Protein-like Materials Research Articles

Fluorescence regional integration and differential fluorescence spectroscopy for analysis of structural characteristics and proton binding properties of fulvic acid sub-fractions

Structural characteristics and proton binding properties of sub-fractions (FA3–FA13) of fulvic acid (FA), eluted stepwise by pyrophosphate buffer were examined by use of fluorescence titration combined with fluorescence regional integration (FRI) and differential fluorescence spectroscopy (DFS). Humic-like (H-L) and fulvic-like (F-L) materials, which accounted for more than 80% of fluorescence response, were dominant in five sub-fractions of FA. Based on FRI analysis, except the response of F-L materials in FA9 and FA13, maximum changes in percent fluorescence response were less than 10% as pH was increased from 2.5 to 11.5. Contents of carboxylic and phenolic groups were compared for fluorescence peaks of FA sub-fractions based on pH-dependent fluorescence derived from DFS. Static quenching was the dominant mechanism for binding of protons by FA sub-fractions. Dissociation constants (pKa) were calculated by use of results of DFS and the modified Stern-Volmer relationship. The pKa of H-L, F-L, tryptophan-like and tyrosine-like materials of FA sub-fractions exhibited ranges of 3.17–4.06, 3.12–3.97, 4.14–4.45 and 4.25–4.76, respectively, for acidic pHs. At basic pHs, values of pKa for corresponding materials were in ranges of 9.71–10.24, 9.62–10.99, 9.67–10.31 and 9.33–10.28, respectively. At acidic pH, protein-like (P-L) materials had greater affinities for protons than did either H-L or F-L materials. The di-carboxylic and phenolic groups were likely predominant sites of protonation for both H-L and F-L materials at both acidic and basic pHs. Amino acid groups were significant factors during proton binding to protein-like materials of FA sub-fractions at basic pH.

Investigating the composition characteristics of dissolved and particulate/colloidal organic matter in effluent-dominated stream using fluorescence spectroscopy combined with multivariable analysis.

Fluorescence excitation-emission matrix (EEM) spectroscopy combined with principal component analysis (PCA) and parallel factor analysis (PARAFAC) were used to investigate the compositional characteristics of dissolved and particulate/colloidal organic matter and its correlations with nitrogen, phosphorus, and heavy metals in an effluent-dominated stream, Northern China. The results showed that dissolved organic matter (DOM) was comprised of fulvic-like, humic-like, and protein-like components in the water samples, and fulvic-like substances were the main fraction of DOM among them. Particulate/colloidal organic matter (PcOM) consisted of fulvic-like and protein-like matter. Fulvic-like substances existed in the larger molecular form in PcOM, and they comprised a large amount of nitrogen and polar functional groups. On the other hand, protein-like components in PcOM were low in benzene ring and bound to heavy metals. It could be concluded that nitrogen, phosphorus, and heavy metals in effluent had an effect on the compositional characteristics of natural DOM and PcOM, which may deepen our understanding about the environmental behaviors of organic matter in effluent.

Removal of PhACs and their impacts on membrane fouling in NF/RO membrane filtration of various matrices

The removal of pharmaceutically active compounds (PhACs) by fouled nanofiltration (NF) and reverse osmosis (RO) membranes has been extensively studied. Investigations on the effects of PhACs on organic fouling or biofouling in the NF/RO membrane application are still lacking. In this study, NF/RO membranes were fed with both synthetic (SRNOM solution and synthetic wastewater containing pure culture inoculum) and real (secondary effluent) water matrices spiked with three PhACs to elucidate the impact of PhACs on membrane fouling in comparison with control experiments in the absence of PhACs. Results showed that the PhACs mitigated flux decline during NF/RO filtration of SRNOM solution. The total organic foulants on both membrane surfaces decreased in the presence of PhACs due to the increased negative charges of the membranes and the enhanced size and charge effects of PhAC–macromolecule complexes in SRNOM solution. PhACs appeared to inhibit cell growth in the early stages of biofouling, causing a decline in total biomass, and then induced cell lysis, releasing EPS to protect from chemical stress in the later stages of biofouling, especially protein-like materials, causing more severe biofouling. The alleviation of declines in flux and salt rejection during the filtration of secondary effluent were found in the presence of PhACs. Therefore, we hypothesized that organic fouling or early-stage biofouling occurred during 100h of filtration of secondary effluent. The decrease in PhAC retention was more obvious due to the higher ionic strength in the secondary effluent. This study may aid understanding of PhAC removal from various matrices and the effects of PhAC mixtures on membrane fouling by in practical NF/RO membranes applications.

Protonation-dependent heterogeneity in fluorescent binding sites in sub-fractions of fulvic acid using principle component analysis and two-dimensional correlation spectroscopy

Heterogeneous distributions of proton binding sites within sub-fractions of fulvic acid (FA3–FA13) were investigated by use of synchronous fluorescence spectra (SFS), combined with principle component analysis (PCA) and two-dimensional correlation spectroscopy (2D-COS). Tryptophan-like, fulvic-like and humic-like materials were observed in SFS. Tyrosine-like materials were identified by use of SFS-PCA analysis. Combined information from synchronous-asynchronous maps and dissociation constants (pKa) was used to describe heterogeneity of binding sites for protons within each sub-fraction. Heterogeneous distributions of proton binding sites were observed in fulvic-like, humic-like, tryptophan-like, and tyrosine-like materials of five sub-fractions and even in the single fulvic-like materials in FA3 and tryptophan-like materials in FA9 and FA13. Values of pKa of sub-fractions ranged from 2.20 to 5.29, depending on associated wavelengths in synchronous-asynchronous maps and use of the modified Stern-Volmer equation. The larger values of pKa (4.17–5.29) were established for protein-like materials (including tryptophan-like and tyrosine-like materials) in comparison to those (2.20–3.38) for humic-like and fulvic-like materials in sub-fractions. Sequential variations of 274nm (pKa 4.15–5.29)→360–460nm (pKa 2.78–2.39) for FA5–FA13 revealed that binding of protons to tryptophan-like materials appeared prior to humic-like/fulvic-like materials. In FA9, protons were preferentially binding to tryptophan-like materials than tyrosine-like materials. In FA3, protons were preferentially binding to humic-like materials than fulvic-like materials. Relative differences of values of pKa for fluorescent materials within each sub-fraction were consistent with sequential orders derived from asynchronous maps. Such an integrated approach, SFS-PCA/2D-COS, has superior potential for further applications in exploring complex interactions between dissolved organic matter and contaminants in engineered and natural environments.

Characterization of UF foulants and fouling mechanisms when applying low in-line coagulant pre-treatment

Fluorescence spectroscopy was used as a characterization method to examine organic fouling of single ultrafiltration (UF) fibres at bench-scale. Low doses of coagulant were applied to modify organic properties, without significant formation of precipitates. This approach compliments previous studies investigating coagulation as a pre-treatment method for UF fouling control, which have principally focused on reduction of foulant concentrations. Using a continuous system, short time-scale fluorescence results demonstrated significant adsorption of humic components to virgin membrane fibres. Following an initial adsorption phase, protein-like material was the only organic component to be significantly removed by UF. Low doses of coagulant (<1 mg/L as alum; < 0.043 mg/L as Al3+) were observed to significantly reduce irreversible fouling rates for two different surface waters. Paralleling reduced irreversible fouling, surface tryptophan fluorescence resulting from material adsorbed to the fouled membrane increased, as measured using a fibre optic probe. Analysis of peak shifts in the protein-like component revealed a red-shift at low coagulant dose, possibly indicative of greater exposure of tryptophan residues resulting from conformational changes in the protein structure. It is hypothesized that low coagulant doses modified membrane-foulant interactions, resulting in increased adsorption of protein-like matter to the surface. Subsequent interactions of bulk foulants with the adsorbed organic monolayer discouraged further adsorption and reduced irreversible fouling potential.

Tracking changes in composition and amount of dissolved organic matter throughout drinking water treatment plants by comprehensive two-dimensional gas chromatography–quadrupole mass spectrometry

Dissolved organic matter (DOM) can affect the performance of water treatment processes and produce undesirable disinfection by-products during disinfection. Several studies have been undertaken on the structural characterization of DOM, but its fate during drinking water treatment processes is still not fully understood. In this work, the nontargeted screening method of comprehensive two-dimensional gas chromatography-quadrupole mass spectrometry (GC×GC-qMS) was used to reveal the detailed changes of different chemical classes of compounds in DOM during conventional and advanced drinking water treatment processes at three drinking water treatment plants in China. The results showed that when the dissolved organic carbon removal was low, shifts in the DOM composition could not be detected with the specific ultraviolet absorbance at 254nm, but the changes were clear in the three-dimensional fluorescence excitation-emission matrix or GC×GC-qMS analyses. Coagulation-sedimentation processes selectively removed 37–59% of the nitrogenous compounds, alcohols and aromatic hydrocarbons but increased the concentrations of halogen-containing compounds by 17–26% because of the contact time with chlorine in this step. Filtration was less efficient at removing DOM but preferentially removed 21–60% of the acids. However, other organic matter would be released from the filter (e.g., nitrogenous compounds, acids, and aromatic hydrocarbons). Biological activated carbon (BAC) treatment removed most of the compounds produced from ozonation, particularly ketones, alcohols, halogen-containing compounds and acids. However, it should be noted that certain highly polar or high molecular weight compounds not identified in this study might be released from the BAC bed. After the whole treatment processes, the concentrations of nitrogenous compounds, alcohols, alkenes, aromatic hydrocarbons and ketones were decreased more by the advanced treatment processes than by the conventional treatment processes. Alcohol and ketone removals were probably related to the reduction in protein-like materials. Alkane removal was probably related to the reduction in fulvic acid-like and humic acid-like materials.

Chemical structures of extra- and intra-cellular algogenic organic matters as precursors to the formation of carbonaceous disinfection byproducts

Algal eutrophication in reservoirs is frequently accompanied by a remarkable increase in the concentration of algogenic organic matter (AOM). Because AOM is well-known as an important precursor to disinfection byproducts (DBPs) in drinking water, algal eutrophication poses severe concerns for public health. This study aimed to characterize the chemical properties of AOM from two major origins, i.e. extra- (EOM) and intra-cellular organic matter (IOM), of a commonly found green alga Chlorella sp. as precursors to trihalomethanes (THMs) and haloacetic acids (HAAs). Particularly, the corresponding relation between the chemical functional structure of EOM and IOM and their THM and HAA formation potential (THMFP and HAAFP) was comprehensively investigated. Results show that IOM chiefly comprised of aromatic and other aliphatic protein-like materials (high organic nitrogen content) those have high activity for chlorine substitution (high UV253/UV203 value) due to the high hydroxyl and amide contents in its chemical structures. EOM alternatively exhibited the characteristics of humic- and fulvic-like materials accompanying with high DOC/DON ratio and aromaticity. However, the chemical structure of EOM had a low tendency for chlorine substitution (low UV253/UV203 value); it was also accompanied by a considerable content of carboxylic moisture, which likely resulted in an unfavorable substitution reaction of EOM with chlorine. As a result, the carbonaceous DBP formation potential (C-DBPFP) showed that IOM yielded higher levels of both THMFP and HAAFP than that yielded by EOM.

Influence of surface properties of RO membrane on membrane fouling for treating textile secondary effluent.

Reverse osmosis (RO) is a promising technology for treating and reusing textile secondary effluent (SE). To better understand the effect of membrane surface properties on membrane fouling, the performances of three commercial polyamide thin-film composite RO membranes (BW30-4040, CPA2-4040, and RE-4040-FEN) with different roughness and hydrophilicity were investigated for treating textile SE. The RO membranes were characterized by ATR-FTIR, SEM, AFM, and contact angle, respectively. The results showed that the flux increased with an increase in the surface hydrophilicity of membrane. CPA2-4040 had the highest hydrophilic surface and thus the largest initial flux. There was a strong correlation between the membrane fouling and the surface roughness; the fouling increased with an increase in the surface roughness. The roughest surface of CPA2-4040 led to the most significantly flux decline. However, the fouling reversibility was not related directly to surface roughness. BW30-4040 with the secondary roughness and the most hydrophobic surface had the highest fouling reversibility. This was mainly due to the primary hydrophilicity of textile SE in nature. Fluorescence excitation-emission matrix (EEM) showed that hydrophilic neutral protein-like matters and soluble microbial products (SMP) were the main foulants, thus stronger affinity with hydrophilic surface of membrane. Graphical abstract ᅟ.

Pollutant-removal performance and variability of DOM quantity and composition with traditional ecological concrete (TEC) and improved multi-aggregate eco-concrete (IMAEC) revetment treatments

This study comparatively analyzed the performance of water quality purification on stormwater road runoff, and the changes in the structure and composition of dissolved organic matter (DOM), after traditional ecological concrete (TEC) revetment treatment and a new improved multi-aggregate ecological concrete (IMAEC) revetment treatment. The results showed that the removal rates for chemical oxygen demand (COD), total nitrogen (TN) and total phosphorus (TP) reached 14.56%–30.49%, 38.21%–67.96%, and 24.22%–41.14% respectively, in the TEC treatment, and 51.22%–57.90%, 64.61%–81.95%, and 40.29%–53.45% respectively, in the IMAEC treatment, suggesting that the IMAEC revetment treatment showed higher water purification performance than the TEC revetment treatment. The results of SUVA254, a250/a365 and a253/a203 indicated that the IMAEC treatment showed relatively high removal efficiencies of refractory aromatic compounds. Parallel factor (PARAFAC) analysis indicated that the removal rates for three fluorescent components (humic-like Components 1 and 2, and protein-like Component 3) reached 27.94%, 9.69% and 27.86 respectively, in the TEC treatment, and 51.35%, 30.10%, and 52.97% respectively, in the IMAEC treatment. 2D-COS mapping suggested that protein-like materials were more susceptible than humic-like substances, to the addition of metal ions. Protein-like materials can preferentially interact with metal ions, resulting in the effective removal of DOM-metal complexes, and can further influence the migration and transformation of metal ions.

Complexation Between Copper(Ⅱ) and Colored Dissolved Organic Matter from Municipal Solid Waste Landfill

In order to elucidate the evolution mechanism of heavy metal species in landfill cells, three-dimensional excitation emission matrix fluorescence spectroscopy (3DEEM), fluorescence quenching titration and parallel factor analysis (PARAFAC) were employed to study the complexation process between Cu(Ⅱ) and colored dissolved organic matter (CDOM) from landfill with different ages. The experimental results indicated that the landfilled CDOM comprised protein-like, humic-like and fuvic-like matter. The relative content of protein-like matter decreased during the landfill process, whereas the humic-like and fuvic-like matter increased during the process. The range of the conditional stability constants and the percentage of fluorophores participated the complextion between Cu(Ⅱ) and protein-like matter with different ages were 4.00-5.75 and 22.78%-95.30%, respectively. Those parameters changed slightly for humic-like matter with different ages, which ranged from 4.71 to 5.54 and from 42.35% to 61.46%, respectively. As regard to fulvic-like matter, those parameters were 4.44-5.25 and 46.14%-57.22%, respectively. The complexation ability of humic-like substances with Cu(Ⅱ) decreased during the landfill process, though the percentage of fluorophores participated the complexation increased. The complexation ability of humic-like substances with Cu(Ⅱ) was stronger than that of fulvic-like matter, though the percentage of fluorophores participated the complexation in humic-like matter was low compared with fulvic-like matter.

Formation of known and unknown disinfection by-products from natural organic matter fractions during chlorination, chloramination, and ozonation

Natural organic matter (NOM) is the main precursor of disinfection by-products (DBPs) formed during drinking water treatment processes. Previous studies of the relationships between DBP formation and NOM fractionation have mainly been focused on currently regulated DBPs and a few certain emerging DBPs. In this work, the Suwannee River NOM solution was fractionated into groups with different hydrophobicities using DAX-8 resins, and volatile and semi-volatile DBPs formed during the chlorination, chloramination and ozonation of the NOM fractions were examined by a nontargeted screening of comprehensive two-dimensional gas chromatography-quadrupole mass spectrometry procedure. The results showed that a total of 302 DBPs representing nine chemical classes were detected, of which 266 were possibly newly detected, based on library searching with NIST 08 library (using similarity and reverse values of at least 600 and 700, respectively) and linear retention indices. The characterization of DBP precursors suggests that hydrophobic (HPO) NOM contains the major fraction of precursor for the formation of nitrogenous DBPs (contributing about 60% of the total nitrogenous DBPs) during all three disinfection processes. Much larger amounts of heterocyclic DBPs were formed from the HPO fraction than from the hydrophilic fraction during chlorination. During chloramination and ozonation, 5–15 times more ketones were formed from the hydrophilic fraction than from the HPO fraction. During ozonation, more than twice the amounts of esters and alcohols were formed from the hydrophilic fraction than from the HPO fraction. Three-dimensional excitation-emission matrix spectra suggest that similar to the formation of regulated DBPs, humic acid-like substances are probably the precursors of halogen-containing DBPs. Relatively higher nitrogenous DBPs formation from the HPO fraction might be because of the existence of protein-like materials.

Fluorescence spectroscopy and parallel factor analysis as a dissolved organic monitoring tool to assess treatment performance in drinking water trains.

Fluorescence excitation emission matrix (FEEM) spectroscopy was used to evaluate its applicability as a tool to track dissolved organic matter (DOM) in a drinking water treatment plant (DWTP) that incorporates a conventional line (consisting in ozonation and GAC filtration) and a membrane-based line (consisting in ultrafiltration, reverse osmosis and mineralization) working in parallel. Seven sampling points within the different process stages were characterized monthly during 2014. A global Parallel Factor Analysis (PARAFAC) was used to pull out underlying organic fractions from the fluorescence spectra. Accordingly a five components model was selected to describe the system and the pros and cons of the model were discussed by analysis of the residuals. Among the five fluorescent components, those associated to humic-like matter (C1, C3 and C4) showed a similar season variability in the river water feeding the DWTP (which resembled that of UV254 and TOC), whereas the two components associated to protein-like matter (C2 and C5) exhibited a different behavior. The maximum fluorescence intensity values (Fmax) were used to quantify DOM removals across the plant. Compared to the conventional line, water from the UF/RO membrane-based line showed between 6 and 14 times lower fluorescence intensity signal for the humic-like components and between 1 and 3 for the protein-like components as compared to the conventional line. The differences in DOM composition due to seasonal variations and along the treatment trains point out the suitability of using fluorescence measurements over other parameters such as UV254 as a monitoring tool to help optimize operation conditions of each treatment stage and improve produced water quality in a DWTP.

The role of extracellular polymeric substances on the sorption of pentachlorophenol onto natural biofilms in different incubation times: a fluorescence study

ABSTRACTExtracellular polymeric substances (EPS) have been regarded as the most significant components in sorbing organic contaminants onto natural biofilms. However, few investigations have reported the effects of EPS on the sorption of organic contaminants onto biofilms in different incubation times. Here, pentachlorophenol (PCP), selected as a model organic pollutant, was sorbed by biofilms and EPS-free biofilms cultured for 15, 30, and 45 days, to evaluate the role of EPS in the sorption process. EPS were extracted from biofilms to investigate the binding mechanism of PCP to the fluorescence matters in EPS by fluorescence quenching titration. Results showed that EPS, bound with biofilms or released to water, could increase or decrease the sorption amounts of PCP on biofilms in various incubation times. The presence of bound EPS in biofilms enhanced the sorption amounts of 30-day biofilms (6.0 ± 0.11 μmol g−1) because of the formation of the EPS-PCP complex between PCP and fluorescence matters in EPS, such as protein-like matters. In contrast, the release of PCP-bound EPS in 15- and 45-day biofilms decreased the sorption amounts of PCP on biofilms. All the results suggested that EPS dominated the sorption of PCP onto biofilms.

Changes in degrading ability, populations and metabolism of microbes in activated sludge in the treatment of phenol wastewater

With an increase in phenol concentration, biodegradable soluble microbial by-product-like matter in sludge EPS is gradually replaced by non-biodegradable tryptophan protein-like matter.

Short-term pre-aeration applied to the dry anaerobic digestion of MSW, with a focus on the spectroscopic characteristics of dissolved organic matter

There is a growing trend toward considering municipal solid waste (MSW) with a large organic fraction as a source of renewable energy using a dry anaerobic digestion (AD) process. Pre-aeration is effective in improving the dry AD of MSW. However, due to a lack of information regarding the modification of organic components during pre-aeration and the relationship with the subsequent AD, the mechanisms and optimum strength of this process remain unclear.In this study, the role of different short-term pre-aeration durations (4, 8, and 14days) in dry AD of MSW was evaluated in batch-tests, with a focus on changes in the organic components during pre-aeration and their impact on the subsequent spectral evolution of dissolved organic matter (DOM) and bulk performance. Dry AD of MSW operated effectively after the 8-day pre-aeration. The accelerated degradation of proteins during pre-aeration is critical for the subsequent AD, by reducing the organic loading and providing a buffer for the ammonia generated. A favorable methanogenesis, facilitated by pre-aeration, rapidly decreased protein-like fluorescent matter by ∼2.8 times, by converting it to stable humic- and fulvic-like groups. MSW with an 8-day pre-aeration produced the highest biogas yield (192.4NL/kg dry matter), representing ∼24.9% of the initial carbon recovered as methane. Excessive pre-aeration of 14days decreased the biogas yield by ∼33%. An insufficient pre-aeration led to an excessive butyric-type acidification, with protein-like matter dominating the bulk DOM (∼81% of total fluorescence intensity). Multivariate analysis methods confirmed that spectroscopic indicators could evaluate the stability of dry AD.

Vertical Distribution Characteristics of Dissolved Organic Matter in Groundwater and Its Cause

Dissolved organic matter (DOM) can change the species, migration and transformation of foreign pollutants in groundwater, and the investigations of its composition and distribution characteristics play a role in environment protection. The groundwater DOMs were obtained at the depths of 1.2, 1.5 and 1.8 m, and its origin, composition, concentration, distribution characteristics and influencing factors were studied using UV-Vis and fluorescence spectra combined with parallel factor analysis and principle components analysis. The results showed that, DOM in the groundwater originated from both terrigenous input and microbial activities, and was comprised of humic-like matter, heterogeneous component, and protein-like matter. Humic-like matter and heterogeneous components showed a high concentration at 1.5 m and a low one at 1.2 m, whereas the protein-like matter exhibited a low concentration at 1.5 m and a high one at 1.2 m. The groundwater DOM at 1.5 m exhibited the highest aromaticity, humification, molecular weight and polar functional group content, while that at 1.2 m depth showed the lowest aromaticity, humification, molecular weight and polar functional group content. The vertical distribution of DOM in groundwater was related to aromaticity, humification, molecular weight and polar functional group, and the DOM with high aromaticity, humification, molecular weight and polar functional group resisted to biodegradation, and could easily enter into the bottom layer groundwater.

Kinetics of natural organic matter (NOM) removal during drinking water biofiltration using different NOM characterization approaches

To better understand biofiltration, concentration profiles of various natural organic matter (NOM) components throughout a pilot-scale drinking water biofilter were investigated using liquid chromatography – organic carbon detection (LC-OCD) and fluorescence excitation and emission matrices (FEEM). Over a 2 month period, water samples were collected from six ports at different biofilter media depths. Results showed substantial removal of biopolymers (i.e. high molecular weight (MW) NOM components as characterized by LC-OCD) and FEEM protein-like materials, but low removal of humic substances, building blocks and low MW neutrals and low MW acids. For the first time, relative biodegradability of different NOM components characterized by LC-OCD and FEEM approaches were investigated across the entire MW range and for different fluorophore compositions, in addition to establishing the biodegradation kinetics. The removal kinetics for FEEM protein-like materials were different than for the LC-OCD-based biopolymers, illustrating the complementary nature of the LC-OCD and FEEM approaches. LC-OCD biopolymers (both organic carbon and organic nitrogen) and FEEM protein-like materials were shown to follow either first or second order biodegradation kinetics. Due to the low percent removal and small number of data points, the performance of three kinetic models was not distinguishable for humic substances. Pre-filtration of samples for FEEM analyses affected the removal behaviours and/or kinetics especially of protein-like materials which was attributed to the removal of the colloidal/particulate materials.

Spectroscopic and microscopic characteristics of natural aquatic nanoscale particles from riverine waters

The physicochemical characterization of colloids in waters is vital for the understanding of their crucial role in transportation of pollutants and biogeochemical processes of trace elements in aquatic systems. However, there are still lack of knowledge about quantitative properties of natural aquatic nanoscale particles owing to their small size and matrix complexity. In the present work, the complementary spectroscopic and microscopic methods were applied to characterize the fluorescent properties of organic colloids, morphology of complex nanoparticles and colloidal speciation of Fe and Mn in rivers, namely Pu River (PR), Xi River (XR) and Haicheng River (HCR), located in northeast of China. Parallel factor analysis (PARAFAC) of excitation-emission matrix (EEM) spectra reveals ten fluorescent components occurring in colloidal organic matter fractionated by ultrafiltration process with cut off 1kDa or 100kDa membrane: five humic-like fluorophores (C1, C2, C3, C6 and C8) and five protein-like components (C4, C5, C7, C9 and C10). The majority of humic-like substances is present in small size colloids (1–100kDa) in these waters and the protein-like materials are, not truly dissolved or “free”, but associated with colloidal materials. Atomic force microscopy (AFM) measurement indicates that small near-spherical particles with height dimensions up to 6nm are main form in the three rivers and occasionally fibrillary material. The significant shift in the size distribution of natural colloids occurs across three rivers with average particle size of 1.43±1.01nm in the XR, 1.53±1.22nm in the PR and 2.22±1.31nm in the HCR. Analysis by Inductively Coupled Plasma-Optical Emission Spectrometer (ICP-OES) combined with ultrafiltration shows that over 73% of total dissolved Fe and <45% of total dissolved Mn are present in the colloidal phase despite diverse distribution of colloidal Fe and Mn in small size (1–100kDa) or large size (>100kDa) fractions across selected rivers.

Spatial Distribution Characteristics and Source Analysis of Dissolved Organic Matter in Beiyun River

Dissolved organic matter (DOM) in aquatic ecosystems has gained wide concern because of its influence on the light attenuation, nutrient availability and contaminant transport. Human activities strongly influence the DOM of rivers in different ways, including increased agricultural activities and industrial and domestic emissions. However, recent socio-economic development with rapid urban development has significantly enhanced the discharge of sewage, and has caused high loads of DOM, which in turn pose a great risk to aquatic ecosystems. To effectively guide water management for protecting aquatic ecosystem health, it is very critical to investigate the distribution and source of dissolved organic matter in urban rivers. In this study, the distribution and source analysis of DOM in Beiyun River were evaluated, where covers the most populated area with a population of 14 million, representing the most urbanized watershed of Beijing. Since the main receiving source of the river is treated and untreated wastewater in Beijing City, the water quality is highly polluted by anthropogenic inputs. However, information on DOM of Beiyun river has not been reported. Therefore, this study can not only reveal the biogeochemistry of DOM in Beiyu River, but also provide useful implications of pollution control for similar urban rivers. The fingerprint features were extracted from the Excitation-Emission Matrix Spectrum of fluorescent dissolved organic matter (FDOM) in 23 sampling sites of Beiyun river during November 2013. Three separate fluorescent components were identified by Parallel factor analysis (PARAFAC) model, including two humic-like components (C1: 240, 300/385 nm; C2: 255, 350/400 nm) and one protein-like component (C3: 230, 280/340 nm). The results indicated that humic-like materials were generally the dominated component of FDOM, accounting for 76.18% of the average total fluorescence intensity. Positive relationships were found between the fluorescence intensity and the concentrations of some water quality indicators, such as total nitrogen, ammonia nitrogen and total phosphorus, indicating the same sources of these components. Thus, the migration and transformation of nitrogen & phosphorus could also influence the level of FDOM. The distribution of total fluorescence intensity showed a distinctly different spatial pattern. The fluorescence intensity decreased firstly along the upstream to midstream continuum, and then increased from the midstream to downstream. The FDOM in the upstream could be attributed to the industrial effluent and agricultural runoff inputs. Among the upstream to downstream continuum, the content of FDOM in the midstream was the lowest. Limited domestic pollution was suggested as the major source. In the downstream, the sources of FDOM could be interpreted as industrial, agricultural wastewater and livestock wastewater discharge. The relative abundance of protein-like materials was markedly increased in this area, indicating the sources of DOM was highly impacted by human activities. In addition, our study also concluded that the removal efficiency of DOM in wastewater plants is not very desirable, which implied that stronger support for DOM removal in sewage system is needed to alleviate DOM pollution and improve water quality.

Investigating the effect of landfill leachates on the characteristics of dissolved organic matter in groundwater using excitation-emission matrix fluorescence spectra coupled with fluorescence regional integration and self-organizing map.

For the purpose of investigating the effect of landfill leachate on the characteristics of organic matter in groundwater, groundwater samples were collected near and in a landfill site, and dissolved organic matter (DOM) was extracted from the groundwater samples and characterized by excitation-emission matrix (EEM) fluorescence spectra combined with fluorescence regional integration (FRI) and self-organizing map (SOM). The results showed that the groundwater DOM comprised humic-, fulvic-, and protein-like substances. The concentration of humic-like matter showed no obvious variation for all groundwater except the sample collected in the landfill site. Fulvic-like substance content decreased when the groundwater was polluted by landfill leachates. There were two kinds of protein-like matter in the groundwater. One kind was bound to humic-like substances, and its content did not change along with groundwater pollution. However, the other kind was present as "free" molecules or else bound in proteins, and its concentration increased significantly when the groundwater was polluted by landfill leachates. The FRI and SOM methods both can characterize the composition and evolution of DOM in the groundwater. However, the SOM analysis can identify whether protein-like moieties was bound to humic-like matter.