Removal of COD from Secondary Effluent Using Fenton Iron Sludge-Based Biochar/Fe(VI)/H2O2 Process

The conventional Fenton process generates large amounts of Fenton sludge during wastewater treatment. Achieving effective utilization of Fenton sludge and reducing its production remain pivotal challenges. In this study, Fenton sludge biochar catalysts (Cat) were prepared using Fenton sludge via pyrolysis. In addition, chemical oxygen demand (COD) from secondary effluent was removed by Fenton sludge biochar catalysts activated with H2O2/Fe(VI). Specifically, the removal efficiency of COD could reach 46.2% in the Cat−2/H2O2/Fe(VI) system under weakly alkaline conditions. The mechanistic analysis confirmed that high-valent iron, •OH, O2•−, and 1O2 all participate in the degradation process. Furthermore, a continuous-flow reactor was applied to treat secondary effluent, with COD decreasing from 65 mg/L to 36 mg/L. This study provides new insights into the resource utilization of Fenton sludge and the treatment of complex wastewater.