The removal of tetracyclines by microscale zerovalent iron (MZVI) from aqueous solutions

The Removal of Tetracyclines by Microscale Zerovalent Iron (mZVI) from Aqueous Solutions The main objective of this study was to determine the removal mechanism of tetracycline (TC), oxytetracycline (OTC) and chlorotetracycline (CTC) by microscale zerovalent iron (mZVI) and the formation of transformation products during the removal studies. Solution pH, iron dose and reaction temperature were studied with a batch experimental series in order to evaluate the removal efficiency of TC, OTC and CTC and the adsorption kinetics. The results showed that pH was a key factor in removing all three tetracycline compounds, although increasing the temperature and iron dose enhanced their removal efficiency. When the optimal pH was similarly for tetracycline and oxytetracycline, different behaviour was observed for chlorotetracycline. When the optimal pH was 3 for TC and OTC, this value was determined as 9 for CTC. The adsorption kinetics fitted perfectly the pseudo-second-order model. Data was interpreted by the Langmuir Model with the maximum adsorption capacity of 23.98, 34.01 and 28.17 mg/g (600C) of TC, OTC and CTC on mZVI, respectively. The main transformation product was 4-epi-tetracycline for TC which quickly sorbed onto mZVI within 15 min. Transformation products were found as β-Apo-OTC and α-Apo-OTC for OTC and 4-epi-chlorotetracycline and anhydrochlorotetracycline for CTC. The removal mechanism of TC, OTC and CTC using mZVI surface was concluded as adsorption rather than degradation process. Keywords: Tetracyclines, Transformation product, Adsorption kinetic, Microscale zerovalent iron