Comparison of Oxidants Used in Advanced Oxidation for Potable Reuse: Non-Target Analysis and Bioassays

Free chlorine (HOCl) and monochloramine (NH2Cl) are less-used oxidants than hydrogen peroxide (H2O2) in ultraviolet advanced oxidation processes (UV-AOPs) but have garnered interest from the water reuse industry and scientific community because they can be more costeffective than H2O2 and provide a protective disinfectant residual. The destruction of organic compounds, creation of UV-AOP byproducts, and change in toxicity during UV-AOP with H2O2, HOCl, NH2Cl, or ambient residual chloramine were evaluated in recycled wastewater by suspect and non-target screening as well as bioanalytical tests (bioassays). Ten compounds were identified in reverse osmosis (RO) permeate via suspect screening with removal near 100% by UV/H2O2 and UV/HOCl, greater than decomposition by UV/NH2Cl and UV/ambient (similar to 60%), based on suspect screening mass spectrometry peak area. Non-target analysis based on organic features in mixed-mode cation exchange cartridge extracts indicated that UV/H2O2 destroyed a similar or slightly greater fraction of organic compounds, formed fewer transformation products, and reduced the summed peak area of non-target features to the greatest extent. Fewer chlorinated byproducts were produced from the RO permeate treated by UV/H2O2 than exposure to the chlorine-containing oxidants. Addition of NH2Cl to RO permeate resulted in a slight increase in the bioassay oxidative stress response but dropped below the response limit for all samples after UV-AOP for all oxidants.

Automated summary

Free chlorine (HOCl) and monochloramine (NH2Cl) are cost-effective oxidants for water reuse and provide protection against residual contaminants. In UV advanced oxidation processes (UV-AOPs), UV/H2O2 and UV/HOCl were found to remove a greater fraction of organic compounds, form fewer transformation products, and reduce non-target features to the greatest extent compared to UV/NH2Cl and UV/ambient. Additionally, UV/H2O2 resulted in fewer chlorinated byproducts and a slight increase in the oxidative stress response in bioassays.