Occurrence, polarity and bioavailability of dissolved organic matter in the Huangpu River, China

Investigation of the variations in dissolved organic matter properties and complexations with two typical heavy metals under the influence of biodegradation: A survey of an entire lake

Biodegradation is a key factor determining the properties and metal binding behaviour of dissolved organic matter (DOM). In this study, the contributions of biodegradation to DOM properties and metal binding behaviour in Dongping Lake were explored by using synchronous fluorescence (SF) spectroscopy, two-dimensional correlation spectroscopy (2D-COS) excitation-emission matrix and parallel factor analysis (EEM-PARAFAC). According to the ratio of the fluorescence intensity of different materials to the entire fluorescence intensity (%F_max), protein-like substances were the main substances of DOM in this lake. The reduction of protein-like substances and the enhancement of humification could be found in the whole lake under the influence of biodegradation. 3 areas (Area A, Area B and Area C) were obtained by principal component analysis (PCA), however, PCA results suggested that DOM properties and sources had some differences in the 3 areas, and DOM bioavailability in Area C was stronger than that in the other 2 areas. With copper (Cu²⁺) and lead (Pb²⁺) addition, different substances exhibited various affinities to different metal types. The locations of crosspeaks in asynchronous maps illustrated that protein-like substances were more affiliative with Cu²⁺, while humic-like substances were bound to Pb²⁺ earlier. Biodegradation had a conspicuous impact the metal binding ability of DOM in Dongping Lake. The effective quenching constants (LogK) of protein-like substances (protein-like component 2: LogK_Cu = 3.85 ± 0.23, LogK_Pb = 3.32 ± 0.23) were higher than those of humic-like substances (humic-like component 3: LogK_Cu = 3.15 ± 0.02, LogK_Pb = 2.93 ± 0.17) for both Cu²⁺ and Pb²⁺ before biodegradation. When biodegradation was finished, binding ability of humic-like substances was enhanced from 3.15 ± 0.02 to 3.41 ± 0.10 for DOM-Cu and 2.93 ± 0.17 to 3.79 ± 0.15 for DOM-Pb. On a spatial scale, metal binding ability of DOM in Dongping Lake also changed due to the influence of biodegradation. For both DOM-Cu and DOM-Pb, binding ability in south of Dongping Lake was stronger than that in other areas with the end of biodegradation.

Tracking spatio-temporal dynamics of fluorescence characteristics of Huangpu River, China by parallel factor analysis: Correlation with disinfection by-product precursor and pesticide level variations

The components and characteristics of dissolved organic matter (DOM), the main precursor of toxic disinfection by-products (DBPs), have attracted increasing attention in water sources. In this study, fluorescence excitation-emission matrix (EEM) coupled with parallel factor (PARAFAC) analysis was used to investigate the DOM fluorescence characteristics of river water along the Huangpu River, China. Four fluorescence components were identified, including two protein-like components (C1 and C2) and two humic-like components (C3 and C4). The fluorescence characteristics showed spatial and temporal variations with the highest total fluorescence intensities observed in autumn, and the increased relative abundance of humic-like substance in the metropolitan area of Shanghai. Fluorescence index and biological index indicated that the DOM of Huangpu River water had both terrestrial and microbial origins and mainly autochthonous characteristic. Moreover, the formation potentials (FPs) of DBP for Huangpu River water were determined, and trihalomethanes were the predominant species formed in all samples. The correlation analysis further showed that PARAFAC C4 (microbial humic-like fluorescence) significantly correlated with the FP of N-DBPs, providing an insight for drinking water treatment to control specific DBPs precursor. In addition, the humic-like components also correlated with the concentrations of triazole and organophosphate pesticides detected in the Huangpu River. These results indicated that fluorescence-PARAFAC analysis is a promising tool to assess the DBPFPs and pesticide occurrence in surface waters.

Removal of disinfection by-product precursors in drinking water treatment processes: Is fluorescence parallel factor analysis a promising indicator?

This work investigated the removal efficiency of disinfection by-product (DBP) precursors by different drinking water treatment processes and evaluated the feasibility of using fluorescence components removal as an indicator. A four-component (including tryptophan-like, protein-bound, tyrosine-like, and humic-like components) parallel factor analysis model was developed basing on 288 fluorescence excitation-emission matrices. Among all treatment processes, coagulation-sedimentation process showed the best performance, with mean removal ratios of 30% in total fluorescence intensity and 31% in total formation potential (FP) of DBPs, respectively. It preferentially removed humic-like component C4 (43%). Advanced treatment processes were less effective in comparison. Ozone and biological activated carbon (BAC) combined process reduced 20% of total fluorescence intensity, while ultrafiltration process reduced < 3%. Ozonation and BAC filtration preferentially removed free amino acids (i.e., C1 and C3) and protein-bound (i.e., C2) components, with mean removal ratios of 12% and 17%, respectively. Significant correlations (p < 0.01, double-tailed) were observed between four fluorescence components removal and FPs reduction of three trihalomethanes, dichloroacetonitrile (DCAN), and 1,1-dichloropropanone (1,1-DCP). Specifically, the correlation coefficients for three trihalomethanes and 1,1-DCP followed the order of C4 > C1 > C2 > C3, while the order for DCAN was C2 > C4 > C1 > C3.

Comparative removal efficiencies of natural organic matter by conventional drinking water treatment plants in Zimbabwe and South Africa

Natural organic matter (NOM) influences the quality and treatability of drinking water; therefore, its removal is paramount. A few studies exist on NOM removal in developing countries, and comparative studies are even fewer globally. This study compared the removal efficiencies for bulk NOM and biodegradable organic carbon (BDOC) fractions of drinking water treatment plants in Zimbabwe (Z) and South Africa (S). NOM removal efficiency at the coagulation stage of plant Z and plant S was 11% and 13%, respectively. The fluorescence index (FI) for the raw water feeding plant Z (1.66) indicated a mixture of both microbial and terrestrially derived NOM, whereas for plant S the FI (4.08) showed terrestrially derived NOM. Based on the log-transformed absorbance at the disinfection stage, plant S had a 58% greater opportunity to produce disinfection by-products than plant Z. The BDOC results for plant Z showed humic fractions were the major substrates for bacterial assimilation, whereas the heterotrophic bacteria in plant S were not particularly selective toward DOC fractions. Overall, the plants had comparable NOM removal performances. PRACTITIONER POINTS: NOM removal efficiency at the coagulation stage of plant Z and plant S was 11% and 13%, respectively. Plant Z had a mixture of both microbial and terrestrially derived NOM, whereas plant S had terrestrially derived NOM. Plant S had a 58% greater opportunity to produce disinfection by-products than plant Z. Humic fractions were the major substrates for bacterial assimilation for plant Z, whereas the heterotrophic bacteria in plant S were not selective towards DOC fractions.

Photocatalytic Oxidation of Natural Organic Matter in Water

Increased concentrations of natural organic matter (NOM), a complex mixture of organic substances found in most surface waters, have recently emerged as a substantial environmental issue. NOM has a significant variety of molecular and chemical properties, which in combination with its varying concentrations both geographically and seasonally, introduce the opportunity for an array of interactions with the environment. Due to an observable increase in amounts of NOM in water treatment supply sources, an improved effort to remove naturally-occurring organics from drinking water supplies, as well as from municipal wastewater effluents, is required to continue the development of highly efficient and versatile water treatment technologies. Photocatalysis has received increasing interest from around the world, especially during the last decade, as several investigated processes have been regularly reported to be amongst the best performing water treatment technologies to remove NOM from drinking water supplies and mitigate the formation of disinfection by products. Consequently, this overview highlights recent research and developments on the application of photocatalysis to degrade NOM by means of TiO2-based heterogeneous and homogeneous photocatalysts. Analytical techniques to quantify NOM in water and hybrid photocatalytic processes are also reviewed and discussed.

Deciphering the origins, composition and microbial fate of dissolved organic matter in agro-urban headwater streams

Landscape urbanization and intensive agriculture dramatically alter stream ecosystems, but it is little known how urban and agriculture land use change the quantity, quality and ultimate fate of dissolved organic matter (DOM) in stream ecosystems via nonpoint source pathways. Size-exclusion chromatography with fluorescence excitation-emission matrices, as well as absorbance and lignin biomarkers were applied to investigate the characteristics and microbial fate of DOM in 15 first-order agricultural, urban and forest headwater streams in Taihu Lake Watershed, a subtropical region of SE China. Results showed that both urban and agricultural land cover increased the amount of dissolved organic matter (DOC) with a lower C/N ratio, and that the majority of DOC was bound to terrestrial humic-like substances. Compared to forest-impacted headwater streams, the aromaticity and molecularity of OM were greatly decreased as the amounts of anthropogenic/aquagenic fulvic acid-like and protein-like DOM enriched in urban streams, and that of microbially soil-derived humic-like DOM and low molecular-weight substances (e.g., neutrals and acids) increased in agricultural streams, respectively. Human-influenced land use also influenced the seasonal variability of stream DOM biogeochemistry. Natural watersheds produced high DOC specific loads and concentrations only in the rainy season (high-flow period). Agricultural streams contributed a higher amount of terrestrial humic-like and protein-like fractions and urbanized watersheds had high values of autochthonous protein-like fractions only. Redundancy analysis (RDA) revealed that DOM quality (explainable variables: molecular source, 43.29%; molecular-weight, 29.74%) were the most prominent factor impacting microbial carbon processing, followed by inorganic nutrients (17.29%). A higher proportion of DOM from urban streams was eventually mineralized to carbon dioxide mainly due to the inefficient utilization of humic and nonhumic (e.g., protein, polysaccharides and lignin) substances as well as higher levels of inorganic nitrogen and phosphorus, whereas a significant fraction of DOM from agricultural and forest streams tended to enter microbial production and the recalcitrant-DOM pool due to the presence of less labile substrates. Our findings indicate that differences in stream-DOM and environmental properties due to urbanization and farming practices may influence stream microbial carbon processing and cause bottom-up changes in the fate of organic carbon moving through freshwater ecosystems.

Impacts of global changes on the biogeochemistry and environmental effects of dissolved organic matter at the land-ocean interface: a review

Dissolved organic matter (DOM) is an important component in the biogeochemistry and ecosystem function of aquatic environments at the highly populated land-ocean interface. The mobilization and transformation of DOM at this critical interface are increasingly affected by a series of notable global changes such as the increasing storm events, intense human activities, and accelerating glacier loss. This review provides an overview of the changes in the quantity and quality of DOM under the influences of multiple global changes. The profound implications of changing DOM for aquatic ecosystem and human society are further discussed, and future research needs are suggested for filling current knowledge gaps. The fluvial export of DOM is strongly intensified during storm events, which is accompanied with notable changes in the chemical composition and reactivity of DOM. Land use not only changes the mobilization of natural DOM source pools within watersheds but also adds DOM of distinct chemical composition and reactivity from anthropogenic sources. Glacier loss brings highly biolabile DOM to downstream water bodies. The changing DOM leads to significant changes in heterotrophic activity, CO₂ out gassing, nutrient and pollutant biogeochemistry, and disinfection by-product formation. Further studies on the source, transformations, and downstream effects of storm DOM, temporal variations of DOM and its interactions with other pollutants in human-modified watersheds, photo-degradability of glacier DOM, and potential priming effects, are essential for better understanding the responses and feedbacks of DOM at the land-ocean interface under the impacts of global changes.

Characterizing spatiotemporal variations of chromophoric dissolved organic matter in headwater catchment of a key drinking water source in China

Natural surface drinking water sources with the increasing chromophoric dissolved organic matter (CDOM) have profound influences on the aquatic environment and drinking water safety. Here, this study investigated the spatiotemporal variations of CDOM in Fengshuba Reservoir and its catchments in China. Twenty-four surface water samples, 45 water samples (including surface water, middle water, and bottom water), and 15 pore water samples were collected from rivers, reservoir, and sediment of the reservoir, respectively. Then, three fluorescent components, namely two humic-like components (C1 and C2) and a tryptophan-like component (C3), were identified from the excitation-emission matrix coupled with parallel factor analysis (EEM-PARAFAC) for all samples. For spatial distributions, the levels of CDOM and two humic-like components in the reservoir were significantly lower than those in the upstream rivers (p < 0.01), indicating that the reservoir may act as a reactor to partly reduce the levels of exogenous input including CDOM and humic-like matters from the surrounding catchment. For temporal variations, the mean levels of CDOM and three fluorescent components did not significantly change in rivers, suggesting that perennial anthropic activity maybe an important factor impacting the concentration and composition of river CDOM but not the precipitation and runoff. However, these mean values of CDOM for the bulk waters of the reservoir changed markedly along with seasonal variations, indicating that the hydrological processes in the reservoir could control the quality and quantity of CDOM. The different correlations between the fluorescent components and primary water parameters in the river, reservoir, and pore water samples further suggest that the reservoir is an important factor regulating the migration and transformation of FDOM along with the variations of different environmental gradients.

Characterization of dissolved organic matter in an urbanized estuary located in Northeastern Brazil

The Sal River estuary, which is located in the state of Sergipe, Northeastern Brazil, stands out as an urban estuary, anthropogenically impacted by untreated and treated wastewater discharge. Synchronous fluorescence spectroscopy and measurement of dissolved organic carbon (DOC) were used for characterization of dissolved organic matter (DOM) in the estuarine water. Dissolved organic carbon concentrations ranged from 7.5 to 19.0 mg L^-1 and, in general, the highest values were recorded during dry season. For both seasons (dry and rainy), DOC presented an inverse linear relationship with salinity, which indicates a conservative dilution of organic matter coming into the estuary. During rainy season, anthropogenic organic constituents and humic substances from land-based sources predominated in DOM composition, carried by river flow. Whereas during the dry season, it has been observed a significant increase of products generated by microbial degradation of anthropogenic organic matter. The relationships between fluorescence intensity and salinity suggest a conservative behavior during rainy season and a non-conservative behavior during dry season, with addition of fluorescent organic matter into the intermediate zone of the estuary. Photodegradation by action of sunlight caused a decrease in fluorescence intensity of humic and tryptophan-like constituents and the release of photoproducts, resulting in an increase in fluorescence intensity of protein-like constituents.

Fate and fouling characteristics of fluorescent dissolved organic matter in ultrafiltration of terrestrial humic substances

Ultrafiltration (UF) membrane fouling caused by terrestrial input of dissolved organic matter (DOM), especially during high flood periods, is poorly understood. In this study, we examined the fouling characteristics of three different terrestrial humic substances (HS) on regenerated cellulose (RC) UF membranes with the pore sizes of 30 k-3 kDa via conventional bulk HS measurements as well as an advanced fluorescence spectroscopy. The fluorescence excitation-emission matrix coupled with parallel factor analysis (EEM-PARAFAC) identified one protein-like (C1) and three humic-like fluorescent components (C2-C4) from soil and leaf-derived HS. The fate of the different fluorescent components was individually tracked for the UF processes. The higher removal rates were found generally on the order of high molecular weight (HMW) C1 to smaller sized humic-like components (C4 > C3 > C2) regardless of the HS sources, implying the importance of HS molecular sizes on the UF operation. Among the humic-like components, C2 was the most associated with irreversible fouling, while other two humic-like components contributed more to reversible fouling. For soil-derived HS, C4 can be suggested as a good surrogate for membrane fouling, as evidenced by the highest correlation between the removal rates and the total fouling indices among the tested HS variables including conventional bulk parameters. Our study demonstrated a promising application of EEM-PARAFAC for probing membrane fouling of terrestrial DOM, which provided additional insight into the fate of different fluorescent components on the UF processes.

Influence of dissolved organic matter on dissolved vanadium speciation in the Churchill River estuary (Manitoba, Canada)

Diffusive gradients in thin films (DGT) devices were used to investigate the temporal and spatial changes in vanadium (V) speciation in the Churchill estuary system (Manitoba). Thirty-six DGT sets and 95 discrete water samples were collected at 8 river and 3 estuary sites during spring freshet and summer base flow. Dissolved V concentration in the Churchill River at summer base flow was approximately 5 times higher than those during the spring high flow (27.3 ± 18.9 nM vs 4.8 ± 3.5 nM). DGT-labile V showed an opposite trend with greater values found during the spring high flow (2.6 ± 1.8 nM vs 1.4 ± 0.3 nM). Parallel factor analysis (PARAFAC) conducted on 95 excitation-emission matrix spectra validated four humic-like (C1C4) and one protein-like (C5) fluorescent components. Significant positive relationship was found between protein-like DOM and DGT-labile V (r = 0.53, p < 0.05), indicating that protein-like DOM possibly affected the DGT-labile V concentration in Churchill River. Sediment leachates were enriched in DGT-labile V and protein-like DOM, which can be readily released when river sediment began to thaw during spring freshet.

The effect of feed water dissolved organic carbon concentration and composition on organic micropollutant removal and microbial diversity in soil columns simulating river bank filtration

This study investigated organic micropollutant (OMP) biodegradation rates in laboratory-scale soil columns simulating river bank filtration (RBF) processes. The dosed OMP mixture consisted of 11 pharmaceuticals, 6 herbicides, 2 insecticides and 1 solvent. Columns were filled with soil from a RBF site and were fed with four different organic carbon fractions (hydrophilic, hydrophobic, transphilic and river water organic matter (RWOM)). Additionally, the effect of a short-term OMP/dissolved organic carbon (DOC) shock-load (e.g. quadrupling the OMP concentrations and doubling the DOC concentration) on OMP biodegradation rates was investigated to assess the resilience of RBF systems. The results obtained in this study imply that - in contrast to what is observed for managed aquifer recharge systems operating on wastewater effluent - OMP biodegradation rates are not affected by the type of organic carbon fraction fed to the soil column, in case of stable operation. No effect of a short-term DOC shock-load on OMP biodegradation rates between the different organic carbon fractions was observed. This means that the RBF site simulated in this study is resilient towards transient higher DOC concentrations in the river water. However, a temporary OMP shock-load affected OMP biodegradation rates observed for the columns fed with the river water organic matter (RWOM) and the hydrophilic fraction of the river water organic matter. These different biodegradation rates did not correlate with any of the parameters investigated in this study (cellular adenosine triphosphate (cATP), DOC removal, specific ultraviolet absorbance (SUVA), richness/evenness of the soil microbial population or OMP category (hydrophobicity/charge).

Characterization of Dissolved Organic Matter in River Water by Conventional Methods and Direct Sample Analysis-Time of Flight-Mass Spectrometry

The dissolved organic matter in surface waters is composed of fractions of different molecular weight and polarity, characteristics that determine their capacity for complexing different types of pollutants and their environmental impact. In this study, the dissolved organic matter in the surface water of the Bio-Bio River (Central Region of Chile) was characterized chemically and spectroscopically after fractionating by molecular weight and polarity. The technique of direct sample analysis-time of flight-mass spectrometry (DSA-TOF-MS) was used to obtain more information on the composition of dissolved organic matter. It is concluded that dissolved organic matter found in the water of the river from the site of minor human impact (Rucalhue) has a predominantly natural origin, with a high content of aromatic carbon, in contrast to dissolved organic matter found in the waters of the sites that have higher human impact (Laja and Concepción), characterized by a greater molecular size and higher organic carbon content. These results are consistent with those obtained from DSA-TOF-MS, where higher correlation was observed between the mass spectrum of the standard commercial humic acid and dissolved organic matter found in the sectors of Laja and Concepción, unlike the spectrum mass of lignin which is more like dissolved organic matter found in the sector Rucalhue.

Tracking the behavior of different size fractions of dissolved organic matter in a full-scale advanced drinking water treatment plant

In this study, five different dissolved organic matter (DOM) fractions, defined based on a size exclusion chromatography with simultaneous detection of organic carbon (OCD) and ultraviolet (UVD), were quantitatively tracked with a treatment train of coagulation/flocculation-sand filtration-ozonation-granular activated carbon (GAC) filtration in a full-scale advanced drinking water treatment plant (DWTP). Five DOM samples including raw water were taken after each treatment process in the DWTP every month over the period of three years. A higher abundance of biopolymer (BP) fraction was found in the raw water during spring and winter than in the other seasons, suggesting an influence of algal bloom and/or meltwater on DOM composition. The greater extent of removal was observed upon the coagulation/flocculation for high-molecular-weight fractions including BP and humic substances (HS) and aromatic moieties, while lower sized fractions were preferentially removed by the GAC filtration. Ozone treatment produced the fraction of low-molecular-weight neutrals probably resulting from the breakdown of double-bonded carbon structures by ozone oxidation. Coagulation/flocculation was the only process that revealed significant effects of influent DOM composition on the treatment efficiency, as revealed by a high correlation between the DOM removal rate and the relative abundance of HS for the raw water. Our study demonstrated that SEC-OCD-UVD was successful in monitoring size-based DOM composition for the advanced DWTP, providing an insight into optimizing the treatment options and the operational conditions for the removal of particular fractions within the bulk DOM.

Spatiotemporal Distribution, Sources, and Photobleaching Imprint of Dissolved Organic Matter in the Yangtze Estuary and Its Adjacent Sea Using Fluorescence and Parallel Factor Analysis

To investigate the seasonal and interannual dynamics of dissolved organic matter (DOM) in the Yangtze Estuary, surface and bottom water samples in the Yangtze Estuary and its adjacent sea were collected and characterized using fluorescence excitation-emission matrices (EEMs) and parallel factor analysis (PARAFAC) in both dry and wet seasons in 2012 and 2013. Two protein-like components and three humic-like components were identified. Three humic-like components decreased linearly with increasing salinity (r>0.90, p<0.001), suggesting their distribution could primarily be controlled by physical mixing. By contrast, two protein-like components fell below the theoretical mixing line, largely due to microbial degradation and removal during mixing. Higher concentrations of humic-like components found in 2012 could be attributed to higher freshwater discharge relative to 2013. There was a lack of systematic patterns for three humic-like components between seasons and years, probably due to variations of other factors such as sources and characteristics. Highest concentrations of fluorescent components, observed in estuarine turbidity maximum (ETM) region, could be attributed to sediment resuspension and subsequent release of DOM, supported by higher concentrations of fluorescent components in bottom water than in surface water at two stations where sediments probably resuspended. Meanwhile, photobleaching could be reflected from the changes in the ratios between fluorescence intensity (F_max) of humic-like components and chromophoric DOM (CDOM) absorption coefficient (a355) along the salinity gradient. This study demonstrates the abundance and composition of DOM in estuaries are controlled not only by hydrological conditions, but also by its sources, characteristics and related estuarine biogeochemical processes.