Biomedical subjects

Y Andrès

Publications and source records attributed to Y Andrès.

7 recordsLinked to original sources

PubMed2005

Microbial reduction of 99Tc in organic matter-rich soils.

For safety assessment purposes, it is necessary to study the mobility of long-lived radionuclides in the geosphere and the biosphere. Within this framework, we studied the behaviour of (99)Tc in biologically active organic matter-rich soils. To simulate the redox conditions in soils, we stimulated the growth of aerobic and facultative denitrifying and anaerobic sulphate-reducing bacteria (SRB). In the presence of either a pure culture of denitrifiers (Pseudomonas aeruginosa) or a consortium of soil denitrifiers, the solubility of TcO(4)(-) was not affected. The nonsorption of TcO(4)(-) onto bacteria was confirmed in biosorption experiments with washed cells of P. aeruginosa regardless of the pH. At the end of denitrification with indigenous denitrifiers in soil/water batch experiments, the redox potential (E(H)) dropped and this was accompanied by an increase of Fe concentration in solution as a result of reduction of less soluble Fe(III) to Fe(II) from the soil particles. It is suggested that this is due to the growth of a consortium of anaerobic bacteria (e.g., Fe-reducing bacteria). The drop in E(H) was accompanied by a strong decrease in Tc concentration as a result of Tc(VII) reduction to Tc(IV). Thermodynamic calculations suggested the precipitation of TcO(2). The stimulation of the growth of indigenous sulphate-reducing bacteria in soil/water systems led to even lower E(H) with final Tc concentration of 10(-8) M. Experiments with glass columns filled with soil reproduced the results obtained with batch cultures. Sequential chemical extraction of precipitated Tc in soils showed that this radionuclide is strongly immobilised within soil particles under anaerobic conditions. More than 90% of Tc is released together with organic matter (60-66%) and Fe-oxyhydroxides (23-31%). The present work shows that ubiquitous indigenous anaerobic bacteria in soils play a major role in Tc immobilisation. In addition, organic matter plays a key role in the stability of the reduced Tc.

Models, Theoretical↗

PubMed2004

Lead removal by a natural polysaccharide in membrane reactors.

Industrial wastewaters often contain heavy metal ions that are toxic to many living species. Therefore, economic treatment methods are investigated, involving the sorption of metal ions onto wastes or natural materials. In the present work, the ability of sugar beet pulp, a common waste of the sugar industry, to remove Pb2+ polluted waters is investigated. The kinetic and equilibrium experiments were performed in batch reactor in order to determine the Pb2+ adsorption mechanisms onto the polysaccharide. The dynamic studies of Pb2+ fixation onto the natural polysaccharide involve an adsorption reactor coupled with microfiltration membrane in order to confine the adsorbent particles. A mass balance model based on the Langmuir equilibrium isotherm was used to describe the Pb2+ breakthrough curves. This model successfully simulated the entire breakthrough curves whatever the operating conditions used. It provides a useful tool for process simulation and optimisation.

Adsorption↗

PubMed2003

Study of the interaction between europium (III) and Bacillus subtilis: fixation sites, biosorption modeling and reversibility.

In order to elucidate the underlying mechanisms involved in the biosorption of metal ions, potentiometric titrations, complexation studies, and time-resolved laser-induced fluorescence spectroscopy (TRLFS) measurements were used to characterize the interaction between Eu(III) and Bacillus subtilis. The reversibility of the interaction between Eu(III) and Bacillus subtilis was studied by a cation-exchange technique using the Chelex resin. For complexation studies in the presence of 0.15 mol/l of NaCl, the metal ion, the biomass, concentrations and the pH were varied. The adsorption data were quantified by a surface complexation model without electrostatic term. The data on the Eu(III)/B.subtilis system at pH 5 were satisfactorily described by one site at which Eu(III) was bound through one carboxylic function of the bacteria. With increasing pH, another site should be considered, involving a phosphate-bound environment. This was partially confirmed by time-resolved laser-induced fluorescence spectroscopy. In addition to this, it was evidenced that the site availability was dependent on the nature of the cation, i.e., a proton or Eu(III). Finally, it was shown that, at pH 5, the Eu(III)/Bacillus subtilis equilibrium was reversible.

Adsorption↗

PubMed2003

Transfer of Eu (III) associated with polymaleic acid to Bacillus subtilis.

The aim of this study is to contribute to the understanding of the distribution of Eu(III) between dissolved organic matter and microorganisms, and to investigate the effect of competitive ions such as Ca(+2) on adsorption properties. Polymaleic acid (PMA), is used as synthetic organic matter, having similar properties as natural fulvic acid, and Bacillus subtilis is chosen as microorganism. A double labeling method was used: [14C]MPA and 152Eu to quantify the behavior of the various components. Preliminary experiments showed that the adsorption of polymaleic acid onto Bacillus subtilis was negligible at pH=5 in 0.15mol/l of NaCl. In the absence of Ca(+2), the transfer of Eu(III) from PMA to B. subtilis could be described by a simple empirical model based on data obtained from sorption isotherms on the reference systems Eu(III)/PMA and Eu(III)/B. subtilis. In the presence of Ca(+2), the transfer was increased. The hypothesis that Ca(+2) ions acted as a bridging agent between PMA and the bacteria was proposed.

Adsorption↗

PubMed2003

Rare earth elements removal by microbial biosorption: a review.

This paper reviews published work on the sorption of rare earth elements by microbial biomass. In a first part, the biosorption capacities and the various experimental conditions performed in batch reactor experiments are compared. Secondly, sorption modelling generally used in biosorption studies are described. Thirdly, the microbial cell wall characteristics of the metallic ion binding sites are considered. From these observations it seems that the important functional groups for metallic ion fixation are the carboxyl and the phosphate moieties. Moreover, the competing effect of various ions like aluminium, iron, glutamate, sulphate etc. is described. Finally, some adsorption results of the rare earth elements in dynamic reactors are presented.

Adsorption↗

PubMed2002

Fixed-bed study for lanthanide (La, Eu, Yb) ions removal from aqueous solutions by immobilized Pseudomonas aeruginosa: experimental data and modelization.

A fixed-bed study was carried out by using cells of Pseudomonas aeruginosa immobilized in polyacrylamide gel as a biosorbent for the removal of lanthanide (La, Eu, Yb) ions from aqueous solutions. The effects of superficial liquid velocity based on empty column, particle size, influent concentration and bed depth on the lanthanum breakthrough curves were investigated. Immobilized biomass effectively removed lanthanum from a 6 mM solution with a maximum adsorption capacity of 342 micromolg(-1) (+/-10%) corresponding closely to that observed in earlier batch studies with free bacterial cells. The Bohart and Adams sorption model was employed to determine characteristic parameters useful for process design. Results indicated that the immobilized cells of P. aeruginosa enable removal of lanthanum, europium and ytterbium ions from aqueous effluents with significant and similar maximum adsorption capacities. Experiments with a mixed cation solution showed that the sequence of preferential biosorption was Eu3+ > or = Yb3+ > La3+. Around 96+/-4% of the bound lanthanum was desorbed from the column and concentrated by eluting with a 0.1 M EDTA solution. The feasibility of regenerating and reusing the biomass through three adsorption/desorption cycles was suggested. Neural networks were used to model breakthrough curves performed in the dynamic process. The ability of this statistical tool to predict the breakthrough times was discussed.

Adsorption↗

PubMed2000

Factors influencing the biosorption of gadolinium by micro-organisms and its mobilisation from sand.

The present work was devoted to the study of the biosorption capacities of various microbial species (Bacillus subtilis, Pseudomonas aeruginosa, Ralstonia metallidurans CH34 previously Alcaligenes eutrophus CH34, Mycobacterium smegmatis, Saccharomyces cerevisiae) for ions of the lanthanide gadolinium (Gd3+). The uptake by sand of this element was also measured. Saturation curves and Scatchard models were established for all biosorbants used in this work. The results enabled us to determine the binding affinities and the maximum capacities for biosorption of Gd3+, which ranged from 350 micromol g(-1) for B. subtilis to 5.1 micromol g(-1) for S. cerevisiae. This study demonstrated the usefulness of optimisation of experimental conditions in biosorption investigations. Experimental results showed that biosorption could be influenced by the growth stage and by the composition of the growth medium of microbial cells. Finally, particular attention was given to the transfer of gadolinium ions from a loaded sand to a bacterial suspension.

Adsorption↗