Evaluation of the Degradation Performance of Pharmaceuticals in Environmental Water by Multi-wavelength UV Irradiation and the Estimation of their Degradation Pathways

Abstract

UV-LEDs are a promising technology to degrade pharmaceuticals in water. However, to consider the installation of a UV-LED system to actual treatment systems, the degradation by-products of pharmaceuticals, their toxicities, and their degradation pathways should be better understood to determine optimal UV irradiation conditions. In addition, it is necessary to estimate the impact of co-existing substances such as nitrate ion (NO₃⁻) and dissolved organic matter (DOM). We analyzed degradation by-products of five common pharmaceuticals by high resolution mass spectrometry, and ion chromatography to understand the decomposition mechanisms of pharmaceuticals in Milli-Q water and evaluated the influence of NO₃⁻ and DOM in environmental water in UV-LED degradation experiments. The results showed that pharmaceutical degradation percentage was nearly 100% for most of the target compounds (except ibuprofen) in Milli-Q water. Additionally, a part of the degradation mechanism of sulfamethoxazole was clarified. It is suggested that UV absorption occurred at the benzene ring and transfer energy resulted in S-N bond cleavage via homolysis. UV irradiation in the presence of DOM or NO₃⁻ promoted the dichlorination reaction by the photosensitizing effect of chlorinated organic compounds such as diclofenac and triclosan, suggesting that 280 nm irradiation is effective for the degradation of pharmaceuticals in water treatment.