Degradation of DEET in aqueous solution by water falling film dielectric barrier discharge : Effect of three operating modes and analysis of the mechanism and degradation pathway

This study investigated the degradation feasibility of N, N-diethyl-m-toluamide (DEET) in aqueous solution by water falling film dielectric barrier discharge (DBD) plasma under three different operating modes. The results exhibited that bubbling the gas of discharge area into DEET solution at the same time of DEET solution flowing through the discharge area (model-3) achieved better effect, the degradation efficiency and rate constant of 300 mL DEET solution with initial concentration of 20 mg/L could reach 76.8% and 0.0526 min(-1), respectively, after 27 min. In addition, the energy yield of model-3 was highest. The reactive species (H2O2, O-3) generated from the DBD system were measured, and the effects of different radical scavengers were analysed. Meanwhile, the removal efficiency of total organic carbon (TOC) in model-3 was much higher, could reach about 24%. The effects of various parameters such as discharge voltage, initial pH, gas bubbling flowrate and liquid circulation flowrate on the degradation of DEET in model-3 were further examined and it was also observed that higher discharge voltage, lower pH, larger gas bubbling flowrate and larger liquid circulation flowrate could promote the removal of DEET. Finally, the DEET degradation pathway was deduced based on HPLC-MS analysis and Gaussian calculation. (C) 2017 Elsevier B.V. All rights reserved.