Efficient peroxymonosulfate activation for practical wastewater treatment by Biochar-Iron oxide composite-based hydrogel beads

Developing a highly stable catalyst for advanced oxidation to eliminate organic pollutants from wastewater is of considerable practical importance. In this study, we presented a biochar-iron oxide composite-based hydrogel bead system, designated as Fe2O3/BC/CS, designed for the efficient activation of peroxymonosulfate (PMS). Utilizing the degradation of sulfadiazine (SDZ) as a probe, our results revealed that the Fe2O3/BC/CS catalyst demonstrated exceptional performance in column tests. It maintained over 80 % SDZ removal efficiency for the first 150 bed volumes and achieved a removal efficiency of 68.4 % even after processing 384 bed volumes of wastewater. Additionally, the Fe2O3/BC catalyst achieved over 90 % degradation of three other common organic pollutants (bisphenol A, atrazine, and tetracycline) within 360 min. The degradation efficiency for SDZ reached 98.4 %, with a degradation rate constant (kobs) of 0.0115 min-1. After five cycles of 180 min, the SDZ degradation efficiency remained at 68.8 %, further demonstrating its potential for practical applications. Electron paramagnetic resonance analysis and quenching tests indicated that the catalyst-PMS system undergoes a catalytic oxidation process involving both radical and nonradical pathways. Combining the results of electrochemical tests and density functional theory calculations, we discovered that the main pathway for Fe2O3/BC to activate PMS involves electron transfer. The positively charged biochar layer was essential to induce PMS to donate electrons to the catalyst, leading to the formation of SO5 center dot-, which was subsequently decomposed into 1O2. Overall, this study highlights the Fe2O3/BC/CS system as a highly effective and versatile catalyst for PMS-based advanced oxidation processes.