Ozonation of Pharmaceuticals and Their Human Metabolites in WastewaterInsights from Laboratory Experiments and Field Data

Pharmaceuticals and their human metabolites are contaminants
of
emerging concern in aquatic environments. While monitoring usually
targets parent compounds, metabolites, often excreted at higher loads,
are largely overlooked. This study investigates the behavior of both
during wastewater treatment, focusing on ozonation as an advanced
treatment step. Second-order rate constants for reactions of 87 parent
compounds and 130 metabolites with ozone were determined using a multicompound
competition kinetics method, enabling exploration of functional group-specific
reactivity trends. Aromatic hydroxylation generally increased ozone
reactivity (up to 5 orders of magnitude), whereas N-oxides (up to 5 orders of magnitude) and N-dealkylated
metabolites (up to 2 orders of magnitude) showed reduced reactivity
compared to their parents. These constants, combined with predicted
second-order rate constants for the reaction with hydroxyl radicals,
as well as estimated ozone exposures and experimentally determined
hydroxyl radical exposures, were used to model the abatement in three
Swiss wastewater treatment plants. Modeled and observed abatement
agreed well. A derivative-based sensitivity analysis highlighted ozone
exposure as most crucial for moderately to highly ozone-reactive compounds,
whereas hydroxyl radical exposure dominated for ozone-resistant compounds.
This study emphasizes the importance of considering both parent compounds
and metabolites in wastewater treatment processes to address contaminants
holistically.