Molecular Characteristics and Formation Mechanisms of Unknown Ozonation Byproducts during the Treatment of Flocculated Nanofiltration Leachate Concentrates Using O and UV/O Processes.

Both ozone (O) and UV/O treatment processes can effectively remove organic matter in the flocculated membrane filtration concentrate from landfill leachate, but the ozonation byproducts (OBPs) generated in the processes remain unknown. Using electrospray ionization-coupled Fourier transform ion cyclotron resonance mass spectrometry (ESI FT-ICR MS), this study investigated the molecular characteristics of unknown OBPs and their formation mechanisms during the treatment of flocculated nanofiltration concentrate (FNFC) using the O and UV/O processes. The results showed that after being treated by the O and UV/O processes, the average value of the oxygen-to-carbon ratio (O/C) in the FNFC organic matter increased substantially from 0.49 to 0.61-0.64 and 0.63-0.71, respectively, with an O dosage of 13.4-54.4 mg/min. The main OBPs were CHO and CHON compounds, which were mainly produced through oxygenation (+O/+O and -H+O), oxidative deamination (-NH+O), decyclopropyl (-CH), and deisopropyl (-CH) reactions. The hydroxyl radical (OH) can intensify these reactions, resulting in an abundance of OBPs with a high oxidation degree and low molecular weight. OBPs at five / values were fragmented and analyzed with tandem mass spectrometry, and abundant hydroxyl groups, carboxyl groups, and carbonyl groups were tentatively identified, presenting a potential toxicity to aquatic organisms. Due to the high molecular diversity of the OBPs in FNFC, their lower Δ compared to natural fulvic acid, and potential toxicity, their impact on the water environment should be given more attention.