Ph.D. Thesis Defense Announcement

Ferrate (Fe(VI)) Oxidation for Mitigation of Pharmaceutical Micropollutants in Source-Separated Hydrolyzed Urine and Related Conditions

by

Cong Luo

Advisor(s):

Dr. Ching-hua Huang (CEE)

Committee Members:

Dr. Yongsheng Chen (CEE), Dr. Spyros G. Pavlostathis (CEE), Ýr. Yuanzhi Tang (EAS), Dr. Virender Sharma ( School of Public Health, TAMU)

Date & Time: May 8th, 3pm EST

Location: https://bluejeans.com/374741835

 Complete announcement, with abstract, is attached

        Human urine accounts for approximately 1% of domestic wastewater by volume yet urine contributes a disproportionate mass load to wastewater—greater than 80% of N, 50% of P, and 60% of pharmaceuticals. As such, destruction of pharmaceutical excreted in urine can be an efficient approach to minimize the environmental pollution of these compounds in wastewater, surface water and drinking water.  However, research about the removal of pharmaceuticals and their metabolites in urine has been scarce. Previously proposed approaches either suffered from strong scavenging effects from urine components or required further chemical treatment to degrade these pharmaceutical wastes, generated from physical separation. Thus, more effective treatment should be introduced to eliminate pharmaceuticals and metabolites in urine. 
            This dissertation focuses on developing Fe(VI)-based advance oxidation technology for destruction of pharmaceutical in source-separated human urine and related conditions, with a particular aim to elucidate the involved reaction mechanisms. First, study was performed to investigate the degradation of selected pharmaceuticals in synthetic hydrolyzed urine (pH 9.0) and in phosphate buffer (pH 9.0) spiked with urine components. The comparison between synthetic urine and phosphate buffer matrices uncovered the specific impacts of inorganic and organic urine constituents on Fe(VI) oxidation. Second, further research was conducted to delineate the reaction kinetics and mechanisms of Fe(VI) oxidation of pharmaceuticals in the presence of bicarbonate or creatinine, both of which enhanced the Fe(VI) oxidation efficiency. By evaluating the reactive moieties and oxidation products of pharmaceuticals in such systems, the underlying oxidation mechanism involving the formation of high-valent iron intermediate species (Fe(V)/Fe(IV)) and their contribution to the enhanced pharmaceutical degradation was elucidated, and the usefulness of the Fe(VI)-activated systems was demonstrated.  
          Several Fe(VI)-activated systems were further investigated via dynamic kinetic modelling to provide new fundamental insights of the kinetic behaviors of Fe(V)/Fe(IV) during Fe(VI) oxidation process. First, kinetic modelling and density functional theory (DFT) calculation of Fe(VI) self-decay at alkaline conditions (pH 9 and 10) were performed and the results indicated different reaction kinetics and mechanisms upon the protonation of Fe(VI). A new kinetic model containing Fe(VI) decay involving Fe(V) and Fe(IV) at pH 9.0 was successfully derived to predict Fe(VI) disappearance and H2O2 generation (a product) under varied conditions, which provided the basis for Fe(VI) oxidation simulation at pH 9.  Second, the Fe(VI)-Fe(III) reaction system was investigated to evaluate the enhancement effect of ferric ion on Fe(VI) self-decay at pH 9.0. The Fe(VI)-Fe(III) kinetic model was constructed to characterize the Fe(III) acceleration of Fe(VI) self-decay into Fe(IV) based on the Fe(VI) self-decay model at pH 9.0 developed previously. Furthermore, Fe(VI)-Fe(III)-substrate model was constructed to evaluate the enhanced effect of ferric ion on Fe(VI) oxidation on 18 pharmaceuticals. The structure-activity relationship between compounds’ molecular descriptors and 2nd -order rate constants between Fe(IV) and substrates derived from Fe(VI)-Fe(III)-Substrate was assessed. Third, the Fe(VI)-ABTS reaction system at pH 7.0 phosphate (10 mM) buffered solution was systematically investigated to quantitatively probe iron intermediate species (Fe(V)/Fe(IV)) in Fe(VI) oxidation. The proposed Fe(VI)-ABTS-substrate model was later developed to successfully determine reactivity pf Fe(V) to different substrates. 
         Overall, the research outcome of this dissertation filled several knowledge gaps for applications of Fe(VI) in pharmaceutical removal in human urine and related conditions, which will be useful toward the management of contaminants of emerging concern. The new knowledge will also help accelerate a broader application of ferrate oxidation technology in various contamination treatment and mitigation. Moreover, this research exemplified probing Fe(V)/Fe(IV) kinetic behaviors during Fe(VI) oxidation via the useful tools of dynamic kinetic modelling. The new models developed in this study could inspire and facilitate future studies to better understand the fate of Fe(V)/Fe(IV) in other Fe(VI)-activated systems and even uncover Fe(V)/Fe(IV) reactivity and selectivity to different organic pollutants.