Sustained release of persulfate and ferrous sulfate encapsulated in stearic acid for continuous pyrene degradation in groundwater

Abstract

Polycyclic Aromatic Hydrocarbons (PAHs) are persistent organic pollutants known for their carcinogenic, teratogenic, and mutagenic properties. A considerable amount of PAHs has been released into groundwater. Persulfate-based advanced oxidation processes (PS-AOP) are commonly employed to remediate such contamination. However, traditional in-situ chemical oxidation (ISCO) faces challenges such as concentration rebound and tailing. To address these issues, sodium persulfate sustained release materials (PDS@SA) and ferrous sulfate sustained release materials (FeSO₄@SA) were developed using stearic acid (SA) as a binder. Batch and column experiments were conducted to evaluate the efficacy of pyrene degradation through PDS@SA activated by FeSO₄@SA. The batch experiments showed that the optimal mass ratio of FeSO₄@SA to PDS@SA was 1:2, achieving degradation efficiencies over 95 % for pyrene with various concentrations (5, 10, 15, 20 mg⸱L⁻¹) within 2 h. The column experiments showed that sustained release materials (FeSO₄@SA and PDS@SA) with a particle size of 5 mm achieved an average removal rate of 89.3 % during days 7–15, while those with particle sizes of 7.5 mm and 10 mm achieved average removal rates of 68.5 % and 74.6 % during days 15–23, respectively. Additionally, electron paramagnetic resonance (EPR) analysis confirmed sulfate radicals SO₄^-⸱ and hydroxyl radicals ⸱OH as the primary oxidative species during pyrene degradation. These findings suggested that the sustained activation of PDS by sustained release Fe²⁺ represents a viable method for degrading PAHs in groundwater.