Effect of UVC pre-irradiation on the Suwannee river Natural Organic Matter (SRNOM) photooxidant properties

•UVC irradiation of SRNOM yielded C1-C6 carbonyls that accounted for up to 46% of TOC.•This SRNOM pre-irradiation strongly increased the rate of glyphosate loss at 254 nm.••OH radicals contributed to the glyphosate degradation.•Chain reactions photoinduced by carbonyls may explain this enhanced phot...

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Bibliographic Details
Published in:Water research (Oxford) 2021-09, Vol.202, p.117395-117395, Article 117395
Main Authors: Palma, Davide, Khaled, Amina, Sleiman, Mohamad, Voyard, Guillaume, Richard, Claire
Format: Article
Language:English
Subjects:
Carbonyls
Chain reaction
Chemical Sciences
Glyphosate
Hydroperoxides
Natural organic matter
OH radicals
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Summary:•UVC irradiation of SRNOM yielded C1-C6 carbonyls that accounted for up to 46% of TOC.•This SRNOM pre-irradiation strongly increased the rate of glyphosate loss at 254 nm.••OH radicals contributed to the glyphosate degradation.•Chain reactions photoinduced by carbonyls may explain this enhanced photoreactivity. The present study aimed to investigate the changes in the chemical composition, and in the optical and photooxidant properties of Suwannee River Natural Organic Matter (SRNOM) induced by UVC (254 nm) treatment. The extent of the photodegradation was first assessed by UV–visible/fluorescence spectroscopies and organic carbon analysis. An in-depth investigation of the chemical changes was also conducted using liquid chromatography-mass spectrometry and gas chromatography-mass spectrometry after derivatizations. A series of mono, di and tricarbonyls and mono and dicarboxylic acids in C1C6 were identified in samples irradiated from 1 to 4 h. After 3 h of irradiation, carbonyls accounted for 46% of the organic carbon remaining in solution whereas carboxylic acids represented about 2%. Then, we investigated the modifications of the photooxidant properties of SRNOM induced by these chemical changes. At 254 nm, UVC pre-irradiated SRNOM photodegraded glyphosate 29 times faster than original SRNOM and the reaction was fully inhibited by 2-propanol (5 × 10−3 M). This enhanced photooxidant properties at 254 nm toward glyphosate was therefore reasonably due to •OH radicals formation, as confirmed by additional ESR measurements. A mechanism involving a chain reaction was proposed based on independent experiments conducted on carbonyl compounds, particularly pyruvic acid and acetone. The findings of this study show that UVC pre-treatment of NOM can enhance the removal of water pollutants and suggests a possible integration of a NOM pre-activation step in engineered water treatment sytems. [Display omitted]
ISSN:0043-1354
1879-2448
DOI:10.1016/j.watres.2021.117395