Sorption and desorption of mercury(II) in saline and alkaline soils of Bahía Blanca, Argentina

The objective of this work was to study sorption–desorption and/or precipitation–dissolution processes of Hg(II) compounds considering an eventual contact of soils with Hg-bearing wastes. In addition, this study contributes new data about Hg(II) chemistry in alkaline systems. Saline and alkaline soils with low organic matter (<1 %) and high clay content (60–70 %) were obtained near a chlor-alkali plant. Batch techniques were used to perform the experiments using 0.1 M NaNO₃ solutions. Total Hg(II) concentrations ranged from 6.2 × 10^?8 to 6.3 × 10^?3 M. Sorption of Hg(II) was evaluated at two concentration ranges: (a) 6.2 × 10^?8 to 1.1 × 10^?4 M, and (b) 6.4 × 10^?4 to 6.3 × 10^?3 M. At low Hg(II) concentrations, adsorption occurred with a maximum sorption capacity ranging from 4 to 5 mmol/kg. At high Hg(II) concentrations, sorption–precipitation reactions occurred and maximum sorption capacity ranged from 17 to 31 mmol/kg. The distribution of Hg(II) hydrolysis products showed that Hg(OH)₂ was the predominant species under soil conditions. According to sorption experiments, X-ray diffraction and chemical speciation modelling, the presence of Hg(OH)₂ in the interlayer of the interstratified clay minerals can be proposed. Hg(OH)₂ was partially desorbed by repeated equilibrations in 0.1 M NaNO₃ solution. Desorption ranged from 0.1 to 0.9 mmol/kg for soils treated with 5.8 × 10^?5 M Hg(II), whereas 2.1–3.8 mmol/kg was desorbed from soils treated with 6.3 × 10^?3 M Hg(II). Formation of soluble Hg(II) complexes was limited by low organic matter content, whereas neutral Hg(OH)₂ was retained by adsorption on clay mineral surfaces.     

Groundwater balance in the Khor Arbaat basin, Red Sea State, eastern Sudan

The Khor Arbaat basin is the main source of potable water supply for the more than 750,000 inhabitants of Port Sudan, eastern Sudan. The variation in hydraulic conductivity and storage capacity is due to the heterogeneity of the sediments, which range from clay and silt to gravely sand and boulders. The water table rises during the summer and winter rainy seasons; it reaches its lowest level in the dry season. The storage capacity of the Khor Arbaat aquifer is estimated to be 21.75?×?10⁶ m³. The annual recharge through the infiltration of flood water is about 1.93?×?10⁶ m³. The groundwater recharge, calculated as underground inflow at the ‘upper gate’, is 1.33?×?10⁵ m³/year. The total annual groundwater recharge is 2.06?×?10⁶ m³. The annual discharge through underground outflow at the ‘lower gate’ (through which groundwater flows onto the coastal plain) is 3.29?×?10⁵ m³/year. Groundwater discharge due to pumping from Khor Arbaat basin is 4.38?×?10⁶ m³/year on average. The total annual groundwater discharge is about 4.7?×?10⁶ m³. A deficit of 2.6?×?10⁶ m³/year is calculated. Although the total annual discharge is twice the estimated annual recharge, additional groundwater flow from the fractured basement probably balances the annual groundwater budget since no decline is observed in the piezometric levels.     

Strain Rate Dependency of Coarse Crystal Marble Under Uniaxial Compression: Strength,Deformation and Strain Energy

Strain rate during testing, uniaxial or triaxial, has important influence on the measured mechanical properties of rocks. Uniaxial compression tests were performed at nine pre-specified static-to-quasistatic strain rates (ranging from 1 × 10^?5 to 1 × 10^?1 s^?1) on coarse crystal marble. The aim is to gain deep insight into the influence of strain rate on characteristic stresses, deformation properties and conversion of strain energy of such rock. It is found that the strain rate of 5 × 10^?3 s^?1 is the threshold to delineate the failure modes the tested coarse marble behaves in. At a strain rate less than this threshold, single-plane shear and conjugate X-shaped shear are the main failure modes, while beyond this threshold, extensile and splitting failures are dominant. The stress for crack initiation, the critical stress for dilation, the peak stress, and Young’s modulus are all found to increase with strain rate, with an exception that the above stresses and modulus appear relatively low compared to the strain rate in the range of between 1 × 10^?4 and 5 × 10^?3 s^?1. The pre-peak absorbed strain energy, damage strain energy and elastic strain energy are found to increase with strain rate. In addition, the elastic strain energy stored before peak point favors brittle failure of the specimen, as the more stored elastic energy in the specimen, the stronger the fragmenting.     

Crystal structure, Raman and FTIR spectroscopy, and equations of state of OH-bearing MgSiO3 akimotoite

MgSiO₃ akimotoite is stable relative to majorite-garnet under low-temperature geotherms within steeply or rapidly subducting slabs. Two compositions of Mg–akimotoite were synthesized under similar conditions: Z674 (containing about 550 ppm wt H₂O) was synthesized at 22 GPa and 1,500 °C and SH1101 (nominally anhydrous) was synthesized at 22 GPa and 1,250 °C. Crystal structures of both samples differ significantly from previous studies to give slightly smaller Si sites and larger Mg sites. The bulk thermal expansion coefficients of Z674 are (153–839 K) of a ₁ = 20(3) × 10^?9 K^?2 and a ₀ = 17(2) × 10^?6 K^?1, with an average of α ₀ = 27.1(6) × 10^?6 K^?1. Compressibility at ambient temperature of Z674 was measured up to 34.6 GPa at Sector 13 (GSECARS) at Advanced Photon Source Argonne National Laboratory. The second-order Birch–Murnaghan equation of state (BM2 EoS) fitting yields: V ₀ = 263.7(2) Å³, K _T0 = 217(3) GPa (K′ fixed at 4). The anisotropies of axial thermal expansivities and compressibilities are similar: α _a  = 8.2(3) and α _c  = 10.68(9) (10^?6 K^?1); β _a  = 11.4(3) and β _c  = 15.9(3) (10^?4 GPa). Hydration increases both the bulk thermal expansivity and compressibility, but decreases the anisotropy of structural expansion and compression. Complementary Raman and Fourier transform infrared (FTIR) spectroscopy shows multiple structural hydration sites. Low-temperature and high-pressure FTIR spectroscopy (15–300 K and 0–28 GPa) confirms that the multiple sites are structurally unique, with zero-pressure intrinsic anharmonic mode parameters between ?1.02 × 10^?5 and +1.7 × 10^?5 K^?1, indicating both weak hydrogen bonds (O–H···O) and strong OH bonding due to long O···O distances.     

Methoxychlor bioremediation by defined consortium of environmental Streptomyces strains

Methoxychlor is an organochlorine pesticide used worldwide against several insect pests, resulting in human exposure. This pesticide mimics endocrine hormone functions, interfering with normal endocrine activity in humans and wildlife. For this reason, it is imperative to develop methods to remove this pesticide from the environment, and though, bioremediation using microorganisms results as an excellent strategy. Five Streptomyces spp. strains previously isolated from organochlorine-polluted sites and capable to grow and remove methoxychlor were combined as different mixed cultures to increase methoxychlor removal. From the 39 consortia tested, one consortium (Streptomyces spp. A6, A12, A14, M7) was selected because of its high pesticide removal and specific dechlorinase activity to be assayed on slurry and soil systems. This consortium showed higher biomass values (8.3 × 10⁶ ± 5.7 × 10⁵ CFU mL^?1) and methoxychlor removal (56.2 ± 2.3 %) on enriched slurry than in non-enriched slurry (7.3 × 10⁵ ± 1.2 × 10⁵ CFU mL^?1 and 45.6 ± 7.4 % of pesticide removal). In soil systems, Streptomyces consortium showed higher growth (1.0 × 10¹¹ ± 5.0 × 10¹⁰ CFU g^?1) than in enriched slurry, although differences in methoxychlor removal between both culture conditions were not statistically significant. Therefore, the selected Streptomyces consortium may be suitable for the development of in situ (soil) and ex situ (slurry bioreactor) bioremediation methods because of their potential to remove methoxychlor from different systems.     

Nanoscale zero-valent iron flakes for groundwater treatment

Even today the remediation of organic contaminant source zones poses significant technical and economic challenges. Nanoscale zero-valent iron (NZVI) injections have proved to be a promising approach especially for source zone treatment. We present the development and the characterization of a new kind of NZVI with several advantages on the basis of laboratory experiments, model simulations and a field test. The developed NZVI particles are manufactured by milling, consist of 85 % Fe(0) and exhibit a flake-like shape with a thickness of <100 nm. The mass normalized perchloroethylene (PCE) dechlorination rate constant was 4.1 × 10^?3 L/g h compared to 4.0 × 10^?4 L/g h for a commercially available reference product. A transport distance of at least 190 cm in quartz sand with a grain size of 0.2–0.8 mm and Fe(0) concentrations between 6 and 160 g/kg (sand) were achieved without significant indications of clogging. The particles showed only a low acute toxicity and had no longterm inhibitory effects on dechlorinating microorganisms. During a field test 280 kg of the iron flakes was injected to a depth of 10–12 m into quaternary sand layers with hydraulic conductivities ranging between 10^?4 and 10^?5 m/s. Fe(0) concentrations of 1 g/kg (sand) or more [up to 100 g/kg (sand)] were achieved in 80 % of the targeted area. The iron flakes have so far remained reactive for more than 1 year and caused a PCE concentration decrease from 20.000–30.000 to 100–200 µg/L. Integration of particle transport processes into the OpenGeoSys model code proved suitable for site-specific 3D prediction and optimization of iron flake injections.     

Analysis of low-flow characteristics for catchments in Dongjiang Basin, China

Low-flow indices have been determined from long-term daily streamflow data for 13 catchments in Dongjiang Basin in southern China. The Brutsaert-Nieber method was applied to estimate catchment-scale effective groundwater parameters; representative values were 4.5?×?10^?4 m² s^?1 for the hydraulic diffusivity; 3.19?×?10^?5 m² s^?1/2 for the hydraulic desorptivity; 2.27?×?10^?4 m s^?1 for the hydraulic conductivity; and 0.2617 for the drainable porosity. The response constants correlate well with the total stream length and catchment area. Solutions of the linearised Boussinesq equation were used to guide the development of regional multivariate regression models for estimating low-flow indices from the catchment-scale effective parameters. Results showed that these catchments exhibit similar low-flow characteristics. The 7-day lowest average streamflows with return periods of 10 and 2 years (7Q10 and 7Q2) are highly correlated with the catchment-scale response constants. The low-flow ratio Q95/Q50 (ratio of daily streamflow exceeded 95 and 50% of the time, respectively) varied between 0.3 and 0.5, indicating a high proportion of groundwater in the streamflow. The advantage of the regional regression model is its conceptual basis and use of the catchment-scale effective parameters. The method has the potential to be applied to ungauged catchments for estimating low-flow statistics from stream length and catchment area.     

Petrophysical properties, composition and deterioration of the Calatorao biogenic stone: case of the sculptures masonry of the Valley of the Fallen (Madrid, Spain)

The huge sculptures placed outdoors in the Valley of the Fallen Memorial Park (El Escorial, Madrid) made with blocks of Black-Limestone from Calatorao-Zaragoza, Spain (BLCZ) and disposed on a concrete core exhibit weathering traces, flaking, saline efflorescence and falling fragments, currently represent a danger for visitors. Frost action is important in the Valley of the Fallen by the large number of freeze–thaw cycles produced during Sculptures‘live under a temperate Mediterranean climate with severe seasonality. The formation of fissures facilitates the water transport within the rock and the salt- and ice-induced deterioration. Temperate climates with frequent freezing and thawing cycles can be the most effective drivers of the visible physical weathering. In order to propose a suitable weathering model, collected black-limestones from sculptures and Calatorao quarries were analyzed by optical microscopy, environmental scanning electron microscopy with energy dispersive spectrometry (ESEM-EDS), inductively coupled mass spectrometry (ICP-MS) and X-ray diffraction. Mercury intrusion porosimetry (MIP), nitrogen absorption and helium pycnometry techniques were used for pore analyses of the BLCZ micro-blocks (10 × 10 × 10 cm) described in terms of pore size distribution, pore volume and specific surface area. The appreciable amount of organic matter was isolated by solvent extraction, acid treatment, flotation and perborate degradation followed by Gas Chromatography–Mass Spectrometry (GC–MS), Analytical Pyrolysis (Py-GC/MS), Fourier Transformed Infrared Spectroscopy and Raman techniques. Both weathered and fresh BLCZ samples contained more than 90 % calcite shells with circa 10 % of pyrite (fresh samples) or iron hydroxides (weathered samples), quartz grains, claystone and fossil organic matter consisting of a condensed matrix with polyalkyl chains and polycyclic methoxyl-lacking aromatic structures. The petrophysical analyses revealed volumes of pores, sized <0.025 μm obtained by N₂ adsorption, of 3.18 × 10^?3 cm³ g^?1 while the measured porosity by MIP in the pore range from 0.005 to 200 μm was 3.30 × 10^?3 cm³ g^?1. These data could be explained by the existence of clay minerals and organic matter in the pore system less than 50 nm of diameter. Concerning BLCZ deterioration it was found that the porous framework of BLCZ was filled with sulphates formed from artificial cement observed in the sculptures inside trough a testing hole and from its intrinsic pyrite. The results suggested that although biological processes were not major agents in rock deterioration, there was also weak compatibility between sculptures‘constituents, (limestone, concrete and oxidized iron clamps) which under, continental Mediterranean conditions, were continuously releasing weathering compounds accelerating disruption of the cut-stone sculptures.     

Characterization of the shallow groundwater system in an alpine watershed: Handcart Gulch,Colorado, USA

Water-table elevation measurements and aquifer parameter estimates are rare in alpine settings because few wells exist in these environments. Alpine groundwater systems may be a primary source of recharge to regional groundwater flow systems. Handcart Gulch is an alpine watershed in Colorado, USA comprised of highly fractured Proterozoic metamorphic and igneous rocks with wells completed to various depths. Primary study objectives include determining hydrologic properties of shallow bedrock and surficial materials, developing a watershed water budget, and testing the consistency of measured hydrologic properties and water budget by constructing a simple model incorporating groundwater and surface water for water year 2005. Water enters the study area as precipitation and exits as discharge in the trunk stream or potential recharge for the deeper aquifer. Surficial infiltration rates ranged from 0.1–6.2×10^?5 m/s. Discharge was estimated at 1.28×10^?3 km³. Numerical modeling analysis of single-well aquifer tests predicted lower specific storage in crystalline bedrock than in ferricrete and colluvial material (6.7×10^?5–2.0×10^?3 l/m). Hydraulic conductivity in crystalline bedrock was significantly lower than in colluvial and alluvial material (4.3×10^?9–2.0×10^?4 m/s). Water budget results suggest that during normal precipitation and temperatures water is available to recharge the deeper groundwater flow system.     

Variability in Concentrations and Fluxes of Methane in the Indian Estuaries

In order to examine the fluxes of methane (CH₄) from the Indian estuaries, measurements were carried out by collecting samples from 26 estuaries along the Indian coast during high discharge (wet) and low water discharge (dry) periods. The CH₄ concentrations in the estuaries located along the west coast of India were significantly higher (113?±?40 nM) compared to the east coast of India (27?±?6 nM) during wet and dry periods (88?±?15 and 63?±?12 nM, respectively). Supersaturation of CH₄ was observed in the Indian estuaries during both periods ((0.18 to 22.3?×?10³ %). The concentrations of CH₄ showed inverse relation with salinity indicating that freshwater is a significant source. Spatial variations in CH₄ saturation were associated with the organic matter load suggesting that its decomposition may be another source in the Indian estuaries. Fluxes of CH₄ ranged from 0.01 to 298 μmol m^?2 day^?1 (mean 13.4?±?5 μmol m^?2 day^?1) which is ~30 times lower compared to European estuaries (414 μmol m^?2 day^?1). The annual emission from Indian estuaries, including Pulicat and Adyar, amounted to 0.39?×?10¹⁰ g CH₄?year^?1 with the surface area of 0.027?×?10⁶ km² which is significantly lower than that in European estuaries (2.7?±?6.8?×?10¹⁰ g CH₄?year^?1 with the surface area of 0.03?×?10⁶ km²). This study suggests that Indian estuaries are a weak source for atmospheric CH₄ than European estuaries and such low fluxes were attributed to low residence time of water and low decomposition of organic matter within the estuary. The CH₄ fluxes from the Indian estuaries are higher than those from Indian mangroves (0.01?×?10¹⁰ g CH₄?year^?1) but lower than those from Indian inland waters (210?×?10¹⁰ g CH₄?year^?1).     

Study of the water saving potential of an irrigation area based on a remote sensing evapotranspiration model

To estimate the water saving potential of an irrigation area and create a scientific water saving plan, the irrigation water use efficiency and water productivity of the Hulanhe irrigation area for 2007–2014 were calculated, and the water saving potentials of different water saving plans were determined from the perspectives of engineering and crop water saving. The results showed that the evapotranspiration calculated from the surface energy balance algorithm for land model (SEBAL) agreed well with the measured results. The irrigation water use efficiency in the Hulanhe irrigation area was positively correlated with precipitation of irrigated land and was negatively correlated with the net irrigation water volume. The engineering water saving potential ranges for periods of 5, 8, 11, and 15 years were (1.702?×?10⁸, 5.103?×?10⁸) m³, (1.783?×?10⁸, 5.184?×?10⁸) m³, (1.865?×?10⁸, 5.266?×?10⁸) m³, and (2.301?×?10⁸, 5.702?×?10⁸) m³, respectively, and the water saving potential increased year over year. Low amounts of precipitation of irrigated land corresponded with small amounts of net irrigation water and greater water saving potential. Based on the cumulative frequency of the water productivity calculated for the Hulanhe irrigation area from 2007 to 2014, the target water productivity for short (50% of the multi-year average cumulative water productivity) and long (70% of the multi-year average cumulative water productivity) terms were 1.03 kg/m³ and 1.22 kg/m³, respectively, and the cumulative crop water saving potentials for short and long terms were 1.18?×?10⁸ and 2.74?×?10⁸ m³, respectively. These results provided a theoretical reference for creating water saving plans for irrigation areas.     

Zero-valent iron/persulfate(Fe0/PS) oxidation acetaminophen in water

Zero-valent iron (Fe⁰), as an alternative iron source, was evaluated to activate persulfate (PS) to degrade acetaminophen (APAP), a representative pharmaceutically active compound in water. Effects of key factors in the so-called Fe⁰/PS process, including Fe⁰ dosage, initial pH, temperatures and chelating agents, were studied. Under all the conditions tested, the APAP degradation followed a pseudo-first-order kinetics pattern. The degradation efficiency of APAP was highest when the Fe⁰ to PS molar ratio increased to 1:1, and the degradation rate constant and removal were 23.19 × 10^?3 min^?1 and 93.19 %, respectively. Comparing with Fe²⁺, Fe⁰ served as an alternative iron source that can gradually release Fe²⁺ into water, thereby consistently activating PS to produce sulfate radicals. The Fe⁰/PS system was effective in a broader pH range from 3 to 8.5. Heat could facilitate production of sulfate radicals and enhance the APAP degradation in the Fe⁰/PS system. High reaction temperature also improved the Fe²⁺/PS oxidation of APAP. Finally, sodium citrate (a chelating agent) at an appropriate concentration could improve the APAP degradation rate in the Fe²⁺/PS and Fe⁰/PS system. The optimal molar ratio of Fe⁰ to citrate depended on solution pH. Our results demonstrated that Fe⁰ was an alternative iron source to activate PS to degrade APAP in water.     

Estimating the hydraulic properties of an aquitard from in situ pore pressure measurements

A workflow is described to estimate specific storage (S _s) and hydraulic conductivity (K) from a profile of vibrating wire piezometers embedded into a regional aquitard in Australia. The loading efficiency, compressibility and S _s were estimated from pore pressure response to atmospheric pressure changes, and K was estimated from the earliest part of the measurement record following grouting. Results indicate that S _s and K were, respectively, 8.8?×?10^?6 to 1.2?×?10^?5 m^?1 and 2?×?10^?12 m s^?1 for a claystone/siltstone, and 4.3?×?10^?6 to 9.6?×?10^?6 m^?1 and 1?×?10^?12 to 5?×?10^?12 m s^?1 for a thick mudstone. K estimates from the pore pressure response are within one order of magnitude when compared to direct measurement in a laboratory and inverse modelled flux rates determined from natural tracer profiles. Further analysis of the evolution and longevity of the properties of borehole grout (e.g. thermal and chemical effects) may help refine the estimation of formation hydraulic properties using this workflow. However, the convergence of K values illustrates the benefit of multiple lines of evidence to support aquitard characterization. An additional benefit of in situ pore pressure measurement is the generation of long-term data to constrain groundwater flow models, which provides a link between laboratory scale data and the formation scale.     

Effect of Water and Leachate on Hydraulic Behavior of Compacted Bentonite,Calcareous Sand and Tuff Mixtures for Use as Landfill Liners

Compacted soil–bentonite liners, consisting of a sandy soil mixed with bentonite as backfill, are used extensively as engineered barriers for contaminant containment. This paper studies the valorization of local materials containing calcareous sand, tuff obtained from Laghouat region (in the South Algeria), to associate with bentonite in order to improve their hydraulic characteristics for use as landfill liner material. Firstly, a geotechnical characterization of mixtures chooses from a fixed percentage to 10% bentonite and different percentages of calcareous sand and tuff so that they are complementary to 90% by not 10%. Thereafter, the determination of saturated hydraulic conductivity at falling-head permeability (K_v) and oedometer (K_id, indirect Measure) tests of all compacted mixtures at Optimum Normal Proctor have been carried out using both permeates by tap water and a landfill leachate in order to simulate long-term conditions. The results showed that the saturated hydraulic conductivity of tap water is relatively lower than the one saturated by leachate in the falling-head test, unlike the oedometer test. The B₁₀CS₂₀T₇₀ mixture has satisfied the hydraulic conductivity criterion of bottom barriers (i.e. water permeated: k_v20° = 1.97 × 10^?9 and k_id from 7 × 10^?9 to 1.83 × 10^?10 < 10^?9m/s; leachate permeated: k_v20° = 2.91 × 10^?9 and k_id from 7 × 10^?9 at 1.44 × 10^?10 < 10^?9 m/s). Finally, a comparison between direct measurements of the saturated hydraulic conductivity by triaxial (K_d) test and oedometer test (K_id) in the range of effective stress applied 100–800 kPa led to propose equations of correlations between these two methods. In conclusion, adopted formulation B₁₀CS₂₀T₇₀ perfectly meets the regulatory requirements in force and constitutes an economic product based on available local materials for engineers barriers.     

Non-woven polypropylene fabric modified with carbon nanotubes and decorated with nanoakaganeite for arsenite removal

Due to its harmful impact on human health, the presence of heavy metals, metalloids and other toxic pollutants in drinking or irrigation water is a major concern. Recent studies have proved that nanosized adsorbents are significantly more effective than their microsized counterparts. Particular attention has been given to nanocomposites with nanoadsorbents embedded in matrixes that could provide stability to the material and contribute to eliminating problems that may appear when using conventional granular systems. This study presents the preparation of a novel hybrid filter from a commercially available polypropylene (PP) non-woven fabric matrix modified with multiwall carbon nanotubes (MWCNT) and iron oxy(hydroxide) nanoparticles, and its use in the removal of As(III). A Box–Behnken statistical experimental design has been chosen to explore relevant variables affecting the filter performance: (1) As(III) concentration, (2) pH and (3) sorbent dose. From an As(III) concentration of 10 mg L^?1, at pH 6.5 and with a sorbent dose of 5 g L^?1, the PP filter modified with MWCNT removes 10% of the initial metalloid concentration, reaching a capacity of 0.27 mg g^?1. After modification with iron oxy(hydroxide), the performance of the material is largely enhanced. The filter, under the same conditions, removes 90% of the initial As(III) concentration, reaching a capacity almost tenfold higher (2.54 mg g^?1). This work demonstrates that the developed hybrid filter is effective toward the removal of As(III) in a wide range of pHs. A cubic regression model to compute the removal of the filter as a function of pH and sorbent dose is provided.     

Silica gel/gold nanoparticles/(NS)<Subscript>2</Subscript> ligand nanoporous platform-modified ionic liquid carbon paste electrode for potentiometric ultratrace assessment of Ag(I)

A novel ionic liquid carbon paste electrode has been developed using sol–gel/Au nanoparticle (SGAN) involving (NS)₂ compound of N,N′-di-(cyclopentadienecarbaldehyde)-1, 2-di (o-aminophenylthio) ethane (CCAE) as an appropriate neutral ion-carrier for ultrahigh-sensitive potentiometric determination of Ag(I). Colloidal gold nanoparticles (AuNPs) also well dispersed self-assembly into the 3-(mercaptopropyl)-trimethoxysilane (MPTS)-derived sol–gel network through Au–S covalent bond engendering continuous and super-conductive nanoporous three-dimensional array. The room-temperature ionic liquid, 1-n-butyl-3-methylimidazolium tetrafluoroborate (BMIM.PF₆), was applied as a super-conductive pasting agent (binder). The SGAN/CCAE/IL-CPE exhibited a significantly enhanced sensitivity and preferential selectivity toward Ag(I) over a wide concentration range of 2.4 × 10^?9 to 2.2 × 10^?2 mol L^?1 (R ² = 0.9996) with a lower limit of detection of 7.9 × 10^?10 M and a Nernstian slope of 58.5 (±0.3) mV decade^?1. The electrode has a short response time of ～5 s and long-time durability of about 2 months without any considerable divergence in potentials. Moreover, the potentiometric examinations could be carried out within the wide pH range of 3.5–9.5. Eventually, the practical utility of the proposed Ag(I)-sensor was evaluated by volumetric titration of AgNO₃ solution by sodium chloride and recovery of silver content in some real samples using flame atomic absorption spectroscopy as a confident reference.     

Adsorption of lead, ethylenediaminetetraacetic acid and lead-ethylenediaminetetraacetic acid complex onto granular activated carbon

This study investigated simultaneous removal of lead and ethylenediaminetetraacetic acid from synthetic wastewater samples using granular activated carbon adsorption. Data from a 1 × 10^?4 M lead-ethylenediaminetetraacetic acid adsorption isotherm study fitted well to Freundlich isotherm. Furthermore, for the pH-dependent 1 × 10?4 M lead-ethylenediaminetetraacetic acid study both lead and ethylenediaminetetraacetic acid adsorptions increased reaching values of 82 % and 93 % respectively at pH 5.8. However, a further increase in pH resulted in decreasing but near equal lead and ethylenediaminetetraacetic acid removals. Results for the 2 × ^10?4 M lead-ethylenediaminetetraacetic acid system showed a behavior that was qualitatively similar to the 1 × ^10?4 M lead-ethylenediaminetetraacetic acid findings. However, the 1×10^?3 M lead-ethylenediaminetetraacetic acid study showed only a decreasing adsorption trend. An increasing-decreasing type lead/ethylenediaminetetraacetic acid adsorption behavior was also noted for the 1× 10^?4 M lead/2 × 10^?4 M ethylenediaminetetraacetic acid system. Nevertheless for the 2×10^?4 M lead/1×10^?4 M ethylenediaminetetraacetic acid system, lead removal at increased pH was comparatively higher. Furthermore, results from a continuous column study completed at 1 × 10^?4 M lead and 0.75 × 10^?4 M ethylenediaminetetraacetic acid showed high saturation times both for lead and ethylenediaminetetraacetic acid. Results from the present work show that a notable removal of aqueous phase lead and ethylenediaminetetraacetic acid could be achieved using activated carbon adsorption. The details related to the effect of pH and pollutants’ concentration on the overall adsorption efficiency, as reported in the present work, would be of much use for an effective carbon adsorption process design for the treatment of respective wastewaters.     

Carbon Dioxide and Methane Emissions from Mangrove-Associated Waters of the Andaman Islands,Bay of Bengal

We estimated CO₂ and CH₄ emissions from mangrove-associated waters of the Andaman Islands by sampling hourly over 24 h in two tidal mangrove creeks (Wright Myo; Kalighat) and during transects in contiguous shallow inshore waters, immediately following the northeast monsoons (dry season) and during the peak of the southwest monsoons (wet season) of 2005 and 2006. Tidal height correlated positively with dissolved O₂ and negatively with pCO₂, CH₄, total alkalinity (TAlk) and dissolved inorganic carbon (DIC), and pCO₂ and CH₄ were always highly supersaturated (330–1,627 % CO₂; 339–26,930 % CH₄). These data are consistent with a tidal pumping response to hydrostatic pressure change. There were no seasonal trends in dissolved CH₄ but pCO₂ was around twice as high during the 2005 wet season than at other times, in both the tidal surveys and the inshore transects. Fourfold higher turbidity during the wet season is consistent with elevated net benthic and/or water column heterotrophy via enhanced organic matter inputs from adjacent mangrove forest and/or the flushing of CO₂-enriched soil waters, which may explain these CO₂ data. TAlk/DIC relationships in the tidally pumped waters were most consistent with a diagenetic origin of CO₂ primarily via sulphate reduction, with additional inputs via aerobic respiration. A decrease with salinity for pCO₂, CH₄, TAlk and DIC during the inshore transects reflected offshore transport of tidally pumped waters. Estimated mean tidal creek emissions were ～23–173 mmol m^?2 day^?1 CO₂ and ～0.11–0.47 mmol m^?2 day^?1 CH₄. The CO₂ emissions are typical of mangrove-associated waters globally, while the CH₄ emissions fall at the low end of the published range. Scaling to the creek open water area (2,700 km²) gave total annual creek water emissions ～3.6–9.2?×?10¹⁰ mol CO₂ and 3.7–34?×?10⁷ mol CH₄. We estimated emissions from contiguous inshore waters at ～1.5?×?10¹¹ mol CO₂?year^?1 and 2.6?×?10⁸ mol CH₄?year^?1, giving total emissions of ～1.9?×?10¹¹ mol CO₂?year^?1 and ～3.0?×?10⁸ mol CH₄?year^?1 from a total area of mangrove-influenced water of ～3?×?10⁴ km². Evaluating such emissions in a range of mangrove environments is important to resolving the greenhouse gas balance of mangrove ecosystems globally. Future such studies should be integral to wider quantitative process studies of the mangrove carbon balance.     

Cadmium (II)-selective electrode based on palm shell activated carbon modified with task-specific ionic liquid: kinetics and analytical applications

In this study, palm shell activated carbon modified with task-specific ionic liquid was used as a novel electrode component for the potentiometric determination of cadmium ions in water samples. The proposed potentiometric sensor has good operating characteristics, including relatively high selectivity towards the Cd (II) ion, a Nernstian response to Cd (II) ions in a working concentration range of 1.0 × 10^?9–1.0 × 10^?2 M, with a reasonable detection limit of 1 × 10^?10 M and a slope of 30.90 ± 1.0 mV/decade. No significant changes in electrode potential were observed when the pH was varied over the range of 4–9. A direct technique based on the use of ion-selective electrode potentiometry has been developed in our laboratory for the study of reaction kinetics and kinetic methods of analysis by continuous monitoring of the rate of production or consumption of an ion. The apparent adsorption rate constant was estimated assuming pseudo-second-order kinetics. Additionally, the proposed electrode has been successfully used for the determination of the cadmium content in real samples without a significant interaction from other cationic or anionic species.     

The effect of uncertainty on estimates of hurricane surge hazards

It is shown here that uncertainty can significantly affect estimated surge levels over a wide range of annual exceedance probabilities (AEPs). For AEPs in the range of 1 × 10^?2–5 × 10^?2 in the New Orleans area, estimated surge values with and without consideration of uncertainty differ by about 0.5–1.0 m. Similarly, suppression of natural variability, such as using a single value for Mississippi River discharge in surge simulations, rather than allowing the discharge to vary probabilistically, is shown to produce deviations up to 1 m for the 1 × 10^?2 AEP in locations within the mainline river levees in this area. It is also shown that uncertainty can play a critical role in the analysis of very low probability events in the AEP range 1 × 10^?4–1 × 10^?6. Such events are typically used in designs of structures with major societal impacts. It is shown here that, for this range of AEPs along the west coast of Florida, the neglect of uncertainty can under-predict design surge levels by about 20 % compared to estimated surge levels that include uncertainty.