Synergistic oxidative removal of sulfamethoxazole using Ferrate(VI) and peroxymonosulfate

[Display omitted] •The study investigates the combined use of Fe(VI) and peroxymonosulfate for the oxidative removal of sulfamethoxazole.•Sulfate radicals generated through Fe(VI)-mediated activation of PMS are highly effective in oxidizing sulfamethoxazole.•Fe(VI), Fe(V), and Fe(IV), also play a crucial role in facilitating efficient sulfamethoxazole oxidation.•The pH of the system is a critical parameter, with an optimal pH value of 6 for sulfamethoxazole removal.•The potential contributions of Fe2O3 or Fe(OH)3 to the oxidation mechanism were presented. The synergic effect of Ferrate(VI) (Fe(VI)) and peroxymonosulfate (PMS) on sulfamethoxazole (SMX) oxidative removal was investigated in this study. The sulfate radicals (SO4−), generated through Fe(VI)-mediated activation of PMS, have been demonstrated as an effective oxidant for the removal of SMX. However, the scavenging experiments have suggested that various iron species, i.e., Fe(VI), Fe(V), and Fe(IV) play a vital role in facilitating efficient SMX oxidation. pH is a crucial parameter in this system because the involved species, including Fe(VI), PMS, and SMX, have acid-base dissociation points. Accordingly, the optimal pH value for the SMX removal was achieved at pH = 6, and the addition of PMS enhanced the degradation efficiency of Fe(VI) at all pH-operating conditions. Several oxidation products of SMX were identified, including sulfanilamide (SAM), 3-amino-5-methylisoxazole (AMI), and other potentially hydroxylated byproducts. Characterization studies on solid particles collected after the Fe(VI)/PMS treatment revealed structural changes during SMX oxidation, and the potential contributions of Fe2O3 or Fe(OH)3 to the oxidation mechanism were evaluated accordingly. While the removal efficiency in a river matrix was slightly reduced, the presence of inorganic ions had minimal impact on SMX removal, which confirms the high potential of the Fe(VI)/PMS technology to operate in environmentally relevant conditions.