Unveiling the degradation behavior of naproxen in an enhanced UV222 advanced oxidation system: Mechanisms, efficiency gains, and actual water applicability.

Ultraviolet radiation at 222 nm (UV222) emitted by KrCl excimer lamps is free of mercury∗ and has demonstrated promising potential as an advanced oxidation source for micropollutant control. However, its photochemical behavior within complex aquatic environments remains insufficiently understood. This study systematically evaluated the removal efficiency and underlying mechanisms of UV222 and its coupled systems, specifically UV222 with H2O2 and UV222 with peroxymonosulfate (PMS), for the degradation of refractory naproxen (NPX). UV222 exhibited superior intrinsic photolysis capabilities attributed to its high photon energy. Furthermore, the introduction of H2O2 and PMS significantly enhanced radical generation due to their strong absorption of UV222 Under optimal dosages, the NPX degradation rate constants were elevated to 0.26 min-1 and 0.25 min-1, respectively. Conversely, excessive oxidants induced radical self scavenging and reaction inhibition. In contrast to UV254, nitrate functioned as an efficient photosensitizer under UV222 irradiation, generating reactive nitrogen species and hydroxyl radicals that boosted the degradation rate to 0.55 min-1. However, humic acid (HA) inhibited the degradation process through inner filter effects and radical quenching mechanisms. LC-MS analysis identified four primary degradation pathways, including naphthalene ring hydroxylation, decarboxylation, and ring opening reactions. ECOSAR modeling confirmed a reduction in both acute and chronic ecotoxicity. Moreover, the process maintained high efficiency across three actual lake and reservoir water matrices, verifying its robust adaptability. This study elucidates the reaction mechanisms and environmental applicability of UV based AOPs, providing theoretical support for replacing traditional UV technologies containing mercury.