Efficient degradation of tetracycline hydrochloride in wastewater through peroxysulphate activation using ferrate

The degradation of tetracycline hydrochloride through peroxysulphate activation using activated carbon, iron powder, ferrous sulfide, ferrous sulfate heptahydrate, and potassium ferrate were carried out, respectively. And, the effects of initial tetracycline hydrochloride concentration, peroxysulphate concentration, ferrate concentration, initial solution pH, reaction temperature, and co-existing ions on degradation of tetracycline hydrochloride were investigated. Besides, the main active species in FeS+Na₂S₂O₈ and K₂FeO₄+Na₂S₂O₈ system were speculated by radical scavenging experiments. The degradation products of tetracycline hydrochloride in K₂FeO₄+Na₂S₂O₈ system were identified by HPLC-MS. The results showed that FeS and K₂FeO₄ were the optimal activators of peroxysulphate. When K₂FeO₄ acted as an activator for peroxymonosulfate, the higher degradation efficiencies of tetracycline hydrochloride were gained in wide concentration range of tetracycline hydrochloride from 10 mg·L⁻¹ to 80 mg·L⁻¹. The co-existing ions of \mathrmSO_4^2- , Cl⁻ and \rmHPO^2-_4 inhibited the degradation of tetracycline hydrochloride. The degradation efficiency reached 99.97% under the optimal conditions in 50 min. \mathrmSO_4^- ·、·OH and ^lO₂ were detected in FeS+Na₂S₂O₈ and K₂FeO₄+Na₂S₂O₈ system, and ·OH and ^lO₂ mainly accounted for degradation of tetracycline hydrochloride. The degradation of tetracycline hydrochloride via peroxymonosulfate activation with ferrate could happen through eight distinct pathways, which referred to hydrogen extraction, hydrogenation, hydroxylation, demethylation, decarbonylation, dealkylation, deamination, dehydration, oxidation of C═C bond, bond rupture of C─N and ring opening, etc.