Persulfate gel sustaining-release materials and nano zero-valent iron for in situ remediation of high- and low-permeability systems

The research on in-situ remediation of heterogeneous aquifers using sustain-release material is scarce. In this study, the persulfate gel sustaining-release material (PGSR) was fabricated, and pollutants dynamic change, remediation efficiency and impact mechanism of nano zero-valent iron (NZVI) activated PGSR on high- and low-permeability systems contaminated with toluene and naphthalene were explored by tank experiments. The results demonstrated that PGSR possesses superior remediation efficiency compared to conventional persulfate solutions, and the pollutants' removal efficiency attains the maximum when the molar ratio of Na2S2O8 in PGSR to NZVI is 2/2. The long-term release of PGSR significantly extends the reaction time between persulfate and NZVI, which is conducive to addressing the tailing issue in the low-permeability zone (LPZ). The influence of process parameters on the remediation efficiency is important. Excessive activators or oxidants exert an influence on sulfate ions, thereby impeding pollutant degradation. Additional, injecting a small amount of PGSR will be diluted due to groundwater flow and unable to form a persistent reaction zone, while injecting a large amount of PGSR will block the pores, causing groundwater to flow around the reaction zone and influencing pollutant removal. Research offers technical support for in-situ remediation of contaminated sites with complex hydrogeological conditions.