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Abstract:
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Anthropogenically -derived substances , including pharmaceuticals and personal care products , endocrine -disrupting chemicals , and pesticides , are increasingly being detected in drinking water supplies and wastewater effluents . Concerns over the presence of these compounds in water supplies include their ability to impart toxicological activity , their capacity to spread antibiotic resistance , and their potential to affect cell -signaling processes . For these reasons , water treatment processes geared towards removal of these trace organic contaminants are vital .
In this work , ozone was used to treat four pharmaceutical contaminants : ciprofloxacin , cyclophosphamide , erythromycin , and ifosfamide . Ciprofloxacin and erythromycin are antibiotic /antimicrobial compounds , and cyclophosphamide and ifosfamide are chemotherapy agents . Ozone effectively transformed all four pharmaceuticals , even in the presence of background natural organic matter , which exerts a considerable ozone demand . The apparent rate constants for the reaction of the pharmaceuticals with ozone at pH 7 were determined : 3 .03 M -1s -1 for cyclophosphamide ; 7 .38 M -1s -1 for ifosfamide ; 1 .57×104 M -1s -1 for ciprofloxacin ; and 7 .18×104 M -1s -1 for erythromycin . Cyclophosphamide and ifosfamide , which do not react quickly with ozone , exhibited high rate constants (2 .7×109 M -1s -1 ) for transformation by hydroxyl radicals , which are formed through ozone decomposition . Nevertheless , complete removal of cyclophosphamide and ifosfamide was achievable using a novel continuous aqueous ozone addition reactor and an ozone -based advanced oxidation process (peroxone ) .
In ozone -based processes , pharmaceuticals are systematically transformed via complex oxidative pathways towards CO2 , H2O , and the oxidized forms of other elements . Intermediate oxidation products containing oxygen atoms or hydroxyl groups substituted into the chemical structure of the parent pharmaceutical were identified using liquid chromatography -mass spectrometry (LC -MS ) . Given the structural similarity of intermediate oxidation products to the parent pharmaceuticals , an antimicrobial activity assay was employed to monitor the removal of pharmacological activity associated with ciprofloxacin , erythromycin , and their respective intermediate oxidation products throughout treatment . For solutions containing ciprofloxacin or erythromycin , ozone was able to completely eliminate the corresponding antimicrobial activity . Ciprofloxacin intermediate oxidation products were pharmacologically active ; however , erythromycin’s intermediate products did not contribute to the residual antimicrobial activity . These results suggest that the design of conventional and advanced ozone -based processes must incorporate ozone demand from background organic matter and account for destruction of pharmacologically active intermediates . |