The molecular weight distribution (MWD) of dissolved organic matter (DOM) in lake waters from Lake Hongfeng was examined using high performance size exclusion chromatography (HPSEC) with UV-vis absorbance and fluoresc...The molecular weight distribution (MWD) of dissolved organic matter (DOM) in lake waters from Lake Hongfeng was examined using high performance size exclusion chromatography (HPSEC) with UV-vis absorbance and fluorescence detection. The elution curves obtained by absorbance and fluorescence techniques expressed similar patterns, with the exception of diminishing of large fraction and the peaks behind several seconds in fluorescence chromatograms. According to its molecular weight (MW), DOM in water samples is divided into several fractions: large ({>3.5} kDa); medium-large ({3.5}-{2.0} kDa); medium ({2.0}-{1.0} kDa) and small ({<1.0} kDa). The average molecular weight was calculated using the elution curve detected by UV-vis absorbance and fluorescence detection techniques. The results showed that the weight-average molecular weight (Mw) and number-average molecular weight (Mn) calculated by UV-vis absorbance techniques range from 1750 to 2050 Dalton and from 1450 to 1850 Dalton, respectively. And the Mw and Mn obtained by fluorescence detection are lower by 50 to 400 Dalton. As a reference, the molecular weight of Fluka humic acid (FHA) is larger than that of water samples by about 200 Dalton. The average molecular weight of DOM for water samples collected in March and July was compared. The results revealed that the molecular weight is lower for water samples obtained in July than that obtained in March, indicating the ambient environment has an influence on the molecular weight, including photo-degradation and biological activity.展开更多
The composition and vertical profiles of low molecular-weight organic acids （LMWOAs） and the contribution of them to dissolved organic matter （DOM） in sediment porewaters in Bosten Lake, Xinjiang, China were inves...The composition and vertical profiles of low molecular-weight organic acids （LMWOAs） and the contribution of them to dissolved organic matter （DOM） in sediment porewaters in Bosten Lake, Xinjiang, China were investigated. The results showed that total concentration of LMWOAs was up to 94.5 μmol/L and their proportion in DOM was 5.6%, suggesting that LMWOAs were important chemical components in DOM in lake sediment porewaters. Among the seven LMWOAs, pyruvic and acetic acid had the highest concentrations with 26.30 and 8.31 μmol/L, accounting for 51.4% and 14.92% of LMWOAs, respectively. Trifluoroacetic and sorbic acid had the lowest concentrations, indicating that the compositions of LMWOAs in relative reducing environments were largely different from those reported in glacier, atmosphere and soils. The concentrations of lactic, acetic, formic, sorbic and oxalic acid decreased with increasing depth, probably relating to stronger microbial activities in the initial stage of early diagenesis. Trifluoroacetic acid was mainly anthropogenic with its concentration, showing a diusive trend from the surface to bottom sediments. The concentrations of lactic acid and nitrate generally showed a consistent profile. The increasing concentration of pyruvic acid in the vertical profile was just opposite to that of sulfate, revealing a significant negative relationship between them. Oxalic acid remained constant except for an obvious peak at 6 cm depth. The results indicated the diversities in sources and behaviors for various LMWOAs during early diagenesis in sediments.展开更多
At present,a growing number of consumer products contain engineered nanoparticle TiO2(nano⁃TiO2),which has resulted in the consequences of nano⁃TiO2 entering the aquatic environment directly or indirectly at some stag...At present,a growing number of consumer products contain engineered nanoparticle TiO2(nano⁃TiO2),which has resulted in the consequences of nano⁃TiO2 entering the aquatic environment directly or indirectly at some stage.The fate of nano⁃TiO2 in the aquatic environment has become the key factor which affects its safety application and nanoecotoxicology.This paper aims to investigate how the dissolved organic matters(DOM),especially the molecular weight fractions in the aquatic environment,affect the aggregation,stability,and fate of nano⁃TiO2,and the interaction mechanism of DOM and nano⁃TiO2.Results of dynamic light scattering(DLS)showed that the molecular weight of DOM molecules caused different aggregation rates of nano⁃TiO2 in aqueous solution.Fourier Transform infrared spectroscopy(FTIR)results indicated the molecular structure is characteristics of DOM fractions and the mechanisms of bonds formation between DOM and nano⁃TiO2.Results of three⁃dimensional excitation⁃emission matrices(3D⁃EEM)confirmed the FTIR results and implied the increase of the stability of theπ-πconjugated system in the presence of DOM.In addition,low molecular weight of DOM fractions appeared to show more affinity with nano⁃TiO2 than high molecular weight fractions.展开更多
With XAD-series and ion exchange resins, dissolved organic matter （DOM） from Lake Hongfeng in Southwestern China Plateau was isolated into 6 fractions, i.e., humic acid （HA）, fulvic acid （FA）, hydrophobic neutra...With XAD-series and ion exchange resins, dissolved organic matter （DOM） from Lake Hongfeng in Southwestern China Plateau was isolated into 6 fractions, i.e., humic acid （HA）, fulvic acid （FA）, hydrophobic neutrals （HON）, hydrophilic acids （HIA）, hydrophilic bases （HIB） and hydrophilic neutrals （HIN）. Those fractions were characterized by high performance size exclusion chromatography, fluorescence spectroscopy and UV absorbance. Among the 6 fractions, FA was predominant and accounted for 51% of the total DOM. The weight-average （Mw） and number-averaged （Mn） molecular weight of these fractions ranged from 1688 to 2355 Da and from 1338 to 1928 Da, respectively. A strong correlation was observed between specific UV absorbance at 280 nm, E2/E3 （absorbance at 250 nm to 365 nm）, and the molecular weight for DOM fractions. UV-Vis fulvic-like fluorescence peaks were found in all fractions. Proteinlike fluorescence peaks existed in HON may indicate that microbial activity was severely in Lake Hongfeng. There was a significant relationship between fluorescence intensities and specific UV absorbance at 254 nm for those DOM fractions, suggesting their similar luminescence characteristics. The values of fluorescence index （f450/500） indicated that hydrophobic fractions may derive from terrestrial sources, and the hydrophilic fractions from microbial and terrestrial origins. Those results suggest that there were inter-relationships between molecular weight, fluorescence and absorbance characteristics, and also subtle consistencies between the hydrophilic and hydrophobic properties and the sources for these 6 fractions from Lake Hongfeng.展开更多
[Objectives]The spatial distribution characteristics of organic acids in two late-blooming Rhododendron species(Rhododendron decorum and Rhododendron stamineum)in Guizhou Baili Rhododendron National Forest Park were e...[Objectives]The spatial distribution characteristics of organic acids in two late-blooming Rhododendron species(Rhododendron decorum and Rhododendron stamineum)in Guizhou Baili Rhododendron National Forest Park were explored,in order to provide reference for exploring the plant-soil relationship of subtropical forest.[Methods]The fresh leaf,stem,root,litter,humus and soil samples of R.decorum and R.stamineum were collected.The contents of eight low molecular weight organic acids including oxalic acid,tartaric acid,malic acid,citric acid,acetic acid,lactic acid,succinic acid and formic acid were determined by high performance liquid chromatography(HPLC).[Results]Oxalic acid is the main organic acid in the two species of Rhododendron.Among different samples,the content of organic acids was in the following order:root>fresh leaf>humus>litter>stem>soil.[Conclusions]The content of organic acids in the root was significantly higher than that in other parts.The types of organic acids in stems were the least.展开更多
Dissolved organic matter (DOM) is one of the most interesting and difficult problems in recent years due to its important functions in the ecological and environmental system and the complexity of its chemical composi...Dissolved organic matter (DOM) is one of the most interesting and difficult problems in recent years due to its important functions in the ecological and environmental system and the complexity of its chemical composition and structure. It is well ac- cepted that fluorescence characteristics and mo- lecular weight distribution are two important pa- rameters in the DOM characterization. However, the relationship between them is still unknown. In this study, fluorescence and molecular weight distribution of DOM in Lake Hongfeng, Lake Baihua and their rivers, and their relationship were investigated using the combination of fluorescence spectroscopy and high-performance size exclusion chromatography (HPSEC) with on-line UV absorbance and fluores- cence detectors. The results show that there were two obvious humic-like fluorescence peaks (Peaks A and B) in DOM from lake water. But there was an- other obvious protein-like fluorescence peak (Peak C) in DOM from river water. The humic-like fluorescence material consisted of DOM fraction with smaller mo- lecular weight, ranging from 1.0 to 3.0 kDa, while the protein-like fluorescence material mainly consisted of DOM fraction with MW larger than 2.0 kDa. The cal- culation of MW using HPSEC was related to the UV absorbance wavelength chosen.展开更多
The aim of this study was to obtain a better understanding of the range of organic molecular weight （MW） causing membrane fouling through the comparison between direct UF and in-line coagulation （without settling）...The aim of this study was to obtain a better understanding of the range of organic molecular weight （MW） causing membrane fouling through the comparison between direct UF and in-line coagulation （without settling）/UF process. The experimental results indicated that, when raw water with organics was treated and the MW of more than half of the organics was less than 1 kDa, membrane fouling was rather serious by only UF and coagulation could improve the fouling for the treatment of raw water. Besides, coagulation/UF could remove organics in each region, and organics with MW greater than 30 kDa were the most possible matters causing membrane fouling, while organics with MW less than 1 kDa were in due to few organics removed. Therefore, organics with MW greater them brane foulingibly responsible for membrane fouling 30 kDa were the major factor of membrane fouling.展开更多
Mesoporous silica （MS）, 3-aminopropyltriethoxysilane （APTES） modified mesoporous silica （AMS）, bis（3- trimethoxysilylpropyl）amine modified mesoporous silica （BAMS） and APTES modified solid spherical silica ...Mesoporous silica （MS）, 3-aminopropyltriethoxysilane （APTES） modified mesoporous silica （AMS）, bis（3- trimethoxysilylpropyl）amine modified mesoporous silica （BAMS） and APTES modified solid spherical silica （AS） were prepared and used to immobilize metallocene catalysts for ethylene polymerization. Gel permeation chromatography results showed that polyethylenes （PEs） catalyzed by AMS （or BAMS） supported metallocene catalysts at the molar ratios of Al/Zr = 100, 300 and 500 were of bimodal molecular weight distribution （BMWD）; while PEs catalyzed by the above catalysts at the molar ratios of Al/Zr 〉 800 were of monomodal molecular weight distribution （MMWD）. However, MS （or AS） supported metallocene catalysts could only produce PEs with MMWD in spite of the molar ratio of Al/Zr. It was because that AMS （or BAMS） supported catalysts possessed two active sites for ethylene polymerization at low molar ratios of Al/Zr due to the combination effects of mesopore geometrical constraint and amino groups of the supports, which was confirmed by X-ray photoelectron spectroscopy. This brings forward a novel and easy method for the synthesis of polyolefin with BMWD.展开更多
Ozonation has been widely applied in advanced wastewater treatment. In this study, the effect of ozonation on assimilable organic carbon （AOC） levels in secondary effluents was investigated, and AOC variation of dif...Ozonation has been widely applied in advanced wastewater treatment. In this study, the effect of ozonation on assimilable organic carbon （AOC） levels in secondary effluents was investigated, and AOC variation of different molecular weight （MW） organic components was analyzed. Although the removal efflciencies were 47%-76% and 94%-100% for UV2s4 and color at ozone dosage of 10 mg/L, dissolved organic carbon （DOC） in secondary effluents was hardly removed by ozonation. The AOC levels increased by 70%-780% at an ozone dosage range of 1-10 mg/L. AOC increased significantly in the instantaneous ozone demand phase, and the increase in AOC was correlated to the decrease in UV254 during ozonation. The results of MW distribution showed that, ozonation led to the transformation of larger molecules into smaller ones, but the increase in low MW （〈1 kDa） fraction did not contribute much to AOC production. The change of high MW （〉100 kDa and 10-100 kDa） fractions itself during ozonation was the main reason for the increase of AOC levels. Furthermore, the oxidation of organic matters with high MWs （〉 100 kDa and 10-100 kDa） resulted in more AOC production than those with low MWs （1-10 kDa and 〈1 kDa）. The results indicated that removing large molecules in secondary effluents could limit the increase of AOC during ozonation.展开更多
Soil low-molecular-weight （LMW） organic acids play important roles in the soil-forming process and the cycling of nutrients in Karst regions. In this study, we quantified the contents of LMW organic acids （includin...Soil low-molecular-weight （LMW） organic acids play important roles in the soil-forming process and the cycling of nutrients in Karst regions. In this study, we quantified the contents of LMW organic acids （including lactate, acetate, formate, malate, and oxalate） in soil solution over the Karst region of Guizhou Province, China using ion chromatography. The concentration of total LMW organic acids in topsoil solution ranged from 0.358 to 1.823pmol＇g-1, with an average of 0.912p.mol.gL The mean concentrations of lactate, acetate, formate, malate, and oxalate were 0.2124-0.089, 0.3024-0.228, 0.301-4-0.214, 0.014zk0.018 and 0.086＋0.118 pmol.g-% respectively. There were also significant difference in the contents of these acids among four phases of rocky desertification, and their concentrations decreased with the aggravation of rocky desertification. The concentrations of the LMW organic acids were significantly positive correlated each other. Significant positive correlations were also observed among individual LMW organic acids in soil solution, and between them and soil available P, available K, exchange- able Ca, respectively. Furthermore, the concentrations of LMW organic acids were significantly positively corre- lated with inorganic anions （chlorides, nitrates, and sulfates） in Karst topsoil solution. Therefore, the concen- trations of soil LMW organic acids might be one of driving force in the Karst rock desertification process in Guizhou Province.展开更多
Dissolved organic matter （DOM） transforma- tion in sequence batch reactor （SBR） fed with carbon sources of different biodegradability was investigated. During the biologic degradation process, the low mole- cular ...Dissolved organic matter （DOM） transforma- tion in sequence batch reactor （SBR） fed with carbon sources of different biodegradability was investigated. During the biologic degradation process, the low mole- cular weight （MW） fraction （〈 1 kDa） gradually decreased, while the refractory compounds with higher aromaticity were aggregated. Size exclusion chromatogra- phy （SEC） and fluorescence of excitation emission matrices （EEM） demonstrated that more biopolymers （polysaccharides or proteins） and humic-like substances were presented in the extracellular polymeric substance （EPS） extracted from the SBR fed with sodium acetate or glucose, while the EPS from SBR fed with slowly biodegradable dissolved organic carbon （DOC） substrate- starch had relatively less biopolymers. Comparing the EfOM in sewage effluent of three SBRs, the effluent from SBR fed with starch is more aromatic. Organic carbon with MW 〉 1 kDa as well as the hydrophobic fraction in DOM gradually increased with the carbon sources changing from sodium acetate to glucose and starch. The DOC fractiona- tion and the EEM all demonstrated that EfOM from the effluent of the SBR fed with starch contained more fulvic acid-like substances comparing with the SBR fed with sodium acetate and glucose.展开更多
Dissolved organic matter（DOM） plays an important role in the process of mercury release from water body.In this study,the influence of DOM from different sources（DOMR,DOMS and DOMH,extracted from rice straw,compost...Dissolved organic matter（DOM） plays an important role in the process of mercury release from water body.In this study,the influence of DOM from different sources（DOMR,DOMS and DOMH,extracted from rice straw,compost and humic soil respectively） on mercury reduction was investigated.The molecular weight distribution and chemical composition of DOM from each source were determined using ultrafiltration membrane technique and elemental analysis respectively.The result showed that mercury release from DOM-added samples was much lower than the control;the lowest mercury release flux was observed in the treatment of DOMH,25.02% of the control,followed by DOMS and DOMR,62.46% and 64.95% of the control,respectively.The higher saturation degree and lower molecular weight of DOMH was responsible for the highest inhibition degree on the mercury release.The link between DOMH,concentration and mercury flux was also estimated and the result showed that mercury flux was increased with DOMH at lower concentration,while decreased with DOMH at higher concentration.Different mechanism dominated the influence of DOM on mercury release with variation of DOM concentration.展开更多
The formation of a dynamic membrane(DM)was investigated using polyethylene glycol(PEG)(molecular weight of 35000 g/mol,concentration of 1 g/L).Two natural organic matters(NOM),Dongbok Lake NOM(DLNOM)and Suwannee River...The formation of a dynamic membrane(DM)was investigated using polyethylene glycol(PEG)(molecular weight of 35000 g/mol,concentration of 1 g/L).Two natural organic matters(NOM),Dongbok Lake NOM(DLNOM)and Suwannee River NOM(SRNOM)were used in the ultrafiltration experiments along with PEG.To evaluate the effects of the DM with PEG on ultrafiltration,various transport experiments were conducted,and the analyses of the NOM in the membrane feed and permeate were performed using high performance size exclusion chromatography,and the effective pore size distribution(effective PSD)and effective molecular weight cut off(effective MWCO)were determined.The advantages of DM formed with PEG can be summarized as follows:(1)PEG interferes with NOM transmission through the ultrafiltration membrane pores by increasing the retention coefficient of NOM in UF membranes,and(2)low removal of NOM by the DM is affected by external factors,such as pressure increases during UF membrane filtration,which decreases the effective PSD and effective MWCO of UF membranes.However,a disadvantage of the DM with PEG was severe flux decline;thus,one must be mindful of both the positive and negative influences of the DM when optimizing the UF performance of the membrane.展开更多
Effluent organic matter （EfOM） is the major cause of fouling in the low pressure membranes process for wastewater reuse. Coagulation and oxidation of biological wastewater treatment effluent have been applied for th...Effluent organic matter （EfOM） is the major cause of fouling in the low pressure membranes process for wastewater reuse. Coagulation and oxidation of biological wastewater treatment effluent have been applied for the fouling control of microfiltration membranes. However, the change in EfOM structure by pre-treatments has not been clearly identified. The changes of EfOM characteristics induced by coagulation and ozonation were investigated through size exclusion chromatography, UV/Vis spectrophotometry, fluorescence spectrophotometry and titrimetric analysis to identify the mechanisms in the reduction of ultrafiltration （UF） membrane fouling. The results indicated that reduction of flux decline by coagulation was due to modified characteristics of dissolved organic carbon （DOC） content. Total concentration of DOC was not reduced by ozonation. However, the mass fraction of the molecules with molecular weight larger than 5 kDa, fluorescence intensity, aromaticity, highly condensed chromophores, average molecular weight and soluble microbial byproducts decreased greatly after ozonation. These results indicated that EfOM was partially oxidized by ozonation to low molecular weight, highly charged compounds with abundant electron- withdrawing functional groups, which are favourable for alleviating UF membrane flux decline.展开更多
文摘The molecular weight distribution (MWD) of dissolved organic matter (DOM) in lake waters from Lake Hongfeng was examined using high performance size exclusion chromatography (HPSEC) with UV-vis absorbance and fluorescence detection. The elution curves obtained by absorbance and fluorescence techniques expressed similar patterns, with the exception of diminishing of large fraction and the peaks behind several seconds in fluorescence chromatograms. According to its molecular weight (MW), DOM in water samples is divided into several fractions: large ({>3.5} kDa); medium-large ({3.5}-{2.0} kDa); medium ({2.0}-{1.0} kDa) and small ({<1.0} kDa). The average molecular weight was calculated using the elution curve detected by UV-vis absorbance and fluorescence detection techniques. The results showed that the weight-average molecular weight (Mw) and number-average molecular weight (Mn) calculated by UV-vis absorbance techniques range from 1750 to 2050 Dalton and from 1450 to 1850 Dalton, respectively. And the Mw and Mn obtained by fluorescence detection are lower by 50 to 400 Dalton. As a reference, the molecular weight of Fluka humic acid (FHA) is larger than that of water samples by about 200 Dalton. The average molecular weight of DOM for water samples collected in March and July was compared. The results revealed that the molecular weight is lower for water samples obtained in July than that obtained in March, indicating the ambient environment has an influence on the molecular weight, including photo-degradation and biological activity.
基金supported by the National Basic Research Program (973) of China (No. 2008CB418200)the National Natural Science Foundation of China (No.U0833603, 40632011, 40873080)
文摘The composition and vertical profiles of low molecular-weight organic acids （LMWOAs） and the contribution of them to dissolved organic matter （DOM） in sediment porewaters in Bosten Lake, Xinjiang, China were investigated. The results showed that total concentration of LMWOAs was up to 94.5 μmol/L and their proportion in DOM was 5.6%, suggesting that LMWOAs were important chemical components in DOM in lake sediment porewaters. Among the seven LMWOAs, pyruvic and acetic acid had the highest concentrations with 26.30 and 8.31 μmol/L, accounting for 51.4% and 14.92% of LMWOAs, respectively. Trifluoroacetic and sorbic acid had the lowest concentrations, indicating that the compositions of LMWOAs in relative reducing environments were largely different from those reported in glacier, atmosphere and soils. The concentrations of lactic, acetic, formic, sorbic and oxalic acid decreased with increasing depth, probably relating to stronger microbial activities in the initial stage of early diagenesis. Trifluoroacetic acid was mainly anthropogenic with its concentration, showing a diusive trend from the surface to bottom sediments. The concentrations of lactic acid and nitrate generally showed a consistent profile. The increasing concentration of pyruvic acid in the vertical profile was just opposite to that of sulfate, revealing a significant negative relationship between them. Oxalic acid remained constant except for an obvious peak at 6 cm depth. The results indicated the diversities in sources and behaviors for various LMWOAs during early diagenesis in sediments.
基金the National Natural Science Foundation of China(Grant No.51408162)the Special Financial Grant from the China Postdoctoral Science Foundation(Grant No.2016T90303)+1 种基金the China Postdoctoral Science Foundation(Grant No.2014M551258)the Heilongjiang Province Postdoctoral Science Foundation(Grant No.LBH-Z14077)。
文摘At present,a growing number of consumer products contain engineered nanoparticle TiO2(nano⁃TiO2),which has resulted in the consequences of nano⁃TiO2 entering the aquatic environment directly or indirectly at some stage.The fate of nano⁃TiO2 in the aquatic environment has become the key factor which affects its safety application and nanoecotoxicology.This paper aims to investigate how the dissolved organic matters(DOM),especially the molecular weight fractions in the aquatic environment,affect the aggregation,stability,and fate of nano⁃TiO2,and the interaction mechanism of DOM and nano⁃TiO2.Results of dynamic light scattering(DLS)showed that the molecular weight of DOM molecules caused different aggregation rates of nano⁃TiO2 in aqueous solution.Fourier Transform infrared spectroscopy(FTIR)results indicated the molecular structure is characteristics of DOM fractions and the mechanisms of bonds formation between DOM and nano⁃TiO2.Results of three⁃dimensional excitation⁃emission matrices(3D⁃EEM)confirmed the FTIR results and implied the increase of the stability of theπ-πconjugated system in the presence of DOM.In addition,low molecular weight of DOM fractions appeared to show more affinity with nano⁃TiO2 than high molecular weight fractions.
基金supported by the China’s Na-tional Basic Research Program (No. 2008CB418200)the National Knowledge Innovation Program of Chinese Academy of Sciences (No. kzcx2-yw-102)the Nation-al Natural Science Foundation of China (No. U0833603,40873079, 40703022).
文摘With XAD-series and ion exchange resins, dissolved organic matter （DOM） from Lake Hongfeng in Southwestern China Plateau was isolated into 6 fractions, i.e., humic acid （HA）, fulvic acid （FA）, hydrophobic neutrals （HON）, hydrophilic acids （HIA）, hydrophilic bases （HIB） and hydrophilic neutrals （HIN）. Those fractions were characterized by high performance size exclusion chromatography, fluorescence spectroscopy and UV absorbance. Among the 6 fractions, FA was predominant and accounted for 51% of the total DOM. The weight-average （Mw） and number-averaged （Mn） molecular weight of these fractions ranged from 1688 to 2355 Da and from 1338 to 1928 Da, respectively. A strong correlation was observed between specific UV absorbance at 280 nm, E2/E3 （absorbance at 250 nm to 365 nm）, and the molecular weight for DOM fractions. UV-Vis fulvic-like fluorescence peaks were found in all fractions. Proteinlike fluorescence peaks existed in HON may indicate that microbial activity was severely in Lake Hongfeng. There was a significant relationship between fluorescence intensities and specific UV absorbance at 254 nm for those DOM fractions, suggesting their similar luminescence characteristics. The values of fluorescence index （f450/500） indicated that hydrophobic fractions may derive from terrestrial sources, and the hydrophilic fractions from microbial and terrestrial origins. Those results suggest that there were inter-relationships between molecular weight, fluorescence and absorbance characteristics, and also subtle consistencies between the hydrophilic and hydrophobic properties and the sources for these 6 fractions from Lake Hongfeng.
基金Supported by Project of Guizhou Provincial Characteristic Key Laboratory(QJHKY[2021]002)Forestry Science and Technology Project of Guizhou Province(QLKH[2018]11).
文摘[Objectives]The spatial distribution characteristics of organic acids in two late-blooming Rhododendron species(Rhododendron decorum and Rhododendron stamineum)in Guizhou Baili Rhododendron National Forest Park were explored,in order to provide reference for exploring the plant-soil relationship of subtropical forest.[Methods]The fresh leaf,stem,root,litter,humus and soil samples of R.decorum and R.stamineum were collected.The contents of eight low molecular weight organic acids including oxalic acid,tartaric acid,malic acid,citric acid,acetic acid,lactic acid,succinic acid and formic acid were determined by high performance liquid chromatography(HPLC).[Results]Oxalic acid is the main organic acid in the two species of Rhododendron.Among different samples,the content of organic acids was in the following order:root>fresh leaf>humus>litter>stem>soil.[Conclusions]The content of organic acids in the root was significantly higher than that in other parts.The types of organic acids in stems were the least.
基金supported by the National Natural Science Foundation of China(Grant Nos.40525011,40403011)973 Projects(Grant No.2002CB412300)the National Knowledge Innovation Program of the Chinese Academy of Sciences(Grant No.KZCX2-W1).
文摘Dissolved organic matter (DOM) is one of the most interesting and difficult problems in recent years due to its important functions in the ecological and environmental system and the complexity of its chemical composition and structure. It is well ac- cepted that fluorescence characteristics and mo- lecular weight distribution are two important pa- rameters in the DOM characterization. However, the relationship between them is still unknown. In this study, fluorescence and molecular weight distribution of DOM in Lake Hongfeng, Lake Baihua and their rivers, and their relationship were investigated using the combination of fluorescence spectroscopy and high-performance size exclusion chromatography (HPSEC) with on-line UV absorbance and fluores- cence detectors. The results show that there were two obvious humic-like fluorescence peaks (Peaks A and B) in DOM from lake water. But there was an- other obvious protein-like fluorescence peak (Peak C) in DOM from river water. The humic-like fluorescence material consisted of DOM fraction with smaller mo- lecular weight, ranging from 1.0 to 3.0 kDa, while the protein-like fluorescence material mainly consisted of DOM fraction with MW larger than 2.0 kDa. The cal- culation of MW using HPSEC was related to the UV absorbance wavelength chosen.
基金Sponsored by the Tianjin Municipal Science and Technology Commission(Grant No.05FZZDSH00500)
文摘The aim of this study was to obtain a better understanding of the range of organic molecular weight （MW） causing membrane fouling through the comparison between direct UF and in-line coagulation （without settling）/UF process. The experimental results indicated that, when raw water with organics was treated and the MW of more than half of the organics was less than 1 kDa, membrane fouling was rather serious by only UF and coagulation could improve the fouling for the treatment of raw water. Besides, coagulation/UF could remove organics in each region, and organics with MW greater than 30 kDa were the most possible matters causing membrane fouling, while organics with MW less than 1 kDa were in due to few organics removed. Therefore, organics with MW greater them brane foulingibly responsible for membrane fouling 30 kDa were the major factor of membrane fouling.
基金supported by the National Natural Science Foundation of China(Nos.50525311,20734006 and 50621302)
文摘Mesoporous silica （MS）, 3-aminopropyltriethoxysilane （APTES） modified mesoporous silica （AMS）, bis（3- trimethoxysilylpropyl）amine modified mesoporous silica （BAMS） and APTES modified solid spherical silica （AS） were prepared and used to immobilize metallocene catalysts for ethylene polymerization. Gel permeation chromatography results showed that polyethylenes （PEs） catalyzed by AMS （or BAMS） supported metallocene catalysts at the molar ratios of Al/Zr = 100, 300 and 500 were of bimodal molecular weight distribution （BMWD）; while PEs catalyzed by the above catalysts at the molar ratios of Al/Zr 〉 800 were of monomodal molecular weight distribution （MMWD）. However, MS （or AS） supported metallocene catalysts could only produce PEs with MMWD in spite of the molar ratio of Al/Zr. It was because that AMS （or BAMS） supported catalysts possessed two active sites for ethylene polymerization at low molar ratios of Al/Zr due to the combination effects of mesopore geometrical constraint and amino groups of the supports, which was confirmed by X-ray photoelectron spectroscopy. This brings forward a novel and easy method for the synthesis of polyolefin with BMWD.
基金supported by Key Program of the National Natural Science Foundation of China (No. 51138006)the special fund from the State Key Joint Laboratory of Environment Simulation and Pollution Control (No. 13L01ESPC)supported by the Collaborative Innovation Center for Regional Environmental Quality
文摘Ozonation has been widely applied in advanced wastewater treatment. In this study, the effect of ozonation on assimilable organic carbon （AOC） levels in secondary effluents was investigated, and AOC variation of different molecular weight （MW） organic components was analyzed. Although the removal efflciencies were 47%-76% and 94%-100% for UV2s4 and color at ozone dosage of 10 mg/L, dissolved organic carbon （DOC） in secondary effluents was hardly removed by ozonation. The AOC levels increased by 70%-780% at an ozone dosage range of 1-10 mg/L. AOC increased significantly in the instantaneous ozone demand phase, and the increase in AOC was correlated to the decrease in UV254 during ozonation. The results of MW distribution showed that, ozonation led to the transformation of larger molecules into smaller ones, but the increase in low MW （〈1 kDa） fraction did not contribute much to AOC production. The change of high MW （〉100 kDa and 10-100 kDa） fractions itself during ozonation was the main reason for the increase of AOC levels. Furthermore, the oxidation of organic matters with high MWs （〉 100 kDa and 10-100 kDa） resulted in more AOC production than those with low MWs （1-10 kDa and 〈1 kDa）. The results indicated that removing large molecules in secondary effluents could limit the increase of AOC during ozonation.
文摘Soil low-molecular-weight （LMW） organic acids play important roles in the soil-forming process and the cycling of nutrients in Karst regions. In this study, we quantified the contents of LMW organic acids （including lactate, acetate, formate, malate, and oxalate） in soil solution over the Karst region of Guizhou Province, China using ion chromatography. The concentration of total LMW organic acids in topsoil solution ranged from 0.358 to 1.823pmol＇g-1, with an average of 0.912p.mol.gL The mean concentrations of lactate, acetate, formate, malate, and oxalate were 0.2124-0.089, 0.3024-0.228, 0.301-4-0.214, 0.014zk0.018 and 0.086＋0.118 pmol.g-% respectively. There were also significant difference in the contents of these acids among four phases of rocky desertification, and their concentrations decreased with the aggravation of rocky desertification. The concentrations of the LMW organic acids were significantly positive correlated each other. Significant positive correlations were also observed among individual LMW organic acids in soil solution, and between them and soil available P, available K, exchange- able Ca, respectively. Furthermore, the concentrations of LMW organic acids were significantly positively corre- lated with inorganic anions （chlorides, nitrates, and sulfates） in Karst topsoil solution. Therefore, the concen- trations of soil LMW organic acids might be one of driving force in the Karst rock desertification process in Guizhou Province.
文摘Dissolved organic matter （DOM） transforma- tion in sequence batch reactor （SBR） fed with carbon sources of different biodegradability was investigated. During the biologic degradation process, the low mole- cular weight （MW） fraction （〈 1 kDa） gradually decreased, while the refractory compounds with higher aromaticity were aggregated. Size exclusion chromatogra- phy （SEC） and fluorescence of excitation emission matrices （EEM） demonstrated that more biopolymers （polysaccharides or proteins） and humic-like substances were presented in the extracellular polymeric substance （EPS） extracted from the SBR fed with sodium acetate or glucose, while the EPS from SBR fed with slowly biodegradable dissolved organic carbon （DOC） substrate- starch had relatively less biopolymers. Comparing the EfOM in sewage effluent of three SBRs, the effluent from SBR fed with starch is more aromatic. Organic carbon with MW 〉 1 kDa as well as the hydrophobic fraction in DOM gradually increased with the carbon sources changing from sodium acetate to glucose and starch. The DOC fractiona- tion and the EEM all demonstrated that EfOM from the effluent of the SBR fed with starch contained more fulvic acid-like substances comparing with the SBR fed with sodium acetate and glucose.
基金supported by the National Natural Science Foundation of China(No.40673063,40973079)the Construction Project of Chongqing Engineering Research Center(CSTC)(No.2010CB7008)the Ecology National Key Discipline of Southwest University
文摘Dissolved organic matter（DOM） plays an important role in the process of mercury release from water body.In this study,the influence of DOM from different sources（DOMR,DOMS and DOMH,extracted from rice straw,compost and humic soil respectively） on mercury reduction was investigated.The molecular weight distribution and chemical composition of DOM from each source were determined using ultrafiltration membrane technique and elemental analysis respectively.The result showed that mercury release from DOM-added samples was much lower than the control;the lowest mercury release flux was observed in the treatment of DOMH,25.02% of the control,followed by DOMS and DOMR,62.46% and 64.95% of the control,respectively.The higher saturation degree and lower molecular weight of DOMH was responsible for the highest inhibition degree on the mercury release.The link between DOMH,concentration and mercury flux was also estimated and the result showed that mercury flux was increased with DOMH at lower concentration,while decreased with DOMH at higher concentration.Different mechanism dominated the influence of DOM on mercury release with variation of DOM concentration.
基金the National Research Laboratory Program by the Korea Science and Engineering Foundation(NOM Lab:R0A-2007-000-20055-0).
文摘The formation of a dynamic membrane(DM)was investigated using polyethylene glycol(PEG)(molecular weight of 35000 g/mol,concentration of 1 g/L).Two natural organic matters(NOM),Dongbok Lake NOM(DLNOM)and Suwannee River NOM(SRNOM)were used in the ultrafiltration experiments along with PEG.To evaluate the effects of the DM with PEG on ultrafiltration,various transport experiments were conducted,and the analyses of the NOM in the membrane feed and permeate were performed using high performance size exclusion chromatography,and the effective pore size distribution(effective PSD)and effective molecular weight cut off(effective MWCO)were determined.The advantages of DM formed with PEG can be summarized as follows:(1)PEG interferes with NOM transmission through the ultrafiltration membrane pores by increasing the retention coefficient of NOM in UF membranes,and(2)low removal of NOM by the DM is affected by external factors,such as pressure increases during UF membrane filtration,which decreases the effective PSD and effective MWCO of UF membranes.However,a disadvantage of the DM with PEG was severe flux decline;thus,one must be mindful of both the positive and negative influences of the DM when optimizing the UF performance of the membrane.
基金supported by the National Research Foundation of Korea (NRF) grant funded by the Korean government (MEST) (No. 2012R1A1B3002152, 2013R1A2A2A03016095)
文摘Effluent organic matter （EfOM） is the major cause of fouling in the low pressure membranes process for wastewater reuse. Coagulation and oxidation of biological wastewater treatment effluent have been applied for the fouling control of microfiltration membranes. However, the change in EfOM structure by pre-treatments has not been clearly identified. The changes of EfOM characteristics induced by coagulation and ozonation were investigated through size exclusion chromatography, UV/Vis spectrophotometry, fluorescence spectrophotometry and titrimetric analysis to identify the mechanisms in the reduction of ultrafiltration （UF） membrane fouling. The results indicated that reduction of flux decline by coagulation was due to modified characteristics of dissolved organic carbon （DOC） content. Total concentration of DOC was not reduced by ozonation. However, the mass fraction of the molecules with molecular weight larger than 5 kDa, fluorescence intensity, aromaticity, highly condensed chromophores, average molecular weight and soluble microbial byproducts decreased greatly after ozonation. These results indicated that EfOM was partially oxidized by ozonation to low molecular weight, highly charged compounds with abundant electron- withdrawing functional groups, which are favourable for alleviating UF membrane flux decline.
