The interface mechanism of sludge biochar activating persulfate to remove tetracycline: The role of the C-O-Fe bridge at the carbon surface

Abstract

In recent years, with the widespread use of antibiotics and the dramatic increase in municipal sludge production, the removal of antibiotics from the water environment and the resourceful and harmless treatment of municipal sludge have become major issues in environmental management. Herein, sewage sludge containing Fe was prepared as biochar (SSBC) for activating peroxydisulfate (PDS) to remove tetracycline (TC) in water. The results showed that SSBC/PDS system removed 86.7% of TC, which was higher than the removal of TC by PDS alone (29%). SEM-EDS, FT-IR, XRD, and other characterizations showed that the Fe on SSBC existed as functional groups rather than as iron oxide crystals. Based on this, we proposed the presence of a C-O-Fe structure on the surface of unmodified SSBC. XPS analysis and DFT calculations showed that the presence of C-O-Fe changed the charge distribution on the SSBC surface and formed a Fe-centered electron reaction zone to better activate PDS for TC degradation. The active species in the degradation process included 1O2, ·OH, SO4·-, O2·-, where ·OH originated from activating PDS by C-O-Fe. Toxicity prediction of intermediates showed that hydroxylation and demethylation were the major degradation steps and most intermediates were less toxic than TC.