New evidence on the formation of oxidizing species in corona discharge in contact with liquid and their reactions with organic compounds

• The formation of O3, H2O2, OH was investigated in a corona discharge above liquid.
• The degradation of methylparaben was enhanced when combining plasma with ozonation.
• O3 consumption is correlated with MeP degradation and evolution of by-products.
• The presence organic compounds can promote the accumulation of H2O2 in solution.
• OH radicals have an essential contribution to the mineralization of MeP.

The objective of these investigations is to understand in more detail how organic compounds in water are degraded during plasma treatment. The formation of oxidizing species (ozone (O3), hydrogen peroxide (H2O2) and hydroxyl radicals (OH)) in a pulsed corona discharge in contact with liquid is investigated. The degradation of a target organic compound (methylparaben) in aqueous solution was increased when combining plasma treatment with ozonation, using the O3 generated in the discharge. Enhanced mass transfer of O3 obtained in this plasma+O3 configuration leads to a six fold increase of MeP oxidation rate.The evolution of oxidants concentration during treatment of MeP solutions provides information on their consumption in reactions with MeP and its oxidation products. The correlation of MeP degradation results (MeP removal and mineralization) with O3 consumption and the identified reaction products confirms that although O3 plays an important role in the degradation, for the mineralization OH radicals have an essential contribution. The concentration of OH radicals is diminished in the solutions containing MeP as compared to plasma-treated water, indicating OH consumption in reactions with the target compound and its degradation products. The concentration of H2O2 in the liquid can be either increased or reduced in the presence of MeP, depending on its initial concentration. On the one hand, decomposition of H2O2 by OH or O3 is suppressed in the presence of MeP, but on the other hand less OH radicals are available for its formation.