Comprehending the practical implementation of permanganate and ferrate for water remediation in complex water matrices

Most previous studies examined permanganate or ferrate oxidation using various emerging pollutants (EPs) spiked in ultrapure water with concentrations of orders-of-magnitude higher than those in natural waters. In present study, we assessed the efficiency of permanganate and ferrate (with ozone as a comparison) at mg L⁻¹ level to remove selected EPs at μg L⁻¹ level in complex water matrices. The efficiency of permanganate and ferrate is more easily affected by the humic acid in synthetic water or dissolved organic matter (DOM) in natural river water compared to ozone. Experiment results revealed that humic acid or DOM were not mineralized by oxidants, but changed in compositional nature, including decreases in the aromaticity, electron-donating capacity, and average molecular weight. At molecular level, condensed aromatic, lignin-like, and tannin-like components in humic acid and DOM are the critical sites being attacked by permanganate or ferrate, the alkene groups and aromatic structures were oxidized predominantly to carboxylic acids. Overall, the present study provided insights into the performance of permanganate and ferrate used for EPs treatment under realistic conditions, as well as alternations of DOM that can be expected following exposure to these oxidants.