Depth dependence of p-nitrophenol removal in soil by pulsed discharge plasma

• PNP degradation and active species diffusion in soils was studied during pulsed discharge process.
• Organic matter blocks active species transport and inhibits PNP degradation.
• Metal oxides affect PNP degradation through catalyzing ozone decomposition.
• Soil moisture benefits active species transfer, and thus promotes PNP degradation.
• Intermediates distribution in soils confirms diffusion behaviors of active species.

A series of soil column experiments were performed to investigate p-nitrophenol (PNP) degradation and active species diffusion behaviors in soil layers during pulsed discharge processes. The effects of organic matter, metal oxides, soil moisture, discharge voltage, treatment time, and pollutant concentration on PNP degradation and active species transport were evaluated. PNP degradation efficiency was inversely proportional to organic matter content, due to its adsorption for PNP and blocking for active species transport. For layer 0–2 mm, 99.2% of PNP was removed after 45 min of discharge treatment in column packed with quartz sand, followed in descending order, by sand (85.0%), by sandy soil (77.9%), and by clay soil (61.9%). Metal oxides affected PNP degradation through catalyzing ozone decomposition. Moist soil, higher discharge voltage, and lower PNP initial concentration benefitted active species diffusion and thus promoted PNP degradation. PNP degradation processes in soil layers followed first-order kinetic model, and the reaction rate constant decreased from 0.0458 min−1 in soil layer 0–2 mm to 0.0078 min−1 in soil layer 10–12 mm. PNP mineralization and degradation intermediates were also identified in soil layers. The distribution of intermediates in soil layers confirmed the different diffusion behaviors of active species.