Comparison of Removal Characteristics of Organophosphorus Flame Retardants Using Ozone and UV-Based Advanced Oxidation Processes in the Downstream of Nakdong River

Abstract

Objectives This study aimed to evaluate the removal efficiency of trace organic contaminants (TrOCs) in UVbased advanced oxidation processes (AOPs) as an alternative to the post-ozonation process in a drinking water treatment plant (DWTP) in the downstream of Nakdong River. The results are expected to be utilized as basic data for modernizing aging water treatment facilities. Methods Eight organophosphorus flame retardants (OPFRs), known for their persistence and resistance to degradation, were selected as the target TrOCs for evaluating the efficiency of ozonation and UV-based AOPs. Experiments were conducted using sand-filtered water from a DWTP in the downstream of Nakdong River, with the OPFRs spiked into the sample matrix. Lab-scale experiments of ozonation and UV-based AOPs (UV, UV/H2O2, and UV/Cl2) were performed, and the concentrations of the OPFRs were analyzed using stir bar sorptive extraction (SBSE) system, followed by GC-MS/MS. Results and Discussion The second-order rate constants (kOH) for the reaction of OPFRs with OH radicals were estimated using the group contribution method and ranged from 1.4(±0.6)×109 to 1.8(±0.1)×1010 M⁻1 s⁻1, depending on their structural characteristics. In the ozonation process, the removal of Cl-containing aliphatic OPFRs was not effective, likely due to the electron-withdrawing effects of the -Cl groups, which inhibited their reactivity with both ozone and OH radicals. However, for non-Cl-containing aliphatic and aromatic OPFRs, more than 90% removal efficiency was achieved at a specific ozone dose of 1.5 mgO3/mgDOC. In the UV-based AOPs, the aliphatic OPFRs showed poor removal efficiency of 5~35% at a UV fluence of 1,000 mJ/cm2 under direct UV photolysis. However, in the presence of oxidants (H2O2 or free available chlorine), the UV/H2O2 process showed up to an 89% increase in removal efficiency, and the UV/Cl2 process exhibited up to a 49% increase. The difference in removal patterns between the UV/H2O2 and UV/Cl2 processes is likely attributed to the difference in reactivity between reactive chlorine species and aliphatic OPFRs. For aromatic OPFRs, direct UV photolysis achieved high enough removal efficiencies of 90~98% at a UV fluence of 1,000 mJ/cm2. These results demonstrate the potential of UV/H2O2 and UV/Cl2 processes for the effective removal of OPFRs, particularly for Cl-containing aliphatic OPFRs, which exhibited low removal efficiency in the ozonation process. Conclusion The comparative evaluation of removal efficiencies of OPFRs in ozone and UV-based AOPs confirmed the potential of UV processes for efficient removal of OPFRs. The UV/H2O2 and UV/Cl2 processes showed promise as alternative treatments to ozonation for the removal of OPFRs during drinking water treatment.

Keywords

• organophosphorus flame retardants
• advanced oxidation process
• ozone
• uv
• nakdong river