Degradation of 1H-benzotriazole by UV/H2O2 and UV/TiO2: kinetics, mechanisms, products and toxicology

Abstract

Benzotriazoles are emerging contaminants widespread in environmental waters. As they are robust against conventional biological wastewater treatment, it is desirable to develop cost-effective and safe treatment methods for benzotriazole removal. The current study attempted to investigate the degradation of water dissolved 1H-benzotriazole (1H-BTA) with UV/H₂O₂ and UV/TiO₂. Pseudo-first order degradation kinetics were observed in low power 280 nm UV/H₂O₂ and UV/TiO₂ systems (UV intensity = 0.023 mW cm⁻², k_app reached 1.63 × 10⁻³ s⁻¹ and 1.87 × 10⁻³ s⁻¹, respectively), and radical oxidation was the dominant reaction mechanism with k_˙OH-BTA at (7.1 ± 0.8) × 10⁹ M⁻¹ s⁻¹ and (6.9 ± 0.7) × 10⁹ M⁻¹ s⁻¹. Both systems were affected by the pH value, natural organic matter and anions, leading to incomplete mineralization in actual water treatment processes. As the reaction proceeded, 1H-BTA was progressively transformed into eight organic products. The number of preliminary hydroxylated products (e.g. C₆H₅N₃O) increased rapidly at the early stage, while the further open-loop products (e.g. C₄H₃N₃O₄) were dominant at the later stage. Based on the proteomics analysis, the significant activation of ribosome, transporter and tricarboxylic acid cycle metabolisms in Escherichia coli, which exposed to the later degradation product mixture, suggested that the toxicity of 1H-BTA decreased. In conclusion, incomplete mineralization using hydroxyl radical oxidation likewise has potential for thedetoxification of 1H-BTA.