Growing concerns over water scarcity has increased interest in treating wastewater for reuse. For potable reuse, full advanced treatment (FAT) typically consists of microfiltration, reverse osmosis (RO), and UV-based advanced oxidation processes (AOPs). Chloramines, which are added to prevent biofouling, can pass through RO membranes to enter UV-AOP reactors. The purpose of this study was to evaluate treatment efficiency of UV-hydrogen peroxide (H2O2) system impacted monochloramine (NH2Cl), using six model trace contaminants (1,4-dioxane, acetone, atenolol, caffeine, N,N-diethyl-meta-toluamide, and trichloroethylene) relevant in water reuse scenarios. Bench-scale experiments conducted in UV-, UV-H2O2, UV-NH2Cl, and UV-H2O2-NH2Cl indicated antagonistic effect of mixed oxidants associated with scavenging of reactive species: hydroxyl radicals (HO*) and reactive chlorine species (RCS) such as, chlorine atom (Cl*) and chlorine dimer (Cl2*-). A competition kinetics approach using probe compounds was used to determine second order rate constants for reaction of relevant contaminants with radicals identified above. These findings were used to evaluate treatment efficiency of a pilot-scale UV-AOP reactor in an FAT water reuse system. Experiments for all compounds were conducted in RO permeate by varying [NH2Cl] (0-8 mg/L as Cl2) and [H2O2] (0-6.5 mg/L) at UV fluences comparable to full scale plant (~800-900 mJ/cm2). Overall, increase in [NH2Cl] at a given [H2O2] resulted in decrease in log removal of target compounds due to scavenging of HO* by mixed oxidants; scavenging by RO permeate was not found to be significant. For a fixed [NH2Cl], increase in [H2O2] increased the log removal of target compounds, although the relative increase in log removal was dependent on [NH2Cl]. These results indicate that, although NH2Cl can degrade trace contaminants in UV-AOP system in absence of H2O2, presence of NH2Cl is not favorable in UV-H2O2 treatment in the tested RO permeate. Furthermore, increase in H2O2 at high NH2Cl levels provide limited increase in log removal efficiency of trace contaminants. Findings from this study will be used to optimize UV-based systems for safe, reliable, and efficient water reuse treatment to facilitate the removal of low levels of ubiquitous organic contaminants, enabling timely response towards addressing water scarcity in arid and drought-stricken regions.

New insight into removal of trace organic contaminants in chloramine-impacted UV-H2O2 system for water reuse

2019 Spring National Meeting

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