Degradation of phenolic compounds by dielectric barrier plasma: Process optimization and influence of phenol substituents

Abstract

The degradation of a series of phenolic compounds in a novel dielectric barrier discharge (DBD) plasma reactor was studied in this paper. The effect of various parameters, such as applied voltage, water flowrate, initial concentrations of organics, solution conductivity and pH, was investigated to achieve a high removal efficiency for phenolic compounds. The complete degradation of p-CH3 could be achieved within 32 min, and the highest energy yield was about 3.5 g/kWh. Electron paramagnetic resonance analysis and radical quenching experiment indicated that OH played an important role in phenols degradation, along with ozone molecules. O2− and 1O2 also possibly contributed to phenols degradation. Substituted phenols were more easily degraded, especially nitrophenol with strong electron withdrawing groups, originating from OH and O2− attack. The intermediates of different phenolic compound generated in the degradation process were identified by Mass spectroscopy (MS) and the corresponding mechanism were proposed to strengthen the understanding of mechanism. A DBD plasma and activated carbon combined technique is further proposed to promote the conversion of oxygen into ROS (reactive oxygen species) and enhance the mineralization rate of substituted phenols.