Remediation of pesticide-contaminated soils by a microsecond pseudo-pulsed DBD plasma: optimization, pathway...

Pesticides removal from soil was investigated using a DBD (dielectric barrier discharge) plasma with microsecond pseudo-pulsed high-voltage power supply, focusing on the modeling and optimization of Trifluralin removal as the target pollutant. We performed a detailed parametric analysis (discharge voltage, remediation time, as well as soil moisture and organics content) to determine the optimum operational conditions. Plasma treatment experiments were also carried out on pristine sandy and loam soils. All four factors significantly impacted the herbicide removal, with notable cross effects. Under optimum conditions, 96.1 ± 2.0% Trifluralin and almost 68.5% mineralization were achieved within 17.6 min. In the presence of humic acids, the degradation efficiency decreased considerably, partly due to the competition for reactive species and energy consumption as well. The degradation kinetics fitted well to the pseudo-second-order model (R² = 0.998). The energy efficiencies were respectively 0.997 and 9.252 mg/kWh for 10 and 100 mg/kg Trifluralin, where •OH and ¹O₂ were the dominant reactive species in the targeted herbicide mineralization. The mechanistic degradation pathways were proposed based on the identified transformation products, which primarily encompassed successive hydroxylation, defluorination, and deamination. Furthermore, the toxicity of transformation products was evaluated through both seed germination assessment and the ECOSAR (Ecological Structure-Activity Relationships) predictive model, which indeed verified that the environmental risk was substantially reduced. This study gives a new point of view on cold DBD plasma as a promising and robust technique towards the remediation of soils contaminated with chemically stable and recalcitrant organics that are resistant to conventional treatment methods.