Formation and roles of hydrogen peroxide during soil remediation by direct multi-channel pulsed corona discharge in soil

• H2O2 formation is discussed during soil remediation by pulsed discharge plasma.
• Attacks of electrons to water molecules are the main pathway for H2O2 formation.
• Electrolysis of dissolved O2 and O3 decomposition participate in H2O2 formation.
• OH radicals recombination shows relatively low contribution to H2O2 formation.
• PNP degradation behaviors in soil are evaluated under various species additives.

H2O2 is one of the most major active species generated in discharge plasma process. A multi-channel pulsed discharge plasma system was developed to investigate H2O2 formation characteristics during p-nitrophenol (PNP) contaminated soil remediation. Effects of gas varieties (air, O2, Ar and N2), air flow rate, and species scavengers on H2O2 formation were evaluated, and PNP degradation performance was also evaluated under various species scavengers. The experimental results revealed that the highest H2O2 concentration was obtained in O2 plasma atmosphere, and followed in descends by air, Ar and N2 atmospheres; and H2O2 formation rates in the case of O2, air, Ar and N2 were 2.9 × 10−7, 1.8 × 10−7, 1.2 × 10−7 and 8.9 × 10−8 mol L−1 s−1 under the condition of peak pulse discharge voltage of 27.0 kV and gas flow rate of 0.8 L min−1, respectively. Increasing air flow rate to a certain extent was beneficial for H2O2 formation. The addition of n-butanol or H2PO4− into soil sample displayed negative effects on H2O2 formation, while the addition of HCO3− promoted H2O2 formation. Direct attack of high energy electrons to water molecules was the main pathway for H2O2 formation during direct pulse discharge plasma in soil; electrolysis reaction route of dissolved O2 would take place to generate H2O2 and ozone decomposition in alkaline soil also played significant roles in H2O2 formation; however, the recombination of OH radicals exhibited relatively low contribution to H2O2 formation. PNP degradation efficiency decreased by 12.7%, 19.0% and 30.4% within 45 min’s discharge plasma treatment at 27 kV with n-butanol, HCO3− and H2PO4− addition, respectively, which further confirmed the roles of high energy electrons and OH radicals in H2O2 formation.