Background: In advanced oxidation processes, pH has a significant effect on the removal efficiency of organic compounds. This study examined the effect of pH changes on the removal efficiency and kinetics of methyl tertiary butyl ether (MTBE) concentration in aquatic environment.
Objectives: The primary objective of this study was to evaluate the effect of pH changes on removal kinetics of the mentioned compound, using H₂O₂/nZVI (nano zero-valent iron)/ultrasonic process, and its impact on the reaction rate.
Materials and Methods: In order to create the right conditions for oxidation, first of all iron nanoparticles combined with H₂O₂ oxidizer were synthesized, and then they were subjected to ultrasound waves and used in MTBE oxidation. In MTBE removal via H₂O₂/nZVI/Ultrasonic process, the effects of some parameters such as contact time (2 to 60 minutes), concentration of hydrogen peroxide (5 to 20 mL/L), concentrations of nZVI (0.15 to 0.45 g/L), MTBE concentrations (50 to 750 mg/L), and pH (2 to 9) were investigated. MTBE concentration analysis was performed using gas chromatography (GC).
Results: According to this study, the best removal efficiency of 50 mg/L MTBE concentration in 89.56% under oxidation condition occurred when H₂O₂ level equals to 10 mL/L, nZVI is 0.25 g/L at pH 3.5. The results showed that the increase or decrease of pH from 3.5 results in a loss of oxidation efficiency as well as reduction in the amount of k_ap. In addition, the logarithmic changes curve of MTBE concentration showed that MTBE oxidation in H₂O₂/nZVI/ultrasonic method follows pseudo first order reactions.
Conclusions: Changes of pH could remarkably affect the efficiency and oxidation rate of MTBE. In particular, the amount of k_ap in terms of oxidation declines substantially by moving away from the optimum pH range. In this study, pH 3.5 was considered as the optimal pH in H₂O₂/nZVI/ultrasonic oxidation process, with the elimination of about 89.56% of the high MTBE concentration. In general, we can say that by adjusting pH in this range, the rate and efficiency of MTBE oxidation can be enhanced in H₂O₂/nZVI/ultrasonic method.