Enhanced-oxidation of sulfanilamide in groundwater using combination of calcium peroxide and pyrite

Fenton reaction using hydrogen peroxide (H₂O₂) has been widely applied to achieve the in-situ chemical oxidation of contaminated soil and groundwater. However, injecting and transporting H₂O₂ to a contaminated zone consumes the chemical through reactions with other substances and self-decomposition. Additionally, Fe(II), an activator for the Fenton reaction, scavenges hydroxyl radicals, greatly reducing its activity. Therefore, this study proposes a novel oxidation system combining calcium peroxide (CaO₂) and pyrite for the degradation of oxidizable contaminants in groundwater. CaO₂ is an oxygen releasing compound, and pyrite is a natural mineral that provides Fe(II). The individual applications of CaO₂ and pyrite cannot generate OH radicals and oxidize the target pollutant, sulfanilamide. However, the combination of pyrite and CaO₂ oxidized well sulfanilamide even in mild pH and 1.0 wt% of pyrite. Moreover, H₂O₂ and OH radicals are the dominant oxidants in the reaction. A speciation analysis shows the oxidation of pyrite in this combined system. Furthermore, this system oxidized 80% of 0.1 mM sulfanilamide, whereas only 30% was oxidized by conventional Fenton reaction, indicating that this combined system is effective and applicable to remediate groundwater. This study provides an alternative oxidation process to achieve in-situ chemical oxidation.