Sustainable degradation of tetracycline via biochar-based Fe/Co-alginate beads in a fixed-bed peroxymonosulfate reactor
Weipeng Zou, Meng Zhang, Suyun Chang, Zhiwen Wang, Dan Zhang, Jiang-Bo Huo, Anping Peng, Xinbo Zhang, Wenshan Guo, Huu Hao Ngo
Abstract
The widespread occurrence of tetracycline antibiotics (TCs) in aquatic environments poses serious ecological and human health risks. In this study, novel biochar-iron/cobalt cross-linked alginate beads (BFC-beads) were synthesized from waste coffee grounds and sodium alginate via a polymerization process. These BFC-beads were applied to activate peroxymonosulfate (PMS) for the continuous degradation of tetracycline hydrochloride (TCH) in a fixed-bed reactor. Under optimal conditions (flow rate: 4.4×10 -5 L/s; 2 g BFC-beads; 0.6 g/L PMS), the system achieved a TCH removal efficiency exceeding 93%. The BFC-beads exhibited excellent operational stability across a broad pH range (3-11) and maintained performance in the presence of various anions. Reactive species analysis via quenching experiments and electron paramagnetic resonance (EPR) identified singlet oxygen ( 1 O 2 ), sulfate radicals (SO 4 -• ), hydroxyl radicals (•OH), and superoxide (O 2 • - ) as key contributors to TCH degradation. Electrochemical measurements indicated a synergistic Co-Fe bimetallic effect at the catalytic interface, enhancing redox cycling and reducing charge-transfer resistance. Liquid chromatography-mass spectrometry (LC-MS) revealed a stepwise degradation pathway involving demethylation, hydroxylation, and ring-opening reactions, leading to progressive mineralization. Furthermore, toxicity assessments using the Toxicity Estimation Software Tool (T.E.S.T.) demonstrated a marked reduction in the biotoxicity of degradation intermediates. Overall, the BFC-bead-packed fixed-bed reactor offers a promising and sustainable approach for continuous treatment of antibiotic-contaminated wastewater.