Plasma chemical degradation of phenol in solution by gas–liquid gliding arc discharge

Abstract

A gas–liquid gliding arc (glidarc) discharge reactor is used to degrade high concentration phenol solution. Phenol solution with 1878 mg L−1 initial chemical oxygen demand (COD) is treated by spraying directly into the plasma zone formed between two electrodes through a gas–liquid two phase atomizing nozzle. A number of parameters such as voltage waveform, solution concentration, electrode material, nature of the carrier gases and the gas–liquid ratio are examined. It is found that the voltage waveform of gas–liquid gliding arc discharge is more irregular than that of gas gliding arc discharge, and the breakdown voltage of gas–liquid gliding arc discharge is lower than that of gas gliding arc discharge. The COD abatement of phenol solution with stainless steel as the electrode material is higher than that with brass and aluminium. The increasing electrode thickness and the increasing gas–liquid ratio and carrier gas such as oxygen can increase the degradation of phenol. The final COD of the solution is 173 mg L−1; either air or oxygen is used as the carrier gas, and the solution treated is acidic. The variation of pH and conductivity and the formation of hydrogen peroxide and ozone are measured. The occurrence of CO2 is detected during the plasma treatment: the maximum concentration is 18 000 ppm. While H2 and NOx are also detected during the plasma phase, p-nitrosophenol (C6H5NO2) and p-nitrophenol (C6H5NO3) are detected in the solution treated.