Integration of ozonation and sonication with hydrogen peroxide and persulfate oxidation for polychlorinated biphenyls-contaminated soil treatment

Abstract

Polychlorinated biphenyls (PCBs) are persistent organic contaminants and are known for their strong sorption to soil due to high hydrophobicity. A combination of either ozone or ultrasound with hydrogen peroxide or persulfate was applied to soil contaminated with PCB-containing electrical insulating oil, Clophen A30. Sole ozonation of PCB-contaminated soil resulted in the degradation of 50% of PCBs in 300min treatment. A substantial retardation in PCB degradation was observed after 120min ozonation, with only a 6% degradation in the following 180min. Compared with ozone or sole persulfate, the combined application of ozone with hydrogen peroxide or persulfate did not result in a higher degradation efficacy, thus making the processes integration useless. Process integration, achieved by the joint application of ultrasound and oxidizing chemicals in moderate doses, could be a promising option for the treatment of contaminated soil containing highly sorbed hydrophobic organic pollutants and thereby resulting in an improved efficiency for PCB degradation. Contrary to ozone-based treatment processes, prolonging the treatment time of both sonication and the chemical treatment process, as well as increasing the chemical dosage, favored the improved degradation. Although the energy required for 0.5 h of soil sonication was higher than that for ozonation, sonication can still be effectively integrated into the chemical oxidation process.