Iron coagulant regulating reactive species in ionizing radiation process for enhanced degradation of bisphenol A

In the treatment of industrial wastewater by electron beam technology, the flocculation process was frequently coupled with electron beam radiation to improve the water quality to meet the discharge standard. Iron-containing coagulant was widely used in the flocculation process. Therefore, this study investigated the impact of residual iron-containing coagulants on pollutant degradation by the ionizing radiation process. Results showed that the absorbed dose required for complete removal of 50 mg/L bisphenol A decreased from 5 kGy to 2.5 kGy in the presence of 100 μM typical iron coagulant (FeCl₃). BPA degradation efficiency increased with the increase of FeCl₃ dosage over a wide pH range (3.0-10.0), and the TOC removal efficiency increased from 20% to 45% with the addition of 300 μM Fe(III). The mechanistic investigation demonstrated that ^•OH was the primary reactive species responsible for BPA degradation. The residual iron coagulants (FeCl₃) significantly enhanced the degradation and mineralization efficiency. Under suitable pH conditions (3.0-6.0), the reducing reactive species (e_aq^‒ and ^•H) could effectively reduce Fe(III) to Fe(II), which then reacted with H₂O₂, thus inducing in-situ Fenton reaction to generate more ^•OH, thus promoting the radiolysis degradation of micropollutants. This study explored the potential of using residual iron coagulants from the flocculation process to enhance the performance of electron beam technology for wastewater treatment.