Optical properties and photochemical production of hydroxyl radical and singlet oxygen after ozonation of dissolved organic matter

Chlorine is commonly used in disinfection processes in wastewater treatment plants prior to discharge of the effluents into receiving waters. Effluent organic matter and humic substances constitute up to 90% of dissolved organic matter (DOM) in receiving water, which induces photogeneration of reactive species (RS) such as excited triplet state of DOM ( 3 DOM*), singlet oxygen ( 1 O 2 ), and hydroxyl radical ( • OH). The RS plays an important role in the attenuation of trace pollutants. However, the effect of chlorine disinfection on the photoreactivity of the DOM has remained unclear. Here, we investigated the physicochemical properties and subsequent RS variation after chlorination of DOM. Solid-state 13 C cross-polarization/magic angle-spinning NMR and Fourier transform ion cyclotron resonance mass spectrometry verified that the aromaticity, electron-donating capacity (EDC), and average molecular weight of DOM decreased markedly after chlorination. It was found for the first time that the photoproduction of 3 DOM*, 1 O 2 , and • OH increased markedly after chlorination of DOM upon irradiation of simulated sunlight. The quantum yields of 3 DOM*, 1 O 2 , and • OH were positively correlated with E2/E3 (ratio of the absorbance at 254 to 365 nm) while negatively correlated with EDC before and after chlorination. These findings highlight the synergetic effect of chlorine disinfection on the photosensitization of DOM under irradiation of sunlight, which will promote the removal of trace pollutants in surface waters.

Section: Resultssupporting

confidence: 91%

Section: •−mentioning

confidence: 77%

Mechanistic Investigation of Enhanced Photoreactivity of Dissolved Organic Matter after Chlorination

Wan

Wang

Sharma

et al. 2021

“…However, we suggest that CPs may present differential reactivities toward • OH and • OH-like species since CPs mainly react with • OH through H abstraction, while • OH-like species prefer to react with aromatic moieties through OH addition . As the photoproduction of • OH-like species could be proportional to that of • OH, a similar analysis as done for • OH could be useful for • OH-like species . Nevertheless, [ • OH] aq could be overestimated by the use of BA as a probe.…”

Section: Resultsmentioning

confidence: 89%

Microheterogeneous Distribution of Hydroxyl Radicals in Illuminated Dissolved Organic Matter Solutions

Yan

Sun

Sha

et al. 2021

Hydroxyl radicals ( • OH) are important reactive species that are photochemically generated through solar irradiation of chromophoric dissolved organic matter (CDOM) in surface waters. However, the spatial distribution within the complex three-dimensional structure of CDOM has not been examined. In this study, we used a series of hydrophobic chlorinated paraffins as chemical probes to elucidate the microheterogeneous distribution of • OH in illuminated CDOM solutions. The steady-state concentration of • OH inside the CDOM microphase is 210 ± 31-fold higher than the concentration in the aqueous phase. Our results suggest that the most photochemically generated • OH are confined into the CDOM microphase. Thus, illuminated CDOM behaves as a natural microreactor for • OH-based oxidations. By including intra-CDOM • OH, the quantum yield of • OH for CDOM solutions was estimated to be 2.2 ± 0.5 × 10 −3 , which is 2 orders of magnitude greater than previously thought. The elevated concentrations of photogenerated • OH within the CDOM microphase may improve the understanding of hydrophobic pollutant degradation in aqueous environments. Moreover, our results also suggest that • OH oxidation may play more important roles in the phototransformation of CDOM than previously expected.

“…The methods used to quantify the production and quantum yields of 1 O 2 and • OH using probe compounds (furfuryl alcohol and benzoic acid, respectively) are described elsewhere ,, and are additionally described in the Supporting Information, Texts S2 and S3.…”

Section: Methodsmentioning

confidence: 99%

Photochemical Aging of Atmospheric Particulate Matter in the Aqueous Phase

Leresche

Salazar

Pfotenhauer

et al. 2021

Self Cite

This study focused on the photoaging of atmospheric particulate matter smaller than 2.5 μm (PM2.5) in the aqueous phase. PM2.5 was collected during a winter, a spring, and a summer campaign in urban and rural settings in Colorado and extracted into water. The aqueous extracts were photoirradiated using simulated sunlight, and the production rate (r •OH) and the effects of hydroxyl radicals (•OH) were measured as well as the optical properties as a function of the photoaging of the extracts. r •OH was seen to have a strong seasonality with low mean values for the winter and spring extracts (4.8 and 14 fM s–1 mgC –1 L, respectively) and a higher mean value for the summer extracts (65.4 fM s–1 mgC –1 L). For the winter extracts, •OH was seen to mostly originate from nitrate photolysis while for the summer extracts, a correlation was seen between r •OH and iron concentration. The extent of photobleaching of the extracts was correlated with r •OH, and the correlation also indicated that non-•OH processes took place. Using the •OH measurements and singlet oxygen (1O2) measurements, the half-life of a selection of compounds was modeled in the atmospheric aqueous phase to be between 1.9 and 434 h.