Selective Oxidation of Pharmaceuticals and Suppression of Perchlorate Formation during Electrolysis of Fresh Human Urine
Preprints are manuscripts made publicly available before they have been submitted for formal peer review and publication. They might contain new research findings or data. Preprints can be a draft or final version of an author's research but must not have been accepted for publication at the time of submission.
Many pharmaceutical compounds are excreted unchanged or as active metabolites via urine. They pass through conventional wastewater treatment processes and present a risk to aquatic ecosystems and humans. Point-source remediation of source-separated urine provides a promising alternative to destroy pharmaceuticals before dilution with wastewater. Electrochemical advanced oxidation processes are one possible option for degrading pharmaceuticals in urine, but they often lead to the formation of oxidation byproducts (OBPs) including chlorate, perchlorate, and halogenated organics at hazardous concentrations due to high background chloride concentrations. Here, we show that the high urea content of fresh human urine suppresses the formation of oxychlorides by inhibiting formation of HOCl/OCl‒ during electrolysis, while still enabling the oxidation of pharmaceuticals by •OH due to the slow rate of urea oxidation by •OH. This results in improved performance when compared to equivalent treatment of hydrolyzed aged urine. This (primarily indirect) electrochemical oxidation scheme is shown to degrade the model pharmaceuticals cyclophosphamide and sulfamethoxazole with surface-area-to-volume-normalized pseudo-first-order observed rate constants greater than 0.08 cm/min in authentic fresh human urine matrixes. It results in two orders-of-magnitude decrease in pharmaceutical concentrations in 2 hours while generating three orders-of-magnitude lower oxychloride byproduct concentrations in synthetic fresh urine as compared to synthetic hydrolyzed aged urine matrixes. Importantly, this proof-of-principle shows that simple and safe electrochemical methods can be used for point-source-remediation of pharmaceuticals in fresh human urine (before storage and hydrolysis), without formation of significant oxychloride byproducts.