Stratification of Persulfate in Porous Aquifers and Its Impact on Remediation of Light Non-Aqueous Phase Liquid Contamination
Persulfate (PS) is a common oxidant in in-situ chemical oxidation (ISCO) for groundwater organic contamination, but its vertical concentration stratification may lead to inefficient remediation of light non-aqueous phase liquids (LNAPLs). To investigate the vertical stratification characteristics of PS in porous aquifers and its impact on LNAPLs remediation, static water column experiments and flowing water sand tank experiments were conducted. The migration behavior of PS under non-slow-release and slow-release conditions was compared, with Br− as a reference tracer and benzene, toluene, and xylene (BTX) as LNAPLs contaminants. Results showed that in static water columns, Br− exhibited weak vertical migration, short migration distance, and a low decay rate (0.009 d−1), consistent with a stable tracer. In contrast, PS showed strong vertical migration, with concentrations increasing with depth; under slow-release conditions, the concentration difference between the top and bottom of the column could reach two orders of magnitude. Br− migration was dominated by molecular diffusion (effective diffusion coefficient 2.2×10−9 m2·s−1), while PS migration was driven by both diffusion and density. Under slow-release conditions, the average PS decay rate was 0.072 d−1, slightly higher than the non-slow-release rate (0.059 d−1). In both column and sand tank experiments, BTX exhibited a distinct shallow-layer distribution, contrasting with PS. When the aquifer thickness is large, PS stratification limits its contact with LNAPLs contaminants, increasing remediation cost and difficulty. These findings provide theoretical reference for PS-based ISCO remediation of LNAPLs in porous aquifers.