Kinetic modeling of sulfonamide degradation by UV/H₂O₂: Deduction of R_OH,UV modeling and application

Eight sulfonamide (SA) antibiotics were effectively degraded using a UV/H₂O₂ process in a quasi-collimated beam apparatus, utilizing optimized fluence quantification. Fluence-based rate constants (kk'_SA) for the UV/H₂O₂ process were established. A curve-fitting method, derived from R_OH,UV modeling, was developed for the UV/H₂O₂ process to quantitatively assess the impact of critical factors, including water quality and direct UV photolysis. It was observed that k'_SA values approached a limiting value as initial H₂O₂ concentration increased. The specific second-order rate constants for ^•OH reactions with neutral and anionic SA species were determined to be within (2.2-5.7) × 10⁹ M⁻¹ s⁻¹, showing minimal variation among species. For the eight SAs studied, k'_SA values were calculated from 3.9 × 10⁻⁴ to 6.0 × 10⁻² cm² mJ⁻¹ across a typical pH range of 6.5-9.5. Direct UV photolysis was notably significant in SA degradation, particularly for sulfisoxazole, contributing at least 35%. An energy cost equation was formulated to evaluate the cost-effectiveness of SA degradation by UV/H₂O₂ and optimize operational parameters. This model, validated in real water scenarios, shows promise for predicting SA removal in UV/H₂O₂ processes. The developed curve-fitting method, pH-independent and accounting for both direct photolysis and OH radical reactions, is apt for modeling mixed-contaminant degradation in UV/H₂O₂ processes, simplifying calculations in R_OH,UV modeling.