Using allelochemicals to suppress cyanobacteria growth is a prospective method for its high efficiency and ecological safety.However,the suppression efficiency is affected inevitably by the extracellular polymeric sub...Using allelochemicals to suppress cyanobacteria growth is a prospective method for its high efficiency and ecological safety.However,the suppression efficiency is affected inevitably by the extracellular polymeric substances(EPS)produced by cyanobacteria,and the knowledge about the roles of EPS in resistance to allelochemical stress is scarce.For the study,two typical anti-cyanobacterial allelochemicals were adopted to investigate the role of EPS in resistance to allelochemical stress on Microcystis aeruginosa.Results show that EPS was crucial in alleviating the toxicity of allelochemicals to algae,especially in stabilizing the metabolism and photosynthetic activity of algal cells.The aggregation rate of algal cells increased with the increase of EPS secretion,which alleviated the stress of allelopathy.Tryptophan proteins and humic acids in EPS provided a binding site for allelochemicals,and the EPS-allelochemicals complex were formed by chemical bonding.This study improved our comprehension of the role of EPS in algal inhibition by allelochemicals.展开更多
Dolichospermum,a typical model filamentous of cyanobacteria,has the potential to cause severely bloom.Extracellular polymeric substances(EPSs)are considered to influence the aggregation of the algae,and temperature is...Dolichospermum,a typical model filamentous of cyanobacteria,has the potential to cause severely bloom.Extracellular polymeric substances(EPSs)are considered to influence the aggregation of the algae,and temperature is a significant factor affecting EPSs secretion.However,the mechanism of how EPSs affects the aggregation of Dolichospermum is still unclear because the structure and composition of EPSs are complex.In this study,the effects of EPSs on the aggregation of Dolichospermum during the rise of temperature(7-37℃)were determined.The results showed that the concentration of extracellular polysaccharides and proteins changed significantly with increasing temperature(P<0.01).Firstly,during the increasing temperature,the polysaccharide content of EPSs increased from 20.34 to 54.64 mg/L,and the polysaccharides in the soluble EPS(S-EPS)layer changed significantly.The protein content reached maximum value at 21℃(14.52 mg/L)and varied significantly in S-EPS and loosely bound EPS(LB-EPS).In the EPSs matrix,humus substances and protein were main components of S-EPS and LB-EPS,and protein was the main component of tightly bound EPS(TB-EPS).Secondly,the cell density of Dolichospermum increased during the temperature rise while the aggregation ratio decreased.Moreover,zeta potential and surface thermodynamic analysis of Dolichospermum revealed that the interfacial free energy and electrostatic repulsion increased gradually with increasing temperature,which further reduced the aggregation of Dolichospermum.Finally,principal component analysis(PCA)analysis showed the aggregation of Dolichospermum was directly related to the changes of protein in EPSs(especially S-EPS and LB-EPS)and zeta potential,and polysaccharides in EPSs inhibited the aggregation of Dolichospermum.Based on these results,it was illustrated that the composition and concentration of EPSs affected the cell surface properties of Dolichospermum with the change of temperature and thus affected the aggregation of Dolichospermum.展开更多
Colony formation of cyanobacteria is crucial for the formation of surface blooms in lakes.However,the underlying mechanisms of colony formation involving in physiological and cell surface characteristics remain to not...Colony formation of cyanobacteria is crucial for the formation of surface blooms in lakes.However,the underlying mechanisms of colony formation involving in physiological and cell surface characteristics remain to not well be established.Six cyanobacterial Microcystis strains(including both unicellular and colonial ones)were employed to estimate the influences of their physiological traits and the composition of extracellular polymeric substances(EPS)on colony or aggregate formation.Results show that raising the number of the photosynthetic reaction center and light-harvesting antenna in the PSII and reducing the growth rate were the major physiological strategies of Microcystis to produce excess EPS enhancing colony formation.Tightly bound EPS(T-EPS)was responsible for colony formation,which approximately accounted for 50%of the total amount of EPS.Five fluorescent components(protein-,tryptophan-,and tyrosine-like components and two humic-like components)were found in the T-EPS,although the amounts of these components varied with strains.Importantly,colonial strains contained much higher tyrosine-like substances than unicellular ones.We suggest that tyrosine-like substances might serve as a crosslinking agent to connect other polymers in EPS(e.g.,proteins or polysaccharides)for colony formation.Our findings identified key physiological traits and chemical components of EPS for colony formation in Microcystis,which can contribute to a better understanding on the formation of Microcystis blooms.展开更多
Extracellular polymeric substances(EPS) are the predominant constituen ts of activated sludge and represent up to 80% of the mass of activated sludge. They play a crucial role in the flocculation, settling and dewater...Extracellular polymeric substances(EPS) are the predominant constituen ts of activated sludge and represent up to 80% of the mass of activated sludge. They play a crucial role in the flocculation, settling and dewatering of activat ed sludge. Furthermore, EPS also show great efficiency in binding heavy metals. So EPS are key factors influencing reduction in sludge volume and mass, as well as activity and utilization of sludge. EPS are of considerable environmental int erest and hundreds of articles on EPS have been published abroad, while informat ion on EPS in China is limited. In this paper, results of over 60 publications r elated to constituents and characteristics of EPS and their influences on floccu lation, settling and dewatering of sludge are compiled and analyzed. Metal-bindi ng ability of EPS is also discussed, together with a brief consideration of poss ible research interests in the future.展开更多
Effect of ultrasonic pretreatment on sludge dewaterability was determined and the fate of extracellular polymeric substances (EPS) matrix in mesophilic anaerobic digestion after ultrasonic pretreatment was studied. Ch...Effect of ultrasonic pretreatment on sludge dewaterability was determined and the fate of extracellular polymeric substances (EPS) matrix in mesophilic anaerobic digestion after ultrasonic pretreatment was studied. Characteristics of proteins (PN), polysaccharides (PS), excitation-emission matrix (EEM) fluorescence spectroscopy and molecular weight (MW) distribution of dissolved organic matters (DOM) in different EPS fractions were evaluated. The results showed that after ultrasonic pretreatment, the normalized capillary suction time (CST) decreased from 44.4 to 11.1 (sec·L)/g total suspended solids (TSS) during anaerobic digestion, indicating that sludge dewaterability was greatly improved. The normalized CST was significantly correlated with PN concentration (R2 = 0.92, p < 0.01) and the PN/PS ratio (R2 = 0.84, p < 0.01) in the loosely bound EPS (LB-EPS) fraction. Meanwhile, the average MW of DOM in the LB- EPS and tightly bound EPS (TB-EPS) fractions also had a good correlation with the normalized CST (R2 > 0.66, p < 0.01). According to EEM fluorescence spectroscopy, tryptophan-like substances intensities in the slime, LB-EPS and TB-EPS fractions were correlated with the normalized CST. The organic matters in the EPS matrix played an important role in influencing sludge dewaterability.展开更多
This paper describes the investigation of the secretion of extracellular polymeric substances(EPS)by an extremely thermoacidophilic archaea,Metallosphaera sedula(M.sedula),during the bioleaching of pyrite under differ...This paper describes the investigation of the secretion of extracellular polymeric substances(EPS)by an extremely thermoacidophilic archaea,Metallosphaera sedula(M.sedula),during the bioleaching of pyrite under different temperatures and discusses the relationship among the EPS secretion,its heat resistance,and its ability to bioleach pyrite.The investigation results indicate that the amount of extracellular proteins is significantly higher than the amount of extracellular polysaccharides in the extracted EPS whether free cells or attached cells;these results are quite different from the behavior of mesophilic Acidithiobacillus ferrooxidans.Although the growth of M.sedula is inhibited at 80℃,the bioleaching ability of M.sedula is only slightly lower than that at the optimum growth temperature of 72℃ because of the heat resistance mechanism based on EPS secretion.The secretion of more extracellular proteins is an important heat resistance mechanism of M.sedula.展开更多
A model, for evaluating the effect of porosity and volume fraction of extracellular polymeric substances (EPS) within multispecies biofilms on the effective diffusivity, is developed and experimentally validated, base...A model, for evaluating the effect of porosity and volume fraction of extracellular polymeric substances (EPS) within multispecies biofilms on the effective diffusivity, is developed and experimentally validated, based on the extraction of EPS from intact biofilms. The amount of EPS in biofilms significantly affects the effective diffusivity. For biofilms with porosity of 77%—95% in the top layers and 54%—58% in the bottom layers, the value of De/Dw decreases from 0.52—0.83 in the top layers to 0.23—0.31 in the bottom layers. Generally, the effective diffusivity in the heterotrophic/autotrophic biofilms is slightly lower than that in the heterotrophic biofilms, due to the lower porosity in the heterotrophic/autotrophic biofilms.展开更多
Extracellular polymeric substances(EPS)are an importantmedium for communication and material exchange between iron-oxidizing bacteria and the external environment and could induce the iron(oxyhydr)oxides production wh...Extracellular polymeric substances(EPS)are an importantmedium for communication and material exchange between iron-oxidizing bacteria and the external environment and could induce the iron(oxyhydr)oxides production which reduced arsenic(As)availability.The main component of EPS secreted by iron-oxidizing bacteria(Ochrobactrum EEELCW01)was composed of polysaccharides(150.76-165.33 mg/g DW)followed by considerably smaller amounts of proteins(12.98–16.12 mg/g DW).Low concentrations of As(100 or 500μmol/L)promoted the amount of EPS secretion.FTIR results showed that EPS was composed of polysaccharides,proteins,and a miniscule amount of nucleic acids.The functional groups including-COOH,-OH,-NH,-C=O,and-C-O played an important role in the adsorption of As.XPS results showed that As was bound to EPS in the form of As3+.With increasing As concentration,the proportion of As3+adsorbed on EPS increased.Ferrihydrite with a weak crystalline state was only produced in the system at 6 hr during the mineralization process of Ochrobactrum sp.At day 8,the minerals were composed of goethite,galena,and siderite.With the increasing mineralization time,the main mineral phases were transformed from weakly crystalline hydrous iron ore into higher crystallinity siderite(FeCO_(3))or goethite(α-FeOOH),and the specific surface area and active sites of minerals were reduced.It can be seen from the distribution of As elements that As is preferentially adsorbed on the edges of iron minerals.This study is potential to understand the biomineralizationmechanism of iron-oxidizing bacteria and As remediation in the environment.展开更多
Antibiotics,the most frequently prescribed drugs,have been widely applied to prevent or cure human and veterinary diseases and have undoubtedly led to massive releases into sewer networks and wastewater treatment syst...Antibiotics,the most frequently prescribed drugs,have been widely applied to prevent or cure human and veterinary diseases and have undoubtedly led to massive releases into sewer networks and wastewater treatment systems,a hotspot where the occurrence and transformation of antibiotic resistance take place.Extracellular polymeric substances(EPS),biopolymers secreted via microbial activity,play an important role in cell adhesion,nutrient retention,and toxicity resistance.However,the potential roles of sludge EPS related to the resistance and removal of antibiotics are still unclear.This work summarizes the composition and physicochemical characteristics of state-of-the-art microbial EPS,highlights the critical role of EPS in antibiotics removal,evaluates their defense performances under different antibiotics exposures,and analyzes the typical factors that could affect the sorption and biotransformation behavior of antibiotics.Next,interactions between microbial EPS and antibiotic resistance genes are analyzed.Future perspectives,especially the engineering application of microbial EPS for antibiotics toxicity detection and defense,are also emphatically stressed.展开更多
Aluminum ions produced by aluminum mining,electrolytic industry and aluminum-based coagulants can enter wastewater treatment plants and interact with activated sludge.They can subsequently contribute to the removal of...Aluminum ions produced by aluminum mining,electrolytic industry and aluminum-based coagulants can enter wastewater treatment plants and interact with activated sludge.They can subsequently contribute to the removal of suspended solids and affect activated sludge flocculation,as well as nitrogen and phosphorus removal.In this study,the effects of Al^3+on pollutant removal,sludge flocculation and the composition and structure of extracellular polymeric substances(EPS)were investigated under anaerobic,anoxic and oxic conditions.Results demonstrated that the highest chemical oxygen demand(COD)and total nitrogen(TN)removal efficiencies were detected for an Al^3+concentration of 10 mg/L.In addition,the maximal dehydrogenase activity and sludge flocculation were also observed at this level of Al^3+.The highest removal efficiency of total phosphorus(TP)was achieved at an Ar+concentration of30 mg/L.The flocculability of sludge in the anoxic zone was consistently higher than that in the anaerobic and oxic zones.The addition of Al^3+promoted the secretion of EPS.Tryptophan-like fluorescence peaks were detected in each EPS layer in the absence of Al^3+.At the Al^3+concentration of 10 mg/L,fulvic acid and tryptophan fluorescence peaks began to appear while the majority of protein species and the highest microbial activity were also detected.Low Al^3+concentrations(<10 mg/L)could promote the removal efficiencies of COD and TN,yet excessive Al^3+levels(>10 mg/L)weakened microbial activity.Higher Al^3+concentrations(>30 mg/L)also inhibited the release of phosphorus in the anaerobic zone by reacting with PO4^3-.展开更多
Extracellular polymeric substances(EPS)in activated sludge from wastewater treatment plants(WWTPs)could affect interactions between nanoparticles and alter their migration behavior.The influence mechanisms of silver n...Extracellular polymeric substances(EPS)in activated sludge from wastewater treatment plants(WWTPs)could affect interactions between nanoparticles and alter their migration behavior.The influence mechanisms of silver nanoparticles(Ag NPs)and silver sulfide nanoparticles(Ag_(2)S NPs)aggregated by active EPS sludge were studied in monovalent or divalent cation solutions.The aggregation behaviors of the NPs without EPS followed the Derjaguin-Landau-Verwey-Overbeek(DLVO)theory.The counterions aggravated the aggregation of both NPs,and the divalent cation had a strong neutralizing effect due to the decrease in electrostatic repulsive force.Through extended DLVO(EDLVO)model analysis,in NaNO3 and low-concentration Ca(NO_(3))_(2)(<10 mmol/L)solutions,EPS could alleviate the aggregation behaviors of Cit-Ag NPs and Ag_(2)S NPs due to the enhancement of steric repulsive forces.At high concentrations of Ca(NO_(3))_(2)(10‒100 mmol/L),exopolysaccharide macromolecules could promote the aggregation of Cit-Ag NPs and Ag_(2)S NPs by interparticle bridging.As the final transformation form of Ag NPs in water environments,Ag_(2)S NPs had better stability,possibly due to their small van der Waals forces and their strong steric repulsive forces.It is essential to elucidate the surface mechanisms between EPS and NPs to understand the different fates of metal-based and metal-sulfide NPs in WWTP systems.展开更多
Extracellular polymeric substances(EPS),produced by microorganisms,establish the functional and structural integrity of microbial biofilms.In biological wastewater treatments,the transformation of pollutants largely r...Extracellular polymeric substances(EPS),produced by microorganisms,establish the functional and structural integrity of microbial biofilms.In biological wastewater treatments,the transformation of pollutants largely relies on microbial electron transfer.As a bridge between the microbial cytomembrane/cytoderm and terminal electron acceptors,the role of EPS in microbial electron transfer cannot be ignored.However,due to the complexity of its composition,the in situ function of EPS in extracellular electron transfer is still unclear.In this work,we constructed an epsH gene knockout mutant of Methylomonas sp.LW13 with significantly reduced EPS formation.The content of protein and polysaccharide,two major components of EPS,of theΔepsH mutant and wild-type during different growth stages were compared.The redox signal and in situ Au reduction of theΔepsH mutant were obviously stronger than those of the wild-type,which suggested that EPS can hinder extracellular electron transfer in this system.Although redox activity was detected in EPS,high faradaic resistance of EPS was demonstrated.Our results enlighten the in situ role of EPS in extracellular electron transfer with the help of molecular manipulations and provide insights into how to regulate the microbial process of wastewater treatments.展开更多
The changes of protein secondary structures in the extracellular polymeric substances(EPS) extracted from activated sludge by four different methods were studied by analyzing the amide I region(1700–1600 cm-1) of the...The changes of protein secondary structures in the extracellular polymeric substances(EPS) extracted from activated sludge by four different methods were studied by analyzing the amide I region(1700–1600 cm-1) of the Fourier transform infrared spectra and model protein test. The results showed the molecular weight distribution of organic matter extracted by centrifugation, heating and cation exchange resin(CER) was similar, while the EPS extracted by centrifugation(Control) and CER had similar fluorescent organic matter. The protein secondary structures of extracted EPS by the four methods were different. The similarities of protein secondary structures between the EPS extracted by CER with the Control were the highest among the four extracted EPS. Although the EPS yield extracted by formaldehyde + NaOH method were the highest, its protein secondary structures had the lowest similarity with those extracted by the Control. Additionally, the effects of centrifugation and CER extraction on the secondary structures of bovine serum albumin were also lower than that of other extraction processes. CER enables the second maximum extraction of EPS and maximum retention of the original secondary structure of proteins.展开更多
The distribution of metallic elements in a submerged membrane bioreactor(MBR) was revealed at different temperatures using inductively coupled plasma-optical emission spectrometry(ICP-OES), and the role of extracellul...The distribution of metallic elements in a submerged membrane bioreactor(MBR) was revealed at different temperatures using inductively coupled plasma-optical emission spectrometry(ICP-OES), and the role of extracellular polymeric substances(EPS) was probed by integrating scanning electron microscopy(SEM) with confocal laser scanning microscopy(CLSM) over long-term operation. More metallic elements in the influent were captured by suspended sludge and built up in the fouling layer at lower temperature. The concentration of metallic elements in the effluent was 5.60 mg/L at 10°C operational temperature, far lower than that in the influent(51.35 mg/L). The total contents of metallic elements in suspended sludge and the membrane fouling layer increased to 40.20 and 52.19 mg/g at 10°C compared to 35.14 and 32.45 mg/g at 30°C, and were dominated by the organically bound fraction. The EPS contents in suspended sludge and membrane fouling layer sharply increased to 37.88 and 101.51 mg/g at 10°C, compared to 16.87 and 30.03 mg/g at 30°C. The increase in EPS content at lower temperature was responsible for the deposition of more metallic ions. The strong bridging between EPS and metallic elements at lower temperature enhanced the compactness of the fouling layer and further decreased membrane flux. This was helpful for understanding the mechanism of membrane fouling at different operational temperatures and the role of EPS, and also of significance for the design of cleaning strategies for fouled membranes after long-term operation.展开更多
Biopolymer solubilization is considered to be the rate-limiting stage of anaerobic digestion of waste activated sludge(WAS). Oxidation processes have been proven to be effective in disrupting sludge flocs and causing ...Biopolymer solubilization is considered to be the rate-limiting stage of anaerobic digestion of waste activated sludge(WAS). Oxidation processes have been proven to be effective in disrupting sludge flocs and causing solubilization of the solid biopolymers. In this study,WAS was treated by NaNO2 or H2 O2 oxidation at p H of 2. The changes in extracellular polymeric substances properties and the speciation of heavy metals were investigated. The results revealed that both NaNO2 and H2 O2 treatments were effective in solubilizing organics in WAS, while the conversion of biopolymers in the two treatment processes was different. Free nitrous acid destroyed the gel network structure of EPS, and organic materials were released from the solid phase to the supernatant. Indigenous peroxidase catalyzed H2 O2 to produce hydroxyl radicals which caused significant solubilization of biopolymers, and the protein-like substances were further degraded into micro-molecule polypeptides or amino acids at high dosages of H2 O2. During the oxidation processes, Zn, Cd and Cu, with excellent mobility, tended to migrate to the supernatant, and thus were easy to remove through the liquid–solid separation process. Ni and As showed moderate migration ability, of which the residual fraction tended to transform into reducible and soluble fractions. With poor mobility, Cr and Pb mainly existed in the forms of residual and oxidizable fractions, which were difficult to dissolve and remove from WAS. Both NaNO2 and H2 O2 treatment resulted in the enhancement of sludge solubilization efficiency and heavy metal mobility in WAS, but different heavy metals showed distinct migration and transformation behaviors.展开更多
Extracellular polymeric substances(EPS) extracted from electroactive bacteria show promising redox activity, but the electron transfer(ET) mechanism of the EPS has been rarely elucidated because of their structural co...Extracellular polymeric substances(EPS) extracted from electroactive bacteria show promising redox activity, but the electron transfer(ET) mechanism of the EPS has been rarely elucidated because of their structural complexity and lack of efficient methodologies. In this study, the charge transfer theory of surface-enhanced Raman spectroscopy(SERS) was applied to evaluate the redox properties of EPS adsorbed on Ni and Ag nanoparticles(NPs). These metal NPs were used to simultaneously magnify Raman signals and reduce/oxidize the redox moieties in EPS. As a result, the ET between EPS and metal NPs was evaluated through the changes in Raman signals. In this regard, we compared the redox activity of EPS extracted from two typical electroactive bacteria(Shewanella oneidensis and Geobacter sulfurreducens) and another two nonelectroactive strains(Escherichia coli and Bacillus subtilis). Electrochemical measurements show that the electroactive strains have higher redox capabilities than nonelectroactive strains. The SERS analysis shows that the porphyrin present in cytochrome c is the dominating redox moiety in the EPS of electroactive bacteria. The results of this study show that SERS with active metal substrates is a sensitive tool to probe the redox response of EPS, offering an opportunity to better understand the redox nature of biomolecules.展开更多
The composition and effects of solution conditions on the physicochemical properties of the stratification components of extracellular polymeric substances (EPS) in anaerobic digested sludge were determined. The total...The composition and effects of solution conditions on the physicochemical properties of the stratification components of extracellular polymeric substances (EPS) in anaerobic digested sludge were determined. The total EPS in anaerobic digested sludge were extracted by the cation exchange resin method. Another EPS extraction method, the centrifugation and sonication technique was employed to stratify the EPS into three fractions: slime, loosely bound (LB)-EPS, and tightly bound (TB)-EPS from the outside to the inside of the anaerobic digested sludge. Proteins and polysaccharides were dispersed uniformly across the different EPS fractions, and humic-like substances were mainly partitioned in the slime, with TB-EPS second. Protein was the major constituent of the LB-EPS and TB-EPS, and the corresponding ratios ranged from 54.0% to 65.6%. The hydrophobic part in the EPS chemical components was primarily comprised of protein and DNA, while the hydrophilic part was mainly composed of polysaccharide. In the slime, the hydrophobic values of several EPS chemical components (protein, polysaccharide, humic-like substances and DNA) were all below 50%. The protein/polysaccharide ratio had a significant influence on the Zeta potentials and isoelectric point values of the EPS: the greater the protein/polysaccharide ratio of the EPS was, the greater the Zeta potential and the higher the isoelectric point value were. All Zeta potentials of the EPS showed a decreasing trend with increasing pH. The corresponding isoelectric point values (pH) were 2.8 for total EPS, 2.2 for slime, 2.7 for LB-EPS, and 2.6 for TB-EPS. As the ionic strength increased, the Zeta potentials sharply increased and then gradually became constant without charge reversal. In addition, as the temperature increased (< 40°C), the apparent viscosity of the EPS decreased monotonically and then gradually became stable between 40 and 60°C.展开更多
Preliminary characterization of bound extracellular polymeric substances(bEPS) of cyanobacteria is crucial to obtain a better understanding of the formation mechanism of cyanobacterial bloom. However,the characterizat...Preliminary characterization of bound extracellular polymeric substances(bEPS) of cyanobacteria is crucial to obtain a better understanding of the formation mechanism of cyanobacterial bloom. However,the characterization of bEPS can be affected by extraction methods. Five sets(including the control) of bEPS from Microcystis extracted by different methods were characterized using three-dimensional excitation and emission matrix(3DEEM) fluorescence spectroscopy combined chemical spectrophotometry; and the characterization results of bEPS samples were further compared. The agents used for extraction were NaOH,pure water and phosphate buffered saline(PBS) containing cationic exchange resins,and hot water. Extraction methods affected the fluorescence signals and intensities in the bEPS. Five fluorescence peaks were observed in the excitation and emission matrix fluorescence spectra of bEPS samples. Two peaks(peaks T1 and T2) present in all extractions were identified as protein-like fluorophores,two(peaks A and C) as humic-like fluorophores,and one(peak E) as a fulvic-like substance.Among these substances,the humic-like and fulvic-like fluorescences were only seen in the bEPS extracted with hot water. Also,NaOH solution extraction could result in strong fluorescence intensities compared to the other extraction methods. It was suggested that NaOH at pH 10.0 was the most appropriate method to extract bEPS from Microcystis. In addition,dialysis could affect the yields and characteristics of extracted bEPS during the determination process. These results will help us to explore the issues of cyanobacterial blooms.展开更多
Aluminum flocculant can enhance the flocculating performance of activated sludge.However,the binding mechanism of aluminum ion(Al 3+) and extracellular polymeric substances(EPS) in activated sludge is unclear due to t...Aluminum flocculant can enhance the flocculating performance of activated sludge.However,the binding mechanism of aluminum ion(Al 3+) and extracellular polymeric substances(EPS) in activated sludge is unclear due to the complexity of EPS.In this work,threedimensional excitation emission matrix fluorescence spectroscopy(3DEEM),fluorescence quenching titration and Fourier transform infrared spectroscopy(FT-IR) were used to explore the binding behavior and mechanism between Al 3+ and EPS.The results showed that two fluorescence peaks of tyrosineand tryptophan-like substances were identified in the loosely bound-extracellular polymeric substances(LB-EPS),and three peaks of tyrosine-,tryptophanand humic-like substances were identified in the tightly boundextracellular polymeric substances(TB-EPS).It was found that these fluorescence peaks could be quenched with Al 3+ at the dosage of 3.0 mg/L,which demonstrated that strong interactions took place between the EPS and Al 3+.The conditional stability constants for Al 3+ and EPS were determined by the Stern-Volmer equation.As to the binding mechanism,the-OH,N-H,C=O,C-N groups and the sulfurand phosphorus-containing groups showed complexation action,although the groups in the LB-EPS and TB-EPS showed different behavior.The TB-EPS have stronger binding ability to Al 3+ than the LB-EPS,and TB-EPS play an important role in the interaction with Al 3+.展开更多
基金Supported by the National Natural Science Foundation of China(Nos.51979137,51779079,41931292)。
文摘Using allelochemicals to suppress cyanobacteria growth is a prospective method for its high efficiency and ecological safety.However,the suppression efficiency is affected inevitably by the extracellular polymeric substances(EPS)produced by cyanobacteria,and the knowledge about the roles of EPS in resistance to allelochemical stress is scarce.For the study,two typical anti-cyanobacterial allelochemicals were adopted to investigate the role of EPS in resistance to allelochemical stress on Microcystis aeruginosa.Results show that EPS was crucial in alleviating the toxicity of allelochemicals to algae,especially in stabilizing the metabolism and photosynthetic activity of algal cells.The aggregation rate of algal cells increased with the increase of EPS secretion,which alleviated the stress of allelopathy.Tryptophan proteins and humic acids in EPS provided a binding site for allelochemicals,and the EPS-allelochemicals complex were formed by chemical bonding.This study improved our comprehension of the role of EPS in algal inhibition by allelochemicals.
基金Supported by the National Natural Science Foundation of China(Nos.41877336,41907202,91951112,41773077)the China Postdoctoral Science Foundation(No.2019M651877)+2 种基金the Natural Science Foundation of Jiangsu Province(No.SBK2019043965)the Yancheng Fishery High Quality Development Project(No.YCSCYJ2021030)the Postgraduate Research&Practice Innovation Program of Jiangsu Province(No.KYCX22_1581)。
文摘Dolichospermum,a typical model filamentous of cyanobacteria,has the potential to cause severely bloom.Extracellular polymeric substances(EPSs)are considered to influence the aggregation of the algae,and temperature is a significant factor affecting EPSs secretion.However,the mechanism of how EPSs affects the aggregation of Dolichospermum is still unclear because the structure and composition of EPSs are complex.In this study,the effects of EPSs on the aggregation of Dolichospermum during the rise of temperature(7-37℃)were determined.The results showed that the concentration of extracellular polysaccharides and proteins changed significantly with increasing temperature(P<0.01).Firstly,during the increasing temperature,the polysaccharide content of EPSs increased from 20.34 to 54.64 mg/L,and the polysaccharides in the soluble EPS(S-EPS)layer changed significantly.The protein content reached maximum value at 21℃(14.52 mg/L)and varied significantly in S-EPS and loosely bound EPS(LB-EPS).In the EPSs matrix,humus substances and protein were main components of S-EPS and LB-EPS,and protein was the main component of tightly bound EPS(TB-EPS).Secondly,the cell density of Dolichospermum increased during the temperature rise while the aggregation ratio decreased.Moreover,zeta potential and surface thermodynamic analysis of Dolichospermum revealed that the interfacial free energy and electrostatic repulsion increased gradually with increasing temperature,which further reduced the aggregation of Dolichospermum.Finally,principal component analysis(PCA)analysis showed the aggregation of Dolichospermum was directly related to the changes of protein in EPSs(especially S-EPS and LB-EPS)and zeta potential,and polysaccharides in EPSs inhibited the aggregation of Dolichospermum.Based on these results,it was illustrated that the composition and concentration of EPSs affected the cell surface properties of Dolichospermum with the change of temperature and thus affected the aggregation of Dolichospermum.
基金Supported by the National Natural Science Foundation of China(No.32071569)the Scientific Instruments and Equipment Development Project+2 种基金Chinese Academy of Sciences,2020(No.YJKYYQ20200048)the Fundamental Research Funds for the Central Universities(No.B210202010)the China Postdoctoral Foundation(No.2020M681472)。
文摘Colony formation of cyanobacteria is crucial for the formation of surface blooms in lakes.However,the underlying mechanisms of colony formation involving in physiological and cell surface characteristics remain to not well be established.Six cyanobacterial Microcystis strains(including both unicellular and colonial ones)were employed to estimate the influences of their physiological traits and the composition of extracellular polymeric substances(EPS)on colony or aggregate formation.Results show that raising the number of the photosynthetic reaction center and light-harvesting antenna in the PSII and reducing the growth rate were the major physiological strategies of Microcystis to produce excess EPS enhancing colony formation.Tightly bound EPS(T-EPS)was responsible for colony formation,which approximately accounted for 50%of the total amount of EPS.Five fluorescent components(protein-,tryptophan-,and tyrosine-like components and two humic-like components)were found in the T-EPS,although the amounts of these components varied with strains.Importantly,colonial strains contained much higher tyrosine-like substances than unicellular ones.We suggest that tyrosine-like substances might serve as a crosslinking agent to connect other polymers in EPS(e.g.,proteins or polysaccharides)for colony formation.Our findings identified key physiological traits and chemical components of EPS for colony formation in Microcystis,which can contribute to a better understanding on the formation of Microcystis blooms.
基金The National Natural Science Foundation of China (No. 50578053) and the Harbin Young Scientist Fund (No. 2003AFXXJ025)
文摘Extracellular polymeric substances(EPS) are the predominant constituen ts of activated sludge and represent up to 80% of the mass of activated sludge. They play a crucial role in the flocculation, settling and dewatering of activat ed sludge. Furthermore, EPS also show great efficiency in binding heavy metals. So EPS are key factors influencing reduction in sludge volume and mass, as well as activity and utilization of sludge. EPS are of considerable environmental int erest and hundreds of articles on EPS have been published abroad, while informat ion on EPS in China is limited. In this paper, results of over 60 publications r elated to constituents and characteristics of EPS and their influences on floccu lation, settling and dewatering of sludge are compiled and analyzed. Metal-bindi ng ability of EPS is also discussed, together with a brief consideration of poss ible research interests in the future.
基金supported by the National Natural Science Foundation of China (No. 20977066)the National Key Project for Water Pollution Control (No.2008ZX07316-002, 2008ZX07317-003)the Specialized Research Found for Doctoral Program of Higher Education of China (No. 200802470029)
文摘Effect of ultrasonic pretreatment on sludge dewaterability was determined and the fate of extracellular polymeric substances (EPS) matrix in mesophilic anaerobic digestion after ultrasonic pretreatment was studied. Characteristics of proteins (PN), polysaccharides (PS), excitation-emission matrix (EEM) fluorescence spectroscopy and molecular weight (MW) distribution of dissolved organic matters (DOM) in different EPS fractions were evaluated. The results showed that after ultrasonic pretreatment, the normalized capillary suction time (CST) decreased from 44.4 to 11.1 (sec·L)/g total suspended solids (TSS) during anaerobic digestion, indicating that sludge dewaterability was greatly improved. The normalized CST was significantly correlated with PN concentration (R2 = 0.92, p < 0.01) and the PN/PS ratio (R2 = 0.84, p < 0.01) in the loosely bound EPS (LB-EPS) fraction. Meanwhile, the average MW of DOM in the LB- EPS and tightly bound EPS (TB-EPS) fractions also had a good correlation with the normalized CST (R2 > 0.66, p < 0.01). According to EEM fluorescence spectroscopy, tryptophan-like substances intensities in the slime, LB-EPS and TB-EPS fractions were correlated with the normalized CST. The organic matters in the EPS matrix played an important role in influencing sludge dewaterability.
基金financially supported by the National Natural Science Foundation of China (Nos. 31470230, 51320105006, 51604308, and 31100173)the Youth Talent Foundation of Hunan Province of China (No. 2017RS3003)the National Science Foundation of Hunan Province of China (No. 2018JJ2486)
文摘This paper describes the investigation of the secretion of extracellular polymeric substances(EPS)by an extremely thermoacidophilic archaea,Metallosphaera sedula(M.sedula),during the bioleaching of pyrite under different temperatures and discusses the relationship among the EPS secretion,its heat resistance,and its ability to bioleach pyrite.The investigation results indicate that the amount of extracellular proteins is significantly higher than the amount of extracellular polysaccharides in the extracted EPS whether free cells or attached cells;these results are quite different from the behavior of mesophilic Acidithiobacillus ferrooxidans.Although the growth of M.sedula is inhibited at 80℃,the bioleaching ability of M.sedula is only slightly lower than that at the optimum growth temperature of 72℃ because of the heat resistance mechanism based on EPS secretion.The secretion of more extracellular proteins is an important heat resistance mechanism of M.sedula.
基金Supported by the National Natural Science Foundation of China (Project No. 29976030)863 Hi-Technology Research and Development Program of China (2004AA649340).
文摘A model, for evaluating the effect of porosity and volume fraction of extracellular polymeric substances (EPS) within multispecies biofilms on the effective diffusivity, is developed and experimentally validated, based on the extraction of EPS from intact biofilms. The amount of EPS in biofilms significantly affects the effective diffusivity. For biofilms with porosity of 77%—95% in the top layers and 54%—58% in the bottom layers, the value of De/Dw decreases from 0.52—0.83 in the top layers to 0.23—0.31 in the bottom layers. Generally, the effective diffusivity in the heterotrophic/autotrophic biofilms is slightly lower than that in the heterotrophic biofilms, due to the lower porosity in the heterotrophic/autotrophic biofilms.
基金supported by the National Natural Science Foundation of China(No.42177392)the Dean’s Research Fund 2020/21(No.04626)of the Education University of Hong Kong.
文摘Extracellular polymeric substances(EPS)are an importantmedium for communication and material exchange between iron-oxidizing bacteria and the external environment and could induce the iron(oxyhydr)oxides production which reduced arsenic(As)availability.The main component of EPS secreted by iron-oxidizing bacteria(Ochrobactrum EEELCW01)was composed of polysaccharides(150.76-165.33 mg/g DW)followed by considerably smaller amounts of proteins(12.98–16.12 mg/g DW).Low concentrations of As(100 or 500μmol/L)promoted the amount of EPS secretion.FTIR results showed that EPS was composed of polysaccharides,proteins,and a miniscule amount of nucleic acids.The functional groups including-COOH,-OH,-NH,-C=O,and-C-O played an important role in the adsorption of As.XPS results showed that As was bound to EPS in the form of As3+.With increasing As concentration,the proportion of As3+adsorbed on EPS increased.Ferrihydrite with a weak crystalline state was only produced in the system at 6 hr during the mineralization process of Ochrobactrum sp.At day 8,the minerals were composed of goethite,galena,and siderite.With the increasing mineralization time,the main mineral phases were transformed from weakly crystalline hydrous iron ore into higher crystallinity siderite(FeCO_(3))or goethite(α-FeOOH),and the specific surface area and active sites of minerals were reduced.It can be seen from the distribution of As elements that As is preferentially adsorbed on the edges of iron minerals.This study is potential to understand the biomineralizationmechanism of iron-oxidizing bacteria and As remediation in the environment.
基金supported by the funding from the National Key Research and Development Program of China(2019YFC1803802)the National Natural Science Foundation of China(No.51878213)+1 种基金the State Key Laboratory of Urban Water Resource and Environment(No.2020TS01)the Heilongjiang Nature Science Foundation(YQ2020E022).
文摘Antibiotics,the most frequently prescribed drugs,have been widely applied to prevent or cure human and veterinary diseases and have undoubtedly led to massive releases into sewer networks and wastewater treatment systems,a hotspot where the occurrence and transformation of antibiotic resistance take place.Extracellular polymeric substances(EPS),biopolymers secreted via microbial activity,play an important role in cell adhesion,nutrient retention,and toxicity resistance.However,the potential roles of sludge EPS related to the resistance and removal of antibiotics are still unclear.This work summarizes the composition and physicochemical characteristics of state-of-the-art microbial EPS,highlights the critical role of EPS in antibiotics removal,evaluates their defense performances under different antibiotics exposures,and analyzes the typical factors that could affect the sorption and biotransformation behavior of antibiotics.Next,interactions between microbial EPS and antibiotic resistance genes are analyzed.Future perspectives,especially the engineering application of microbial EPS for antibiotics toxicity detection and defense,are also emphatically stressed.
基金This research was financially supported by the National Natural Science Foundation of China(Grant Nos.51678119 and 51808254)the Science and Technology Development Program of Jilin Province(Nos.20180201016SF and 20180101079JC)the Scientific Research Foundation from Education Department of Jilin Province(Nos.JJKH20180453KJ and JJKH20180454KJ).
文摘Aluminum ions produced by aluminum mining,electrolytic industry and aluminum-based coagulants can enter wastewater treatment plants and interact with activated sludge.They can subsequently contribute to the removal of suspended solids and affect activated sludge flocculation,as well as nitrogen and phosphorus removal.In this study,the effects of Al^3+on pollutant removal,sludge flocculation and the composition and structure of extracellular polymeric substances(EPS)were investigated under anaerobic,anoxic and oxic conditions.Results demonstrated that the highest chemical oxygen demand(COD)and total nitrogen(TN)removal efficiencies were detected for an Al^3+concentration of 10 mg/L.In addition,the maximal dehydrogenase activity and sludge flocculation were also observed at this level of Al^3+.The highest removal efficiency of total phosphorus(TP)was achieved at an Ar+concentration of30 mg/L.The flocculability of sludge in the anoxic zone was consistently higher than that in the anaerobic and oxic zones.The addition of Al^3+promoted the secretion of EPS.Tryptophan-like fluorescence peaks were detected in each EPS layer in the absence of Al^3+.At the Al^3+concentration of 10 mg/L,fulvic acid and tryptophan fluorescence peaks began to appear while the majority of protein species and the highest microbial activity were also detected.Low Al^3+concentrations(<10 mg/L)could promote the removal efficiencies of COD and TN,yet excessive Al^3+levels(>10 mg/L)weakened microbial activity.Higher Al^3+concentrations(>30 mg/L)also inhibited the release of phosphorus in the anaerobic zone by reacting with PO4^3-.
基金We sincerely thank the National Natural Science Foundation of China(No.51878092 and No.52070029)for their support.
文摘Extracellular polymeric substances(EPS)in activated sludge from wastewater treatment plants(WWTPs)could affect interactions between nanoparticles and alter their migration behavior.The influence mechanisms of silver nanoparticles(Ag NPs)and silver sulfide nanoparticles(Ag_(2)S NPs)aggregated by active EPS sludge were studied in monovalent or divalent cation solutions.The aggregation behaviors of the NPs without EPS followed the Derjaguin-Landau-Verwey-Overbeek(DLVO)theory.The counterions aggravated the aggregation of both NPs,and the divalent cation had a strong neutralizing effect due to the decrease in electrostatic repulsive force.Through extended DLVO(EDLVO)model analysis,in NaNO3 and low-concentration Ca(NO_(3))_(2)(<10 mmol/L)solutions,EPS could alleviate the aggregation behaviors of Cit-Ag NPs and Ag_(2)S NPs due to the enhancement of steric repulsive forces.At high concentrations of Ca(NO_(3))_(2)(10‒100 mmol/L),exopolysaccharide macromolecules could promote the aggregation of Cit-Ag NPs and Ag_(2)S NPs by interparticle bridging.As the final transformation form of Ag NPs in water environments,Ag_(2)S NPs had better stability,possibly due to their small van der Waals forces and their strong steric repulsive forces.It is essential to elucidate the surface mechanisms between EPS and NPs to understand the different fates of metal-based and metal-sulfide NPs in WWTP systems.
基金supported by the National Natural Science Foundation of China(Grants No.41907027,22025603 and 41471260)。
文摘Extracellular polymeric substances(EPS),produced by microorganisms,establish the functional and structural integrity of microbial biofilms.In biological wastewater treatments,the transformation of pollutants largely relies on microbial electron transfer.As a bridge between the microbial cytomembrane/cytoderm and terminal electron acceptors,the role of EPS in microbial electron transfer cannot be ignored.However,due to the complexity of its composition,the in situ function of EPS in extracellular electron transfer is still unclear.In this work,we constructed an epsH gene knockout mutant of Methylomonas sp.LW13 with significantly reduced EPS formation.The content of protein and polysaccharide,two major components of EPS,of theΔepsH mutant and wild-type during different growth stages were compared.The redox signal and in situ Au reduction of theΔepsH mutant were obviously stronger than those of the wild-type,which suggested that EPS can hinder extracellular electron transfer in this system.Although redox activity was detected in EPS,high faradaic resistance of EPS was demonstrated.Our results enlighten the in situ role of EPS in extracellular electron transfer with the help of molecular manipulations and provide insights into how to regulate the microbial process of wastewater treatments.
基金supported by the Major Science and Technology Program for Water Pollution Control and Treatment of China (Nos. 2017ZX07106003-002 and 2017ZX07102004-002)
文摘The changes of protein secondary structures in the extracellular polymeric substances(EPS) extracted from activated sludge by four different methods were studied by analyzing the amide I region(1700–1600 cm-1) of the Fourier transform infrared spectra and model protein test. The results showed the molecular weight distribution of organic matter extracted by centrifugation, heating and cation exchange resin(CER) was similar, while the EPS extracted by centrifugation(Control) and CER had similar fluorescent organic matter. The protein secondary structures of extracted EPS by the four methods were different. The similarities of protein secondary structures between the EPS extracted by CER with the Control were the highest among the four extracted EPS. Although the EPS yield extracted by formaldehyde + NaOH method were the highest, its protein secondary structures had the lowest similarity with those extracted by the Control. Additionally, the effects of centrifugation and CER extraction on the secondary structures of bovine serum albumin were also lower than that of other extraction processes. CER enables the second maximum extraction of EPS and maximum retention of the original secondary structure of proteins.
基金supported by the National Key Research and Development Program (No.2016YFC0400707)the Research and Innovation Project for Postgraduates of Higher Education Institutions of Jiangsu Province (Nos.KYLX16_0812 and SJZZ16_0216)
文摘The distribution of metallic elements in a submerged membrane bioreactor(MBR) was revealed at different temperatures using inductively coupled plasma-optical emission spectrometry(ICP-OES), and the role of extracellular polymeric substances(EPS) was probed by integrating scanning electron microscopy(SEM) with confocal laser scanning microscopy(CLSM) over long-term operation. More metallic elements in the influent were captured by suspended sludge and built up in the fouling layer at lower temperature. The concentration of metallic elements in the effluent was 5.60 mg/L at 10°C operational temperature, far lower than that in the influent(51.35 mg/L). The total contents of metallic elements in suspended sludge and the membrane fouling layer increased to 40.20 and 52.19 mg/g at 10°C compared to 35.14 and 32.45 mg/g at 30°C, and were dominated by the organically bound fraction. The EPS contents in suspended sludge and membrane fouling layer sharply increased to 37.88 and 101.51 mg/g at 10°C, compared to 16.87 and 30.03 mg/g at 30°C. The increase in EPS content at lower temperature was responsible for the deposition of more metallic ions. The strong bridging between EPS and metallic elements at lower temperature enhanced the compactness of the fouling layer and further decreased membrane flux. This was helpful for understanding the mechanism of membrane fouling at different operational temperatures and the role of EPS, and also of significance for the design of cleaning strategies for fouled membranes after long-term operation.
基金supported by the Fundamental Research Funds for the Central Universities, China University of Geosciences (Wuhan) (Nos. CUGL170411, CUG160824)the National Nature Science Foundation of China (No. 51678546)
文摘Biopolymer solubilization is considered to be the rate-limiting stage of anaerobic digestion of waste activated sludge(WAS). Oxidation processes have been proven to be effective in disrupting sludge flocs and causing solubilization of the solid biopolymers. In this study,WAS was treated by NaNO2 or H2 O2 oxidation at p H of 2. The changes in extracellular polymeric substances properties and the speciation of heavy metals were investigated. The results revealed that both NaNO2 and H2 O2 treatments were effective in solubilizing organics in WAS, while the conversion of biopolymers in the two treatment processes was different. Free nitrous acid destroyed the gel network structure of EPS, and organic materials were released from the solid phase to the supernatant. Indigenous peroxidase catalyzed H2 O2 to produce hydroxyl radicals which caused significant solubilization of biopolymers, and the protein-like substances were further degraded into micro-molecule polypeptides or amino acids at high dosages of H2 O2. During the oxidation processes, Zn, Cd and Cu, with excellent mobility, tended to migrate to the supernatant, and thus were easy to remove through the liquid–solid separation process. Ni and As showed moderate migration ability, of which the residual fraction tended to transform into reducible and soluble fractions. With poor mobility, Cr and Pb mainly existed in the forms of residual and oxidizable fractions, which were difficult to dissolve and remove from WAS. Both NaNO2 and H2 O2 treatment resulted in the enhancement of sludge solubilization efficiency and heavy metal mobility in WAS, but different heavy metals showed distinct migration and transformation behaviors.
基金supported by the National Natural Science Foundation of China(Grant Nos.51678162,41877045,21876032)the Guangzhou City Science-Technology Project(Grant No.201707010250)the Major Scientific Project of Guangdong University(Grant No.2017KZDXM029)
文摘Extracellular polymeric substances(EPS) extracted from electroactive bacteria show promising redox activity, but the electron transfer(ET) mechanism of the EPS has been rarely elucidated because of their structural complexity and lack of efficient methodologies. In this study, the charge transfer theory of surface-enhanced Raman spectroscopy(SERS) was applied to evaluate the redox properties of EPS adsorbed on Ni and Ag nanoparticles(NPs). These metal NPs were used to simultaneously magnify Raman signals and reduce/oxidize the redox moieties in EPS. As a result, the ET between EPS and metal NPs was evaluated through the changes in Raman signals. In this regard, we compared the redox activity of EPS extracted from two typical electroactive bacteria(Shewanella oneidensis and Geobacter sulfurreducens) and another two nonelectroactive strains(Escherichia coli and Bacillus subtilis). Electrochemical measurements show that the electroactive strains have higher redox capabilities than nonelectroactive strains. The SERS analysis shows that the porphyrin present in cytochrome c is the dominating redox moiety in the EPS of electroactive bacteria. The results of this study show that SERS with active metal substrates is a sensitive tool to probe the redox response of EPS, offering an opportunity to better understand the redox nature of biomolecules.
基金This work was supported by Program of 100 Distinguished Young Scientists of the Chinese Academy of Sciences and National Natural Science Foundation of China （Grant Nos. Ul120302 and 21177127）.
基金supported by the Fundamental Research Funds for the Central University (No.JC2011-1,TD2010-5)the National Natural Science Foundation of China(No. 51078035, 21177010)the Ph.D Programs Foundation of the Ministry of Education of China (No.20100014110004)
文摘The composition and effects of solution conditions on the physicochemical properties of the stratification components of extracellular polymeric substances (EPS) in anaerobic digested sludge were determined. The total EPS in anaerobic digested sludge were extracted by the cation exchange resin method. Another EPS extraction method, the centrifugation and sonication technique was employed to stratify the EPS into three fractions: slime, loosely bound (LB)-EPS, and tightly bound (TB)-EPS from the outside to the inside of the anaerobic digested sludge. Proteins and polysaccharides were dispersed uniformly across the different EPS fractions, and humic-like substances were mainly partitioned in the slime, with TB-EPS second. Protein was the major constituent of the LB-EPS and TB-EPS, and the corresponding ratios ranged from 54.0% to 65.6%. The hydrophobic part in the EPS chemical components was primarily comprised of protein and DNA, while the hydrophilic part was mainly composed of polysaccharide. In the slime, the hydrophobic values of several EPS chemical components (protein, polysaccharide, humic-like substances and DNA) were all below 50%. The protein/polysaccharide ratio had a significant influence on the Zeta potentials and isoelectric point values of the EPS: the greater the protein/polysaccharide ratio of the EPS was, the greater the Zeta potential and the higher the isoelectric point value were. All Zeta potentials of the EPS showed a decreasing trend with increasing pH. The corresponding isoelectric point values (pH) were 2.8 for total EPS, 2.2 for slime, 2.7 for LB-EPS, and 2.6 for TB-EPS. As the ionic strength increased, the Zeta potentials sharply increased and then gradually became constant without charge reversal. In addition, as the temperature increased (< 40°C), the apparent viscosity of the EPS decreased monotonically and then gradually became stable between 40 and 60°C.
基金supported by the Natural Scientific Foundation of China (Nos.40825004,40971252,41301544)the Water Pollution Control and Management Project (No.2012ZX07101-010)the Shandong Province Natural Science Foundation of China (No.ZR2012DQ003)
文摘Preliminary characterization of bound extracellular polymeric substances(bEPS) of cyanobacteria is crucial to obtain a better understanding of the formation mechanism of cyanobacterial bloom. However,the characterization of bEPS can be affected by extraction methods. Five sets(including the control) of bEPS from Microcystis extracted by different methods were characterized using three-dimensional excitation and emission matrix(3DEEM) fluorescence spectroscopy combined chemical spectrophotometry; and the characterization results of bEPS samples were further compared. The agents used for extraction were NaOH,pure water and phosphate buffered saline(PBS) containing cationic exchange resins,and hot water. Extraction methods affected the fluorescence signals and intensities in the bEPS. Five fluorescence peaks were observed in the excitation and emission matrix fluorescence spectra of bEPS samples. Two peaks(peaks T1 and T2) present in all extractions were identified as protein-like fluorophores,two(peaks A and C) as humic-like fluorophores,and one(peak E) as a fulvic-like substance.Among these substances,the humic-like and fulvic-like fluorescences were only seen in the bEPS extracted with hot water. Also,NaOH solution extraction could result in strong fluorescence intensities compared to the other extraction methods. It was suggested that NaOH at pH 10.0 was the most appropriate method to extract bEPS from Microcystis. In addition,dialysis could affect the yields and characteristics of extracted bEPS during the determination process. These results will help us to explore the issues of cyanobacterial blooms.
基金funded by the National Natural Science Foundation of China (No. 51138009,50921064)
文摘Aluminum flocculant can enhance the flocculating performance of activated sludge.However,the binding mechanism of aluminum ion(Al 3+) and extracellular polymeric substances(EPS) in activated sludge is unclear due to the complexity of EPS.In this work,threedimensional excitation emission matrix fluorescence spectroscopy(3DEEM),fluorescence quenching titration and Fourier transform infrared spectroscopy(FT-IR) were used to explore the binding behavior and mechanism between Al 3+ and EPS.The results showed that two fluorescence peaks of tyrosineand tryptophan-like substances were identified in the loosely bound-extracellular polymeric substances(LB-EPS),and three peaks of tyrosine-,tryptophanand humic-like substances were identified in the tightly boundextracellular polymeric substances(TB-EPS).It was found that these fluorescence peaks could be quenched with Al 3+ at the dosage of 3.0 mg/L,which demonstrated that strong interactions took place between the EPS and Al 3+.The conditional stability constants for Al 3+ and EPS were determined by the Stern-Volmer equation.As to the binding mechanism,the-OH,N-H,C=O,C-N groups and the sulfurand phosphorus-containing groups showed complexation action,although the groups in the LB-EPS and TB-EPS showed different behavior.The TB-EPS have stronger binding ability to Al 3+ than the LB-EPS,and TB-EPS play an important role in the interaction with Al 3+.
