Degradation of Ketamine and Methamphetamine by the UV/H₂O₂ System: Kinetics, Mechanisms and Comparison

• Main Authors: De-Ming Gu, Chang-Sheng Guo, Qi-Yan Feng, Heng Zhang, Jian Xu
• Format: Article
• Language: English
• Published: MDPI AG 2020-10-01
• Series: Water
• Subjects: ketamine; methamphetamine; UV/H₂O₂; degradation kinetics; reaction intermediates
• Online Access: https://www.mdpi.com/2073-4441/12/11/2999

The illegal use and low biodegradability of psychoactive substances has led to their introduction to the natural water environment, causing potential harm to ecosystems and human health. This paper compared the reaction kinetics and degradation mechanisms of ketamine (KET) and methamphetamine (METH) by UV/H₂O₂. Results indicated that the degradation of KET and METH using UV or H₂O₂ alone was negligible. UV/H₂O₂ had a strong synergizing effect, which could effectively remove 99% of KET and METH (100 μg/L) within 120 and 60 min, respectively. Their degradation was fully consistent with pseudo-first-order reaction kinetics (R² > 0.99). Based on competition kinetics, the rate constants of the hydroxyl radical with KET and METH were calculated to be 4.43 × 10⁹ and 7.91 × 10⁹ M⁻¹·s⁻¹, respectively. The apparent rate constants of KET and METH increased respectively from 0.001 to 0.027 and 0.049 min⁻¹ with the initial H₂O₂ dosage ranging from 0 to 1000 μM at pH 7. Their degradation was significantly inhibited by HCO₃⁻, Cl⁻, NO₃⁻ and humic acid, with Cl⁻ having relatively little effect on the degradation of KET. Ultraperformance liquid chromatography with tandem mass spectrometry was used to identify the reaction intermediates, based on which the possible degradation pathways were proposed. These promising results clearly demonstrated the potential of the UV/H₂O₂ process for the effective removal of KET and METH from contaminated wastewater.