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

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.

Micropollutants removal by full-scale UV-C/sulfate radical based Advanced Oxidation Processes.

The high chemical stability and the low biodegradability of a vast number of micropollutants (MPs) impede their correct treatment in urban wastewater treatment plants. In most cases, the chemical oxidation is the only way to abate them. Advanced Oxidation Processes (AOPs) have been experimentally proved as efficient in the removal of different micropollutants at lab-scale. However, there is not enough information about their application at full-scale. This manuscript reports the application of three different AOPs based on the addition of homogeneous oxidants [hydrogen peroxide, peroxymonosulfate (PMS) and persulfate anions (PS)], in the UV-C tertiary treatment of Estiviel wastewater treatment plant (Toledo, Spain) previously designed and installed in the facility for disinfection. AOPs based on the photolytic decomposition of oxidants have been demonstrated as more efficient than UV-C radiation alone on the removal of 25 different MPs using low dosages (0.05-0.5 mM) and very low UV-C contact time (4-18 s). Photolysis of PMS and H2O2 reached similar average MPs removal in all the range of oxidant dosages, obtaining the highest efficiency with 0.5 mM and 18 s of contact time (48 and 55% respectively). Nevertheless, PMS/UV-C reached slightly higher removal than H2O2/UV-C at low dosages. So, these treatments are selective to degrade the target compounds, obtaining different removal efficiencies for each compound regarding the oxidizing agent, dosages and UV-C contact time. In all the cases, H2O2/UV-C is more efficient than PMS/UV-C, comparing the ratio cost:efficiency (€/m3·order). Even H2O2/UV-C treatments are more efficient than UV-C alone. Thus, the addition of 0.5 mM of H2O2 compensates the increased of UV-C contact time and therefore the increase of electrical consumption, that it should be need to increase the removal of MPs by UV-C treatments alone.