Polycyclic aromatic hydrocarbons remobilization from contaminated porous media by (bio)surfactants washing.

Biosurfactants, surface-active agents produced by microorganisms, are increasingly studied for their potential use in soil remediation processes because they are more environmentally friendly than their chemically produced homologues. In this work, we report on the use of a crude biosurfactant produced by a bacterial consortium isolated from a PAHs-contaminated soil, compared with other (bio)surfactants (Tween80, Sodium dodecyl sulfate - SDS, rhamnolipids mix), to wash PAHs from a contaminated porous media. Assays were done using columns filled with sand or sand-clay mixtures (95:5) spiked with four model PAHs. The crude biosurfactant showed less adsorption to the [sand] and the [sand + clay] columns compared to Tween 80, SDS and the rhamnolipid mix. The biosurfactant showed the second best capacity to remove PAHs from the columns (as dissolved and particulate phases), both from [sand] and [sand + clay], after SDS when applied at lower concentrations than the other sufactants. The effluent concentrations of phenanthrene (PHE), pyrene (PYR) and benzo[a]pyrene (BAP) increased in the presence of the crude biosurfactant. Compared to the control experiment using only water, the global PAHs washed mass (amount of PAHs removed from the columns) increased between 9 and 1000 times for PHE and BAP in the [sand] column, and between 55 and 6000 times respectively for PHE and BAP in the [sand + clay] columns. Moreover, in the [sand + clay] columns, leaching of a part of the clays was observed in the SDS and the biosurfactant injections assays. This clay leaching resulted in higher PAHs removal, due not to desorption but rather to particulate transport. In the context of washing PAH-contaminated soils in biopiles or subsurface remediation, our results could help in sizing the remediation approach using an environmental friendly biosurfactant, before a pump-and-treat process.

Production of biosurfactant using the endemic bacterial community of a PAHs contaminated soil, and its potential use for PAHs remobilization.

Biosurfactants are surface-active agents produced by microorganisms whose use in soil remediation processes is increasingly discussed as a more environmentally friendly alternative than chemically produced surfactants. In this work, we report the production of a biosurfactant by a bacterial community extracted from a polluted soil, mainly impacted by PAHs, in order to use it in a soil-washing process coupled with bioremediation. Nutrient balance was a critical parameter to optimize the production. Best conditions for biosurfactant production were found to be 20 g/L of glucose, 2 g/L of NH4NO3, and 14.2 g/L of Na2HPO4, corresponding to a C/N/P molar ratio equal to 13/1/2. Purification of the produced biosurfactant by acidification and double extraction with dichloromethane as a solvent allowed measuring the Critical Micellar Concentration (CMC) as equal to 42 mg/L. The capacity of the purified biosurfactant to increase the apparent solubility of four reference PAHs (naphthalene, phenanthrene, pyrene and benzo[a]pyrene) was completed. The solubilisation ratios, in mg of PAH/g of biosurfactant for phenanthrene, pyrene and benzo[a]pyrene are 0.214, 0.1204 and 0.0068, respectively. Identification of the bacteria found in the colony producing the biosurfactant showed the presence of bacteria able to produce biosurfactant (Enterobacteriaceae, Pseudomonas), as well as, others able to degrade PAHs (Microbacterium, Pseudomonas, Rhodanobacteraceae).

Browning phenomenon of medieval stained glass windows.

In this work, three pieces of historical on-site glass windows dated from the 13th to 16th century and one archeological sample (8th century) showing Mn-rich brown spots at their surface or subsurface have been characterized by optical microscopy and Scanning Electron Microscopy coupled with Energy Dispersive X-ray spectroscopy. The oxidation state of Mn as well as the Mn environment in the alteration phase have been characterized by X-ray absorption spectroscopy at the Mn K-edge. Results show that the oxidation state of Mn and therefore the nature of the alteration phase varies according to the sample considered and is correlated with the extent of the brown alteration. The larger the brown areas the more oxidized the Mn. However, by contrast with literature, the samples presenting the more extended brown areas are not similar to pyrolusite and contain Mn mainly under a (+III) oxidation state.

Fluorescence detection to determine proteins and humic-like substances fingerprints of exopolymeric substances (EPS) from biological sludges performed by size exclusion chromatography (SEC).

Fingerprints of extracellular polymeric substances (EPS) from activated and anaerobic granular sludges were obtained by size exclusion chromatography coupled to UV (210 and 280 nm) and fluorescence (221/350 nm (protein-like molecules) and 345/443 nm (humic-like substances)) detection. The total area below the peaks obtained with fluorescence detection is linked to the protein or humic-like substances EPS content. The EPS protein fingerprints, usually recorded with UV-280 nm, change dramatically, mainly in the relative size of peaks when they were measured by a florescence detection method. It means that the apparent molecular weight (aMW) distribution of EPS chomatophores and fluorophores is different. Protein-like and humic-like substances were found to be specific fingerprints of the EPS, affected by the type and origin of the bacterial aggregate and improve EPS sample differentiation. The protein-like fraction of EPS displays a wide range of aMW (>600 kDa-<10 kDa) whereas the humic-like substances fraction is composed of molecules of low aMW (6-<1.2 kDa).

Site partitioning of Cr3+ in the trichroic alexandrite BeAl2O4:Cr3+ crystal: contribution from x-ray absorption spectroscopy.

X-ray absorption spectroscopy measurements at the Cr K-edge of a trichroic crystal of alexandrite BeAl(2)O(4):Cr(3+) for different orientations of the crystal with respect to the polarization and direction of the x-ray incident beam have been performed. Analysis of the experimental spectra with the help of first-principles calculations of x-ray absorption spectra allowed us to estimate the proportion of chromium Cr(3+) cations among the two different octahedral sites of the alexandrite structure (70% in the C(s) site-30% in the C(i) site). The methodology presented in this work opens up new possibilities in the field of mineralogy for the study of complex minerals containing several sites potentially occupied by several transition elements or for solid solutions.

Contribution of molecular dynamics simulations and ab initio calculations to the interpretation of Mg K-edge experimental XANES in K(2)O-MgO-3SiO(2) glass.

The structural environment of Mg in a K-bearing silicate glass of composition K(2)MgSi(3)O(8) is investigated by x-ray absorption near-edge structure (XANES) spectroscopy at the Mg K-edge. XANES calculations are performed using a plane-wave electronic structure code, and a structural model obtained by classical molecular dynamics coupled to ab initio relaxation. Bond valence theory is used to validate plausible environments within the structural models. Comparison between the experimental and calculated spectra enables us to conclude that the Mg atoms are located in distorted tetrahedral sites. Site distortions are found to be correlated to the theoretical shift of the XANES edge position.

Order and disorder in titanosilicate glass by 17O MAS, off-MAS, and 3Q-QCPMG-MAS solid-state NMR.

An 17O-enriched version of the titanosilicate glass, KTS2 (K(2)O.TiO(2).2SiO(2)), was analyzed by 17O MAS, off-MAS, and 3Q-QCPMG-MAS experiments. Exploiting the variations in EFG and CSA parameters for the 17O sites in KTS2 glass, we detected four types of oxygen by reduction of spinning sideband intensities in the off-MAS experiments. From the 17O off-MAS and 3Q-QCPMG-MAS experiments, the Si-O-Ti and K-O-Ti resonances were characterized by a distribution of isotropic chemical shifts, whereas the Si-O-Si resonance was characterized by very small distributions of both EFG tensor and isotropic chemical shift, which means that the disorder in the glass is closely related to Ti. In addition to the order/disorder issue, the most striking feature about the 17O off-MAS experiments on KTS2 is the lack of signals from Ti-O-Ti, which contradicts linking between corner sharing TiO(5) units. Therefore, the structure must consist of linkages between TiO(5) units and SiO(4) tetrahedra and linkages between SiO(4) tetrahedra.

First-principles calculation of 17O and 25Mg NMR shieldings in MgO at finite temperature: rovibrational effect in solids.

The temperature dependence of (17)O and (25)Mg NMR chemical shifts in solid MgO have been calculated using a first-principles approach. Density functional theory, pseudopotentials, a plane-wave basis set, and periodic boundary conditions were used both to describe the motion of the nuclei and to compute the NMR chemical shifts. The chemical shifts were obtained using the gauge-including projector augmented wave method. In a crystalline solid, the temperature dependence is due to both (i) the variation of the averaged equilibrium structure and (ii) the fluctuation of the atoms around this structure. In MgO, the equilibrium structure at each temperature is uniquely defined by the cubic lattice parameters, which we take from experiment. We evaluate the effect of the fluctuations within a quasiharmonic approximation. In particular, the dynamical matrix, defining the harmonic Hamiltonian, has been computed for each equilibrium volume. This harmonic Hamiltonian was used to generate nuclear configurations that obey quantum statistical mechanics. The chemical shifts were averaged over these nuclear configurations. The results reproduce the previously published experimental NMR data measured on MgO between room temperature and 1000 degrees C. It is shown that the chemical shift behavior with temperature cannot be explained by thermal expansion alone. Vibrational corrections due to the fluctuations of atoms around their equilibrium position are crucial to reproduce the experimental results.