Heterogeneous Fenton system driven by iron-loaded sludge biochar for sulfamethoxazole-containing wastewater treatment

In this study, the treatment performance of a heterogeneous Fenton system (Fe-BC + H₂O₂) driven by iron-loaded sludge biochar (Fe-BC) on wastewater containing sulfamethoxazole (SMX) was investigated using the CODcr removal efficiency (φ) as an indicator. The batch experimental results showed that the optimal operating conditions were as follow: initial pH 3, H₂O₂ concentration 20 mmol L^-1, Fe-BC dose 1.2 g L^-1, temperature 298 K. The corresponding φ was as high as 83.43%. The removal of CODcr was better described by BMG model and revised BMG (BMGL) model. According to the BMGL model, the φ_max could be 98.37% (298 K). Moreover, the removal of CODcr was a diffusion-controlled process, while liquid film diffusion and intraparticle diffusion together determined its removal rate. The removal of CODcr should be a synergistic effect of adsorption and Fenton oxidation (real heterogeneous Fenton and homogeneous Fenton) and other pathways. Their contributions were 42.79%, 54.01% and 3.20%, respectively. For homogeneous Fenton, there seemed to be two simultaneous SMX degradation pathways: SMX→4-(pyrrolidine-11-sulfonyl)-aniline→N-(4-aminobenzenesulfonyl) acetamide/4-amino-N-ethyl benzene sulfonamides→4-amino-N-hydroxy benzene sulfonamides; SMX→N-ethyl-3-amino benzene sulfonamides→4-methanesulfonylaniline. In summary, Fe-BC had potential for practical application as a heterogeneous Fenton catalyst.