Humic-like Components Research Articles

Enhanced landfill leachate treatment performance by adsorption-assisted membrane distillation

Membrane fouling and high-strength membrane concentrate production are two limitations of membrane distillation (MD) for landfill leachate treatment. In this study, activated carbon- and biochar-based adsorption processes were integrated into a conventional MD system to overcome these limitations. The organic matter fractionations of the leachate were thoroughly investigated during the treatment. Membrane-reversible and irreversible foulants differed remarkably from the inlet leachate in the non-assisted MD system. Specifically, reversible foulants were characterized by a high abundance of humic-like fluorescent components, high-molecular-weight humic-size constituents, peptides, and unsaturated compounds. In contrast, irreversible foulants were enriched with fulvic-like fluorescent components, low-molecular-weight neutrals, unsaturated compounds, and polyphenols. The adsorption-based pre-treatment effectively removed foulant precursors from landfill leachate, with a relatively higher (20%) adsorption performance for specific biochar used in this study than for activated carbon. Compared with the non-assisted MD system, the biochar-assisted MD system showed improved performance, achieving 40% overall membrane flux recovery, 42% higher filtration fluxes, and 53% lower concentrate production. In addition, a 15% higher removal of irreversible foulants was observed as compared to the reversible foulants, which can potentially increase the membrane lifespan. This study demonstrates the effectiveness of an adsorption-assisted MD system supported by increased filtration, membrane fouling alleviation, and low-strength leachate concentrate generation.

Elucidating the conformation effects within adsorption of natural organic matter on mesoporous graphitic carbon

The conformation effects were frequently reported to affect the adsorption of natural organic matter (NOM), but such a specific mechanism is poorly understood. To address this knowledge gap, based on the adsorption of NOM on mesoporous graphitic carbon nitride (MCN) prepared via a novel pseudo-templating method, the conformation effects were elucidated. The results showed that MCNs nano-architectures with uniform mesopores were successfully fabricated and showed prominent adsorption capacity. The maximum adsorption amounts of MCN-0.5 for fulvic acid (FA) and leonardite humic acid (HA) were 73.61 mgC g−1 and 135.57 mgC g−1, respectively. The adsorptive affinities of components for HA and Elliott soil HA (ESHA) were related to structural condensation; the components with the more coiled conformation exhibited higher affinities because of occupying less active sites and weakening the electrostatic repulsion. Such conformation effects were further established with respect to NOM types and components, as well as solution chemistry. HA and ESHA suffered from variations from the coiled to linear conformations as pH increased, but not the other four types of NOM tested, and particularly the humic-like and territorial humic-like components were critical in such conformational variations. The adsorption of HA and ESHA was affected by pH via both the conformation effects and the interaction mechanism. By contrast, the conformation of six types of NOM was not affected by the common cations (Na+, K+, Mg2+, Ca2+), and these cations impacted NOM adsorption only through the conventional interactions.

The overlooked role of the association between 2-methylisoborneol and natural organic matters in the nanofiltration treatment of authentic water

The presence of natural organic matter (NOM) in surface water and its significance for removing pollutants during nanofiltration (NF) are overlooked since most previous studies were conducted in synthetic water rather than real water. In this paper, using raw water collected from Lake Tai (the third largest lake in China), we investigate the removal of 2-methylisoborneol (2-MIB, one of the most concerned off-flavor compounds in raw water) by NF and analyze the binding behaviors between 2-MIB and NOM, which affect their corresponding migration and removal behaviors of 2-MIB during NF. The results show that the removal of 2-MIB in real raw water is 12.2 ∼ 22.0 % higher than that in pure water (PW). Additionally, we evaluate the increment of the removal of 2-MIB under different backgrounds, which follow the order NOM (17.2 %∼22.0 %) > bovine serum albumin (BSA 16.0 %∼19.1 %) > intracellular organic matter (IOM) of M. aeruginosa (8.3 %∼9.4 %) > sodium carboxymethyl cellulose (CMC 3.9 %∼6.5 %) > humic acid (HA 0.28 %∼0.31 %). These findings demonstrate that the protein-like components in raw water play a major role in binding to 2-MIB, while humic-like components exhibit a weak association with 2-MIB. Overall, the conclusion and findings in this study provide a new perspective on the NOM effect on micropollutant removal during water treatment.

Quantitative source tracking for organic foulants in ultrafiltration membrane using stable isotope probing approach

Quantitatively identifying the primary sources of organic membrane fouling is essential for the effective implementation of membrane technology and optimal water resource management prior to the treatment. This study leveraged carbon stable isotope tracers to estimate the quantitative contributions of various organic sources to membrane fouling in an ultrafiltration system. Effluent organic matter (EfOM) and aquatic natural organic matter (NOM), two common sources, were combined in five different proportions to evaluate their mixed effects on flux decline and the consequent fouling behaviors. Generally, biopolymer (BP) and low molecular weight neutral (LMWN) size fractions - abundantly present in EfOM - were identified as significant contributors to reversible and irreversible fouling, respectively. Fluorescence spectroscopy disclosed that a protein-like component notably influenced overall membrane fouling, whereas humic-like components were predominantly responsible for irreversible fouling rather than reversible fouling. Fluorescence index (FI) and biological index (BIX), common fluorescence source tracers, showed promise in determining the source contribution for reversible foulants. However, these optical indices were insufficient in accurately determining individual source contributions to irreversible fouling, resulting in inconsistencies with the observed hydraulic analysis. Conversely, applying a carbon stable isotope-based mixing model yielded reasonable estimates for all membrane fouling. The contribution of EfOM surpassed 60 % for reversible fouling and increased with its content in DOM source mixtures. In contrast, aquatic NOM dominated irreversible fouling, contributing over 85 %, regardless of the source mixing ratios. This study emphasizes the potential of stable isotope techniques in accurately estimating the contributions of different organic matter sources to both reversible and irreversible membrane fouling.

Evolution of dissolved organic nitrogen chemistry during transportation to the marginal sea: Insights from nitrogen isotope and molecular composition analyses

Estuaries are hotspots where terrestrially originated dissolved organic matter (DOM) is modified in molecular composition before entering marine environments. However, very few research has considered nitrogen (N) modifications of DOM molecules in estuaries, limiting our understanding of dissolved organic nitrogen (DON) cycling and the associated carbon cycling in estuaries. This study integrated optical, stable isotopes (δ15N and δ13C) and molecular composition (FT-ICR MS) to characterize the transformation of DOM in the Yangtze River Estuary. Both concentration of dissolved organic carbon (DOC) and DON decreased with increasing salinity, while their δ13C and δ15N increased with the increasing salinity. A significant positive correlation was found between δ15N and δ13C during the transportation of DOM to marginal seas, indicating that the behavior of both DOC and DON are primarily controlled by the mixing of freshwater and the seawater in the YRE. During the mixing process, the DON addition was observed using the conservative mixing curves. In the view of molecular composition, DOM molecules became more aromatic as the number of N atoms increased. Spearman correlations reveal that DOM molecules with fewer N atoms exhibited a higher enrichment in protein-like components, while those with more N atoms were more enriched in humic-like components. In addition, the δ15N and δ13C tended to increase as the N content of DOM decreased. Therefore, DON molecules with fewer N atoms were likely to be transformed into those with more N atoms based on the isotopic fractionation theory. This study establishes a linkage between the molecular composition and the δ15N of DOM, and discovers the N transformation pattern within DOM molecules during the transportation to marginal seas.

Enhancing the transformation of carbon and nitrogen organics to humus in composting: Biotic and abiotic synergy mediated by mineral material

To investigate the conversion of carbon and nitrogen organic matter to humus mediated by mineral material additives through biotic and abiotic pathways, three chicken manure composting experiments were conducted using calcium superphosphate (CS) and fly ash (FA). Results showed that CS and FA promoted carbon and nitrogen organic degradation and improved compost maturity. The ratio of humic acid-like to fulvic acid-like substances for FA (30) was significantly higher than for control (18) and CS (13). Excitation-emission-matrix spectra and parallel factor analysis identified a higher transformation of protein-like components into humic-like components in FA. Network analysis showed that CS improved compost maturity by promoting the rapid conversion of humus precursors to humus, while FA increased the richness and diversity of the microbial community, such as Chloroflexi, the unique phylum in FA. Overall, CS and FA facilitated the humification process through abiotic and biotic pathways, and FA had better humification performance.

Unveiling changes in the complexation of dissolved organic matter with Pb(II) by photochemical and microbial degradation using fluorescence EEMs-PARAFAC

Dissolved organic matter (DOM) is very important in determining the speciation, behaviors, and risk of metal pollutants in aquatic ecosystems. Photochemical and microbial degradation are key processes in the cycling of DOM, yet their effects on the DOM-Pb(II) interaction remain largely unknown. This was studied by examining the complexation of river DOM with Pb(II) after degradation, using fluorescence quenching titration and excitation-emission matrices-parallel factor analysis (EEMs-PARAFAC). Three humic-like and two protein-like components were identified, with strong removals of humic-like components and decreasing average molecular weight and humification degree of DOM by photo- and photo-microbial degradation. The changes in humic-like abundance and structure resulted in notable weakening of their interaction with Pb(II). The tryptophan-like C2 was also mainly removed by photo-degradation, while the tyrosine-like C3 could be either removed or accumulated. The Pb(II)-binding of protein-like components was generally weaker but was enhanced in some degradation groups, which might be related to the lowering competition from humic-like components. The binding parameters correlated significantly with the DOM indices, which were dominated by photo-degradation for humic-like components but by seasonal variations for the tyrosine-like component. These results have implications for understanding the key mechanisms underlying the variability of the DOM-metal interaction in aquatic environments.

MIEX resin and enhanced coagulation treatment of high-bromide natural water: Chlorine reactivity and DBP precursors removal

Both organic and inorganic constituents play a major role in the formation and speciation of disinfection by-products (DBPs) under chlorination. In this study, the removal of organic and inorganic precursors to DBPs by ion exchange and coagulation was examined, and the relationships between characteristics of dissolved organic matter (DOM), chlorine reactivity, and the formation of DBPs in high-bromide natural water were investigated. Formation potential tests were conducted for trihalomethanes (THMs) and haloacetronitriles (HANs) before and after the different treatments (coagulation, magnetic ion exchange (MIEX) resin, and combined MIEX/coagulation). At a low resin dose, MIEX was more effective than coagulation for DOM removal. The advantages of the MIEX resin were more prominent at a high resin dose because substantial amounts of DOM and bromide were simultaneously removed. The maximum bromide uptake on the MIEX resin was 0.02 mg-Br/mL. A 4-component PARAFAC model was developed using a dataset of 148 fluorescence excitation-emission matrices (EEMs) generated from pre-chlorinated and post-chlorinated samples. The maximum fluorescence intensities of humic-like components were found to be strongly correlated to THMs formation (R2 = 0.79–0.89). The MIEX treatment substantially lowered the formation of THMs (19–51%) and HANs (70–95%) due to its ability to remove humic-like DOM and bromide. The fluorescence loss for humic-like DOM was found to increase over a chlorination time of 3 days, suggesting that these compounds had stronger reactivity to chlorine compared to protein-like DOM. The chlorine reactivity of protein-like DOM increased after treatments as the residual chlorine was able to react with the less reactive fractions of DOM after chlorine-reactive compounds were removed.

Impact of nCuO containing treated wastewater on soil microbes and dissolved organic matter in paddy field leachate

Using treated wastewater (TWW) resources in agriculture is a major pathway for disseminating nanoparticles. Copper–oxide nanoparticles (nCuO) offer potential benefits, but their presence in the environment poses risks to agricultural and environmental sustainability. This study examined soil microbial transformations and the composition of leachate dissolved organic matter (DOM) of paddy soils irrigated with nCuO-contaminated TWW at different concentrations (T2: 0.02 mgL−1, T3: 0.2 mgL−1, T4: 2.0 mgL−1) and examined the differences in Cu source (T5: 0.2 mgL−1 CuSO4). Results showed negative impacts on the absolute microbial abundance with up to 46 % reduction relative to the control treatment (T1). Changes in relative abundance of specific microbes at the genus level deviated from the corresponding phyla. Acidobacteria, Actinobacteria, Chloroflexi, and Verrucomicrobia phyla increased in the surface (0–3 cm) and subsurface (3–15 cm) layers responding differently to nCuO. In the 0–3 cm layer, Nitrospirae, Euryarchaeota, and Crenarchaeota increased, but only Dechloromonas genus from Proteobacteria increased with increasing nCuO. No significant variations were observed in the DOM composition, except in T4, which had a significantly low content of dissolved organic carbon (DOC), total dissolved nitrogen, and terrestrial humic-like and protein-like components. Ninety-eight distinct genera were identified, of which 44%, including 15 bacteria and two archaea, varied between the surface and subsurface, among treatments, and significantly correlated with more DOM parameters in the subsurface. T4 had the highest microbial diversity in the 0–3 layer, and Cu treatments slightly increased the diversity index in the subsurface. Moreover, the effects differed by Cu source, with T3 showing 10 % more reduction in the subsurface and 17 % less reduction in the surface than T5. The variable microbial responses to nCuO and their strong correlations with DOM highlight the need to consider the potential consequences of low nCuO concentrations on biogeochemical cycles.

Contrasting occurrence of arsenic concentrations in Quaternary aquifers inside and outside the oxbow lakes along the middle reaches of the Yangtze river

Geogenic arsenic (As) contaminated groundwater poses a threat to drinking water safety and ecological health. Dissolved organic matter (DOM) plays a crucial role in As mobilization in Quaternary groundwater systems. Significant spatial variations in As concentrations in groundwater inside and outside the oxbow lakes were observed, but the controlling mechanisms remains unknown. In this study, carbon stable isotopes and fluorescence excitation-emission matrices (EEMs) combined with parallel factor analysis (PARAFAC) were used to elucidate the influence of DOM on contrasting occurrence of As in both inside and outside groundwater of the oxbow lakes along the middle reaches of the Yangtze River. The results showed that groundwater As concentrations outside the oxbow lakes (0.37–485 μg/L) were significantly higher than those in the groundwater inside (0.75–204 μg/L). Stable carbon isotopes suggest that methanogenesis promotes the reductive dissolution of As-bearing Fe(III) oxides/hydroxides, which is the primary process responsible for As enrichment in groundwater outside of oxbow lakes. In contrast, microbial fermentation dominated As mobilization in the groundwater inside of the oxbow lakes. The DOM in the groundwater outside of the oxbow lakes is characterized by a more reductive, predominantly more highly humified and less biologically active humus, while DOM in the groundwater inside consists mainly of microbial humic-like components that is less humified but more biologically active. This study provides new insight to decipher the controlling mechanism of As mobilization in the alluvial-lacustrine aquifers around typical oxbow lakes and is applicable to similar geogenic As-affected floodplain aquifer systems.

Particulate Organic Carbon Released during Macroalgal Growth Has Significant Carbon Sequestration Potential in the Ocean.

Substantial amounts of particulate organic carbon (POC) are released during macroalgal growth; however, the fate of these POCs and their carbon sequestration effects remain unclear. Here, field investigations found that Ulva prolifera caused a significant increase of POC in seawater below the surface during a macroalgal bloom. However, laboratory simulations revealed that 77.6% of these POC was easily degraded by microorganisms in a short period of time, concurrently resulting in the production of dissolved organic carbon (DOC) from POC transformation. Over a period of 3 months, the bioavailable components of macroalgae-released POC and POC-transformed DOC were degraded, leaving 39.6% of the antibiodegradable substances composed of biorecalcitrant POC and biorecalcitrant DOC. However, although the biorecalcitrant POC was rich in humic-like components resisting biodegradation, the biorecalcitrant POC exhibited greater sensitivity to photodegradation than biorecalcitrant DOC. The photodegradation removal rate of biorecalcitrant POC (14.1%) was more than 10 times that of biorecalcitrant DOC (1.2%). Ultimately, a substantial portion (36.3%) of the POC released by growing macroalgae could potentially perform long-term carbon sequestration after conversion to recalcitrant POC and recalcitrant DOC, and these inert carbons derived from macroalgal POC have been previously ignored and should also be included in macroalgal carbon sequestration accounting.

Characteristics of Microplastic-derived Dissolved Organic Matter(MPDOM) and the Complexation Between MPDOM and Sulfadiazine/Cu2

Microplastic-derived dissolved organic matter(MPDOM) during the aging process could be complexed with organic pollutants, heavy metals, and other contaminants and thus affect their migration and transformation. In this study, two types of microplastics, polyethylene terephthalate(PET) and polystyrene(PS), were selected to investigate the spectral properties of MPDOM and their effect on the complexation between MPDOM and sulfadiazine(SDZ)/copper ion(Cu2+) using the fluorescence quenching method, various spectroscopic analysis techniques, and the Ryan-Weber quenching model. The results of UV-vis absorption spectroscopy analysis showed that the molecular weight of the two MPDOMs decreased; the aromaticity and humification increased; and the carboxyl, carbonyl, hydroxyl, and ester substituents on aromatic rings increased after aging. The fluorescence quenching process between MPDOM and SDZ/Cu2+ was static quenching. After quenching, the aromaticity and humification of the two MPDOMs were similar, and the molecular weights were comparable. Combined with three-dimensional fluorescence spectra and parallel factor analysis, two humic-like components and one protein-like component were identified. In addition, the protein-like components of MPDOM reacted preferentially with SDZ and were more sensitive to Cu2+. The results of the Ryan-Weber quenching model revealed that the binding ability of humic-like components to PET-DOM was higher in both SDZ and Cu2+ quenching systems, but the binding ability of MPDOM in the SDZ quenching system was generally stronger than that in the Cu2+ system.

Dynamics of chromophoric dissolved organic matter in a highly productive Amundsen Sea polynya

Dissolved organic carbon (DOC) is the largest organic carbon pool in the ocean, and is the most active component in respect to the ocean carbon cycling. However, its study in Antarctica has been limited due to challenges associated with sample collection. In this study, we conduct an investigation on the chromophoric dissolved organic matter (CDOM) in a highly productive Amundsen Sea Polynya (ASP), where phytoplankton blooms occur annually during the austral summer, serving as the primary source of DOC and CDOM. The relative abundances of CDOM, as indicated by the absorption coefficient at 254 nm (a254), exhibit significant variability, reaching up to 6.34 m−1. Four fluorescent components, including two humic-like components (C1 and C4) and two protein-like components (C2 and C3), are identified by excitation emission matrix coupled with parallel factor analysis (EEM-PARAFAC). Our findings suggest that heterotrophic metabolism primarily contributes to the formation of humic-like fluorescent components and DOC removal. Water mass, solar radiation, primary productivity as well as microbial degradation are identified as the main factors influencing CDOM dynamics in ASP. This study bears significant implications for advancing our understandings of the CDOM and DOC dynamics in the coastal polynyas of Antarctica, thus facilitating improved evaluation of carbon cycle in the Antarctica.

The apoptosis of Chlorella vulgaris and the release of intracellular organic matter under metalimnetic oxygen minimum conditions

Metalimnetic oxygen minimum (MOM) is a frequent occurrence in lakes and reservoirs, and its formation is related to the blooming and apoptosis of algae. In this study, the apoptosis mechanism of Chlorella vulgaris (C. vulgaris) and the release of intracellular organic matter (IOM) under different MOM conditions were analyzed by changing the dissolved oxygen (DO) (7.0 mg/L, 3.0 mg/L, and 0.3 mg/L) and water pressure (0.3 MPa and normal pressure). The integrity and auto-fluorescence of algae cells decreased rapidly in the first 8 days, and then stabilized gradually during the development of MOM. Compared with that of water pressures, DO had a significant effect on the activity of algal cells, and higher initial DO levels (3.0 mg/L and 7.0 mg/L) accelerated the lysis of algal cells. The integrity of algae cells decreased to 28.8 %, 31.8 % and 56.6 % at the initial DO of 7 mg/L, 3 mg/L and 0.3 mg/L under 0.3 MPa, respectively. Meanwhile, the concentration of dissolved organic carbon (DOC) and dissolved organic nitrogen (DON) continued to increase and reached their maximum at 8 or 12 days, respectively, due to the IOM release caused by algal cell rupture, and then gradually decreased due to microbial degradation. Consistent with the results of membrane integrity, the highest DOC and DON concentrations were found at higher initial DO conditions. By parallel factor analysis, the change in total organic matter fluorescence intensity was consistent with DOC, once again increasing in the first 8 days and then gradually decreasing. The increased humic-like component, which is related to higher aromaticity, led to the monotonic increase of HAAFPs and THMFPs. However, the released IOM of C. vulgaris had lower N-DBPFPs, with TCNMFP predominating primarily. In summary, these results shed new lights on exploring the apoptosis of algae and the release of IOM during the development of MOM.

Effective and low-toxicity: A membrane cleaning method using peroxymonosulfate catalytic chlorination

In chemical membrane cleaning, the challenge is to efficiently remove irreversible fouling while minimizing the impact on membrane materials. Particularly, traditional hypochlorite cleaning will further lead to the generation of toxic halogenated by-products. To address these issues, a combined system composed of peroxymonosulfate and chloride (PMS/Cl−) was applied to clean irreversible-humic-acid-fouled polyethersulfone (PES) membranes. After fouled membranes were soaked for 1 h in a PMS/Cl− solution (10 mM/15 mM) at 25 °C under neutral conditions, 94% flux recovery and 96% resistance removal were realized. Surface properties of virgin and cleaned membranes were very similar, confirming the effectiveness of the PMS/Cl− solution in removing irreversible foulants. The stability of membrane separation performance during multiple fouling and cleaning cycles further confirmed the minimal impact on membrane materials. Rapid diminution of the peaks centered in the region of fulvic-like and humic-like components, monitored under 3D-fluorescence for the cleaning solution, was attributed to PMS-catalyzed chlorination, thereby revealing the primary foulant detachment mechanism. Crucially, the approach exhibited lower toxicity than hypochlorite, as evidenced by reduced halogenated by-products and lower acute toxicity to Photobacterium phosphoreum T3. Overall, this novel cleaning system is promising for the efficient and environmentally friendly removal of irreversible organic foulants in practical water-treatment.

Magnetic ion exchange resin for reducing disinfection byproducts in drinking water: Pilot-scale study and organic matter characterization

Disinfection is an essential step in drinking water treatment to prevent waterborne illnesses. However, reaction of disinfectants with organic matter in the water can produce carcinogenic disinfection byproducts (DBPs), including trihalomethanes (THMs) and haloacetic acids (HAAs). Magnetic ion exchange (MIEX) resin has been used as a pretreatment to remove organics and reduce DBPs. In this study, a pilot-scale water treatment plant in Birmingham, AL (USA) that employed MIEX as a pretreatment to the conventional pilot treatment train was compared against an adjacent full-scale train that did not use MIEX. THM and HAA formation was tested via simulated distribution system (SDS) testing, and changes in organic character were assessed using fluorescence spectroscopy. MIEX treatment provided 20 % and 25 % removal of THMs and HAAs, respectively, compared to the full-scale treatment under typical SDS conditions. With higher residence times and incubation temperatures (15 days at 35 °C), MIEX treatment reduced HAAs by 36 %. Parallel factor (PARAFAC) analysis revealed that MIEX treatment reduced loadings for a terrestrial humic-like component. Additionally, MIEX treatment resulted in secondary benefits, including a reduction in the coagulant feed rate and a more stable pH and chlorine residual in the MIEX-treated water compared to full-scale treatment.

Fluorescence spectroscopic characterization of dissolved organic matter in the wastewater treatment plant and hybrid constructed wetlands coupling system in winter: A case study in eastern China

Dissolved organic matter (DOM) in municipal wastewater can have a detrimental effect on aquatic ecosystems, as DOM can participate in the global carbon cycle and change the transport of other pollutants. The characteristics of DOM can also affect the utilization efficiency of dissolved organic carbon by microorganisms in water. In this study, variations in DOM quantity and quality in a full-scale wastewater treatment plant (WWTP) coupled with a hybrid constructed wetland (CW) system during cold periods were characterized by using excitation-emission matrix spectroscopy combined with parallel factor analysis (EEM-PARAFAC). The results showed that the DOM concentration significantly decreased after exiting the WWTP, while a slight increase was found in the CW. The coupled system could significantly eliminate influent DOM with a removal efficiency of 92.1%. The CW system could still remove DOM even in winter. Five fluorescent components, including three humic-like components, one protein-like component and one tyrosine-like component, were identified. Although the biological treatment process in the WWTP contributed a large number of protein-like substances, the optical indices showed that the bioavailability of wastewater was gradually reduced, indicating that DOM was selectively removed by the integrated system. Moreover, there were significant correlations between water quality parameters and DOM indices. This study could contribute to a better understanding of the elimination process of dissolved organic carbon in coupled systems of WWTPs and CWs and offer novel ideas for organic carbon resource recovery and water quality monitoring in watershed environments.

Spatiotemporal evolution of dissolved organic matter (DOM) and its response to environmental factors and human activities.

The South-to-North Water Diversion East Project (SNWDP-E) is an effective way to realize the optimal allocation of water resources in China. The North Dasha River (NDR) is the reverse recharge section that receives water from the Yufu River to the Wohushan Reservoir transfer project line in the SNWDP. However, the dissolved organic matter (DOM) evolution mechanism of seasonal water transfer projects on tributary waters has not been fully elucidated. In this paper, the NDR is the main object, and the changes in the composition and distribution of spectral characteristics during the winter water transfer period (WT) as well as during the summer non-water transfer period (NWT) are investigated by parallel factor analysis (PARAFAC). The results showed that the water connectivity caused by water transfer reduces the environmental heterogeneity of waters in the basin, as evidenced by the ammonia nitrogen (NH4+-N) and total phosphorus (TP) in the water body were significantly lower (p<0.05, p<0.01) during the water transfer period than the non-water transfer period. In addition, the fluorescence intensity of DOM was significantly lower in the WT than the NWT (p<0.05) and was mainly composed of humic substances generated from endogenous sources with high stability. While the NWT was disturbed by anthropogenic activities leading to significant differences in DOM composition in different functional areas. Based on the redundancy analysis (RDA) and multiple regression analysis, it was found that the evolution of the protein-like components is dominated by chemical oxygen demand (COD) and NH4+-N factors during the WT. While the NWT is mainly dominated by total nitrogen (TN) and TP factors for the evolution of the humic-like components. This study helps to elucidate the impact of water transfer projects on the trunk basin and contribute to the regulation and management of inter-basin water transfer projects.

Rainwater extracting characteristics and its potential impact on DBPs generation: A case study

Frequent extreme precipitation events due to global warming can lead to large amounts of pollutants entering source water bodies via surface runoff and wet deposition, thus posing a threat to water supply security. In order to better understand the source characteristics and leaching mechanisms of rainwater dissolved organic matter (DOM), as well as its disinfection by-products formation potential (DBPsFP) during disinfection processes, rainwater samples were collected and extracting experiments were conducted. Three components were identified in rainwater through Parallel factor (PARAFAC) analysis, which were microbial humic-like component C1 (63.1 %), protein (tryptophan-like) component C2 (28.9 %), marine or terrestrial humic-like component C3 (8.1 %). The average molecular weight of rainwater fractions was ordered: hydrophobic neutral (HON) < hydrophobic bases (HOB) < hydrophobic acidic (HOA) < hydrophilic (HIS). The HOA and HON fractions of rainwater were the dominant precursors of trihalomethanes (THMs), while the rainwater HON fraction and hydrophilic fraction were the main precursor of haloacetic acids (HAAs) and trihloroacetonitrile (TCAN), respectively. Subsoil extracts had a higher concentration of dissolved organic carbon (DOC) and total dissolved nitrogen (TDN) than topsoil extracts. Partial least squares path modeling (PLS-PM) demonstrated that the extraction temperature was the dominant factor affecting the abundance of DOM in the topsoil extracts (R2 = 0.28), while the extraction time accounted more for the abundance of fluorescence substance and physicochemical indices in the subsoil extracts (R2 = 0.23 and 0.32, respectively). These results provide key information for controlling the impacts of global warming, in particular the risk of water sources being heavily contaminated by request rainfalls.

Terrigenous humic substances regulate the concentrations of dissolved Fe and Cu (but not Al, Mn, Ni or Zn) in the Gaoping River plume

The small mountainous rivers of Oceania discharge a large fraction of their dissolved and particulate load of materials within a very small percentage of the time. As a result, the yearly inputs and physicochemical forms of dissolved metals exported to the ocean by these rivers are poorly quantified. We investigated the wet-season distribution patterns of metals and fluorescent organic substances in the surface waters of the Gaoping River plume, SW Taiwan, under both moderate (Sep 2020) and strong flow conditions (Aug 2021). The mixing behaviour of both soluble (<5 kDa) and colloidal (>5 kDa) metals and fluorescent components was examined over the salinity range 3.0–32.2 in 2020 and 5.8–31.1 in 2021. We detected two humic-like and one protein-like fluorescent components, the same on both surveys. The humic-like components, C1 and C3, originated from the Gaoping River and correlated strongly with Cu and Fe, respectively. Component C3 showed a greater enrichment relative to C1 in the colloidal (C3/C1 > 0.8) than in the soluble phase (C3/C1 = 0.4). The protein-like component, C2, came from both terrestrial and marine sources and displayed a more complex mixing behaviour than the other two. One striking result was that the effective zero-salinity concentrations of Fe (∼300 nM) and Cu (∼23 nM) did not change significantly in response to a 10-fold increase in river discharge between Sep 2020 and Aug 2021. Similarly to Fe and Cu, the distribution patterns of Components C1 and C3 did not change significantly between the moderate and the strong plume, and C3 and C1 correlated strongly with Fe and Cu, respectively. We conclude that subtropical mountainous rivers can provide soil-derived humic substances which facilitate and regulate the delivery of Fe and Cu to the ocean, provided mountain forests are preserved.