Roles of the mineral constituents in sludge-derived biochar in persulfate activation for phenol degradation

Biochar as an environmental-friendly and low-cost catalyst has gained increasing attention in the catalytic degradation of organic pollutants. However, the roles of endogenous mineral constituents in biochar in the catalytic degradation are still unclear. In this study, the mineral-rich biochar produced from sewage sludge at 400 °C (SS400) and 700 °C (SS700) and their corresponding demineralized biochar (DSS400 and DSS700) were used to be the persulfate (PS) activator for phenol degradation. Results showed that the mineral-rich biochar + PS system had negligible phenol degradation (≤12.6 %), whereas distinct degradation of phenol were obtained in the demineralized biochar + PS system where DSS400 + PS and DSS700 + PS exhibited 36.3 % and 57.8 % degradation, respectively. Different minerals in mineral-rich biochar exhibited varying functions on phenol degradation. Mg and K in biochar had less effect on the phenol degradation, while Fe-containing minerals favored the phenol degradation. However, Ca-containing minerals more greatly reduced the formation of hydroxyl radical, resulting in more inhibited degradation of phenol. Thus, the overall degradation of phenol was reduced by the mineral-rich biochar. The findings indicated that the inherent minerals in biochar were not favorable for the phenol degradation, which guides us the application of biochar containing different minerals in the remediation of organic pollutants.