A statistical experimental design approach for mineralization and detoxification of diethyl phthalate by H₂O₂/UV-C process

In the present study, a three-factor central composite design (CCD) was implemented to evaluate the major factors (treatment time, initial H₂O₂ dose and initial diethyl phthalate (DEP) concentration) influencing the H₂O₂/UV-C treatment of aqueous DEP solution. Significant regression models for total organic carbon (TOC) removal and residual H₂O₂ concentration were derived using analysis of variance (ANOVA), which were found to be adequate to perform the process variables optimization. According to the applied ANOVA, treatment time (positive effect) and initial H₂O₂ dose (negative effect after an optimum value) were found to be significant on the H₂O₂/UV-C process performance. TOC removal efficiencies were enhanced with increasing initial H₂O₂ dose up to an optimum value, and further increases in H₂O₂ dose resulted in a decrease in TOC removals due to the hydroxyl radical scavenging effect. When initial H₂O₂ dose increased from 10 to 30 mM, the TOC removal efficiency improved from 41 to 100% for DEP_o of 100 mg/L for treatment time of 50 min. Further increase in initial H₂O₂ dose to 50 mM decreased the TOC removal efficiency down to 38%. The results of toxicity assessments with Vibrio fischeri on aqueous DEP solutions subjected to H₂O₂/UV-C treatment revealed complete detoxification at the optimum conditions.