Changes and characteristics of dissolved organic matter in a constructed wetland system using fluorescence spectroscopy

Abstract

Domestic wastewater was treated by five constructed wetland beds in series. Dissolved organic matter (DOM) collected from influent and effluent samples from the constructed wetland was investigated using fluorescence spectroscopy combined with fluorescence regional integration (FRI), parallel factor (PARAFAC) analysis, and two-dimensional correlation spectroscopy (2D-COS). This study evaluates the capability of these methods in detecting the spectral characteristics of fluorescent DOM fractions and their changes in constructed wetlands. Fluorescence excitation-emission matrix (EEM) combined with FRI analysis showed that protein-like materials displayed a higher removal ratio compared to humic-like substances. The PARAFAC analysis of wastewater DOM indicated that six fluorescent components, i.e., two protein-like substances (C1 and C6), three humic-like substances (C2, C3 and C5), and one non-humic component (C4), could be identified. Tryptophan-like C1 was the dominant component in the influent DOM. The removal ratios of six fluorescent components (C1-C6) were 56.21, 32.05, 49.19, 39.90, 29.60, and 45.87 %, respectively, after the constructed wetland treatment. Furthermore, 2D-COS demonstrated that the sequencing of spectral changes for fluorescent DOM followed the order 298 nm → 403 nm → 283 nm (310-360 nm) in the constructed wetland, suggesting that the peak at 298 nm is associated with preferential tryptophan fluorescence removal. Variation of the fluorescence index (FI) and the ratio of fluorescence components indicated that the constructed wetland treatment resulted in the decrease of fluorescent organic pollutant with increasing the humification and chemical stability of the DOM.

Removal of organic carbon, nitrogen, emerging contaminants and fluorescing organic matter in different constructed wetland configurations

“…Similarly to the results found in this work, protein and tryptophan-like substances, which represent the most biodegradable fraction of DOM, revealed the highest removal, whereas lower elimination rates were observed for fulvic and humiclike fluorescence components [44,50]. Studies on DOM removal by fluorescence spectroscopy in conventional WWTPs have also reported the highest removal (40-99%) for fluorescing substances in the region of EEM with emission < 380 nm (i.e., protein, tryptophan-like and tyrosine-like fluorescence) and the observed removal rates were similar under aerobic or anoxic/anaerobic conditions [16,22,49,[51][52][53].…”

“…(Table S8). Specifically, component C1 represents the contribution of a microbial humic-like component, and component C3 that of terrestrial fulvic/humic-like fluorescence, as has been established in prior PARAFAC studies of surface water and wastewater [18,22,[42][43][44][45]. Component C2 corresponds to a group of humic-like fluorescing species found in prior studies in high nutrient and wastewater impacted environments [18,42,43,46].…”

“…Component C2 corresponds to a group of humic-like fluorescing species found in prior studies in high nutrient and wastewater impacted environments [18,42,43,46]. Component C4 (λex/λem= <240/340 and 295/340) was relatively rarely reported in published literature and it was mainly associated with amino acids and biologically labile matter produced in aquatic environments [42,44,47]. Finally, protein and tryptophan-like fluorescing compounds observed in prior studies are associated with components C5 (λex/λem= <240/330 and 275/330) [18,[42][43][44]48].…”

“…Studies on the removal of fluorescent organic matter in CW systems are very limited and related to investigations of DOM removal in five CW beds in series and alternating biological ponds and plant gravel beds, and in a pilot-scale UVF unit [44,50]. Similarly to the results found in this work, protein and tryptophan-like substances, which represent the most biodegradable fraction of DOM, revealed the highest removal, whereas lower elimination rates were observed for fulvic and humiclike fluorescence components [44,50].…”

Variation in the Humification Degree of Dissolved Organic Matter from Cattle Manure during Composting as Analyzed by Ultraviolet‐Visible and Fluorescence Spectroscopy

“…6). Component 2, identified in this study, was attributed to short‐wavelength, humic‐like materials that primarily originated from fulvic‐like substances (Yao et al, 2016). Terrestrial‐like and marine‐like humic fluorophores have also been reported that are similar to Component 2 in this work (Stedmon and Bro, 2008).…”