Iron-loaded Chinese herbal medicine residue biochar for heterogeneous catalytic ozonation of malathion wastewater

• Fe-C biochar from TCM residues efficiently degrades MAL in wastewater. • Fe-C/O 3 system enhances MAL degradation and reduces toxicity in contaminated water. • DFT analysis reveals key reactive sites and degradation pathways for MAL. • Precise quantification of MAL and its intermediate products. China is a major producer of medicinal materials, with northern Anhui as a key production area. The accumulation of herbal residues from medicinal plant cultivation, along with organophosphate pesticide pollution, poses serious environmental challenges, which have garnered significant attention. To enable resource utilization of herbal residues and meet the deep treatment needs for organophosphate pesticides, especially malathion (MAL), this study prepared iron-based biochar (Fe-C) using pyrolysis and hydrothermal methods, developing an iron-based biochar-ozone (Fe-C/O 3 ) advanced oxidation system. Results show that iron oxides are uniformly distributed on the biochar surface, providing abundant active sites for MAL degradation. With an initial MAL concentration of 50 mg/L, the study investigated the effects of iron content, pH, processing methods, and ozone dosage, confirming the Fe-C/O 3 system’s ability to efficiently degrade MAL within 30 min. Density functional theory (DFT) analysis revealed MAL’s strong nucleophilic reactivity, and UPLC-MS/MS identified six degradation intermediates, suggesting a degradation pathway with malaoxon (P1) as a key intermediate. Toxicity assessments of degradation products indicated an overall decrease in toxicity, with •O 2 – and 1 O 2 as primary reactive oxygen species. In summary, this research provides a viable approach for high-value utilization of herbal residues and demonstrates the Fe-C/O 3 system’s potential for efficient degradation of organophosphate pesticides, offering valuable insights for environmental remediation and sustainable agricultural waste management.