Tetracycline Degradation by Persulfate Assisted by Fe and N Co-Doped Biochar Derived from Spent Mushroom Substrate for Sustainability: Effect of Pyrolysis Temperature

Mushroom production is increasing rapidly worldwide, raising public concern about the contamination effects of spent mushroom substrates (SMS). Preparation of Fe–N-doped biochar (Fe-N-BC) from SMS as a raw material for catalytic degradation of antibiotics in water may be an effective and sustainable solid waste treatment. However, there is limited information available. This study investigated the effect and potential mechanism of SMS-based Fe-N-BC prepared at 300, 600, and 900 °C to catalyze persulfate (PS) for tetracycline (TC) removal. The results indicated that the catalytic performance of Fe-N-BC was significantly enhanced with increasing pyrolysis temperature. Notably, Fe-N-BC prepared at 900 °C exhibited high TC removal efficiency, with 95% TC removal at 120 min. This might be closely related to the fact that the Fe-N-BC prepared at high temperatures had more Fe oxides and active sites. Adsorption and radical and non-radical pathways were the main mechanisms for TC removal by Fe-N-BC/PS systems, especially the contribution of SO4·−. By identifying the degradation products, three possible pathways of TC degradation were proposed, and the toxicity of the degradation intermediates was evaluated. The results of the reusability analysis indicated that the Fe-N-BC prepared at 900 °C had good potential for practical application, and the TC removal rate still reached 76%, even after five cycles. These findings provide valuable reference information for solid waste resources’ sustainable utilization and the remediation of antibiotic-contaminated water.