Direct photolysis at 184.9 nm: An underestimated pathway for organic micropollutant removal during VUV/UV treatment

“Vacuum UV (VUV, 184.9 nm)/UV (253.7 nm) irradiation is increasingly investigated for the removal of organic micropollutants (OMPs) from water. Commonly, degradation during VUV/UV treatment is attributed to hydroxyl radical (HO•)-mediated reactions, while the relative importance of direct VUV photolysis is assumed to be negligible. Here, we introduce and apply a novel methodology that differentiates and resolves the individual contributions of direct VUV photolysis, UV photolysis, and radical-induced degradation. Using controlled radical scavenging conditions, we systematically assessed degradation pathways for twenty representative OMPs. Direct VUV photolysis was found to constitute a substantial fraction of total removal. Under conditions suppressing radical reactions, VUV photolysis was estimated to be 63% and 25% of the total degradation of 1H-benzotriazole and paracetamol, respectively. Even under conditions favoring radical-induced degradation, VUV photolysis remained measurable and, for several compounds, non-negligible. The contribution of secondary radical species was additionally evaluated to refine mechanistic interpretation. Experiments conducted in tap water and canal water confirmed the relevance of VUV photolysis under realistic water matrices. These findings demonstrate that direct VUV photolysis represents a significant and currently underestimated pathway in VUV/UV treatment. The proposed methodology improves pathway-level mechanistic resolution and provides experimental evidence to inform future kinetic modeling and reactor design strategies in VUV-based water treatment.”

(Citation: Wang, Y., Wols, B.A., Lock Feixas, T., Gernjak, W. – Direct photolysis at 184.9 nm: An underestimated pathway for organic micropollutant removal during VUV/UV treatment – Journal of Water Process Engineering 90(2026)110450 – https://doi.org/10.1016/j.jwpe.2026.110450 – (Open Access))

© 2026 The Authors. Published by Elsevier Ltd. This is an open access article distributed under the terms of the Creative Commons CC-BY license