Enhanced degradation of aqueous doxycycline in an aerobic suspension system with pretreated sucrose-modified nano-zero-valent iron

Abstract

Sucrose-modified nano-zero-valent iron (S-NZVI) was synthesized to effectively treat aqueous doxycycline (DOX), and the reactivity, stability, and durability of S-NZVI and the DOX degradation kinetics were investigated. Under the optimized aerobic conditions, pretreated S-NZVI demonstrated a degradation kinetic rate constant (0.391 min-1) that was 1.8 times (0.207 min-1) higher than that demonstrated by posttreated S-NZVI due to the ability of pretreated S-NZVI to prevent rapid nanoparticle agglomeration. The presence of phosphate strongly influenced the reductive degradation of DOX, whereas sulfate and nitrate did not show any competing effect at various concentrations. The pretreated S-NZVI could be reused over 4 continuous cycles of DOX removal without requiring regeneration of its oxidized surface, while the reactivity of posttreated S-NZVI and bare NZVI dramatically decreased after the first cycle, suggesting that pretreated S-NZVI can be practically applied to aqua-spheres with prolonged stability to treat pharmaceutical contaminants. Total organic carbon and liquid chromatography-mass spectrometry results confirmed that the sorption and subsequent reduction of DOX were the main degradation pathways. According to the TOC analysis results, approximately 92% TOC removal was obtained during the reaction and the remnant could be present in the form of various degradation products. The experimental results provide a background for understanding aqueous DOX removal by S-NZVI and the DOX degradation kinetics and pathways under aerobic conditions to develop practical and durable novel water treatment technologies.