The role of different DOMs in the degradation of ciprofloxacin under UV222 and UV222/percarbonate systems

Abstract

The effectiveness of ultraviolet advanced oxidation processes (UV-AOPs) was influenced by the prevalence of dissolved organic matter (DOM) in natural water bodies. This study investigated the impact of humic acid (HA), fulvic acid (FA), and extracellular organic matter (EOM) on the degradation of Ciprofloxacin (CIP) by UV₂₂₂/Sodium Percarbonate (UV₂₂₂/SPC) and UV₂₂₂. The results demonstrated that all three types of DOMs suppressed CIP degradation in UV₂₂₂/SPC, with EOM exhibiting stronger inhibitory effects than HA and FA. This suppression primarily arose from DOM's light-shielding properties and scavenging of hydroxyl radicals (•OH) and carbonate radicals (CO₃•⁻), which outweighed the compensatory effects of DOM-photosensitized reactive species. In contrast, EOM enhanced direct UV₂₂₂ photolysis of CIP due to its high absorption coefficient at 222 nm, which promoted the generation of excited triplet state EOM (³EOM*) and singlet oxygen (¹O₂) via photosensitization. These reactive species compensated for EOM’s light-shielding effect, enabling efficient indirect photodegradation of CIP. The organic matter in EOM rather than NO₃^- promoted the degradation of CIP in UV₂₂₂. The fluorescence spectra and dissolved organic carbon (DOC) changes of DOM were analyzed in depth. In addition, both CO₃•⁻ and •OH contribute to CIP degradation in UV₂₂₂/SPC, with the second-order rate constant of CO₃•⁻ with CIP measured at 4.79 × 10⁸ M⁻¹ s⁻¹ . UV₂₂₂/SPC showed lower energy consumption than UV₂₅₄/SPC in treating the real water sample. This study deepens the understanding of the impact of DOM in UV₂₂₂ water purification.