The Impacts of Precipitation on Fluorescent Dissolved Organic Matter (FDOM) in an Urban River System

Identifying the fate of dissolved organic matter in wastewater treatment plant effluent-dominated urban river based on fluorescence fingerprinting and flux budget approach

Effluent organic matter from wastewater treatment plants (WWTPs) is an important source of dissolved organic matter (DOM) in urban rivers worldwide and is an important water quality factor. Identifying the fate of DOM in urban river is crucial for water quality management. To address this concern, a fluorescent flux budget approach was conducted to probe the fate of DOM in WWTP effluent-dominated urban river, in combination with field measurement and fluorescence fingerprinting. An urban river receiving two WWTP effluents in Hefei City, China was chosen as the study site, where longitudinal measurements of river hydrology and water quality were performed. The fluorescence fingerprinting revealed the presence of two humic-like components (C1, C4), one fulvic-like component (C2) and one protein-like component (C3) in this investigated river, among which C2 and C4 were indicative of anthropogenic influences, closely associated with treated effluents. For each fluorescent component, the WWTP effluent contributed over 80 % of the total fluorescent dissolved organic matter (FDOM) input in this river. Using the developed FDOM flux budget model, it was found that the C1 and C3 were almost conserved within the waterbody, while the C2 and C4 experienced losses due to biogeochemical reactions. The decay rates of C2 and C4 were estimated to be 0.109-0.174 d-1 and 0.096-0.320 d-1, respectively. Spatial heterogeneity of decay rates for C2 and C4 were associated with the varied chemistries of the lateral input sources including two treated effluents and one tributary flow. Our study highlights that after treated effluent is released into the receiving waterbody, the FDOM would undergo loss from the waters particularly for anthropogenic fulvic-like substance C2 and humic-like substance C4. Additionally, the quantified FDOM decay rate in actual urban water environment provides insights for river water quality management, especially when using DOM as the surrogate indicator of organic pollutants.

Fluorescence fingerprint as an indicator to identify urban non-point sources in urban river during rainfall period

Nowadays, the urban non-point source (NPS) pollution gradually evolved as the main contributor to urban water contamination since the point source pollution was effectively controlled. It was imperative to perform urban NPS identification in urban river to meet the requirements of precise source governance. In this study, the real-time detection about water quality parameters and fluorescence fingerprints (FFs) was performed for BX River and its outlets during rainfall period. EEM-PARAFAC and component similarity analyses discovered that the pollution encountered by BX River mainly came from road runoff and untreated municipal wastewater (UMWW) overflow. The C1 (tryptophan-like) and C3 (terrestrial humic-like) components located at Ex/Em = ∼230(280)/340 and ∼275/430 nm were both detected in these two kinds of urban NPS. The C2 components of road runoff and UMWW overflow displayed remarkable differences, which located at Ex/Em = 250/385 and 245/365 nm, respectively, thus could be served as indicators for distinguishing them. During rainfall period, the outflow from rainwater outlets (RWOs) constantly showed similar FF features to road runoff, while the FFs of outflow from combined sewer outlets (CSOs) alternated between those of road runoff and UMWW overflow. The FF features of sections in BX River changed in response to the dynamic variations in FFs of the outlets, which revealed real-time pollution causes of BX River. This work not only realized the identification and differentiation of urban NPS, but also elucidated the dynamic variations of pollution characteristics throughout the entire process of "urban NPS-outlets-urban river", and demonstrated the feasibility of FF technique in quickly diagnosing the pollution causes of urban river during rainfall period, which provided important guidance for urban NPS governance.

Field evidences of fluorescent dissolved organic matter (FDOM) as potential fingerprints for agricultural and urban sources in river environment

Field evidences of the fluorescence differences between agricultural and urban river reaches are still lack. In this study, the middle reaches of Danhe River (DH) and Mihe River (MH) in Shouguang, China, were designed as agricultural and urban river reaches, respectively, to compare the the fluorescence differences in disparate river reaches using excitation-emission matrix coupled with parallel factor analysis (EEM-PARAFAC). Three fluorescence components were identified. C1 (Ex/Em=230,255,295 nm/420 nm) was categorized as humic-like fluorophores, C2 (Ex/Em=230,275 nm/330 nm) was recognized as tryptophan-like substances, and C3 (Ex/Em=215 nm/290 nm) was noted as tyrosine-like and phenylalanine-like compounds. The results showed that the FDOM posed significant differences between agricultural and urban river reaches (P < 0.001). The monitoring sites in DH were rich in C2 (1.90 ± 0.62 Raman Unit (RU), mean ± standard deviation), and the monitoring sites in MH were rich in C3 (1.32 ± 0.51 RU). Redundancy analysis revealed that C2 could be regarded as a fluorescence indicator of agricultural sewage in river environment, while C3 was recognized as a fluorescence indicator of domestic sewage in river environment. In conclusion, this study provided field evidences of FDOM as potential fingerprints for agricultural and urban sources in river environment.