The high costs of waste management and adverse environmental impact associated with the disposal of reverse osmosis (RO) concentrates hinder the wide application of RO-based systems for potable reuse of municipal wastewater effluent. This study investigates four UV-based treatment options for RO concentrate from a municipal potable reuse facility: direct UV irradiation at 254 nm and three UV-based advanced oxidations processes (AOPs) using hydrogen peroxide, free chlorine, and persulfate. Dissolved organic matter (DOM) from RO concentrates was characterized using parallel factor analysis (PARAFAC). The final four-component consisted of two terrestrial humic-like components (C1 and C3), one wastewater/nutrient tracer component (C2) and a protein-like (tyrosine-like) component (C4). All components displayed pseudo-first order kinetics in UV-only systems, with C3 being most photolabile, followed by C2, C4, and C1, respectively. For the three UV-AOPs tested, the degradation rates observed for each component were a function of UV fluence, oxidant dose, and bulk DOM loading (i.e., dilution factor of RO concentrate). In general, UV-H₂O₂ and UV-S₂O₈^2- had comparable performance in degradation; UV-Cl₂ was the least effective UV-AOP. A chemical probe-based analysis was used to estimate the steady-state concentrations of primary reactive species; hydroxyl radical (HO) was the dominant species in all UV-AOPs, despite the formation of reactive chlorine- and sulfur- species. The photodegradation trends in UV and UV-AOPs for C2 and C4 suggested that the chemical behavior of these components was dominated by chemical moieties that were susceptible to reactive oxygen species (HO) but not to reactive chlorine species. Furthermore, C3, the visible range humic-like component, was sensitive to all primary reactive species generated in the three UV-AOPs tested. Compared to other components, C1 (UV humic -like component) was relatively recalcitrant in all treatment scenarios tested. The outcomes of this study provide a foundation for understanding RO concentrate reactivity in UV-based treatment technologies, to ultimately improve the sustainability of water reuse systems.

Haizhou Liu

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