Application of response surface methodology for dimethyl phthalate treatment via H₂O₂/UV-C process

In the present study, the reaction conditions required for the oxidation of dimethyl phthalate (DMP), being selected as a model endocrine disrupting compound, with the H₂O₂/UV-C treatment process were optimized using central composite design and response surface methodology (CCD–RSM). Initial DMP (DMP_o = 20–100 mg/L) concentration, initial H₂O₂ dosages (H₂O_2o = 5–45 mM), and treatment time (t_r = 2–18 min) were selected as critical process parameters (independent variables) while DMP and total organic carbon (TOC) abatements were chosen as the responses (dependent variables). Analysis of variance revealed that the variables “treatment time” and “initial DMP” were the process-independent parameters most positively and negatively affecting the treatment performance, respectively. According to the established polynomial regression models, for the degradation of the DMP at an initial concentration of 60 mg/L, the optimized treatment conditions were 25 mM of H₂O_2o and treatment time of 10 min. At these reaction conditions, complete DMP degradation and 28% TOC removal were obtained. By GC/MS analysis, phthalic acid and 4-hydroxy-1,2-benzoic dicarboxylic acid, dimethyl ester were identified as the aromatic oxidation intermediates.