Metformin degradation in aqueous solutions by electro-activation of persulfate and hydrogen peroxide using natural and synthetic ferrous ion sources

Abstract

In this study, the performances of natural (pyrite) and synthetic (nano-magnetite) heterogeneous iron catalysts as a source of ferrous ion on electro-activation of hydrogen peroxide (HP) and persulfate (PS) were compared for degradation of metformin (MET) as an emerging contaminant in aqueous solutions. The effects of catalyst type and dosage, oxidant type and dosage, applied current (10–50 mA), drug concentration (15–80 mg/L), and time on MET removal were evaluated. The removal capacity of the processes was determined by evaluating the stoichiometry ratio of MET: oxidant. The process mechanism study showed that hydroxyl radical and sulfate radical were the main responsible for MET degradation in the HP-activating and PS-activating systems, respectively. The synergy between various mechanisms including adsorption, electrochemical precipitation, oxidation, and electrocoagulation was more prominent in nano-magnetite systems. A comparative study of oxidants function showed that although PS was more effective, it was more dependent on the presence of activators to remove MET. The results suggested that there was a positive correlation between the catalysts ability to distribute Fe2+ and mineralization rate. However, the highest removal efficiency of MET (89.25%) and TOC (68.42%) belonged to the natural catalyst (pyrite/PS), while lower energy demand (1.43 Wh/L), higher removal capacity, and more stability were observed in the synthetic catalyst.