Effect of soil composition on electrokinetically enhanced persulfate oxidation of polychlorobiphenyls

In situ oxidation processes for the remediation of organic contaminants in soils have gained much interest in last decade. They are rapid, aggressive and easy to apply, but their application in low permeability soils is limited due to the ineffective delivery of oxidants in such soils. In this study, electrokinetically enhanced persulfate delivery and oxidation is investigated in two diverse low permeability soils: artificially contaminated kaolin and glacial till soil. These two soils were used to investigate the effects of soil type on persulfate oxidation of tetrachlorobiphenyl (PCB 44), a representative polychlorobiphenyl (PCB). Laboratory batch tests were conducted using the soils spiked with PCB 44 at an initial concentration of 50mg/kg to determine the optimal conditions for effective oxidation. This study also investigated the activation of persulfate by elevated temperature (45°C) and high pH (at anode) as a means to maximize PCB degradation. The activation of persulfate improved the oxidation of PCB in kaolin, but the effect in the glacial till was insignificant. The final pH values of the kaolin were around 1, while they were around 7 for glacial till because of the high buffering capacity of glacial till. Low pH conditions are also shown to activate persulfate, leading to higher PCB oxidation. The degradation of PCB 44 was significantly higher for the kaolin than the glacial till. In kaolin, the highest level of PCB oxidation, 77.9%, was achieved with temperature activated persulfate in 7 days. However, in the glacial till the highest PCB oxidation was 14.4% with 30% Na-persulfate concentration without any activation. The high buffering capacity, non-homogeneous mineral content and high organic content of glacial till may have contributed to the low persulfate oxidation of PCB.