Ferrate(VI) Oxidation of Pharmaceuticals in Hydrolyzed Urine: Enhancement by Creatinine and the Role of Fe(IV)

Abstract

Treatment of human urine is an emerging approach to minimize environmental pharmaceutical contamination. This study investigated the application of ferrate(VI) (Fe VI O 4 2−, Fe(VI)) oxidation to degrade pharmaceuticals (i.e., carbamazepine (CBZ), naproxen (NAP), sulfamethoxazole (SMX), and trimethoprim (TMP)) in synthetic hydrolyzed human urine, with the emphasis on the effects of urine endogenous organic metabolites. Creatine and hippuric acid showed limited to moderate scavenging effects. Creatinine (CRE) was first discovered to significantly enhance the oxidation rates of CBZ, TMP, SMX, and other amine-containing compounds by Fe(VI). Fe(IV) was proposed as the major intermediate reactive iron species in the Fe(VI)−CRE system, based on the DFT calculation and experimental measurements. A kinetic model involving Fe(IV) contribution in the decay of the pharmaceuticals was developed for the first time to successfully describe the pharmaceutical removal in the Fe(VI)−CRE−micropollutant system. Moreover, the model was used to predict the rate constants of Fe(IV) reacting with different compounds, which ranged from (2.2 ± 0.1) × 10 4 to (8.3 ± 0.6) × 10 4 M −1 s −1 . Overall, this study further demonstrated the promise of Fe(VI) oxidation to degrade pharmaceuticals in hydrolyzed urine owing to the enhanced effects from urine constituents. This study also advanced the mechanistic and kinetic understanding of enhanced oxidation involving highvalent iron intermediate species.

Generation of Iron(IV) in the Oxidation of Amines by Ferrate(VI): Theoretical Insight and Implications in Oxidizing Pharmaceuticals

“…The amines in surface water are present in the form of dissolved organic nitrogen from wastewater discharges, algal blooms, and agricultural runoff activities. Amines as co-contaminants with pharmaceuticals would enhance and accelerate the oxidation of the target contaminants by Fe­(VI), for example, the enhanced efficiency of the oxidation of pharmaceuticals in the presence of creatinine in hydrolyzed urine . However, this effect of amines depends on the concentration of amines compared to that of Fe­(VI) because the formation of the Fe IV –amine complex and its enhanced performance depend on the molar ratio of amine to Fe­(VI).…”

“…The mechanism of oxidation of pollutants, including amine-containing molecules, by Fe­(VI) possibly involves iron­(IV) (Fe IV ), iron­(V) (Fe V ), or both as the intermediate(s). − In the past, the complexation of ammonia with Fe IV and Fe V has been proposed to describe the observed results for the oxidation of ammonia by Fe­(VI). , Recently, we have found that creatinine (2-amino-1-methyl-5 H -imidazol-4-one, CRE), an amine-containing major organic constituent of urine, could enhance the degradation of pharmaceuticals by Fe(VI) . CRE is known to be a ligand for metal ions, including iron .…”

“…Many researchers, including us, applied a chemical probe molecule, i.e., methyl phenyl sulfoxide (PMSO), to demonstrate the formation of Fe IV /Fe V intermediates during the oxidations by Fe­(VI). Studies did not establish which of the two intermediates dominated during Fe­(VI) oxidations. , The Fe IV /Fe V species are present at low steady-state concentrations and only for time scales in the range from microseconds to milliseconds. ,, Therefore, attempts of spectroscopic approaches to identify Fe IV /Fe V species in an aqueous environment were not successful. , The demonstration of the intermediate Fe IV /Fe V species is restricted to a non-aqueous (or organic) solvent in which the central iron is complexed by bulky organic ligands such as porphyrins and 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane. ,, In other words, the direct experimental evidence of the high-valent iron intermediate in the oxidative chemistry of Fe­(VI) requires overcoming of limitations imposed by the inherent instability of Fe IV /Fe V species and their trapping in aqueous solutions.…”

Ultrasound-Induced Intensification of Electrochemical Treatment of Bulk Drug Pharmaceutical Wastewater

“…3,4 Inadequate disposal of expired medicines via toilets, trash, or drains is also a major source of pharmaceutical pollution. 5 The complex structure of these ingredients makes wastewater toxic, persistent, and complex. 6 Bulk drug pharmaceuticals include various types of chemical substances, such as antibiotics, analgesics, and antiinflammatories, that are used to treat various diseases.…”

“…The presence of emerging contaminants, including pharmaceuticals, in the aquatic system has become a global issue because of their harmful effects on aquatic life and physiological effects on humans. , Pharmaceutical compounds enter the aquatic environment either directly from the production plant or indirectly through anthropogenic activities such as sewage discharge, breeding, and landfill leachate, which results in their presence in groundwater and surface water. , Inadequate disposal of expired medicines via toilets, trash, or drains is also a major source of pharmaceutical pollution . The complex structure of these ingredients makes wastewater toxic, persistent, and complex .…”