New Insights into the Seasonal Variation of DOM Quality of a Humic-Rich Drinking-Water Reservoir—Coupling 2D-Fluorescence and FTICR MS Measurements

Abstract

Long-term changes in dissolved organic matter (DOM) quality, especially in humic-rich raw waters, may lead to intensive adaptions in drinking-water processing. However, seasonal DOM quality changes in standing waters are poorly understood. To fill this gap, the DOM quality of a German drinking water reservoir was investigated on a monthly basis by Fourier-transform ion cyclotron resonance mass spectrometry (FTICR MS) measurements and 2D fluorescence for 18 months. FTICR MS results showed seasonal changes of molecular formula (MF) intensities, indicating photochemical transformation of DOM as a significant process for DOM quality variation. For an assessment of the two humic-like components, identified by parallel factor analysis (PARAFAC) of excitation–emission matrices (EEM), their loadings were Spearman’s rank-correlated with the intensities of the FTICR MS-derived MF. One of the two PARAFAC components correlated to oxygen-rich and relatively unsaturated MF identified as easily photo-degradable, also known as coagulants in flocculation processes. The other PARAFAC component showed opposite seasonal fluctuations and correlated with more saturated MF identified as photo-products with some of them being potential precursors of disinfection byproducts. Our study indicated the importance of elucidating both the chemical background and seasonal behavior of DOM if raw water-quality control is implemented by bulk optical parameters.

Thorough Validation of Optimized Size Exclusion Chromatography-Total Organic Carbon Analysis for Natural Organic Matter in Fresh Waters

“…The remaining characterization method, i.e., HPSEC, is a suitable candidate for routine, long-term monitoring of NOM in water treatment processes and has been proven useful to assess removal efficiencies in typical drinking water treatment plants [9][10][11]. Its efficacy lies in its capability to separate NOM in different fractions based on molecular size and shape [7].…”

A Temporal Graph Model to Predict Chemical Transformations in Complex Dissolved Organic Matter

“…Dissolved organic matter (DOM) in surface waters is a highly dynamic component of the terrestrial carbon cycle and an important nutrient source for aquatic organisms. − Due to its negative impact on color and odor and contribution to disinfection byproduct formation, it needs to be removed during drinking water production. , Photochemical reactions of DOM play an important role in freshwater, as they modulate radiation (i.e., alter the available light), contribute to highly reactive species (reactive oxygen and hydroxyl radicals), , and change the chemical composition of DOM during stratification periods in lakes or along the flow path of a stream/river. , An increase in the number of sunny days, a widespread decline of spruce forests in temperate mountain ranges in middle Europe, as well as increased dissolved organic carbon (DOC) concentrations in many catchments have been reported. , As a consequence, increased solar irradiation to previously shaded small streams and drinking water reservoirs and enhanced phototransformation of DOM are expected with currently unknown consequences for drinking water production from such waters. , …”