The role of different DOMs in the degradation of ciprofloxacin under UV222 and UV222/percarbonate systems
Yanyan Liu, Bangxiao Zheng, Min Zhao, Feng Zheng, Xiaoqing Chen, Lei Wang
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 UV 222 /Sodium Percarbonate (UV 222 /SPC) and UV 222 . The results demonstrated that all three types of DOMs suppressed CIP degradation in UV 222 /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 UV 222 photolysis of CIP due to its high absorption coefficient at 222 nm, which promoted the generation of excited triplet state EOM ( 3 EOM*) and singlet oxygen ( 1 O 2 ) 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 NO 3 - promoted the degradation of CIP in UV 222 . 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 UV 222 /SPC, with the second-order rate constant of CO₃•⁻ with CIP measured at 4.79 × 10⁸ M⁻¹ s⁻¹ . UV 222 /SPC showed lower energy consumption than UV 254 /SPC in treating the real water sample. This study deepens the understanding of the impact of DOM in UV 222 water purification. • EOM promoted the degradation of CIP in UV 222 direct photolysis. • The organic matter in EOM rather than NO 3 - promoted the degradation of CIP in UV 222 . • CIP could be degraded effectively by UV 222 /SPC in the presence of HA and FA. • The energy consumption of UV 222 /SPC was lower than that of UV 254 /SPC for removing CIP in real water.