Degradation mechanism of metronidazole using persulfate activated by boron/copper doped biochar derived from Chlorella vulgaris

Abstract

Chlorella biochar modified with boron and copper (B/Cu-BC) was created and used to break down the antibiotic metronidazole (MNZ) through peroxymonosulfate (PMS) activation. The physicochemical properties of B/Cu-BC were analyzed using SEM, BET, FTIR, XRD and XPS. The results showed that the modified Chlorella biochar, which included several oxygen-containing functional groups, exhibited a rise of 7.1 times in specific surface area and a rise of 8 times in pore volume compared to the unmodified variant. Under the optimal conditions, the B/Cu-BC+PMS system removed 86.6 % of MNZ in 90 min. The reaction mechanism of the system was confirmed by Quenching and electron paramagnetic resonance (EPR) experiments. The B/Cu-BC+PMS system was accompanied by SO₄•^-, •OH, •O₂^- and ¹O₂, in which •O₂^-was the main reactive oxygen species (ROS). The intermediates in the degradation process of MNZ were investigated using HPLC-MS, and two potential degradation pathways of MNZ were suggested. Finally, the toxicology of the intermediates from the MNZ degradation process was analyzed by toxicity estimation software tool. The bioconcentration coefficients and mutagenicity coefficients showed a significant decrease, indicating that the system could efficiently degrade the antibiotic MNZ in an environmentally friendly manner.