Facile synthesis of urea-modified sewage sludge biochar for efficient sulfamethoxazole degradation via an electron transfer pathway

The widespread presence of antibiotic residues in environmental matrices poses significant ecological risks. In this study, N-doped sludge biochar (NSBC) was synthesized through a straightforward and practical method using waste activated sludge and urea. The synthesized NSBC was employed to activate periodate (PI) for the efficient removal of sulfamethoxazole (SMX) from aqueous solutions. The incorporation of urea markedly enhanced the biochar's adsorption capacity and catalytic oxidation performance, achieving complete SMX removal within 60 min, while maintaining high removal efficiency across wide pH conditions (3–9). Interference experiments revealed that common anions (Cl⁻, SO₄²⁻, and NO₃⁻) exerted minor inhibitory effects on SMX removal, while the presence of humic acid and the complex matrices of three natural water systems maintained SMX removal efficiencies above 70 %. Quenching experiments, electron paramagnetic resonance, and electrochemical analyses confirmed that the degradation of SMX primarily occurs via a non-radical pathway facilitated by an electron transfer mechanism. Analysis of degradation products and predictions from the ECOSAR model suggested that SMX was transformed into a series of smaller, low-toxicity intermediate products, significantly diminishing its inhibitory effect on seed germination. This study offers a sustainable strategy for waste sludge valorization and an eco-friendly solution for antibiotic pollution mitigation.