Degradation and mineralization of organic UV absorber compound 2-phenylbenzimidazole-5-sulfonic acid (PBSA) using UV-254 nm/H₂O₂

Graphical abstract: - Highlights: • UV-254 nm/H₂O₂ AOP was utilized for the degradation and mineralization of PBSA and BSA. • Promotion of k_obs with [H₂O₂]₀ ≤ 4 mM and inhibition at higher [H₂O₂]₀ were observed. • The S and N were released and monitored as SO₄²⁻ and NH₄⁺, respectively. • Br⁻ inhibited both the degradation and mineralization much more significantly than Cl⁻. • There was an increase in [NH₄⁺] at higher [H₂O₂]₀ and its further destruction at higher UV fluence. - Abstract: Various studies have revealed the non-biodegradable and endocrine disrupting properties of sulfonated organic UV absorbers, directing people's attention toward their risks on ecological and human health and hence their removal from water. In this study, UV-254 nm/H₂O₂ advanced oxidation process (AOP) was investigated for degrading a model UV absorber compound 2-phenylbenzimidazole-5-sulfonic acid (PBSA) and a structurally similar compound 1H-benzimidazole-2-sulfonic acid (BSA), with a specific focus on their mineralization. At 4.0 mM [H₂O₂]₀, a complete removal of 40.0 μM parent PBSA and 25% decrease in TOC were achieved with 190 min of UV irradiation; SO₄²⁻ was formed and reached its maximum level while the release of nitrogen as NH₄⁺ was much lower (around 50%) at 190 min. Sulfate removal was strongly enhanced by increasing [H₂O₂]₀ in the range of 0–4.0 mM, with slight inhibition in 4.0–12.0 mM. Faster and earlier ammonia formation was observed at higher [H₂O₂]₀. The presence of Br⁻ slowed down the degradation and mineralization of both compounds while a negligible effect on the degradation was observed in the presence of Cl⁻. Our study provides important technical and fundamental results on the HO^· based degradation and mineralization of -SO₃H and N-containing UV absorber compounds