Degradation of sulfamethazine by amorphous zero-valent iron microspheres (A-mZVI) activated peroxydisulfate in groundwater

Abstract

Amorphous zero-valent iron microspheres (A-mZVI) were synthesized by introduction of ethylenediamine (EDA) and used to activate peroxydisulfate (PDS) to eliminate sulfamethazine (SMT) in groundwater. Experimental results indicated that the A-mZVI/PDS system exhibited a much better performance in the removal of SMT (93.2%) than conventional crystalline nanoscale ZVI (C-nZVI) induced PDS activation system (45.3%). The A-mZVI/PDS system had a better performance under neutral and alkaline conditions than the acidic condition, showing excellent decontamination performance in actual groundwater. The co-existing groundwater components (Na+, Ca2+, Cl−, SO42−, humic acid) had no obvious impact on the removal of SMT except for HCO3−. Characterization of as-synthesized A-mZVI particles demonstrated that the addition of EDA resulted in the formation of amorphous structure of ZVI, and there is an optimum EDA/Fe(II) molar ratio. It was proposed that the amorphous structure favored the release of electrons from the iron core to the surface of A-mZVI to continuously generate ≡Fe(II), leading to the generation of abundant free radicals (both SO4•−and •OH) via the activation of PDS. The intermediates and possible degradation pathways of SMT were revealed, and the developmental toxicity and bioaccumulation factors of SMT and its intermediates were predicted by quantitative structure-activity relationship (QSAR) analysis.