETmix technology can be a good solution for application in photochemical processes.