Important role of cosolvent addition and soil permeability on electrokinetic-persulfate remediation of benzo(a)pyrene

Benzo(a)pyrene (BaP) is a common soil pollutant that is difficult to remove from low-permeability soil. The effects of cosolvent and soil permeability on electrokinetic (EK) + persulfate (PS) remediation of BaP are not well understood. This study investigated BaP removal in two soil types of different low permeabilities (low: Soil-L; much lower: Soil-ML) under different types and concentrations of cosolvent-enhanced EK+PS remediation. In Soil-ML, BaP removal varied significantly, reaching up to 86.6% under EK+PS+ 5% hydroxypropyl-beta-cyclodextrin (HPCD) treatment. Compared to EK+PS alone, the promoting effect of HPCD on EK+PS increased with increased concentrations of HPCD; however, adding 1% Tween 80 (TW 80) suppressed BaP removal by 2.5-10.5% in the soil compared with that under EK+PS alone. The inhibition was further enhanced at 10% TW 80, with an average BaP removal of 36.2%. In contrast, in Soil-L, BaP removal was higher than in Soil-ML under EK+PS alone (additional 4.4-22.5%). Adding HPCD slightly inhibited BaP removal and adding 1% TW 80 had a slightly positive effect. PS migration (measured S2O82-) was impeded because of the low electroosmotic flow generated in Soil-ML, with higher clay, silt, and bound water contents. Overall, this study provides valuable insights into the EK remediation of polycyclic aromatic hydrocarbons in low-permeability soils.