Effects of Ozone on the Photochemical and Photophysical Properties of Dissolved Organic Matter

Abstract

This study focused on the effects of ozonation on the photochemical and photophysical properties of dissolved organic matter (DOM). Upon ozonation, a decrease in DOM absorbance was observed in parallel with an increase in singlet oxygen (1O2) and fluorescence quantum yields (Φ1O2 and ΦF). The increase in Φ1O2 was attributed to the formation of quinone-like moieties during ozonation of the phenolic moieties of DOM, while the increase in ΦF can be explained by a significant decrease in the internal conversion rate of the first excited singlet state of the DOM (1DOM*). It is a consequence of an increase in the average energy of the first electronic transition (S1 → S0) that was assessed using the wavelength of maximum fluorescence emission (λF,max). Furthermore, ozonation did not affect the ratio of the apparent steady-state concentrations of excited triplet DOM (3DOM*) and 1O2, indicating that ozonation does not affect the efficiency of 1O2 production from 3DOM*. The consequences of these changes for the phototransformation rates of micropollutants in surface waters were examined using photochemical model calculations. The decrease in DOM absorbance caused by ozonation leads to an enhancement of direct photolysis rates due to the increased transparency of the water. Rates of indirect photooxidation induced by 1O2 and 3DOM* slightly decrease after ozonation.

Effect of UV/chlorine treatment on photophysical and photochemical properties of dissolved organic matter

“…The 1O2 -values for the selected low molecule DOM analogs were calculated and the results showed that the 1O2 for BP ((8.48 ± 0.09) × 10 −2 ) containing a ketone functionality and for p -BQ ((2.92 ± 0.01) × 10 −2 ) with a quinone functional group were much higher than the value of 1O2 for the other analogs, which is in accordance with the results observed in previous literature ( Leresche et al, 2019 ;McNeill and Canonica, 2016 ). Thus, the formation of quinone and ketone functional groups during the UV/chlorine treatment are the reason for the increase of the 1O2 from SRFA and SRNOM.…”

Molecular-Level Transformation of Dissolved Organic Matter during Oxidation by Ozone and Hydroxyl Radical

“…Similar decreases in molecular weight due to ozonation are observed using direct measurements such as SEC 1,13,15 and sequential ultrafiltration, 14 as well as using UV-vis spectroscopy-derived parameters. 21,33,34,58 Large decreases in SUVA254 are observed with increasing specific O3 doses (Figures 1c and S4c), which agrees with previous observations 12,13,[16][17][18]34 and correlates with decreasing aromaticity.…”

“…Many of the oxidized product formulas observed here occupy the same van Krevelen space as formulas associated with triplet DOM and singlet oxygen production, 53,55 confirming observations that ozonation increases quantum yields of these species in undiluted wastewater. 20,21 Finally, the molecular composition of DOM observed after ozonation is highly oxidized, with many formulas with O:C values that are outside the range encountered in natural and engineered waters (i.e., >1.0). 17,41,42,53,55,65…”

“…[9][10][11] Ozonation of DOM results in limited mineralization of dissolved organic carbon (DOC), [12][13][14][15][16][17][18] but can dramatically alter DOM composition. For example, ozonation changes DOM photoreactivity [19][20][21] and produces highly bioavailable assimilable organic carbon (AOC). [22][23][24][25] Low molecular weight organic by-products associated with AOC include carboxylic acids, aldehydes, and ketones (Supporting Information Figure S1).…”

Progress on the photo aging mechanism of microplastics and related impact factors in water environment

“…天然有机质(NOM)一般由中等分子量的疏水性芳香聚电解质组成，包括多 糖、多肽、氨基酸、蛋白质和腐殖质等 [76,77] ，且 NOM 对水环境中有机物光降解 的影响既有促进作用也有抑制作用 [78~80] . NOM 作为光敏化剂促进水中有机污染 物 光降解的机制主要是由于其吸收光能后发生电子跃迁形成激发单线态 NOM( 1 DOM*) [81,82] ，并发生系间窜跃形成激发三线态 NOM( 3 NOM*). 3 NOM*是…”