Chemical and optical phototransformation of dissolved organic matter

Loiselle, Steven; Vione, Davide; Minero, Claudio; Maurino, Valter; Tognazzi, Antonio; Dattilo, Arduino Massimo; Rossi, Claudio; Bracchini, Luca

doi:10.1016/j.watres.2012.02.047

Cited by 59 publications

(37 citation statements)

References 43 publications

(57 reference statements)

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“…A deficiency of HO radicals and other oxidising species caused by the presence of naturally occurring organic matter, anions and bicarbonates in RW and TW can be attributed to the retarded photocatalytic process. [55] The hardness of the sampled RW and TW measured as CaCO 3 was 151.6 and 41.8 mg L À1 , respectively classified as hard and soft.…”

Section: Effect Of Cooling Jacket Materials and Tio 2 Typementioning

confidence: 92%

Photolysis and TiO2-catalysed degradation of diclofenac in surface and drinking water using circulating batch photoreactors

Kanakaraju¹,

Cherie²,

Motti³

et al. 2014

Environ. Chem.

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Environmental context. Diclofenac, a common non-steroidal anti-inflammatory drug, is not completely removed from surface and drinking water by conventional treatment methods. Consequently, this drug is present in the aquatic environment and has been subsequently linked to toxic effects on organisms. We show that photolysis and TiO 2 -catalysed degradation in circulating batch reactors efficiently results in diclofenac removal under a variety of conditions. These photochemical methods thus may lead to more effective water treatment processes.Abstract. The occurrence of diclofenac (DCF) as an emerging pollutant in surface waters and drinking water has been attributed to elevated global consumption and the inability of sewage treatment plants to remove DCF. In this study, DCF spiked drinking water and river water was subjected to photolysis and TiO 2 photocatalytic treatments in a circulating laboratory-scale (immersion-well) and a demonstration-scale loop reactor (Laboclean). The operational parameters for the immersion-well reactor were optimised as follows: TiO 2 P25 loading, 0.1 g L À1 ; natural pH, 6.2; initial concentration, 30 mg L À1 ; water type, distilled water. Complete DCF removal was realised within 15 min under the optimised conditions using the immersion-well reactor. Sunlight-mediated photochemical degradation required a prolonged exposure period of up to 360 min for complete DCF removal. DCF in distilled and drinking water was efficiently degraded in the larger Laboclean reactor. Differences were, however, observed based on their pseudo-first-order rate constants, which implies that the water matrix has an effect on the degradation rate. Six major photoproducts, 2-(8-chloro-9H-carbazol-1-yl)acetic acid, 2-(8-hydroxy-9H-carbazol-1-yl)acetic acid, 2,6-dichloro-N-o-tolylbenzenamine, 2-(phenylamino)benzaldehyde, 1-chloromethyl-9H-carbazole and 1-methyl-9H-carbazole, generated from TiO 2 photocatalysis of DCF were identified by liquid chromatography-mass spectrometry (LCMS) and Fourier transform-ion cyclotron resonance-mass spectrometry (FT-ICR-MS). This work has shown that photocatalytic degradation kinetics of DCF are dependent on both the geometry of the photoreactor and the nature of the water matrices.

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Section: Effect Of Cooling Jacket Materials and Tio 2 Typementioning

confidence: 92%

Photolysis and TiO2-catalysed degradation of diclofenac in surface and drinking water using circulating batch photoreactors

Kanakaraju¹,

Cherie²,

Motti³

et al. 2014

Environ. Chem.

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“…OH − from CDOM is more efficient for UV light (e.g. Loiselle et al, 2012) one could speculate about more significant differences in CH 3 I production if the impact of light would be studied for various water depths. But for now, there is no experimental evidence that CH 3 I production occurs preferentially under UV light.…”

Section: Photochemical Production Of Ch 3 Imentioning

confidence: 99%

Numerical modelling of methyl iodide in the eastern tropical Atlantic

Stemmler¹,

Rothe

Hense³

et al. 2013

Biogeosciences

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Methyl iodide (CH₃I) is a volatile organic halogen compound that contributes significantly to the transport of iodine from the ocean to the atmosphere, where it plays an important role in tropospheric chemistry. CH₃I is naturally produced and occurs in the global ocean. The processes involved in the formation of CH₃I, however, are not fully understood. In fact, there is an ongoing debate whether production by phytoplankton or photochemical degradation of organic matter is the main source term. Here, both the biological and photochemical production mechanisms are considered in a biogeochemical module that is coupled to a one-dimensional water column model for the eastern tropical Atlantic. The model is able to reproduce observed subsurface maxima of CH₃I concentrations. But, the dominating source process cannot be clearly identified as subsurface maxima can occur due to both direct biological and photochemical production. However, good agreement between the observed and simulated difference between surface and subsurface methyl iodide concentrations is achieved only when direct biological production is taken into account. Production rates for the biological CH₃I source that were derived from published laboratory studies are shown to be inappropriate for explaining CH₃I concentrations in the eastern tropical Atlantic

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“…Figure 3b shows the time trend upon irradiation of the spectral slope S, compared with the trend in the dark. Interestingly, a significant decrease of S could be detected in the irradiated vs. dark samples, which would imply an increase of CDOM molecular weight and/or aromaticity [9,21,30].…”

Section: Irradiation Experimentsmentioning

confidence: 95%

“…No change of the tyrosine spectrum was detected in the dark. Hydrogen peroxide was added as source of • OH, a reactive species that is photochemically produced by several photosensitisers in surface waters (nitrite, nitrate and most notably CDOM) [18,30,32,33]. Here H 2 O 2 was added because it is a rather "clean"…”

Section: Irradiation Experimentsmentioning

confidence: 99%

UV–vis spectral modifications of water samples under irradiation: Lake vs. subterranean water

Berto

Isaia

Sur

et al. 2013

Journal of Photochemistry and Photobiology A: Chemistry

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Water samples from subterranean systems (caves and abandoned mines) and from lake epilimnion were optically characterised and irradiated under simulated sunlight, to study the effects that sunlight exposure before sampling may have on the properties and photochemical behaviour of chromophoric dissolved organic matter (CDOM). Differently from lakes, absorption spectra of subterranean water samples showed variations from the typically observed, featureless exponential decay of absorbance vs. wavelength. Fluorescence spectra suggested that, compared to lake water and with a single exception, subterranean water had higher proportion of aquagenic/autochthonous CDOM (e.g. proteinaceous material) compared to pedogenic/allochthonous one (e.g. humic and fulvic substances). Irradiation of subterranean water produced very significant spectral changes, and finally yielded lakewater-like exponential absorption spectra. In contrast, irradiation of lake water produced photobleaching (decrease of the absorbance) but the shapes of absorption spectra underwent very limited variations. Tyrosine and humic acids were irradiated as proxies of the CDOM fractions identified by fluorescence. Irradiated tyrosine underwent a significant increase of the absorbance and finally yielded an exponential absorption spectrum, with close resemblance to the behaviour of a protein-rich and humic-poor sample of subterranean water. In contrast, irradiated humic acids underwent photobleaching in a similar way as lake water, but they retained their typical exponential spectrum. The present findings suggest that exposure of CDOM to sunlight may play a key role in shaping the exponential absorption spectra that are typically observed in surface waters.3

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Chemical and optical phototransformation of dissolved organic matter

Cited by 59 publications

References 43 publications

Photolysis and TiO2-catalysed degradation of diclofenac in surface and drinking water using circulating batch photoreactors

Photolysis and TiO2-catalysed degradation of diclofenac in surface and drinking water using circulating batch photoreactors

Numerical modelling of methyl iodide in the eastern tropical Atlantic

UV–vis spectral modifications of water samples under irradiation: Lake vs. subterranean water

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