Ferrate (Fe(VI)) Application for Municipal Wastewater Treatment: a Novel Process for Simultaneous Micropollutant Oxidation and Phosphate Removal

A novel technology for enhanced municipal wasterwater treatment was assessed based on the dual functions of Fe(VI) to oxidize micropollutants and remove phosphate by formation of ferric phosphates. Second-order rate constants (k) for the reactions of selected pharmaceuticals, endocrine disruptors, and organic model compounds with Fe(VI) were in the range of 1 (trimethylamine) to 9000 M(-1) s(-1) (aniline) in the pH-range 7-8. The selected compounds contained electron-rich moieties (ERM) such as phenols, anilines, amines, and olefins. Oxidation experiments in wastewater spiked with micropollutants at concentrations in the low microM range at pH 7 and 8 showed that Fe(VI) doses higher than 5 mg Fe L(-1) are capable of eliminating various ERM-containing micropollutants by more than 85%. In comparison to ozone, Fe(VI) was as effective or slightly less effective in terms of micropollutants oxidation, with Fe(VI) having the benefit of phosphate removal. To lower phosphate from 3.5 to 0.8 mg PO4-P L(-1) (regulatory limit for wastewater discharge in Switzerland), a Fe(VI) dose of 7.5 mg Fe L(-1) was needed. Overall, this study demonstrates Fe(VI) as a promising tool for an enhanced wastewater treatment to remove micropollutants as well as to control phosphate in a single treatment step.