Tracking changes in the optical properties and molecular composition of dissolved organic matter during drinking water production.
Absorbance, 3D fluorescence and ultrahigh resolution electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI-FT-ICR-MS) were used to explain patterns in the removal of chromophoric and fluorescent dissolved organic matter (CDOM and FDOM) at the molecular level during drinking water production at four large drinking water treatment plants in Sweden. When dissolved organic carbon (DOC) removal was low, shifts in the dissolved organic matter (DOM) composition could not be detected with commonly used DOC-normalized parameters (e.g. specific UV254 absorbance - SUVA), but was clearly observed by using differential absorbance and fluorescence or ESI-FT-ICR-MS. In addition, we took a novel approach by identifying how optical parameters were correlated to the elemental composition of DOM by using rank correlation to connect optical properties to chemical formulas assigned to mass peaks from FT-ICR-MS analyses. Coagulation treatment selectively removed FDOM at longer emission wavelengths (450-600 nm), which significantly correlated with chemical formulas containing oxidized carbon (average carbon oxidation state ≥ 0), low hydrogen to carbon ratios (H/C: average ± SD = 0.83 ± 0.13), and abundant oxygen-containing functional groups (O/C = 0.62 ± 0.10). Slow sand filtration was less efficient in removing DOM, yet selectively targeted FDOM at shorter emission wavelengths (between 300 and 450 nm), which commonly represents algal rather than terrestrial sources. This shorter wavelength FDOM correlated with chemical formulas containing reduced carbon (average carbon oxidation state ≤ 0), with relatively few carbon-carbon double bonds (H/C = 1.32 ± 0.16) and less oxygen per carbon (O/C = 0.43 ± 0.10) than those removed during coagulation. By coupling optical approaches with FT-ICR-MS to characterize DOM, we were for the first time able to confirm the molecular composition of absorbing and fluorescing DOM selectively targeted during drinking water treatment.
Department of Aquatic Sciences and Assessment, Swedish University of Agricultural Sciences (SLU), 75007, Uppsala, Sweden. Electronic address: elin.lavonen@slu.se.
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Lavonen
Department of Aquatic Sciences and Assessment, Swedish University of Agricultural Sciences (SLU), 75007, Uppsala, Sweden; Department of Ecology and Genetics/Limnology, Uppsala University, 75236, Uppsala, Sweden.
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Kothawala
Department of Ecology and Genetics/Limnology, Uppsala University, 75236, Uppsala, Sweden.
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LJ
Tranvik
Department of Thematic Studies, Unit of Environmental Change, Linköping University, 58183, Linköping, Sweden; Chesapeake Biological Laboratory, University of Maryland Center for Environmental Science, Solomons, MD 20688, USA.
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Gonsior
Analytical BioGeoChemistry, German Research Center for Environmental Health, Helmholtz Zentrum München, 85764, Neuherberg, Germany; Analytical Food Chemistry, Technische Universität München, 85354, Freising-Weihenstephan, Germany.
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Schmitt-Kopplin
Department of Aquatic Sciences and Assessment, Swedish University of Agricultural Sciences (SLU), 75007, Uppsala, Sweden.
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SJ
Köhler
D060766:Drinking Water / Q000032:analysis*; D005374:Filtration; D006812:Humic Substances / Q000032:analysis*; D013050:Spectrometry, Fluorescence; D021241:Spectrometry, Mass, Electrospray Ionization; D017550:Spectroscopy, Fourier Transform Infrared; D013548:Sweden; D018508:Water Purification
D060766:Drinking Water; D006812:Humic Substances
Absorbance; Dissolved organic matter; Drinking water; FT-ICR-MS; Fluorescence