Fe(II) activated calcium peroxide/peroxymonosulfate: A practical system for phenanthrene degradation and upholding ecological pH

Groundwater contamination by polycyclic aromatic hydrocarbons (PAHs) can have adverse effects on both the subsurface environment and human health. This study aimed to demonstrate the degradation of PHE using a coupled oxidant system, that involves simultaneous injection of Fe(II) and oxidants, CaO2 (CP) and peroxymonosulfate (PMS). To ensure the environmental compatibility, coupled oxidant strategy was proposed to maintain the pH level between 6.0 and 8.0 following the treatment process. The influence of reaction conditions including concentration of PMS, CP, and Fe(II) concentrations, initial pH, anions, and humic acid on PHE degradation were assessed. Scavenger experiments and electron spin resonance (ESR) analysis confirmed that hydroxyl radical (HO−) and non-radical singlet oxygen (1O2) were the primary reactive oxygen species (ROS) in the reported system. PHE degradation mechanism in the coupled oxidant system was proposed based on by-products identification. In addition, the CP/PMS/Fe(II) system showed promising degradation performance for naphthalene and pyrene, indicating the proposed strategy could be a viable option for removing a broad spectrum of PAHs. Finally, the coupled oxidant system was optimized to achieve best PHE removal efficiency under natural groundwater (NGW) conditions.