Adaptive monitoring approach to assess dissolved organic matter dynamics during rainfall events

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.

Removal of recalcitrant organic matter of landfill leachate by adsorption onto biochar from sewage sludge: A quali-quantitative analysis

Sewage sludge is a byproduct of sewage treatment, whereas landfill leachate is a complex wastewater generated by the decomposition of solid waste. These byproducts require adequate management, and one option for the sludge is the thermal treatment by pyrolysis to produce biochar. The resulting biosolid can be used as an adsorbent to treat landfill leachate. The main objective of this research was to remove recalcitrant organic matter from landfill leachate by adsorption onto biochar produced from sewage sludge. Aerobic and anaerobic sludges were pyrolyzed at 450, 650 and 850 °C, under residence times of 60, 90 and 120 min. Temperature had a positive and more significant impact on the characteristics of the biochars produced, and consequently on the adsorption of recalcitrant organic matter. However, the impact of residence time was less intense and, in some cases negative. Biochars produced from both aerobic and anaerobic sludge pyrolyzed at 850 °C for 120 and 60 min, respectively, showed higher specific surface areas (114.4 m2g-1 and 104.2 m2g-1, respectively) compared with those pyrolyzed at 450 °C and 650 °C. The biochar from anaerobic sludge produced at 850 °C and 60 min showed the best performance regarding the adsorption process, with chemical oxygen demand (COD), dissolved organic carbon (DOC), and color removals from the leachate of 32%, 36%, and 41%, respectively. The results of adsorption capacity for this biochar from anaerobic sludge were 26.1 mg g-1 for COD and 7.9 mg g-1 for DOC. The adsorption of recalcitrant organic matter from leachate was evidenced by the decrease in the UV-Vis absorbances and fluorescence intensities. It indicates that recalcitrant and humic substances were removed mainly by biochars pyrolyzed at 850 °C. Thus, the results allow to stress that the pyrolysis of sewage sludge to produce biochar is a promising alternative to sludge treatment, and the biochar may be applied as a pre-treatment of landfill leachate since it successfully removed the recalcitrant organic matter.

Ca/Na concentration-constrained variations of dissolved organic matter leaching from groundwater-irrigation area soil in North China Plain

This study investigates the quantity and quality variations of dissolved organic matter (DOM) leaching from the soil in groundwater irrigation area of the North China Plain, constrained by the concentration of Ca/Na. Soil samples with dominant humic-like (HLC) and protein-like (PLC) components were paired with parallel concentration gradients of Ca/Na extractants for equilibrium experiments. Fluorescence-PARAFAC, UV-visible spectroscopy, and multiple statistical analyses were combined for data analysis and interpretation. The results reveal that the primary DOM components remained dominant for specific soil sample, with a higher relative abundance of PLC (HLC) in Ca (Na) extract. HLC preferentially binds to soil phase in all extractions, while PLC is readily released into the solution. However, Ca inhibits HLC desorption and promotes PLC release more significantly than Na, as indicated by stronger ion/proton reaction (IPR) and electrostatic effect (ESE). The strongest IPR and ESE are seen in the HLC-dominated DOM extracted with Ca, suggesting a condition where Ca bridges to HLC and forms total dissolved organic carbon (DOC) that decreases. In contrast, Na extraction exhibits only a weaker ESE that is offset by soil-contained HLC and exchangeable Ca, resulting in subtle DOC decrease. The trends in leaching of HLC and PLC are self-dependent, and the level of variation in either component correlates with the increasing concentration of specific cations present. These findings underscore the crucial role of soil organic matter (SOM) composition and its interaction with leaching cations in soil management in large-scale groundwater irrigation areas, where SOM quality and groundwater chemistry vary.

Characterizing the spatiotemporal distribution of dissolved organic matter (DOM) in the Yongding River Basin: Insights from flow regulation

Artificial flow regulation is an important measure to alleviate water shortages and improve the ecological quality of river basins. Dissolved organic matter (DOM) plays a crucial role in the carbon cycle and regulates biogeochemical and ecological processes in aquatic systems. Among the numerous studies on the effects of anthropogenic activities on the quality and quantity of river DOM, few studies have focused on the influence of different artificially regulated flow on the composition, source, and fate of fluvial DOM. This study aims to elucidate the impact of different artificial regulation modes of river flows on the source, migration, and transformation of DOM. The optical properties of DOM were used to explore the temporal and spatial distribution characteristics of DOM in the Yongding River Basin, where artificial regulation of river flows by cross-basin and inner-basin water transfers were implemented. Excitation-emission matrix fluorescence spectroscopy coupled with parallel factor analysis revealed four fluorescent substances of DOM in the water: one microbial humic-like (C1), one terrestrial humic-like (C2), one non-point source pollution humic-like (C4), and one tryptophan-like (C3) substance. Due to cross-basin water transfer from the Yellow River, the flow is the highest (21.79 m³/s) during spring, which was the reason that the signal of C2 was stronger during spring (71.45 QSU) compared to summer (57.12 QSU) and autumn (51.78 QSU). Due to inner-basin water transfer from upstream reservoirs, C3 derived from autochthonous sources were higher during autumn (130.81 QSU) than during spring (77.17 QSU) and summer (93.16 QSU). With no water transfer, more C1 were present at higher temperatures during summer (141.51 QSU) than during spring (126.73 QSU) and autumn (128.8 QSU). Moreover, C4 originating from urban and/or agricultural non-point source runoff increased during summer (57.07 QSU) than during spring (33.29 QSU) and autumn (52.27 QSU) because of increased rainfall. The different modes of artificial regulation of river flows changed the hydrological characteristics of the basin, which in turn altered the temporal and spatial distribution characteristics of the quantity and quality of DOM. The finding of this study can help promote the development of appropriate management strategies for artificial regulation of river flows in the basin. Furthermore, this study provides a basis for investigating the effects of different artificial flow regulations on the carbon cycles and ecological risks of rivers in the basin.

Response Model for Urban Area Source Pollution and Water Environmental Quality in a River Network Region

With the development of cities, urban area source pollution has become more severe and a significant source of water pollution. To study the relationship between urban area source pollution and water environmental quality in a river network, this study uses a city in the Yangtze River Delta, China, as an example. The Storm Water Management Model (SWMM) model and the MIKE11 model were combined into a unified modeling framework and used to simulate dynamic changes in the water quality of a river network under light rain, moderate rain, and heavy rain. In the study period, the annual urban area source input loads of potassium permanganate (COD_Mn), total phosphorus (TP), and ammonia nitrogen were 29.8, 0.9, and 4.8 t, respectively. The influence of light rain on the water quality of the river network was lagging and temporary, and rainfall area pollution was the primary contributor. Under the scenario of moderate rain, overflow from a pipeline network compounded rainfall runoff, resulting in a longer duration of impact on the water quality in the river. Additionally, the water quality in the river course was worse under moderate rain than under light or heavy rain. Under the scenario of heavy rain, rain mainly served a dilutive function. This research can provide support for urban area source pollution control and management.