首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 31 毫秒
1.
The effect of light intensity on the release of dissolved organic carbon during photosynthesis on NaH14CO3 was investigated using the phytoplanktonic CyanobacteriumOscillatoria rubescens. The released products were fractionated by molecular size and chemical identifications attempted using combined thin-layer electrophoresis and chromatography, and high pressure liquid chromatography.Within the range of irradiances tested (from 6 to 60 µmole m–2 sec–1), though the upper one inhibited photosynthesis ofO. rubescens, light had little effect on the quantity and composition of the excreted products. The released carbon was always lower than 3% of the incorporated carbon, and mainly composed (62 to 86%) by small molecular weight compounds. The prevailing identified compounds were amino acids which represented more than 20% of the excreted carbon. Among organic acids, glycolic acid accounted for less than 2% of the recovered radioactivity. Glucose was the only identified sugar.Abbreviations EOC excreted organic carbon - DOC dissolved organic carbon - PER percent extracellular release - LMW low molecular weight - HMW high molecular weight - AA amino acids - µmoles m–2 sec–1 = µEinsteins m–2 sec–1  相似文献   

2.
The water supply of Prague is based upon three different water resources: artesian groundwater and infiltrate of the Jizera river, water of the Vltava and Zelivka rivers. The processing techniques are different; consequently for the purpose of increasing capacity one has to search for the suitable raw water quality as well as for the optimum treatment process. An essential parameter for this is the contents of organic substances whose molar mass distribution is investigated by gel chromatography with the aid of Sephadex G-10, G-25 and G-50. With respect to the total load of organic matter the Jizera shows the lowest values, in the Vltava the C.O.D. values are the highest, in the Zelivka the organic carbon shows the highest values. 80% of the organic substances in water have molar masses below 700. By flocculation 60… 70% of the C.O.D.-Cr can be eliminated, the optimum removal of the high-molecular substances occurring at pH = 6 and with 50… 60 g/m3 aluminium sulphate.  相似文献   

3.
High molecular weight DOM (apparent mol wt. ≥1500) was isolated from lake water, both in summer and in winter. Sephadex G-15 gel permeation chromatography with 0.02 M phosphate buffer yielded one peak. Elution with distilled water gave rise to distinct smaller sized subfractions. It was concluded that these compounds are weakly bound subunits of the macromolecules, which are liberated on elution with distilled water. The macromolecules were not stable in the dark. Exposing them to daylight in the laboratory and to sunlight, in quartz bottles enhanced conversion. During 6 weeks' exposure to weakly photolytic conditions (daylight >300 nm), organic carbon of the high molecular bulk substances decreased by 15% (winter) and by 25% (summer), while the concentrations of the apparent low molecular weight substances increased accordingly. Such a slow but continuous transformation may reduce also the <in situ> persistence of the macromolecules gradually.  相似文献   

4.
Organic phosphonates are widely used, and in general, they are not easily biodegradable. Therefore, our interest was focussed on the development of an analytical method for the trace-level determination of organic phosphonates in water. Our method combines preconcentration of the analytes by evaporating the water sample with the methylation of the phosphonates using diazomethane. Analysis of the totally methylated phosphonates is done by liquid chromatography coupled with mass Spectrometry by the particle-beam interface. The derivatives could be clearly identified by their electron impact mass spectra as well as their chemical ionisation mass spectra. The totally methylated phosphonates can be separated by liquid chromatography using a 125 mm × 4 mm LiChrospher 100 Diol column and a gradient mobile phase containing n-hexane and isopropyl alcohol. After optimizing preconcentration and derivatization procedures as well as all particle-beam and mass spectra conditions, detection limits in the low ppb range were attained.  相似文献   

5.
UV-induced transformation of dissolved organic matter (DOC) is often accompanied by reduction of molecular weight and aromaticity and an increase of low-molecular weight (LMW) matter that can be utilized as a substrate by heterotrophic bacteria. Moreover, the generation of reactive transients and mineralization of DOC occurs. For a better understanding of the modification that starts after irradiation and to distinguish between possible chemical and biological modifications, we selected different natural organic matter (NOM) from Norway and Germany. The aqueous solutions were treated by UV irradiation and divided into two aliquot samples. NaN3 anti-bacterial treatment was applied to one sample, and high-pressure size-exclusion chromatography (HPSEC) analysis was used for both. In all samples, we found typical modifications of NOM after UV irradiation. Incubation (>7?days) of UV-irradiated NOM samples resulted in lower levels of LMW matter and increased aromaticity. Parallel to these changes of carbon fractions, an increase in bacterial cell numbers was observed. Addition of NaN3 to NOM, however, inhibited the reduction of LMW matter, indicating that microbial activity accounted for the observed changes in NOM. Analysis of the bacterial community composition by denaturing gradient gel electrophoresis (DGGE) of the amplified 16S rRNA genes revealed that bacterial communities of non-irradiated and UV-irradiated NOM were different and that UV selected for specific members of ??-proteobacteria, ??-proteobacteria, and Bacteriodetes. Our results imply that after UV-irradiation of NOM, specific bacterial members are well adapted to low pH, high LMW DOC concentrations, and oxidative stress, and therefore thrive well on UV-irradiated humic matter.  相似文献   

6.
Humic substances (HS) were isolated from two contaminated groundwater samples (B22 and B53) from a site of a former gas facility. The isolation yielded almost only the fulvic acid fractions (FA). For characterization spectroscopic (UV, fluorescence) and chromatographic techniques (hydrophobic interaction chromatography – HIC as well as size-exclusion chromatography – SEC) were applied. The sample designated B22 FA was collected from the contamination plume whereas the sample B53 FA was collected downstream. Distinct differences were exhibited by these samples. The UV and fluorescence spectra as well as the HIC and SEC chromatograms of the B53 FA sample resemble those of the FA fraction obtained from natural water (groundwater, bog). The HIC and SEC chromatograms reveal the presence of organic compounds in B22 FA which can be derived from coal tar contaminants or their metabolites. Some of the compounds can be extracted from the FA fraction with non-polar organic solvents indicating adsorptive forces between the contaminants and the FA fraction.  相似文献   

7.
The fate and transport of highly hydrophobic chemicals are affected by the partitioning between water and dissolved organic carbon. Large variation in the partition coefficient (KDOCw) is often found, due to the selection of model organic matter or potential experimental artifacts. To investigate the roles of the type of organic matter on the partitioning of highly hydrophobic compounds, the partition coefficients of eight selected polycyclic aromatic hydrocarbons (PAHs), with 3–6 aromatic rings, were determined using a passive dosing/extraction method between water and model dissolved organic matter (humic acid, fulvic acid, sodium dodecyl sulfate micelle (SDS), and 2‐hydroxypropyl‐β‐cyclodextrin). Although the KDOCw values for 3–4 ring PAHs in this study were close to those reported in the literature, experimental KDOCw values between Aldrich humic acid (AHA) and water were higher than values reported in the literature for 5–6 ring PAHs. The KDOCw values were highest for AHA, followed by SDS and Suwannee river fulvic acid (SFA). The slopes of the linear regression between log KDOCw and log Kow were 1.23 (± 0.13), 0.82 (± 0.09), and 0.59 (± 0.13) for AHA, SDS, and SFA, respectively. The differences in the KDOCw values between AHA and the other organic matter (SDS, SFA, and CD) increased with increasing hydrophobicity of the PAHs, showing that the sorption of highly hydrophobic chemicals to the humic acid fraction may be important in the presence of mixed organic matter.  相似文献   

8.
With carcinogenic benz(a)pyrene as an example the distribution of polycyclic arenes in the hydrocarbon-water system is shown to be independent of the hydrophobicity of hydrocarbon present as their carrier and to be constant for the series of paraffins and benzene studied in both fresh and salt water. The hydrocarbon-carrier hinders the penetration of benz(a)pyrene into water, the free energy of the system increases (~ by 4.5 kJ/mole) due to an increase of the hydrophobic interaction of molecules. The increase in temperature from 20 to 50 °C influences the distribution of benz(a)pyrene in the hydrocarbon-water system insignificantly. Changes in standard thermodynamic parameters of the transition of polycyclic arene from the solution in alkane (benzene) into water (enthalpy Δ H°, entropy Δ S°, and free energy Δ G°) are calculated. Negative values of entropy point to the additional “structurization” of water in the course of the solution of hydrocarbons in it. Mineral salts do not influence the transition of carcinogenic arene into water.  相似文献   

9.
长三角地区大部分湖泊为非通江湖泊,地势低平,港汊及闸坝众多,水流宣泄不畅,水力滞留时间较长,加之周边地区城镇人口稠密.因此与水滞留时间短的通江湖泊相比,非通江湖泊的有色可溶性有机物(CDOM)来源和组成具有差异性.本文选取了3个重要的中型非通江供水湖泊——滆湖、淀山湖和阳澄湖,对枯水期、平水期、丰水期3种水文情景下CDOM组成结构变化特征进行分析,从而进一步揭示该类湖泊CDOM来源和对水文情景响应的内在机理.结果表明:滆湖、淀山湖和阳澄湖通过平行因子分析法得到2种类腐殖质(C1和C4)和2种类蛋白质(C2和C3),湖泊CDOM结构受到降雨事件和人类活动的双重影响.三个湖泊类蛋白质的高值在空间上主要集中在人类活动频繁的湖区,并且类蛋白质平均荧光强度与叶绿素a浓度相关性较差,说明湖泊类蛋白质组分受到内源藻类降解、外源人类生产生活排放双重作用的影响.三个湖泊类蛋白质的平均荧光强度和总氮浓度均在枯水期显著高于丰水期,说明降雨量的增加可以稀释湖泊有机质浓度;同时,陆源类腐殖质C1与溶解性有机碳、总氮、总磷、叶绿素a浓度呈显著正相关,并且随着降雨量增加,类蛋白质的占比逐渐降低,滆湖从86.84%降低至62.49%,淀山湖从96.53%降低至90.56%,阳澄湖从98.40%降低至96.26%,说明降雨事件也可以增强径流的冲刷作用,携带更多腐殖化程度高的陆源有机质进入湖泊.本研究发现降雨过程和人类活动共同作用于滆湖、淀山湖和阳澄湖CDOM库,研究结果可以为进一步保障太湖流域人类用水安全提供参考依据.  相似文献   

10.
In biological wastewater treatment, bacteria tend to aggregate by forming flocs, biofilms and even granules. A large part of the floc structure in activated sludge is composed of extracellular polymers. The extracellular polymeric substances (EPS) are mainly responsible for the structural and functional integrity of biofilms/flocs and they are considered to be important for the physico‐chemical properties of activated sludge. This review considers the composition of EPS and proportion between the constituents. Moreover it includes the relationship between the EPS constituents and sludge properties such as sludge retention time, hydrophobicity and surface charge.  相似文献   

11.
The most effective process for the pesticide removal from a raw water is the adsorption on activated carbon except for polar substances. Activated carbon can be used as powdered carbon or granular carbon. However in both processes it has to be taken into account that the efficiency of the activated carbon adsorption is affected by the origin and the concentration of the natural organic background in the raw water and the initial concentration of the pesticide itself.  相似文献   

12.
This paper aims at examining the increase of phenol adsorption breakthrough curves spreading caused by the chemical heterogeneity of granular activated carbon fixed beds. The local and the thermodynamic equilibrium assumption, as well as the nonlinear adsorption obeying to Langmuir isotherm, are considered. This study particularly tempts to link the reduced variance of phenol breakthrough curves to a measurable quantifying parameter of the chemical heterogeneity. The investigated artificial heterogeneous media are prepared by alternating layers of two types of granular activated carbon, active and non-active ones, that have similar physical properties. On the one hand, the chemical heterogeneity is quantified by the active layer relative thickness of the column length, l1/L. On the other hand, it is quantified by the mean value of the probability distribution γ. The latter also represents the mean active grains mass ratio of the total medium mass, hence the medium mean capacity. The obtained results show an increase in the reduced variance and thus the effective global dispersion with the heterogeneity; the increase is as important as the medium capacity decreases. However, the dispersion increase achieves a limit value, even when the heterogeneity increases. The results are statistically modelled using a regression equation function of the capacity variation in terms of γ and the chemical heterogeneity in terms of l1/L. The relationship combining the medium capacity and the chemical heterogeneity is obtained. The relationship implicitly takes into account the effect of the column length.  相似文献   

13.
An automated HPLC method is presented which combines on-line ion-pair extraction on small exchangeable RP-C18 precolumns (RP-IPE) with ion-pair chromatography (RP-IPC). Weakly acidic herbicides — carboxylic acids, phenols, and the N-H acidic bentazone — and strong acids, e.g. aromatic sulfonic acids, can be determined simultaneously. Performance data are given. The tetrabutylammonium ion pairs of all investigated compounds are readily transferred from the RP-C18 precolumn to the analytical column by a phosphate buffer/methanol gradient. This is also true for the chlorinated phenoxy acids which, in earlier off-line extraction experiments, could not be desorbed from the RP-C18 material by the lower polar acetone. The RP-IPC is carried out at neutral pH where weakly acidic compounds appear in their stronger UV absorbing dissociated form. Compared to conventional reversed phase chromatography using an acidified eluent, the sensitivity of UV detection is markedly enhanced, especially for the phenol herbicides and bentazone. In addition, phenols can be detected more selectively because they show a second intense absorption band in the wavelength range between 280 nm and 290 nm, where there are only little interferences with the matrix. Due to miniaturization and automation, the online combination IPE/IPC allows a large sample throughput at a lower consumption of solid phase material and organic solvents. Time consuming manual steps are totally missing. The IPE/IPC technique is well suited as a screening method for fate studies of polar micropollutants, e. g. for monitoring the efficiency of different water treatment technologies. An example for balancing an activated carbon filter is presented.  相似文献   

14.
The present work involves the study of Se(IV) adsorption onto granular activated carbon (GAC) and powdered activated carbon (PAC). The adsorbents are coated with ferric chloride solution for the effective removal of selenium. The physico-chemical characterization of the adsorbents is carried out using standard methods, e. g., proximate analysis, scanning electron microscopy (SEM), fourier transform infrared spectroscopy (FTIR), thermo-gravimetric (TGA) and differential thermal analysis (DTA), etc. The FTIR spectra of the GAC and PAC indicate the presence of various types of functional groups, e. g., free and hydrogen bonded OH groups, silanol groups (Si-OH), alkenes, and CO group stretching from aldehydes and ketones on the surface of adsorbents. Batch experiments are carried out to determine the effect of various factors such as adsorbent dose (w), initial pH, contact time (t), and temperature (T) on the adsorption process. The optimum GAC and PAC dosage is found to be 10 g/L and 8 g/L, respectively, for Se(IV) removal with C0 = 100 mg/L. The percent removal of Se(IV) increases with increasing adsorbent concentration, while removal per unit weight of adsorbent increases with decreasing adsorbent concentration. Se(IV) adsorption onto both the GAC and PAC adsorbents is high at low pH values, and decreases with increased initial pH. The results obtained are analyzed by various kinetic models. The parameters of pseudo-first order, pseudo-second order kinetics, and Weber-Morris intra particle kinetics are determined. It is seen that the sorption kinetics of Se(IV) onto GAC and PAC can be best represented by the pseudo-second order kinetic model.  相似文献   

15.
With the method used here, it was possible to determine the isotope content of both the initial compounds and their metabolites formed due to microbial degradation. The chemical analysis showed that the dominating degradation metabolite for both PCE and TCE degradation was cis-1,2-dichloroethene (cis-1,2-DCE). Apart from this, the formation of TCE, trans-1,2-DCE, 1,1-DCE, chloroethene (VC), ethene and ethane was observed. The isotope analysis showed no measurable fractionation of stable carbon isotopes, for the microbial degradation of PCE and TCE to cis-1,2-DCE. There was a small effect for trans-1,2-DCE and a stronger one for VC as metabolite of TCE.  相似文献   

16.
The distribution of halogens in various fractions of humic substances (HS), separated by their molecular weight, was found to be different for the different halogens. This was demonstrated for chlorine, bromine, and iodine in sewage and brown water samples by applying inductively coupled plasma mass spectrometry coupled with size‐exclusion chromatography. Quantification of the different fractions of iodinated humic substances was obtained by quadrupole mass spectrometry in connection with the isotope dilution technique using an 129I‐enriched spike solution. Quantitative analysis was not possible for the corresponding chlorine and bromine species because of spectrometric interferences in the quadrupole instrument. The ageing of HS/halogen species was followed with respect to possible transformations of these species in a ground and sewage water sample up to eight weeks. Even if a distinct structural variation of the humic substance was observed with time by measuring the UV absorption, chlorine remained in the same molecular weight fraction and only a small change was found for the HS/bromine species after eight weeks. In contrast to these findings a substantial transformation of HS/iodine compounds took place, which demonstrated that the transfer probability of halogens from one to another HS fraction is increased with decreasing strength of the halogen bond to carbon. By comparing the results of an original sewage water sample with a filtered one and with another one which was enriched by microorganisms cultivated from the same original sample, a strong microbiological influence on the transformation of HS/iodine species was found. A quantitative balance of the corresponding HS/iodine fractions was calculated for an ageing period of eight weeks showing that iodine was preferably transferred to newly formed UV active HS substances of high molecular weight. In total, no iodine was released from the humic substances.  相似文献   

17.
The reductive amination of low‐molecular‐weight saccharides, uronic acids, and amino sugars, followed by a separation of the derivates by means of ion‐pair chromatography or RP‐HPLC, offers an interesting alternative to HPAEC‐PAD for the environmental analysis of these compounds. Under this aspect various potential amination reagents, i.e., p‐amino‐benzoic acid (p‐AMBA), p‐AMBA propyl ester, 1‐aminopyrene, 2‐(2‐aminophenyl)indole, and 4‐aminoazobenzene, were tested with regard to the formation of derivates and to the chromatographic properties of the formed derivates. p‐AMBA, p‐AMBA propyl ester and 4‐aminoazobenzene proved to be especially suited, because they facilitate the amination of all carbohydrate reference components together with a complete separation and sensible detection (detection limits < 0.5 mg/L) of the derivates. Mainly the following elution sequence was ascertained: amino sugars (hexosamines) / disaccharide(s) / monosaccharides (hexoses) / hexuronic acid(s) / N‐acetyl‐D‐glucosamine. Detection limits down to 0.1 μmol/L were realized using p‐AMBA as reagent, facilitating the determination of the target compounds in landfill leachates and lysimeter percolates. Applying the p‐AMBA propyl ester for derivatization, chromatographic interferences with weakly retained derivates and the coelution of the reagent with its galactosamine derivate can be avoided, since the ester elutes after its derivates unlike p‐AMBA itself.  相似文献   

18.
In situ remediation technologies have the potential to alter subsurface properties such as natural organic matter (NOM) content or character, which could affect the organic carbon‐water partitioning behavior of chlorinated organic solvents, including dense nonaqueous phase liquids (DNAPLs). Laboratory experiments were completed to determine the nature and extent of changes in the partitioning behavior of trichloroethene (TCE) caused by in situ chemical oxidation or in situ surfactant flushing. Sandy porous media were obtained from the subsurface at a site in Orlando, Florida. Experiments were run using soil slurries in zero‐headspace reactors (ZHRs) following a factorial design to study the effects of porous media properties (sand vs. loamy sand with different total organic carbon [TOC] contents), TCE concentration (DNAPL presence or absence), and remediation agent type (potassium permanganate vs. activated sodium persulfate, Dowfax 8390 vs. Tween 80). Results revealed that the fraction of organic carbon (foc) of porous media after treatment by oxidants or surfactants was higher or lower relative to that in the untreated media controls. Isotherm experiments were run using the treated and control media to measure the distribution coefficient (Kd) of TCE. Organic carbon‐water partitioning coefficient values (Koc) calculated from the experimental data revealed that Koc values for TCE in the porous media were altered via treatment using oxidants and surfactants. This alteration can affect the validity of estimates of contaminant mass remaining after remediation. Thus, potential changes in partitioning behavior should be considered to help avoid decision errors when judging the effectiveness of an in situ remediation technology.  相似文献   

19.
章奇  居琪  李健欣  曹驰程  江和龙  张晖 《湖泊科学》2020,32(4):1041-1049
为探究富营养化湖泊中自生源可溶有机质(DOM)在泥水界面的吸附行为,以马来眼子菜(Potamogeton malaianus)和铜绿微囊藻(Microcystis aeruginosa)释放的DOM为代表,考察针铁矿对草、藻源DOM中不同组分的吸附特征.三维荧光平行因子分析表明类富里酸组分C1和类胡敏酸组分C4的含量很低,而类蛋白物质(类酪氨酸组分C2和类色氨酸组分C3)分别占草、藻源DOM荧光组成的70%和93%. 2种DOM均可被针铁矿吸附,吸附过程符合伪一级动力学.通过等温线拟合发现针铁矿吸附藻源DOM的非线性更强,饱和吸附量(23.77 mg/g)高于草源DOM(19.10 mg/g).特别地,类蛋白组分呈现非线性吸附,而类腐殖物质的吸附近似线性,且针铁矿对于DOM各荧光组分的吸附量顺序为:C3C2 C4 C1,此非均质吸附特征与DOM组分的初始含量、分子大小、芳香性及有效吸附位点有关.红外光谱证实氨基、羧基和羟基是吸附过程中的重要官能团.因此,草、藻源DOM显著改变了针铁矿表面的有机物质组成,影响湖泊沉积物的生物地球化学行为.  相似文献   

20.
In inland waters, transparent exopolymer particles (TEP) can affect carbon export and sequestration in sediments with consequences for lake C budgets. We measured TEP concentration in 32 lakes from two contrasting lake districts covering wide ranges in biological and chemical characteristics. North temperate lakes, located in a wet region, have low to moderate ionic strength and low to high dissolved organic carbon with corresponding variation in color (light absorbance). Mediterranean lakes located in a semiarid region were characterized by high ionic strength and high concentrations of dissolved organic carbon but low color. TEP concentrations were large relative to the living portion of the particulate organic carbon pool in both Mediterranean (36%) and north temperate (33%) lakes. TEP concentrations ranged from 36 to 1,462 μg [as Gum Xanthan equivalents (GX eq)] L−1 in north temperate lakes. In the Mediterranean lakes, concentrations were higher that previously reported for other systems and ranged from 66 to 9,038 μg GX eq L−1. TEP concentration was positive and significantly related to chlorophyll a (chl a) in north temperate lakes and in the entire data set. Although a significant and positive relationship between TEP and chl a was also detected in the Mediterranean lakes, bacterial abundance was most strongly related to TEP. In contrast with the positive influence of phytoplankton and bacteria on TEP, there were weaker relationships between TEP and the chemical variables tested. We observed a significant and positive relationship between pH and TEP (for all lakes) but this relationship was indirectly driven by a co-variation of pH with phytoplankton biomass based on multiple regression analysis. For the Mediterranean lakes, the negative (but not significant) trends between TEP and both conductivity and divalent cations suggest thresholds above which TEP will likely be destabilized. Under these conditions, TEP may flocculate or disperse in the water column.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号