Study on characteristics of ferrate coupled peracetic acid for advanced treatment of metronidazole in water

Metronidazole(MNZ), prone to accumulate in the environment, is a nitroimidazole antibiotic and its metabolites have potential carcinogenicity and mutagenicity. In this paper, the degradation characteristics of MNZ by coupled ferrate/peroxyacetic acid〔Fe(Ⅵ)/PAA〕technology, as well as the simulation of MNZ degradation and reaction mechanism, were investigated. When the dosages of Fe(Ⅵ) as 500 μmol/L and PAA as 100 μmol/L, the degradation of MNZ reached 94.85% at pH of 8 in 60 min, and the degradation process followed pseudo-first-order kinetics. Variable experiments showed that the degradation of MNZ was positively correlated with the dosage of Fe(Ⅵ) and PAA, and the best effect was achieved at pH=8. Chloride (Cl-) and nitrate (NO3-) in the water matrix had little effect on the degradation of MNZ. Ammonium salt (NH4+) could promote the degradation of MNZ,while bicarbonate (HCO3-) and humic acid (HA) inhibited the degradation. The removal of MNZ in simulated medical wastewater by Fe(Ⅳ)/PAA was similar to that in ultra-pure water, which could achieve better removal effect. Probe experiments and quenching experiments showed that PAA accelerated the removal of MNZ from active species. H2O2 coexisting with PAA was the main activator of Fe(Ⅵ) while the main active species of Fe(Ⅵ)/PAA system were Fe(V) and Fe(Ⅳ). The results were expected to provide theoretical reference and data support for the application of Fe(Ⅵ)/PAA system in the deep treatment of MNZ in medical wastewater.