Impact of the Ultraviolet Photolysis of Monochloramine on 1,4-Dioxane Removal: New Insights into Potable Water Reuse

Abstract

Although chloramines are ubiquitously present during ultraviolet-driven advanced oxidation processes (UV/AOP) that are becoming increasingly important for potable water reuse, the photochemistry of chloramines in treated wastewater, and the associated effects on trace chemical contaminant degradation, are unknown. This study investigated the fundamental radical chemistry involved in monochloramine (NH2Cl) photolysis and its efficiency in degrading 1,4-dioxane using a low-pressure Hg lamp (λ = 254 nm). These results showed that the UV fluence-normalized rate of 1,4-dioxane degradation in UV/NH2Cl ranged between 1.1 × 10–4 and 2.9 × 10–4 cm2·mJ–1. The photolysis of NH2Cl produced NH2 • and Cl•, which further transformed to a series of reactive radical species. An optimal NH2Cl dosage for 1,4-dioxane degradation was observed at a NH2Cl/1,4-dioxane concentration ratio of 8.0, while excess NH2Cl scavenged reactive radicals and decreased the treatment efficiency. Scavenging experiments and probe compound calculations showed that both Cl2 •– and HO• contributed significantly to 1,4-dioxane removal, while the NH2 • radical reacted slowly with 1,4-dioxane. The presence of dissolved oxygen further decreased NH2 • reactivity. This study generated critical knowledge of the photochemistry of NH2Cl and will allow for future optimization of the UV/AOP for more efficient water reuse treatments.

State of the Art of UV/Chlorine Advanced Oxidation Processes: Their Mechanism, Byproducts Formation, Process Variation, and Applications

“…Therefore, it is important to elucidate the reactivity of each radical species with chemical compounds for understanding the efficacy of UV/chlorine AOPs. Table 2 summarizes reaction rate constants of HO˙, Cl˙, ClO˙, and Cl 2˙− with some chemicals reported in literatures [18,[24][25][26][27][28][29][30][31][32]. HO˙ has second-order reaction rate constants with approximately 10 9 -order level regardless of saturated compounds or benzene derivatives.…”

“…An application of UV/NH 2 Cl process to 1,4-dioxane degradation revealed that Cl 2˙− and HO˙ mainly contributed to 1,4-dioxane degradation, and the reactivity of NH 2˙ was very limited [27]. Moreover, dissolved oxygen further decreased 1,4-dioxane degradation through the production of NO˙ that negligibly impacted 1,4-dioxane degradation.…”

Online monitoring of N-nitrosodimethylamine for the removal assurance of 1,4-dioxane and other trace organic compounds by reverse osmosis

“…[8][9][10][11] The former is a disinfection by-product occurring ubiquitously in reclaimed wastewater, 9,12 while the latter is a common industrial 49 solvent often accidentally released into the sewer and the environment. 13 Both NDMA and 1,4-dioxane are probable carcinogens and thus are regulated in potable water reuse applications. The occurrences of NDMA in RO permeate intended for potable water reuse have occasionally been reported 14,15 at above the NDMA notification levels (10 ng/L) by the authority in California, USA.…”

Medium‐Pressure UV/Chlorine Advanced Oxidation of Taste and Odor Compounds

“…Some radicals in this group are more selective in reactivity (Guo et al ), but ·Cl, for example, may still play a significant role in this process (Wang et al , Wu et al ). Other literature suggests that ·Cl may be eventually transformed into ·OH (Chuang et al , Patton et al ).…”