Thorough removal of inorganic and organic mercury from aqueous solutions by adsorption on Lemna minor powder

The adsorption ability of duckweed (Lemna minor) powders for removing inorganic and organic mercury (methyl and ethyl mercury) has been studied using cold vapour atomic absorption spectrometry. The optimal adsorption conditions were: (a) the pH value of the solution 7.0 for inorganic and ethyl mercury, 9.0 for methyl mercury, and (b) equilibrium adsorption time 10, 20, and 40 min for inorganic mercury, methyl mercury, and ethyl mercury, respectively. After adsorption by L. minor powder for 40 min, when the initial concentrations of inorganic and organic mercury were under 12.0 μg L⁻¹ and 50.0 μg L⁻¹, respectively, the residual concentrations of mercury could meet the criterion of drinking water (1.0 μg L⁻¹) and the permitted discharge limit of wastewater (10.0 μg L⁻¹) set by China and USEPA, respectively. Thorough removal of both inorganic and organic mercury from aqueous solutions was reported for the first time. The significant adsorption sites were C–O–P and phosphate groups by the surface electrostatic interactions with aqueous inorganic and organic mercury cations, and then the selective adsorption was resulted from the strong chelating interaction between amine groups and mercury on the surface of L. minor cells.     

The use of protonated Sargassum muticum as biosorbent for cadmium removal in a fixed-bed column

The protonated Sargassum muticum seaweed was studied as a possible biosorbent for cadmium removal in a fixed-bed column. The experiments were conducted in order to determine the effect of flow rate (0.42, 5, 10 and 20 mL min(-1)) and bed height (0.6 and 15.3 cm for the lowest flow rate or 7.4, 13 and 16.6 cm for the others) on breakthrough curves behaviour. The determined breakthrough and exhaustion times increased with the diminution in flow rate and with the increase in bed height. The maximum cadmium uptake capacity, obtained from the area below adsorbed cadmium concentration versus time curves, was found to remain practically constant with bed depth and flow rate. The bed depth service time (BDST) model was applied to analyse experimental data, determining the characteristic process parameters. The optimal lowest sorbent usage rate was evaluated at 2 min contact time and the minimum bed height values necessary to prevent the effluent solution concentration from exceeding 0.02 mg L(-1) at zero time were 5.3, 6.9 and 7.5 cm for flow rates of 5, 10 and 20 mL min(-1), respectively. Several empirical models proposed in the literature (Bohart-Adams, Yan, Belter and Chu models) were investigated in order to obtain the best fit of column data, describing in a simple manner the breakthrough curves. A correlation between model parameters and the variables implied in the process was attempted.     

Batch desorption studies and multiple sorption-regeneration cycles in a fixed-bed column for Cd(II) elimination by protonated Sargassum muticum

The protonated alga Sargassum muticum was employed in batch desorption studies to find the most appropriate eluting agent for Cd(II)-laden biomass regeneration. Eleven types of eluting solutions at different concentrations were tested, finding elution efficiencies higher than 90% for most of the desorbents studied. Total organic carbon and biomass weight loss measurements were made. The reusability of the protonated alga was also studied using a fixed-bed column. Eleven consecutive sorption-regeneration cycles at a flow rate of 10 mL min(-1) were carried out for the removal of 50 mg L(-1) Cd(II) solution. A 0.1M HNO(3) solution was employed as desorbing agent. The column was operated during 605 h for sorption and 66 h for desorption, equivalent to a continuous use during 28 days, with no apparent loss of sorption performance. In these cycles, no diminution of the breakthrough time was found; although, a relative loss of sorption capacity, regarding the found in the first cycle, was observed. The slope of the breakthrough curves experiments a gradual increase reaching its maximum value for the last cycle tested (40% greater than for the first one). The maximum Cd(II) concentration elution peak was achieved in 5 min or less, and the metal effluent concentration was always lower than 0.9 mg L(-1) after 1 h of elution. The maximum concentration factor was determined to be between 55 and 109.     

Use of biogenic and abiotic elemental selenium nanospheres to sequester elemental mercury released from mercury contaminated museum specimens

Mercuric chloride solutions have historically been used as pesticides to prevent bacterial, fungal and insect degradation of herbarium specimens. The University of Manchester museum herbarium contains over a million specimens from numerous collections, many preserved using HgCl(2) and its transformation to Hg(v)(0) represents a health risk to herbarium staff. Elevated mercury concentrations in work areas (～ 1.7 μg m(-3)) are below advised safe levels (<25 μg m(-3)) but up to 90 μg m(-3) mercury vapour was measured in specimen boxes, representing a risk when accessing the samples. Mercury vapour release correlated strongly with temperature. Mercury salts were observed on botanical specimens at concentrations up to 2.85 wt% (bulk); XPS, SEM-EDS and XANES suggest the presence of residual HgCl(2) as well as cubic HgS and HgO. Bacterially derived, amorphous nanospheres of elemental selenium effectively sequestered the mercury vapour in the specimen boxes (up to 19 wt%), and analysis demonstrated that the Hg(v)(0) was oxidised by the selenium to form stable HgSe on the surface of the nanospheres. Biogenic Se(0) can be used to reduce Hg(v)(0) in long term, slow release environments.     

Toxicity of mercury on in vitro development of parthenogenetic eggs of a freshwater cladoceran Daphnia carinata

Chronic toxicity test duration of 21 days for daphnid is time consuming and expensive. Therefore, the developmental stages of Daphnia carinata eggs that could be used as potential endpoints for sublethal and chronic toxicity tests have been investigated and defined. Daphnid egg test is simple, easy to conduct and handle in the laboratory, and cost-effective. The 72 h ‘egg arrest’ bioassay system could be an alternative to the classic 21-day chronic test with neonates of daphnid. The main aims of the study were to establish easy to identify stages of D. carinata egg that could be used as potential endpoints for toxicity tests with in vitro cultures of daphnid parthenogenetic eggs. Commonly available Indian freshwater cladoceran Daphnia carinata parthenogenetic eggs in vitro were exposed to water borne mercury concentrations, ranging from 0.1 to 32 μg l⁻¹. Adult female cladoceran D. carinata have eight main developmental stages of parthenogenetic reproduction based on the release of external and internal membranes, formation of cephalic and body regions, appearance of secondary antennae, presence of two pink eyes, than a single black eye, and finally caudal or shell spine separation and finally free-swimming neonate within 65–72 h. At 1, 3.2 and 10 μg l⁻¹ of Hg concentrations; the 25, 50 and 70% embryonic developmental arrests were observed. The lower concentrations of Hg (0.32, 1, and 3.2 μg l⁻¹) tested in the present study are not generally harmful to the neonates and adults daphnid species, but the same are highly toxic to the embryos of D. carinata. The 48 h and 72 h EC₅₀s and their 95% confidence limits for survival and hatchability were lower than previously reported 48 h EC₅₀s for Daphnia magna immobilization assay. The egg of D. carinata turned out to be a suitable alternative model for ecotoxicological and water quality assessment studies.     

Potential of Sargassum wightii biomass for copper(II) removal from aqueous solutions: application of different mathematical models to batch and continuous biosorption data

This paper reports biosorption of copper(II) ions onto Sargassum wightii biomass in batch and continuous mode of operation. Batch experiments were fundamentally aimed to determine the favorable pH for copper(II) biosorption. Langmuir model was used to describe the copper(II) biosorption isotherm and maximum uptake of 115 mg/g was obtained at pH 4.5. Continuous experiments in a packed column (2 cm i.d. and 35 cm height) were performed to study the influence of bed height, flow rate and inlet solute concentration on copper(II) biosorption. The highest bed height (25 cm), lowest flow rate (5 ml/min) and highest inlet Cu(II) concentration (100 mg/l) resulted in highest copper(II) uptake of 52.6 mg/g, compared to other conditions examined. Column data obtained at different conditions were described using the Thomas, Yoon-Nelson and modified dose-response models. All three models were able to predict breakthrough curves; in particular, the breakthrough curve prediction by the Thomas and Yoon-Nelson models were found to be very satisfactory. Also, the well-established design model, the Bed depth-service time (BDST) model was used to analyze the experimental data. The BDST model plot at 5 ml/min (flow rate) and 100 mg/l (inlet solute concentration) was used to predict bed depth-service time data at different conditions. The BDST model predicted values always coincide with experimental values with high correlation coefficients.     

Influence of boron on strain hardening behaviour and ductility of low carbon hot rolled steel

The beneficial effect of boron on mechanical properties of low carbon Al-killed steel has been reported in recent past. However, the effect of boron on strain hardening exponent (n) and ductility has not been fully understood. This aspect has been discussed in present work. The results of mill trials with reference to n and ductility with boron added steel are compared to those for commercial grade. The lowering of ‘n’ with increased total elongation in boron bearing steel has been related to the microstructural evolution as a result of boron addition.     

Three-dimensional tracking and behaviour monitoring of multiple fruit flies

The increasing interest in the investigation of social behaviours of a group of animals has heightened the need for developing tools that provide robust quantitative data. Drosophila melanogaster has emerged as an attractive model for behavioural analysis; however, there are still limited ways to monitor fly behaviour in a quantitative manner. To study social behaviour of a group of flies, acquiring the position of each individual over time is crucial. There are several studies that have tried to solve this problem and make this data acquisition automated. However, none of these studies has addressed the problem of keeping track of flies for a long period of time in three-dimensional space. Recently, we have developed an approach that enables us to detect and keep track of multiple flies in a three-dimensional arena for a long period of time, using multiple synchronized and calibrated cameras. After detecting flies in each view, correspondence between views is established using a novel approach we call the ‘sequential Hungarian algorithm’. Subsequently, the three-dimensional positions of flies in space are reconstructed. We use the Hungarian algorithm and Kalman filter together for data association and tracking. We evaluated rigorously the system''s performance for tracking and behaviour detection in multiple experiments, using from one to seven flies. Overall, this system presents a powerful new method for studying complex social interactions in a three-dimensional environment.     

Improved photoelectrochemical detection of mercury (II) with a TiO2-modified composite photoelectrode

The spectrophotometric change of a mercury (II) (Hg²⁺) selective small molecule chemosensor has been successfully converted into a photovoltaic response upon ligating Hg²⁺. The photon excitation was followed by charge separation facilitated by TiO₂ and polyaniline (PANI), resulting in an electron transfer to an electrical back contact. The photoresponse of the Hg²⁺ selective chromophore was converted to an electron current equivalent to the amount of Hg²⁺ in solution. The favourable properties of a Hg²⁺ sensitive chemosensor was combined with the semiconductor capabilities of TiO₂ to construct a sensor that is capable of generating a current in the presence of Hg²⁺ under illumination. A composite of the fluorescent chemosensor rhodamine 6G hydrozone derivative (RS) and PANI was immobilized on indium tin oxide (ITO) plates coated with TiO₂ and subjected to photovoltammetric measurements. The photovoltammetric responses of the coated layers were investigated to determine the sensitivity and selectivity of the immobilized sensor to Hg²⁺ in the presence of background ions. The photo-response increased linearly with increasing Hg²⁺ concentration from 10 to 200 μg L⁻¹ with a limit of quantification (LOQ) of 4 μg L⁻¹. The pH independence for the photoresponse was limited by the TiO₂ layer and was optimal between pH 6 and 7.     

Screening for novel antibacterial agents based on the activities of compounds on metabolism of Escherichia coli: a microcalorimetric study

The emergence and prevalence of resistance to antibacterial agents is a pressing threaten for human health. Screening for novel antibacterial agents targeting not only multiplying but also non-multiplying bacteria using appropriate approach is in great demand. In this study, the microcalorimetric method was used to measure the metabolic curves of E. coli growth affected by chenodeoxycholic acid (CDCA) and ursodeoxycholic acid (UDCA). By analyzing the metabolic curves and thermo- kinetic/dynamic parameters, the antibacterial activities of CDCA and UDCA on multiplying and non-multiplying bacteria of Escherichia coli (E. coli) were evaluated. The results illustrated that, for the multiplying metabolism of E. coli, the two compounds controlled the anaerobic fermentative, with IC(50(1)) (half-inhibitory concentration) of 566.2 μg/mL for CDCA and 573.6 μg/mL for UDCA, respectively, but had no effective action on aerobic metabolism of the bacteria. The action of the two compounds on the non-multiplying metabolism was studied by taking the heat output of E. coli in the stationary phase as the additive guideline of the activity. The values of IC(50(2)) were 543.4 and 547.5 μg/mL, and MSC(50) (minimum stationary-cidal concentration 50) were 532.6 and 537.3 μg/mL for CDCA and UDCA, respectively. So, CDCA had more powerful antibacterial activity on E. coli than UDCA either for multiplying bacteria or non-multiplying metabolism, and they both showed stronger activities on non-multiplying metabolism than on multiplying metabolism of the bacteria. The microcalorimetric method should be strongly suggested in screening novel antibacterial agents for fighting against multidrug-resistant bacteria.     

Modeling the adsorption of Cr(III) from aqueous solution onto Agave lechuguilla biomass: study of the advective and dispersive transport

The biosorption of Cr(III) onto packed columns of Agave lechuguilla was analyzed using an advective-dispersive (AD) model and its analytical solution. Characteristic parameters such as axial dispersion coefficients, retardation factors, and distribution coefficients were predicted as functions of inlet ion metal concentration, time, flow rate, bed density, cross-sectional column area, and bed length. The root-mean-square-error (RMSE) values 0.122, 0.232, and 0.285 corresponding to the flow rates of 1, 2, and 3 (10(-3))dm3min(-1), respectively, indicated that the AD model provides an excellent approximation of the simulation of lumped breakthrough curves for the adsorption of Cr(III) by lechuguilla biomass. Therefore, the model can be used for design purposes to predict the effect of varying operational conditions.     

Effects of dissolved organic matter from the rhizosphere of the hyperaccumulator Sedum alfredii on sorption of zinc and cadmium by different soils

Pot experiments were conducted to investigate the changes of the dissolved organic matter (DOM) in the rhizosphere of hyperaccumulating ecotype (HE) and non-hyperaccumulating ecotype (NHE) of Sedum alfredii and its effects on Zn and Cd sorption by soils. After planted with HE, soil pH in the rhizosphere reduced by 0.5-0.6 units which is consistent with the increase of DOM. The hydrophilic fractions (51%) in DOM from the rhizosphere of HE (HE-DOM) was much greater than NHE-DOM (35%). In the presence of HE-DOM, Zn and Cd sorption capacity decreased markedly in the following order: calcareous clay loam > neutral clay loam > acidic silty clay. The sorption isotherms could be well described by the Freundlich equation (R² > 0.95), and the partition coefficient (K) in the presence of HE-DOM was decreased by 30.7-68.8% for Zn and 20.3-59.2% for Cd, as compared to NHE-DOM. An increase in HE-DOM concentration significantly reduced the sorption and increased the desorption of Zn and Cd by three soils. DOM derived from the rhizosphere of the hyperaccumulating ecotype of S. alfredii could significantly reduce metal sorption and increase its mobility through the formation of soluble DOM-metal complexes.     

Removal of Cu(II) and Pb(II) by Pithophora oedogonia: sorption, desorption and repeated use of the biomass

Maximum sorption of Cu(II) and Pb(II) by dried filamentous green alga Pithophora oedogonia occurred at pH 4.5 and 5.0, respectively. Chemical pretreatment could not appreciably enhance the metal sorption ability of the biomass. HCl and EDTA desorbed 92-96% of the sorbed metal from the metal-loaded biomass. Sorption and desorption of both the test metals were very rapid attaining an equilibrium within 15 min. The time course data of both the processes fitted well to the pseudo-first and the pseudo-second-order Lagergren kinetic models with r2> or =0.979. The isotherm equilibrium of Cu(II) and Pb(II) followed the Redlich-Peterson and Sips model very well with r2> or =0.991. The sorption of Cu(II) and Pb(II) at varying biomass doses could be well defined by linear and hyperbolic decrease, respectively. The regenerated biomass of Pithophora has better reusability for Pb(II) than for Cu(II). A good mechanical strength of Pithophora biomass was apparent as only 10-15% loss of biomass occurred at the end of the fifth cycle.     

Influence of the deposition conditions on the crystallographic structure and the GaAs refraction index

An experimental study of the influence of deposition conditions of GaAs thin films growth, by radio frequency sputtering method, on the structure and the refraction index has been performed. The X-ray diffraction and spectrophotometer results, with different deposition conditions, are reported.The refraction index depends on the structure, which also depends on four deposition parameters, namely, the self-bias voltage, V_p, the argon pressure, P_Ar, the target-to-substrate distance, d, and the substrate temperature, T_s. Hence, it has been observed that, the index refraction of the films decreases with V_p and T_s and increases essentially with P_Ar.     

Chemical structure and electrical properties of sputtered HfO2 films on Si substrates annealed by rapid thermal annealing

The chemical structure and electrical properties of HfO₂ thin film grown by rf reactive magnetron sputtering after rapid thermal annealing (RTA) were investigated. The chemical composition of HfO₂ films and interfacial chemical structure of HfO₂/Si in relation to the RTA process were examined by X-ray photoelectron spectroscopy. Hf 4f and O 1s core level spectra suggest that the as-deposited HfO₂ film is nonstoichiometric and the peaks shift towards lower binding energy after RTA. The Hf-Si bonds at the HfO₂/Si interface can be broken after RTA to form Hf-Si-O bonds. The electrical characteristics of HfO₂ films were determined by capacitance-voltage (C-V) and current density-voltage (J-V) measurements. The results showed that the density of fixed charge and leakage current density of HfO₂ film were decreased after the RTA process in N₂ atmosphere.     

Microstructure effect on mechanical properties of in situ synthesized titanium matrix composites reinforced with TiB and La2O3

High temperature titanium matrix composites (TMCs) with different volume fraction of reinforcements were insitu synthesized by casting and hot forging. An effort was made to investigate the mechanical properties as a function of the microstructure of composites. Tensile tests were performed at room temperature, 600 °C, 650 °C and 700 °C respectively. Creep behavior at 650 °C was characterized in the stress range of 200-300 MPa. Results indicated that the composite with 2.11 vol.% reinforcements had the highest tensile strength and lowest steady state creep rate. Morphology of TiB whiskers was critical to mechanical properties of TMCs. TiB whiskers fracture and debonding acted as the dominant failure modes.     

Effects of dissolved low molecular weight organic acids on oxidation of ferrous iron by Acidithiobacillus ferrooxidans

A few researchers have reported on work concerning bioleaching of heavy-metal-contaminated soil using Acidithiobacillus ferrooxidans, since this acidophile is sensitive to dissolved low molecular weight (LMW) organic acids. Iron oxidation by A. ferrooxidans R2 as well as growth on ferrous iron was inhibited by a variety of dissolved LMW organic acids. Growth experiments with ferrous iron as an oxidant showed that the inhibition capability sequence was formic acid>acetic acid>propionic acid>oxalic acid>malic acid>citric acid. The concentrations that R2 might tolerate were formic acid 0.1mmolL(-1) (2mmolkg(-1)soil), acetic and propionic acids 0.4mmolL(-1) (8mmolkg(-1)soil), oxalic acid 2.0mmolL(-1) (40mmolkg(-1)soil), malic acid 20mmolL(-1) (400mmolkg(-1)soil), citric acid 40mmolL(-1) (800mmolkg(-1)soil), respectively. Although R2 was sensitive to organic acids, the concentrations of LMW organic acids in the contaminated soils were rather lower than the tolerable levels. Hence, it is feasible that R2 might be used for bioleaching of soils contaminated with metals or metals coupled with organic compounds because of the higher concentrations of LMW organic acids to which R2 is tolerant.     

Biosorption of zinc from aqueous solution using Azadirachta indica bark: equilibrium and kinetic studies

The removal of zinc ions from aqueous solutions on the biomass of Azadirachta indica bark has been studied by using batch adsorption technique. The biosorption studies were determined as a function of contact time, pH, initial metal ion concentration, average biosorbent size and biosorbent dosage. The equilibrium metal uptake was increased and percentage biosorption was decreased with an increase in the initial concentration and particle size of biosorbent. The maximum zinc biosorption occurred at pH 6 and percentage biosorption increases with increase in the biosorbent dosage. Experimental data obtained were tested with the adsorption models like Langmuir, Freundlich and Redlich-Peterson isotherms. Biosorption isothermal data were well interpreted by Langmuir model with maximum biosorption capacity of 33.49mg/g of zinc ions on A. indica bark biomass and kinetic data were properly fitted with the pseudo-second-order kinetic model.     

On-site determination of tin in geological and water samples using novel organic reagent with iodide

A new, simple and sensitive method for spectrophotometric determination of tin (IV) with iodide and amide is described. The Sn(IV)-I(-) complex is extracted with chloroform solution of amide (N-phenylacetamide, N-alkylacetamide, alkyl=butyl, phenyl, hexyl and octyl group) in the strong sulphuric acid solution. Among five amides studied, N-octylacetamide (OAA) has been selected as it yielded best sensitivity. The apparent (at twofold preconcentration) molar absorptivity with respect to tin is (2.40)x10(5)Lmol(-1)cm(-1) at lambda(max), 410nm. The detection limit of the method is 4microgL(-1) Sn. The method is free from interferences of common ions that are normally associated with Sn. The method is highly sensitive and found to be applicable for the rapid determination of tin in water samples at micro-gram levels.