The properties of dissolved organic matter (DOM) are of interest due to their effects on water quality, ecosystem function, and water treatment efficiency. DOM is composed of reactive moieties which undergo transformation in the presence of oxidants such as ozone. In this study, two DOM isolates, Suwannee River Fulvic Acid (SRFA) and Pony Lake Fulvic Acid (PLFA), were treated with various ozone doses with and without t-butanol, a hydroxyl radical scavenger. A high-performance liquid chromatography (HPLC) and size exclusion chromatography (SEC) system paired with absorbance, fluorescence, and total organic carbon detection was used to characterize DOM samples and determine the fluorescence quantum yield (Φf) as a function of the apparent molecular weight (AMW). The SEC system was used to separate samples into three size-based fractions representing various fluorescence quantum yield values. The fractions were then irradiated in the presence of furfuryl alcohol (FFA) to measure singlet oxygen quantum yield (Φ(1O2 )). Both isolates showed increases in Φ(1O2 ) as AMW decreased for all ozone doses. High and average AMW fractions showed no significant Φ(1O2) changes as ozone dose increased. Low AMW weight fractions showed Φ(1O2) increases from ~3% to ~11% and ~2% to ~7% as ozone dose increased for SRFA and PLFA respectively, indicating phenol moieties are oxidized to quinone moieties primarily in low AMW regions. More pronounced Φ(1O2 ) increases for SRFA were likely due to higher aromatic content present for oxidation as compared to PLFA. Both isolates showed an increase in Φf as AMW decreased. As ozone doses increased, SRFA Φf decreased in all AMW regions, likely due to oxidation of fluorescent phenol moieties to non-fluorescent quinone moieties, while PLFA Φf increased as ozone dose increased. It is possible that the increase in Φf in PLFA is due to the preferential oxidation of low fluorescent DOM moieties. These results provide a new level of detail regarding the complex effects of ozonation on the photophysical and size-based properties of DOM. Additional analysis of wastewater and wastewater-impacted rivers is planned to further investigate the implications of these findings for engineered systems and water reuse scenarios.

Photochemical formation of singlet oxygen in dissolved organic matter size isolated fractions

ACS Spring 2022

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