Zero-valent iron activated persulfate remediation of polycyclic aromatic hydrocarbon-contaminated soils: An in situ pilot-scale study

Zero-valent iron activated persulfate (ZVI/PS) is widely used for the degradation of contaminants. However, the applicability of ZVI/PS has rarely been tested for the in situ pilot-scale remediation of organic-contaminated sites. In this study, different types of ZVI, including micro/nanostructured ZVI (nZVI), stearic-coated micro/nanostructured ZVI (C-nZVI) and commercial micron-sized ZVI (mZVI), were used to activate PS to remove polycyclic aromatic hydrocarbons (PAHs) from the contaminated site. Three reaction pits were excavated for testing the activation ability of different types of ZVI, each with an area of ∼30 m2 and a depth of 4 m. The chemicals (30 g/kg of PS and 3.5 g/kg of ZVI) were added in a soil slurry by in situ stirring. After treatment for 104 days, the PAHs (∼17 mg/kg) removal efficiencies were 82.21%, 62.78%, and 69.14% for PS activated by nZVI, C-nZVI and mZVI, respectively. It was found that the soil pH decreases due to the release of H+ from PS decomposition. The catalase activity was enhanced compared to before the chemical application, while soil bacterial communities, reflected by operational taxonomic unit values, decreased markedly from 250 to ∼100. In particular, the bacteria of the phylum Chloroflexi almost disappeared after remediation. However, the bacteria of the phylum Firmicutes still dominated after remediation and exhibited a tolerance to PS. The findings of this study provide a useful implementation case when PS activation is used in the remediation of PAH-contaminated soil and groundwater.