Although chloramines are present during the ultraviolet-driven advanced oxidation processes (UV/AOPs) 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 (l = 254 nm). These results showed that the UV fluence-normalized rate of 1,4-dioxane degradation in UV/NH2Cl ranged between 6.7×10-5 and 2.1×10-4 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] 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. The NH2● radical has a negligible contribution to 1,4-dioxane degradation. The presence of dissolved oxygen further decreases NH2● reactivity. This study generated critical knowledge on the photochemistry of monochloramine and will allow for future optimization of UV/AOP for more efficient water reuse treatments.

Impact of the UV photolysis of monochloramine on 1,4-dioxane removal: New insights into potable water reuse

253rd National Meeting (2017)

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