Impact of UV-LED photoreactor design on the degradation of contaminants of emerging concern

Abstract

Recent developments in UV-LED technology open up new possibilities for water treatment. TiO2 photocatalysis can benefit from optimized photoreactor design to increase hydroxyl radical production and reduce its electrical energy per order (EEO) demands, which still ranks high among advanced oxidation processes. However, literature on UV-LED photoreactor design is largely lacking. In this work, a detailed investigation of photoreactor design is proposed. The simulation of a lab scale cylindrical reactor with 8 different UV-LED arrays was run with the professional version of an optic software. The increase of radiant flux and irradiance on the reactor’s middle cross section and side walls, respectively, was related to an increasing number of LEDs and to a shorter distance from the reactor but not necessarily to an increase in homogeneity of light distribution. A full factorial experimental design was applied to evaluate the degradation of a representative contaminant of emerging concern (ciprofloxacin) considering 4 independent variables and their interactive effects on kinetic rates and EEO values. The significance of these effects was evaluated with ANOVA and a prediction model was established. The results show that the presence of a TiO2 nanofilm was the most significant tested effect. The number of LEDs, their distance from the reactor’s wall and the adoption of controlled periodic illumination also greatly influenced kinetic rates but were less relevant for reducing EEO values because the energetic trade-off was not sufficient to turn the kinetic gain into lower electricity demands.