Formation Mechanisms of Chlorinated Organic Compounds During Electrochemical Oxidation of Biologically Treated Landfill Leachate: A Comparative Study Using RuO2–IrO2/Ti, SnO2–Sb2O5/Ti, and IrO2–Ta2O5/Ti Anodes

Chlorine-containing organic wastewater from landfills generates chlorinated oxidation byproducts (Cl-OBPs) of an unknown structure during electrochemical oxidation, posing a potential environmental threat. Using ultrahigh-resolution mass spectrometry, the formation mechanisms of unknown Cl-OBPs were investigated during the treatment of biologically treated landfill leachate (BTL) via common dimensionally stable anode systems. During the early stage of electrolysis (0–30 min), the RuO 2 –IrO 2 /Ti system generated 2678 Cl-OBP molecules, the SnO 2 –Sb 2 O 5 /Ti system generated 2884 molecules, and the IrO 2 –Ta 2 O 5 /Ti system generated 3132 molecules. These mainly featured high-oxygen, highly unsaturated phenolic and aliphatic structures. When the electrolysis time was prolonged to 120 min, Cl-OBPs were not effectively removed, although their degree of oxidation increased, while aromaticity and unsaturation decreased. In the RuO 2 –IrO 2 /Ti and IrO 2 –Ta 2 O 5 /Ti systems, Cl – is converted to HOCl/OCl – primarily through direct electron transfer. However, in the SnO 2 –Sb 2 O 5 /Ti system, reactive chlorine species (RCSs) are formed through both a radical-mediated chain reaction and direct electron transfer pathways. When RCSs act on organic compounds in BTL, transformation mainly occurs through chlorine substitution/addition, accompanied by other oxidation reactions. These findings provide a theoretical basis for electrode selection and process optimization in the treatment of chlorine-containing organic wastewater.