Photochemical Fate and Advanced Oxidation Treatment of Pharmaceuticals in Water

This work focuses on two broad areas: the photochemical fate of pharmaceutical compounds in the environment and advanced oxidation technologies designed to remove them from the water supply.;Advanced oxidation processes have been shown to hold potential for the removal of emerging contaminants of concern from water samples in an efficient and economical manner. These processes are based on the production of a reactive species, such as the hydroxyl radical or hydrated electron, which then reacts with, and breaks down, the pharmaceutical molecule. Using fluoroquinolones and antidepressants as representative sets of pharmaceuticals, the hydroxyl radical and hydrated electron were both found to rapidly react with these compounds (∼109-1010 M-1 s-1). Several byproducts and degradation pathways were identified.;While the hydroxyl radical and hydrated electron both react rapidly with organic compounds, the hydroxyl radical plays a larger role in the degradation of pharmaceuticals in surface waters, due to its higher steady state concentration in the natural environment. This was demonstrated for three antidepressant compounds. Experiments were also performed to analyze the role of singlet oxygen, whose contribution to the degradation is approximately an order of magnitude lower than that of the hydroxyl radical.;In addition to reactive oxygen species, excited state natural organic matter may also contribute to the photochemical degradation of pharmaceutical compounds. To measure the rate constants between excited triplet state natural organic matter and pharmaceutical compounds, the excited state was generated by laser flash photolysis at 355 nm and the decay of the transient excited state species absorption was monitored at 525 nm. Rate constants were found to be on the order of 108-109 M-1 s-1, indicating that excited triplet state natural organic matter reacts rapidly with these pharmaceuticals and, if present in the environment, may contribute substantially to their photochemical degradation.;This work represents a small step in the quest to describe and understand the behavior of pharmaceutical compounds in the natural environment and in engineered treatment systems. It is hoped that this knowledge will contribute to the eventual ability to ensure that these compounds are removed from our water supply.