Transformation of dissolved organic matter at molecular level during UV222/chlorine process

The krypton chloride (KrCl*) excimer lamp (222 nm) has become a novel light source used in UV-based advanced oxidation processes (UV-AOPs). Recently, a large number of studies have explored the application of UV 222 /chlorine process in water treatment. However, the transformation patterns of widely present dissolved organic matter (DOM) in water in this process is still unknown, especially at the molecular level. This study investigated the removal, component changes, and potential mechanisms of DOM during UV 222 /chlorine process, with humic acid as a typical DOM. The results showed that the removal efficiency of DOC and UV 254 by UV 222 /chlorine process can reach up to 56.0 % and 69.8 %, significantly higher than that of UV 222 alone and chlorine alone. Electron paramagnetic resonance (EPR) experiments have confirmed that HO•, Cl• and 1 O 2 are the main active species in the reaction. The formation of disinfection by-products (DBPs) was detected. Compared to the UV 254 /chlorine process, the UV 222 /chlorine process can significantly reduce the formation of DBPs, mainly due to the higher removal rate of DBPs precursors. The molecular changes of DOM were analyzed using FT-ICR MS method. The active species generated in the system can cause multi-pathway transformation of phenolic compounds, while the conversion of aliphatic substances can undergo dealkylation reactions. This study provides valuable insights into the molecular transformation of DOM in the Far-UVC/chlorine process, which will help promote the application of Far-UV technology in water treatment.