Environmental Chemistry•2026•DOI: 10.7524/j.issn.0254-6108.2025031105
Colloids significantly influence contaminant transport in groundwater, yet their behavior under varying hydrochemical conditions remains inadequately characterized. This study employed quartz sand as a surrogate porous medium to investigate colloid transport through column experiments under controlled pH and ionic strength (IS). Breakthrough curves (BTCs) were obtained for a conservative tracer and for colloids under nine combinations of pH (5, 7, 9) and IS (1, 5, 10 mmol·L−1). Hydrus-1D, incorporating a two-site kinetic sorption model, was used to simulate colloid transport and derive key parameters: attachment rate (k1a), detachment rate (k1d), straining rate (k2a), and maximum retained concentration on site 2 (Smax2). Results demonstrated that increasing pH and decreasing IS enhanced colloid mobility. Specifically, at IS = 1 mmol·L−1, normalized peak concentrations (C/C0) were 0.33, 0.40, and 0.72 for pH 5, 7, and 9, respectively. At pH = 7, C/C0 decreased from 0.40 to 0.18 and 0.12 as IS increased from 1 to 5 and 10 mmol·L−1. The fitted transport parameters accurately captured these trends, with R² ≥ 0.95 across all conditions. Mechanistically, higher pH increases negative surface charge and electrostatic repulsion, while higher IS compresses the double layer and reduces repulsion, thereby inhibiting transport. These findings provide quantitative insights for predicting colloid-facilitated contaminant migration in subsurface environments.
Chinese Journal of Environmental Engineering•2026•DOI: 10.12030/j.cjee.202512025
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.