Degradation of p-nitrophenol by DBD plasma/Fe2+/persulfate oxidation process

Dielectric barrier discharge (DBD) plasma in situ generates reactive species (e*, center dot OH, center dot O, center dot H, H2O2, O-3, etc.), UV irradiation and local high temperature. These physiochemical effects can non-selectively destroy aqueous organic contaminants, but the energy efficiency of DBD plasma for water decontamination can be further improved. Persulfate (S2O82-, PS) and ferrous ions (Fe2+) were employed for enhancing the degradation of p-nitrophenol (PNP). An addition of both S2O82- ( < 2.5 mM) and Fe2+ ( < 36 mu M) in PNP solution apparently promoted the degradation efficiency of PNP and energy efficiency compared to discharge plasma alone, due to a more production of active center dot OH and SO4 center dot- through Fenton-like reactions and PS activation process. Moreover, the tertiary system of plasma/PS/Fe2+ (81.1%) presented higher PNP degradation efficiency after 50 min treatment than discharge plasma alone (34.8%) and the binary systems of plasma/PS (63.6%), plasma/Fe2+ (69.6%) and PS/Fe2+ (13.7%). However, an excessive addition of S2O82- (2.5-3.6 mM) and Fe2+ (36-360 mu M) had unobvious or even harmful influence on PNP degradation, possibly due to the enhanced recombination or consumption of center dot OH and SO4 center dot- by radical side reactions. The effect of radical scavengers on PNP degradation indicates that center dot OH was the most important radical species in plasma system for PNP degradation, but SO4 center dot- was also very important for PNP degradation when PS was present in solution. Besides Fe2+ and the heat effect from discharge plasma, the electrons produced by electric discharge may also be one of the important contributors to the activation of PS.