Advancement of Urea Elimination Using Pre-Halogenation Processes in UV254/Bromine and UV254/Chlorine Systems

Abstract

This study evaluated the efficiency and practical applicability of an advanced oxidation process (AOP) that combines pre-halogenation using bromine or chlorine with ultraviolet (UV) irradiation for the effective removal of urea in ultrapure water (UPW) production systems. The removal of trace-level urea, a refractory nitrogenous compound, is essential to meet the stringent water quality requirements of the semiconductor and pharmaceutical industries—yet conventional water treatment methods are often inadequate. To address this challenge, this study developed a pre-halogenation approach wherein urea was converted into highly UV-reactive N-halogenated intermediates (i.e., chloroureas and bromoureas) via chlorination or bromination, followed by rapid photolytic degradation under UV exposure. Experimental results demonstrated that the pre-halogenation + UV process significantly outperformed conventional treatment strategies. Bromine-based pre-treatment showed superior removal efficiencies over a broad pH range compared to chlorine-based systems. Complete urea elimination (~100%) was achieved under optimized conditions ([bromine]₀/[urea]₀ = 2–5, pre-contact time = 10–60 min). Even with short pre-bromination times (1–10 min), sufficient accumulation of intermediates allowed for fast and efficient urea degradation. Under low initial urea concentrations (1 μM), effective removal was still achieved within 10 minutes by maintaining appropriate bromine dosing. Moreover, the process exhibited high efficiency with relatively low UV energy input, indicating substantial economic and environmental advantages. Overall, this study demonstrates that the integration of bromine-based pre-halogenation with UV irradiation is a highly effective and sustainable AOP for urea removal in UPW applications. Future work should focus on optimizing operational parameters and evaluating long-term stability under realistic system conditions to facilitate full-scale implementation.