Kinetic and mechanistic investigation on the decomposition of ketamine by UV-254 nm activated persulfate

Abstract Ketamine (KET) has been increasingly used for medical purposes and abused by individuals around the world. In this study, decomposition of KET was investigated by UV-activated persulfate (S 2 O 8 2− , PS). Influence of key parameters, such as pH, PS dosage, HCO 3 − , Cl − , NO 3 − , and humic acid (HA) on KET decomposition was evaluated. The results showed that KET degradation followed pseudo-first order reaction kinetics well (R 2  > 0.99). The combination of UV-254 nm and persulfate could completely degrade 100 μg/L of KET in 30 min with a PS dosage of 500 μM at pH 7. Both hydroxyl radical (radOH) and sulfate radical (SO 4 − rad) were demonstrated to participate in the KET degradation through scavenging experiments. The degradation rate constant of KET was proportional to the PS dosage (0–800 μM), while self-scavenging of SO 4 − rad occurred with an excessive amount of PS dosage (1000 μM). The KET degradation rate was pH-dependent, and was highest at neutral pH condition. The presence of HCO 3 − had a positive impact on the KET decomposition, however, NO 3 − induced a negative effect even at a relatively low concentration. Of note, Cl − had a dual impact on the KET decomposition. The bimolecular reaction rates of KET with SO 4 − rad and radOH at pH 7 were 3.76 × 10 9 and 4.43 × 10 9  M −1  s −1 , respectively. KET decomposition was significantly inhibited by the presence of HA due to the effect of UV absorption and free radical quenching. The intermediates of KET degradation were identified by HPLC-MS and possible transformation pathways were proposed. Results indicated that the combination of UV/PS is an effective approach for the removal of KET in the aquatic environment.