Photochemical transformation of dissolved organic matter: source, particulate matter interaction and disinfection...

Photochemical reaction is one of the dominant drivers shaping the molecular identity and ecological fate of dissolved organic matter (DOM). However, the influence of co-occurring particulate matter on these transformation processes and the consequent implications for drinking water safety are not yet fully understood. This study addresses this knowledge gap by coupling high-resolution mass spectrometry and optical analyses to track the evolution of DOM from diverse sources during simulated solar irradiation. The role of particulate matters was further investigated by dosing wastewater with common mineral particles (hematite, montmorillonite and goethite). Results revealed that heteroatom-enriched DOM exhibited high photochemical reactivity, and anthropogenic DOM yielded distinctive molecular products characterized by high O/C and low H/C ratios. Particle addition markedly influenced the photo-induced change of polyphenolics, condensed aromatics and peptide-like molecules, with the extent and direction of change strongly dependent on particle properties. Following irradiation, the total trihalomethane (THM) formation potential increased across all samples, although the trends for individual THM species varied with DOM source. The impact of particles on disinfection byproducts formation potential was particle-specific. Unsaturated compounds rich in oxygen were identified as positive contributor to THM formation and sulfur-containing molecules and SUVA₂₅₄ were negatively influential indicators. These findings provide new mechanistic insights into DOM photochemistry and its broader environmental implications.