Bromide-Catalyzed Ozonation for Trace Urea Removal: pH-Dependent Kinetics, Catalytic Mechanisms, and Implications for Ultrapure Water Production

초록

Urea is a common organic compound present in natural and reclaimed waters, which poses challenges for ultrapure water (UPW) production because conventional treatment processes are insufficient to achieve the required low concentrations. This study systematically investigated the pH-dependent kinetics, mechanistic pathways, and byproduct formation during treatment with a bromide-catalyzed ozonation (O-3/Br-) process for urea (0.5-1 mu M) removal. In buffered systems, optimal performance was achieved at an [O-3](0):[Br-](0) molar ratio of 1:1-1.5:1, with complete urea removal within 20-30 min at 200/200 mu M dosing. To simulate practical conditions, unbuffered reclaimed reverse osmosis (RO) permeate (initial pH of 3.0-6.0) was evaluated. Pre-adjustment to mildly acidic conditions (pH approximate to 3.5) maintained ozone stability, minimized pH drift, and enabled nearly complete mineralization within 30 min, while suppressing bromate formation to <0.14 mu M (similar to 18 mu g/L). Mechanistic analyses revealed that in situ-formed free available bromine initially brominated urea to form ozone-reactive bromourea intermediates that were subsequently mineralized, radical pathways contributed negligibly, and bromide functioned catalytically. These findings elucidate the reaction chemistry and catalytic coupling mechanisms underlying enhanced urea degradation and define a practical operational window for controllable O-3/Br- implementation in advanced water treatment and UPW production systems.

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