Calcium peroxide-enhanced fe-based zeolite for remediation of MTBE-contaminated groundwater: application in slow-release oxidant systems

• A novel double-column PRB system combining slow-release calcium peroxide (PLA@CP-CA) and Fe-based zeolite (Fe-S-1) was developed for efficient in situ remediation of MTBE-contaminated groundwater. • Citric acid effectively buffered pH during CaO₂ dissolution, enhancing the heterogeneous Fenton reaction and MTBE degradation efficiency (up to 98.9 % within 8 h). • Multiple reactive species (•OH, O₂⁻•, and ¹O₂) were confirmed to synergistically contribute to MTBE degradation via EPR and radical quenching experiments. • Optimized slow-release oxidant (PLA@CP-CA) achieved a H₂O₂ release capacity of 3.22 mmol/g, significantly extending oxidant lifetime and degradation duration. • Column tests demonstrated 97 % MTBE removal over 192 h with low Fe leaching (<0.3 mg/L), confirming the system’s potential for practical groundwater remediation applications. The widespread use of methyl tert‑butyl ether (MTBE) in gasoline has led to persistent groundwater contamination. Recently, permeable reactive barriers (PRBs) have emerged as a key in situ remediation technology for treating with such contamination. Various reactive media have been employed to intercept and degrade pollutants, but their short half-lives, instability, and poor dispersion in heterogeneous geological conditions limit their effectiveness and further applications. In this study, we designed a double-column PRB system incorporating slow-release oxidants (PLA@CP-CA) and Fe-based zeolite as heterogeneous Fenton catalysts. Calcium peroxide (CaO₂) was selected as the oxidant instead of hydrogen peroxide (H₂O₂) due to its higher stability, ease of transport, and prolonged release, facilitating sustained pollutant degradation. However, the direct use of CaO₂ raises groundwater pH, so citric acid (CA) was employed as a buffer to regulate pH during CaO₂ dissolution, thereby enhancing the efficiency of the heterogeneous Fenton process. Electron paramagnetic resonance (EPR) spectroscopy and radical trapping experiments confirmed that multiple reactive species, including ·OH, O 2 – ·, and ¹O₂, contributed synergistically to MTBE degradation. To mitigate calcium peroxide leakage, polylactic acid (PLA) was used to encapsulate the oxidant (PLA@CP-CA) under anhydrous conditions. The Box–Behnken design (BBD) in response surface methodology (RSM) optimized the PLA@CP-CA formulation, achieving an optimal H₂O₂ release capacity of 3.22 mmol/g with a mass ratio of PLA/CP/CA at 0.67:1.77:1.17. Approximately 97% of MTBE was remediated within 192 h using the double-column PRB, demonstrating the efficacy of the controlled oxidant release from PLA@CP-CA in promoting MTBE degradation. This heterogeneous Fenton system, combining PLA@CP-CA with Fe-S-1, offers a promising approach for in situ remediation in MTBE-contaminated environments.