Electrokinetic Delivery and Activation of Persulfate for Oxidation of PCBs in Clayey Soils.

Contamination of soils by polychlorobiphenyls (PCBs) is of environmental concern because of their toxicity, persistence, hydrophobic nature, and slow biodegradation potential. Among the PCB remedial technologies, direct oxidation by persulfate is considered to have great potential to be both simple and rapid. However, to produce faster reaction rates, persulfate is often activated using heat, metal chelates, hydrogen peroxide, or high pH. Furthermore, delivery of persulfate in low permeability clayey soils is difficult. Integrating electrokinetic remediation with persulfate has the potential to overcome such difficulties because the applied electric potential can facilitate the delivery of persulfate in low permeability soils as well as activate oxidizing radicals and simultaneously induce oxidative/reductive reactions directly in the soil. This study investigates the potential for in situ oxidation of PCBs in low permeability soils using persulfate as an oxidant and also evaluates the benefits of integrating oxidation with electrokinetic remediation. Several series of laboratory batch and bench-scale electrokinetic experiments were conducted using kaolin, a representative clayey soil, spiked with 50 mg/kg of 2,2′,3,5′ tetrachlorobiphenyl (PCB 44), a representative PCB. Persulfate oxidation activators [elevated temperature (45°C) and high pH (at the cathode)] were investigated to maximize the PCB degradation. In addition, the effect of oxidant dosage on PCB degradation was investigated. The electrokinetically enhanced temperature-only activated persulfate oxidation test resulted in better PCB 44 remediation (77.9%) than the temperature and high-pH activated persulfate oxidation (76.2%) in a 7-day period. The optimal dosage for effective remediation was 30% Na-persulfate (76.2%) because a 20% concentration of the oxidant yielded a lower rate of degradation (55.2%) of PCB 44. The results are encouraging for the use of electrokinetically enhanced persulfate oxidation for the effective remediation of PCBs in soils. [ABSTRACT FROM AUTHOR]