UV-based advanced oxidation of dissolved organic matter in reverse osmosis concentrate from a potable water reuse facility: A Parallel-Factor (PARAFAC) analysis approach

Disposal of reverse osmosis concentrate (ROC) from advanced water purification facilities is a challenge associated with the implementation of reverse osmosis-based treatment of municipal wastewater effluent for potable reuse. In particular, the dissolved organic matter (DOM) present in ROC diminishes the quality of the receiving water upon environmental disposal and affects the toxicity, fate, and transport of organic contaminants. This study investigates UV-based advanced oxidation processes (UV-AOPs) for treating DOM in ROC using a Parallel Factor Analysis (PARAFAC) approach. DOM composition and degradation were tested in UV-only and three UV-AOPs using hydrogen peroxide (H2O2), free chlorine (Cl-2), and persulfate (S2O82-). The four-component PARAFAC model consisted of two terrestrial humic-like components (C-UVH and C-VisH), a wastewater/nutrient tracer component (C-NuTr), and a protein-like (tyrosine-like) component (C-PrTy). Based on the observed loss in the maximum fluorescence intensity of the components, DOM degradation was determined to be dependent on UV fluence, oxidant dose, and dilution factor of the ROC (i.e., bulk DOM concentration). C-VisH was most the photolabile component in the UV-only system, followed by C-NuTr, C-PrTy, and C-UVH, respectively. Furthermore, UV-H2O2 and UV-S2O82- displayed faster overall reaction kinetics compared to UV-Cl-2. The degradation trends suggested that C-NuTr and C-PrTy consisted of chemical moieties that were susceptible to reactive oxygen species (HO center dot) but not reactive chlorine species; whereas, C-VisH was sensitive to all reactive species generated in the three UV-AOPs. Compared to other components, C-PrTy was recalcitrant in all treatment scenarios tested. Calculations using chemical probe-based analysis also confirmed these trends in the reactivity of DOM components. The outcomes of this study form a foundation for characterizing ROC reactivity in UV-AOP treatment technologies, to ultimately improve the sustainability of water reuse systems.

Automated summary

The disposal of reverse osmosis concentrate (ROC) from advanced water purification facilities poses a challenge in treating municipal wastewater effluent for potable reuse. This study investigates UV-based advanced oxidation processes (UV-AOPs) for treating dissolved organic matter (DOM) in ROC, revealing that DOM degradation is dependent on UV fluence, oxidant dose, and ROC dilution factor. UV-H2O2 and UV-S2O82- showed faster reaction kinetics compared to UV-Cl-2, suggesting potential for improving the sustainability of water reuse systems.