Precise regulation of UV/H2O2 processes: •OH generation/reaction and DOM transformation as the main free radical scavenger

The widespread application of UV/H 2 O 2 is limited by the empirical operational practices, which can lead to excessive energy, chemical input and the generation of uncontrollable by-products. This study presents a precise regulation approach based on the characteristics of free radical generation/reaction and the chemical transformation of organics, assessed through a pilot experiment. The findings indicated that increasing H 2 O 2 dosage was more effective than increasing UV dose in enhancing •OH generation and pollutant removal. As the H 2 O 2 dosage and UV dose increased, the relative influence of water quality on pollutant removal gradually diminished. Dissolved organic matter (DOM) in the water quality background accounted for the largest proportion of •OH scavenging (76.4 %) and the most complex component. Moreover, changes in operating conditions were accompanied by the uncontrollable production of low-molecular-weight (LMW) DOM. Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) revealed the chemical transformation of LMW DOM at the molecular level. Higher H₂O₂ dosages triggered more extensive oxidative degradation, resulting in more complex effluent compositions. Considering treatment efficiency, energy consumption, and effluent product composition, H₂O₂ dosages of 5–10 mg/L and UV doses of 350–450 mJ/cm² were identified as optimal. This research contributes to the efficient purification of organic micropollutants in water using UV/H 2 O 2 technology with low energy consumption, minimal chemical input, and relatively controllable by-products.