Tracking changes in the optical properties and molecular composition of dissolved organic matter during drinking water production

Abstract

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.

Selective Adsorption of Terrestrial Dissolved Organic Matter to Inorganic Surfaces Along a Boreal Inland Water Continuum

“…Accordingly, studies using other methods than mass spectrometry also found that compounds with low H/C such as polyphenols and aromatics are preferentially adsorbed (Kaiser, ; Kaiser et al, ; Kalbitz et al, ; Kothawala et al, ). This is consistent with the use of coagulation (e.g., to metals) to remove aromatic, high molecular weight compounds during drinking water treatment (Lavonen et al, ; Matilainen et al, ).…”

“…2012). This is consistent with the use of coagulation (e.g., to metals) to remove aromatic, high molecular weight compounds during drinking water treatment (Lavonen et al, 2015;Matilainen et al, 2010).…”

“…These results show the same pattern as a study where soil and leaf extracts had been adsorbed onto goethite and gibbsite minerals, and the humic‐like PARAFAC components decreased with 67%–91%, whereas the protein‐like components decreased with only 26%–52% (Banaitis et al, ). Long emission wavelength fluorescing DOM compounds are known to be lost due to a variety of processes (e.g., naturally occurring processes on a catchment scale [Kothawala et al, ]; photochemical degradation [Du et al, ]; FeCl 3 coagulation [Lavonen et al, ]). The tendency for long emission wavelength FDOM to be lost also manifests itself in the observed shifts in peaks A and C (Figures b and c).…”

Comparison of Low Molecular Weight Dissolved Organic Matter Compositions in Lake Inba and Kashima River by Orbitrap Mass Spectrometry

“…However, these conventional approaches are not able to elucidate the molecular compositions of DOM. Recently, non-targeted analysis through ultrahigh resolution mass spectrometry (MS) such as Fourier transform ion cyclotron mass spectrometry (FT-ICR MS) and Orbitrap mass spectrometry (Orbitrap MS) have been applied to analyze DOM in aquatic environments [11][12][13][14][15][16] as well as DOM in drinking water and wastewater effluent [17][18][19][20]. These instruments can resolve complex DOM extracted by solid-phase extraction (SPE) and assign molecular formula to each component based on accurate mass.…”

Fluvial organic carbon composition and concentration variability within a peatland catchment—Implications for carbon cycling and water treatment

“…Increased desire to constrain the role of inland waters in global carbon budgets has shown that fluvial organic carbon (OC) levels do not remain static in the downstream fluvial continuum (Battin et al, ; Cole et al, ; Fasching, Behounek, Singer, & Battin, ; Ward et al, ). Additionally, the nature and mechanisms of downstream changes are also of interest to water suppliers, as many water collection areas particularly at mid‐to‐high northern latitudes (e.g., Lavonen et al, ; Ritson et al, ) contain substantial areas of peatland, commonly resulting in high concentrations of dissolved OC (DOC); the removal of which is a major water treatment cost (Worrall et al, ). Therefore, understanding the within‐catchment relationships between fluvial OC composition, concentration, and transformations is important for effective management of these environments.…”