Transport Through a Clay Barrier with the Contaminant Concentration Dependent Permeability

Transport of contaminants through clays is characterized by a very low dispersivity, but depends on the sensitivity of its intrinsic permeability to the contaminant's concentration. An additional constitutive relationship for a variable intrinsic permeability is thus adopted leading to a coupled system of equations for diffusive–advective transport in multicomponent liquid. A one-dimensional transport problem is solved using finite difference and Newton–Raphson procedure for nonlinear algebraic equations. The results indicate that although diffusion contributes to an increase of transport with respect to pure advection, the flux ultimately depends on end boundary conditions for concentration which, if low, may actually slow down the evolution of concentration and thus of permeability. Indeed, the advective component of flux may still remain secondary if the end portion of the layer remains unaffected by high concentrations. With no constraints on concentration at the bottom (zero concentration gradient boundary condition) and high concentration applied at the top, a significant shortening of the breakthrough time occurs.     

Attenuation lengths in organic materials

Measurements are reported for attenuation lengths in overlayers of guanine, poly(styrene), poly(methyl methacrylate) and poly(2‐vinylpyridine) in the energy range 700–1400 eV to evaluate the accuracy of theoretical computations and generic equations. The layers are deposited on gold, either by evaporation and condensation or by spin casting. Measurements are made by X‐ray photoelectron spectroscopy (XPS) for the substrate Au 4f, 4d and 4p peaks as well as the overlayer N 1s peak in guanine and poly(2‐vinylpyridine). These measurements all correlate with the theory of Tanuma, Powell and Penn, to an RMS deviation of 11%. Correlations with the predictions using the generic equation known as TPP‐2M exhibit a poorer RMS deviation of 20%. Use of an ‘average’ organic material for the inelastic mean free paths for the four materials also leads to a 20% RMS deviation. Additional data are also presented for Irganox 1010 that is used, increasingly, as a reference sample for secondary ion mass spectrometry. Comparisons for 5 materials with the Gries G1 formula gives an RMS deviation of 13%, but a small change to interpolate between Gries' classes of organic materials with H/C being around either 1 or 2, leads to a reduced RMS deviation of 10%. This final version, G1‐SS, requiring only the material density and chemical formula, is very simple to use for all organic materials where these data are known or can be estimated. © Crown copyright 2010. Reproduced with the permission of Her Majesty's Stationery Office. Published by John Wiley & Sons, Ltd.     

The relation between relaxed enthalpy and volume during physical aging

Several papers have recently presented results of measurements of physical aging by studying the behavior of glassy materials quenched from temperatures above their glass transition temperature T_g. The evolution of the aging process is usually followed by plotting the relaxed enthalpy versus the accompanying decrease in volume. Here, we focus on the slope of such plots, which are found to be similar to the inverse value of the isothermal compressibility close to T_g. An explanation of this empirical result is attempted in the frame of a model that interconnects the defect Gibbs energy with properties of the bulk material.     

An Investigation on the Concentration Efficiencies of Some Macroreticular and Ambersorb Resins Using Radio-Labelled Organic Contaminants Commonly Encountered in Water

Abstract

The extraction efficiencies of the three commercially available Ambersorb®, carbonaceous, polymeric resins, XE-340, XE-347 and XE-348 were evaluated for their use as sorbents for environmental pollutants using four model, radio-labelled water-borne organic contaminants. Their accumulation behaviour was compared with that of the thoroughly-studied Amberlite®, macroreticular XAD-2 (hydrophobic) and XAD-7 (hydrophilic) resins. These model compounds were desorbed from the resins using known volumes of commonly-used solvents to select the solvent for a particular resin(s). In this preliminary study, at <4 μg/L concentrations of the labelled compounds in aqueous solution (pH 5.78), the order of extraction efficiency of the resins was found to be XAD-2 > XAD-7 > XE-340?-347?-348 for organics. Several inherent impurities originally present in the carbonaceous resins were desorbed by solvents during elution. These resins therefore required exhaustive soxhlet purification prior to use. Most of the impurities were identified by gas chromatography/mass spectrometry.     

Photodegradation of Chlorinated Organic Wastes with n-TiO2 Promoted by P-CuO

A variety of chlorinated organic wastes were photodecomposed with p-CuO-modified TiO₂ particles (denoted CuO/TiO₂). Based on the photoactivity measured in oxygenated solutions containing sodium 2,2′-dichloropropionate, the photoactivity of TiO₂ is significantly enhanced with p-CuO loading; in the case with 0.4 wt% of CuO, the activity is increased by a facor of 4. Photochemical-TiO₂-slurry cell techniques and voltammetric characterizations suggest this CuO-promoted enhancement is likely to result from the acceleration of oxygen reduction at TiO₂ via Cu_IIO/Cu_I0. Long-term tests showed that these CuO/TiO₂ particles are photochemically robust; within 100-hours' continuous photolysis, insignificant loss in photoactivity was detected. However, increasing loading of p-CuO may jeopardize the photoactivity, due to the deterioration in the TiO₂ absorbability of UV irradiation.     

Energy generation by methanation of persistent wastes

A 15-L anaerobic fixed-film reactor (AFFR) was evaluated for treating a trade effluent containing inhibitory concentrations of persistent branched-chain fatty acids, namely 2-ethylhexanoic acid (2-EHA) and neopentanoic acid (NPA), at a total of 17,000 mg COD/L. The AFFR was packed with fire-expanded clay spheres, and start-up was accomplished in 60 d. The organic load was increased in steps from 1.1 to 8.5 g COD/L/d. Total COD, 2-EHA, and NPA removal efficiencies were maintained above 70, 98, and 75%, respectively. The reactor could recover from a shock load of 150% increase in organic load. Combined mechanisms of organic adsorption and biodegradation rendered the AFFR more stable with shock loads. Mathane gas produced from the process could be used for preheating the effluent.     

Copper Complexation with Soluble and Surface Freshwaters Ligands

Speciation of copper has been done using samples collected at different times of the year (December 92 and October 93) and in three sites of a polluted river (Este River, Northern Portugal). Filtered samples and the suspended particulate matter were titrated with metal ion and the labile metal concentrations measured by anodic stripping voltammetry (DPASV). An extra peak in the Cu voltammograms has been noticed when titrating filtered samples and its origin was investigated. Results have suggested that the extra peak is due to copper(I) stabilized by ligands adsorbed on the mercury electrode and a model for the electrochemical mechanism is proposed. From titrations of the same samples with zinc, cadmium and lead it has been concluded that there are two types of organics in the river water: macromolecules and small molecules with D_ML≈D_M with higher affinity for soft cations such as Cd(II) and Cu(I), that can be adsorbed on mercury electrode as anions.     

The Analysis of volatile compounds by purge and trap with whole column cryotrapping (WCC) on a fused silica capillary column

The purge and trap (P&T) method of analysis has been interfaced with fused silica capillary column gas chromatography. This interfacing has been accomplished without splitting the P&T trap desorption carrier gas. Thus, 100% of the purged compounds are transferred to the column. The analytes are cryofocussed on the column using whole column cryotrapping (WCC) at ?80°C. The resulting P&T/WCC procedure is extremely well-suited to the analysis of trace purgeable aqueous organic compounds. Samples and standards containing a variety of aromatic standard compounds were analyzed. The standards included benzene, toluene, ethylbenzene, xylenes, C₃-C₄-benzenes, and naphthalene, as well as three P&T internal standard compounds. Chromatographic peak widths were uniformly less than 6 s at the base and excellent precision was obtained in the relative retention time data for all compounds. The chromatogram of a groundwater sample contaminated with aromatic gasoline compounds is also presented. Since P&T/WCC works well with fused silica capillary columns, the full sensitivity and chromatographic efficiency of capillary gas chromatography is made available to P&T analyses.     

Charcoal open tubular traps for the analysis of air and headspace samples

5 cm × 0.3 mm i.d. glass capillary tubes coated with fine charcoal particles are used for the analysis of organic compounds, particularly tri- and tetrachloroethylene, benzene, and toluene, in air and headspace samples. Due to their small size, these traps are easy to use with capillary GC. As, e.g. 20 ml of gas can be sucked through this trap in 20 s, it is a simple technique providing high sensitivity; compared to headspace with split injection, sensitivity is increased by a factor exceeding 100. The column effluent is split into FID and ECD in such a way that small as well as large amounts of the chlorinated compounds can be detected.     

Correlations between dynamic fragility and dynamic mechanical properties of several amorphous polymers

In the present paper, dynamic mechanical properties were measured for several amorphous polymers ranging from strong to fragile. The results indicate that the storage modulus changes steadily, and the loss modulus peak and the tanδ peak are broader for strong glass-forming polymers. Three variables, the steepness index (S), the transition wideness (W) of storage modulus and the integration area (A) of tanδ, were defined to illustrate the potential correlation between the dynamic fragility index (m) and the dynamic mechanical properties. It is found that W and A can be correlated with m by power law equations, while an exponential relationship between S and m is observed. Moreover, as m decreases, the tanδ peak is more and more apart from the loss modulus peak and the point where the storage modulus begins to drop. These phenomena are interpreted in terms of chain packing efficiency.