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 effects of heavy metal contamination on soil enzyme activity and earthworm health (bioaccumulation and condition) were studied in contaminated soils collected from an formerly open burning and open detonation (OBOD) site. Soil extraction methods were also evaluated using CaCl2 and DTPA solutions as surrogate measures of metal bioavailability and ecotoxicity. Total heavy metal content of the soils ranged from 0.45 to 9.68 mg Cd kg−1, 8.96 to 5103 mg Cu kg−1, 40.21 to 328 mg Pb kg−1, and 56.61 to 10,890 mg Zn kg−1. Elevated metal concentrations are assumed to be primarily responsible for the reduction in enzyme activities and earthworm health indices. We found significant negative relationships between CaCl2- and DTPA-extractable metal content (Cd, Cu, and Zn) and soil enzyme activity (P < 0.01). Therefore, it could be concluded that soil enzyme activity and metal bioaccumulation by earthworms can be used as an ecological indicator of metal availability. Furthermore, CaCl2 and DTPA extraction methods are proved as promising, precise, and inexpensive surrogate measures of Cd, Cu, Pb, and Zn bioavailability from heavy metal-contaminated soils.  相似文献   

2.
The effect of operational conditions and initial dye concentration on the reductive transformation (decolorization) of the textile dye Reactive Blue 4 (RB4) using zero-valent iron (ZVI) filings was evaluated in batch assays. The decolorization rate increased with decreasing pH and increasing temperature, mixing intensity, and addition of salt (100 g L−1 NaCl) and base (3 g L−1 Na2CO3 and 1 g L−1 NaOH), conditions typical of textile reactive dyebaths. ZVI RB4 decolorization kinetics at a single initial dye concentration were evaluated using a pseudo first-order model. Under dyebath conditions and at an initial RB4 concentration of 1000 mg L−1, the pseudo first-order rate constant (kobs) was 0.029 ± 0.006 h−1, corresponding to a half-life of 24.2 h and a ZVI surface area-normalized rate constant (kSA) of 2.9 × 10−4 L m−2 h−1. However, as the initial dye concentration increased, the kobs decreased, suggesting saturation of ZVI surface reactive sites. Non-linear regression of initial decolorization rate values as a function of initial dye concentration, based on a reactive sites saturation model, resulted in a maximum decolorization rate (Vm) of 720 ± 88 mg L−1 h−1 and a half-saturation constant (K) of 1299 ± 273 mg L−1. Decolorization of RB4 via a reductive transformation, which was essentially irreversible (2–5% re-oxidation), is believed to be the dominant decolorization mechanism. However, some degree of RB4 irreversible sorption cannot be completely discounted. The results of this study show that ZVI treatment is a promising technology for the decolorization of commercial, anthraquinone-bearing, spent reactive dyebaths.  相似文献   

3.
The contamination of subsurface soils with petroleum hydrocarbons is a widespread environmental problem. The objective of this study was to evaluate the potential of applying waste basic oxygen furnace slag (BOF slag) as the catalyst to enhance the Fenton-like oxidation to remediate fuel oil or diesel contaminated soils. The studied controlling factors that affect the removal efficiency of petroleum hydrocarbons included concentrations of H2O2, BOF slag dosages, types of petroleum hydrocarbons (e.g., fuel oil and diesel), and types of iron mineral. Experimental results indicate that oxidation of petroleum hydrocarbon via the Fenton-like process can be enhanced with the addition of BOF slag. Results from the X-ray powder diffraction analysis reveal that the major iron type of BOF slag/sandy loam system was iron mineral (e.g., α-Fe2O3 and α-FeOOH). Approximately 76% and 96% of fuel oil and diesel removal were observed (initial total petroleum hydrocarbon (TPH) concentration = 10,000 mg kg−1), respectively, with the addition of 15% of H2O2 and 100 g kg−1 of BOF slag after 40 h of reaction. Because BOF slag contains extractable irons such as amorphous iron and soluble iron, it can act as an iron sink to supply iron continuously for Fenton-like oxidation. Results demonstrate that Fenton-like oxidation catalyzed by BOF slag is a potential method to be able to remediate petroleum-hydrocarbon contaminated soils efficiently and effectively.  相似文献   

4.
Silver was reclaimed from silver-plating wastewater by using a pulsed electric field (PEF) combined with static cylinder electrodes (SCE). The conditions that produced the maximal silver recovery rate (RRAg) (99%) were as follows: average retention time of 10 min, interelectrode gap of 50 mm, solution pH of 9.0, temperature of 45 °C, initial Ag(I) concentration of 1000 mg L−1, PEF pulse frequency of 1200 Hz, current density of 5.0 A m−2 and a pulse duty cycle of 60%. Compared with the conventional direct current (DC) technology, the PEF process exhibited improvements in the silver recovery rate (RRAg), total energy consumption (TEC) and physical properties of the silver deposits, especially for low Ag(I) concentrations, for example, from 500 to 1000 mg L−1. For an initial Ag(I) concentration of 500 mg L−1, the PEF process produced an RRAg of up to 99%, and the TEC was 4.56 kWh (kg Ag)−1. In comparison, the RRAg and TEC were 90% and 5.66 kWh (kg Ag)−1, respectively, in the DC process. The results of SEM observation and XRD analysis indicated that the silver deposits formed by the PEF process were smaller, denser, and of a higher purity than those produced by the DC process. Therefore, the presented method was effective for reclaiming silver from silver-plating wastewater.  相似文献   

5.
Well dispersed Fe3O4 nanoparticles with a mean diameter of about 160 nm were synthesized by a simple hydrothermal method in the presence of sodium sulfate. The products were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), Raman spectrum, and Fourier transform infrared spectra (FTIR). Electrochemical properties of the nanostructured Fe3O4 as cathode electrodes of lithium ion battery were studied by conventional charge/discharge tests, showing a high initial discharge capacity of 1267 mA h g− 1 at a current density of 0.1 mA cm− 2.  相似文献   

6.
The new type of ion chelating resin (IDA-PUF) has iminodiacetic group that was prepared from polyurethane foam (PUF) by the reaction between primary amine of PUF and monochloro-acetic acid. The IDA-PUF was characterized using infrared spectra, elemental and thermal analysis. The exchange properties and chromatographic behaviour of the new chelating resin were investigated for removal of some alkali metal ions (lithium, sodium and potassium) using batch and column processes. The maximum distribution coefficient (KD) of trace alkali metal ions was in the pH range of 8–10. The kinetics of sorption of the alkali metal ions was found to be fast with average values of half-life of sorption (t1/2) of 4.93 min. The values of ΔG, ΔS and ΔH were −3.86 kJ mol−1, 57.73 J mol−1 K−1 and 14.41 kJ mol−1, respectively, which reflects the spontaneous and endothermic nature of ion exchanger process. The average sorption capacity of IDA-PUF is 4.8 mmol/g for alkali metal ions, enrichment factors ≈40 and the recovery 95–100% were also achieved with average value of RSD% = 1.67. The proposed method has been successfully applied to preconcentrate, determinate and remove the alkali metal ions from different samples of water.  相似文献   

7.
A microwave-assisted emulsion process has been developed to synthesize birnessite-type MnO2 one-dimensional (1D) nanostructures. The prepared samples were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). TEM images confirmed that the particles were composed of nanowires and nanobelts. As a consequence of the small size, such MnO2 nanostructures exhibit a high specific capacitance of 277 F g−1 at the current density of 0.2 mA cm−2. Furthermore, the simple synthetic approach may provide a convenient route for the preparation of birnessite-type MnO2 nanowires and other 1D nanostructured materials on a large scale.  相似文献   

8.
The most important challenge to use phytoremediation is how to improve its efficiency by increasing the accumulation of metals in plants, or by improving key plant biological traits that should enhance metal uptake. In this paper, we used open-top chambers to investigate the effects of elevated CO2 (860 μL L−1) on biomass and Cs uptake by a Sorghum vulgare × Sorghum vulgare var. sudanense hybrid and Trifolium pratense L. growing on soils spiked with various levels of cesium (0, 300, 1500 and 3000 mg Cs kg−1). The results showed that elevated CO2 not only increased aboveground biomass of the Sorghum and Trifolium species by 32–111%, and by 8–11%, respectively, compared to the ambient CO2 treatment, but also caused more accumulation of Cs by Sorghum species (up to 73%) than Trifolium species (up to 43%). It was speculated that the increase in biomass and the improvement in Cs accumulation ability at elevated CO2 could be related to lowered soil pH values, and changes in number and kind of microorganisms in the rhizospheres of the two tested species. This is the first report of a link among elevated CO2, increased biomass and hyperaccumulation of Cs by Sorghum and Trifolium species.  相似文献   

9.
Three additives were evaluated for their effectiveness in the attenuation of Pb2+, Zn2+, Cu2+, Cd2+, Ni2+ in contaminated sediments. Apatite, ferrihydrite and their composite were applied to the sediments. For the remediation, BCR, SEM/AVS and TCLP were adopted as the evaluating method and comparison of their results were used for the first time to test in-situ stabilization effect. The results showed that after 5 months composite treatment, more than 70% Pb2+, 40% Zn2+, 90% Cu2+, 50% Cd2+ and 80% Ni2+ was immobilized in oxidizable and residual phases, respectively. Compared to untreated sediment, Pb2+, Zn2+, Cu2+, Cd2+ in residual fraction increased 20%, 10%, 10%, 10% with composite treatment after 5 months, respectively. ΣSEM/AVS ratio declined from 12.6 to 9.3, in addition, composite treatments reduced the leaching of Pb2+ and Zn2+ from 10.6 mg L−1and 42.5 mg L−1to 5.4 mg L−1 and 24.1 mg L−1 in the sediment by TCLP evaluation. Meanwhile, apatite and ferrihydrite composite additives lowered the bioavailability and toxicity of sediments as well. Ferrihydrite had a positive effect in controlling the bioavailability and toxicity of heavy metals because it effectively retarded the oxidation of AVS in sediment.  相似文献   

10.
A hydroponics experiment was conducted to examine the phytofiltration of Cd by Limnocharis flava (L.) Buchenau grown in low-level Cd-contaminated water. For this, 45 d old seedlings of L .flava were transferred to a floating-support culture system containing nutrient solution spiked with four levels of Cd (0.5, 1, 2 and 4 mg l−1) and were separately harvested after 3, 7, 21 and 30 d. After 30 d harvesting, the percentage removal of Cd from the above four treatments reached up to 98, 96, 95 and 93%, respectively. Interestingly, all treatments had higher growth rate than control at 95% confidence level and plants still remained healthy at 4 mg l−1 Cd exposure. The bioaccumulation study showed a linear relationship of Cd (R2 = 0.896–0.999) in all plant parts with the exposure time (3–30 d) and Cd concentrations in hydroponics system (0.5–4 mg l−1). Although, the root of L. flava had higher Cd concentration than leaf and peduncles, the total Cd concentrations in aerial plant parts were higher than the roots. The maximum bioconcentration factor (BCF) and translocation factor (TF) value of L. flava were calculated as 984.42 and 1.43, respectively. Estimated Cd accumulation capacity of L. flava per unit area (m2) was found to be in the range of 218. 35–1698.92 mg m−2.The experimental results demonstrated that L. flava is a suitable candidate for the phytofiltartion (>93%) of Cd from low-level Cd-contaminated water.  相似文献   

11.
A novel route of anoxic ammonia removal in the presence of organic carbon was identified recently from ecosystems contaminated with ammonia. Sequencing batch reactor (SBR) studies were carried out in anoxic condition at oxidation–reduction potential varied from −185 to −275 mV for anoxic ammonia oxidation with adapted biomass (mixed culture). SBR studies were carried out in absence and in the presence of externally added organic carbon and/or in the presence of inorganic electron acceptors like NO2, NO3 and SO42−. The results showed anoxic ammonia oxidation to nitrate (in contrast to reported anammox process) in the presence of organic carbon available through endogenous respiration whereas anoxic ammonia oxidation was effective in the presence of externally added organic compound for nitrogen removal. The presence of externally added inorganic electron acceptors like NO2, NO3 and SO42− was effective in anoxic ammonia oxidation, but failed to follow the reported anammox reaction's stoichiometry in nitrogen removal in the presence of organic carbon. However, the presence of NO2 affected best in total nitrogen removal compared to other electron acceptors and maximum ammonia removal rate was 100 mg NH4+/g MLVSS/d. Based on the results, it is possible to suggest that rate of anoxic ammonia oxidation depends up on the respiration activities of mixed culture involving organic carbon, NO2, NO3 and SO42−. The process shows possibilities of new pathways of ammonia oxidation in organic contaminated sediments and/or wastewater in anoxic conditions.  相似文献   

12.
This study was carried out to investigate the adsorption equilibrium and kinetics of a pesticide of the uracil group on powdered activated carbon (PAC). The experiments were conducted at a wide range of initial pesticide concentrations (5 μg L−1 to 500 μg L−1 at pH 7.8), corresponding to equilibrium concentrations of less than 0.1 μg L−1 for the weakest, which is compatible with the tolerance limits of drinking water. Such a very broad range of initial solute concentrations resulting powdered activated carbon (PAC) concentrations (0.1–5 mg L−1) is the main particularity of our study. The application of several monosolute equilibrium models (two, three or more parameters) has generally shown that Bromacil adsorption is probably effective on two types of sites. High reactivity sites (KL  103 L mg−1) which are 10–20 less present in a carbon surface than lower reactivity sites (KL  10 L mg−1), according to the qm values calculated by two- or three-parameter models. The maximum capacity of the studied powdered activated carbon (PAC), corresponding to monolayer adsorption, compared to the Bromacil molecule surface, would be between 170 mg g−1 and 190 mg g−1. This theoretical value is very close to the experimental qm values obtained when using linearized forms of Langmuir, Tóth and Fritz–Schluender models.  相似文献   

13.
A new sorbent 1-acylthiosemicarbazide-modified activated carbon (AC-ATSC) was prepared as a solid-phase extractant and applied for removing of trace Cu(II), Hg(II) and Pb(II) prior to their determination by inductively coupled plasma optical emission spectrometry (ICP-OES). The separation/preconcentration conditions of analytes were investigated, including effects of pH, the shaking time, the sample flow rate and volume, the elution condition and the interfering ions. At pH 3, the maximum static adsorption capacity of Cu(II), Hg(II) and Pb(II) onto the AC-ATSC were 78.20, 67.80 and 48.56 mg g−1, respectively. The adsorbed metal ions were quantitatively eluted by 3.0 mL of 2% CS(NH2)2 and 2.0 mol L−1 HCl solution. Common coexisting ions did not interfere with the separation. According to the definition of IUPAC, the detection limits (3σ) of this method for Cu(II), Hg(II) and Pb(II) were 0.20, 0.12 and 0.45 ng mL−1, respectively. The relative standard deviation under optimum conditions is less than 4.0% (n = 8). The prepared sorbent was applied for the preconcentration of trace Cu(II), Hg(II) and Pb(II) in certified and water samples with satisfactory results.  相似文献   

14.
The charge carrier mobility of green phosphorescent emissive layers, tris(2-phenylpyridine) iridium [Ir(ppy)3]-doped 4,4'-N,N'-dicarbazole-biphenyl (CBP) thin films, has been determined using impedance spectroscopy (IS) measurements. The theoretical basis of mobility measurement by IS rests on a theory for single-injection space-charge limited current. The hole mobilities of the Ir(ppy)3-doped CBP thin films were measured to be 10− 10–10− 8 cm2V− 1 s− 1 in the 2–7 wt.% Ir(ppy)3-doped CBP from the frequency dependence of both conductance and capacitance. These hole mobility values are much lower than those of the undoped CBP thin films (~ 10− 3 cm2V− 1 s− 1) because the Ir(ppy)3 molecules act as trapping centers in the CBP host matrix. These mobility measurements in the Ir(ppy)3-doped CBP thin films provide insight into the hole injection process.  相似文献   

15.
An isolated bacterial strain is placed in the branch of the Bacillus genus on the basis of 16S rRNA sequence and biochemical characteristics. It decolorized an individual and mixture of dyes, including reactive, disperse and direct. Bacillus sp. ADR showed 88% decolorization of sulfonated azo dye C.I. Reactive Orange 16 (100 mg L−1) with 2.62 mg of dye decolorized g−1 dry cells h−1 as specific decolorization rate along with 50% reduction in COD under static condition. The optimum pH and temperature for the decolorization was 7–8 and 30–40 °C, respectively. It was found to tolerate the sulfonated azo dye concentration up to 1.0 g L−1. Significant induction in the activity of an extracellular phenol oxidase and NADH–DCIP reductase enzymes during decolorization of C.I. Reactive Orange 16 suggest their involvement in the decolorization. The metal salt (CaCl2), stabilizers (3,4-dimethoxy benzyl alcohol and o-tolidine) and electron donors (sodium acetate, sodium formate, sodium succinate, sodium citrate and sodium pyruvate) enhanced the C.I. Reactive Orange 16 decolorization rate of Bacillus sp. ADR. The 6-nitroso naphthol and dihydroperoxy benzene were final products obtained after decolorization of C.I. Reactive Orange 16 as characterized using FTIR and GC–MS.  相似文献   

16.
The denitrification capacity of refuse at different landfill ages in bioreactor landfill system was studied. Three reactors filled with 1-year-old refuse (R1), 6-year-old refuse (R6) and 11-year-old refuse (R11), respectively, were operated in the experiment. Nitrate solution (1000 mg NO3-N L−1) was added into each reactor. The results showed that the reactors were all able to consume nitrate. However, 1-year-old refuse in R1 had both a higher nitrate reduction rate and concentration of N2. In addition, vertical differences in nitrate removal along the depth of R1 were observed. The bottom-layer refuse and the middle-layer refuse both showed higher efficiency in nitrate depletion than the top layer. Furthermore, N2O accumulation was found in R11 with the concentration up to 19.3% of the released gas. These results suggested that 1-year-old refuse, which was partly degraded, was more suitable to use as denitrification medium.  相似文献   

17.
The impact of waste disposal on marsh soils was assessed in topsoil samples collected at eight randomly selected points in the salt marsh in Ramallosa (Pontevedra, Spain) at 4-month intervals for 2 years. Polluted soil samples were characterized in physico-chemical terms and their heavy metal contents determined by comparison with control, unpolluted samples. The results revealed a marked effect of waste discharges on the soils in the area, which have low contents in heavy metals under normal environmental conditions. In fact, the studied soils were found to contain substantial amounts of total and DTPA-extractable Cd, Cu, Pb and Zn. Based on the relationship of the redox potential with the DTPA-extractable Cd, Cu, Pb, and Zn contents of the soils, strongly reductive conditions raised the total contents in these elements by effect of their remaining in the soils as precipitated sulphides. Such contents, however, decreased as oxidative conditions gradually prevailed. The contents in DTPA-extractable metals increased with increasing Eh through the release of the metals in ionic form to the soil solution under oxidative conditions. The contents in heavy metals concentrating in the polluted soils were several times higher than those in the control soils (viz. 2 vs. 6 for Cd, 4 vs. 6 for Cu, 4 vs. 20 for Pb, and 2 vs. 15 for Zn, all in mg kg−1). This can be expected to influence the amounts of available heavy metals present in the soils, and hence the environmental quality of the area, in the near future. Based on its geoaccumulation index (Class ≥3 for Cd and Cu, and 1–4 for Pb and Zn), the Ramallosa marsh is highly polluted with Cd and moderately to highly polluted with Cu, Pb and Zn. The enrichment factors obtained confirm that the salt marsh is highly polluted (especially with Cd) as the primary result of anthropic activity.  相似文献   

18.
P.H. Tai  C.H. Jung  Y.K. Kang  D.H. Yoon   《Thin solid films》2009,517(23):129-6297
12CaO·7Al2O3 electride (C12A7:e) doped indium tin oxide (ITO) (ITO:C12A7:e) thin films were fabricated on a glass substrate by an RF magnetron co-sputtering system with increasing number of C12A7:e chips (from 1 to 7) and at various oxygen partial pressure ratios. The optical transmittance of the ITO:C12A7:e thin film was higher than 70% in the visible wavelength region. In the electrical properties of the thin film, a decrease of the carrier concentration from 2.6 × 1020 cm− 3 to 2.1 × 1018 cm− 3 and increase of the resistivity from 1.4 × 10− 3 Ω cm to 4.1 × 10− 1 Ω cm were observed with increasing number of C12A7:e chips and oxygen partial pressure ratios. It was also observed that the Hall mobility was decreased from 17.27 cm2·V− 1·s− 1 to 5.13 cm2·V− 1·s− 1. The work function of the ITO thin film was reduced by doping it with C12A7:e.  相似文献   

19.
The purpose of this study was to investigate the sorption of total phenols, which are contained in olive-mill wastewater (OMWW), on solid by-products of olive pomace processing mills. Preliminary batch experiments were conducted using three different types of olive pomace, dried olive pomace (OP-1), dried and solvent extracted olive pomace (OP-2) and dried, solvent extracted and incompletely combusted olive pomace (OP-3). According to the results, OP-3 showed high performance for total phenols sorption and stability. For sorbent concentration of 10 g L−1 and sorbate concentration of 50 mg L−1, more than 40% of initial total phenols concentration was removed. Sorption kinetics was well described by the pseudo-second order rate model (R2 > 0.99). Total phenols removal efficiency was improved by increasing sorbent concentration and solution's pH or decreasing particle size of the sorbent material. The Langmuir and Freundlich isotherms sufficiently described OP-3 sorption capacity for the concentration range studied (50–500 mg L−1). Fixed bed sorption experiments showed that lower flow rates and smaller particle size of sorbent resulted in longer column exhaustion time and higher initial removal efficiency. Experiments with thermally or chemically regenerated OP-3 showed that sorption capacity deteriorated after regeneration.  相似文献   

20.
Electrochemical synthesis of hydroxyapatite powders was performed galvanostatically from homogeneous solution of Na2H2EDTA·2H2O, NaH2PO4 and CaCl2 at a concentration relationship Ca/EDTA/PO43− of 0.25/0.25/0.15 M at current densities of 137 and 207 mA cm−2 and pH values of 9.0 and 12.0. The hydroxyapatite powders were characterized by X-ray diffraction, size distribution measurements, transmission electron microscopy, scanning electron microscopy and thermogravimetric and differential thermal analysis. The influence of the electrochemical synthesis parameters, e.g. applied current density and pH value, on the phase composition, crystallite size, morphology and thermal characteristics of hydroxyapatite powders were investigated.  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