Evaluating and mitigating the adverse effects of halide ions on the sulfamethoxazole degradation in the Co2+/peroxymonosulfate process

Halide ions are commonly found in aquaculture wastewater, yet their halide-specific influence on sulfamethoxazole (SMX) degradation within the Co 2+ /peroxymonosulfate (PMS) process requires further investigation to be fully elucidated. This study systematically evaluated the impacts of halides, revealing that trace concentrations of Br⁻ (0.05 mM) significantly enhanced SMX elimination kinetics, achieving rate constants ∼12 times higher than with Cl⁻ (50 mM) and ∼4.5 times higher than in the baseline Co 2+ /PMS system. The significant enhancement observed with Br⁻ is attributed to the selective singlet oxygen ( 1 O 2 )-mediated oxidation of SMX. However, the formation of halogenated aromatic products and the ecotoxicity of dimeric by-products in the presence of Br⁻ warranted attention. This adverse effect was effectively mitigated through the strategic addition of sulfamic acid (0.1 mM) as a selective inhibitor. A possible degradation pathway of SMX in the Co 2+ /PMS system was proposed. These findings establish a quantitative framework for optimizing the Co 2+ /PMS process, enabling effective degradation of sulfonamide antibiotics in halide-rich wastewater while minimizing ecotoxicological risks through targeted pathway control. • Co 2+ /PMS/Br⁻ and Co 2+ /PMS/X⁻ systems showed exceptional degradation efficiency. • Br⁻ altered the SMX degradation pathway and produced more harmful products. • Halogen ions promoted the formation of 1 O 2 in the Co 2+ /PMS system. • Sulfamic acid eliminated negative effects of Br⁻ with unchanged degradation rate.