Stéphane Simon

AsIII oxidation by Thiomonas arsenivorans in up-flow fixed-bed reactors coupled to As sequestration onto zero-valent iron-coated sand.

The combined processes of biological As(III) oxidation and removal of As(III) and As(V) by zero-valent iron were investigated with synthetic water containing high As(III) concentration (10 mg L(-1)). Two up-flow fixed-bed reactors (R1 and R2) were filled with 2 L of sieved sand (d = 3 ± 1 mm) while zero-valent iron powder (d = 76 μm; 1% (w/w) of sand) was mixed evenly with sand in R2. Thiomonas arsenivorans was inoculated in the two reactors. The pilot unit was studied for 33 days, with HRT of 4 and 1 h. The maximal As(III) oxidation rate was 8.36 mg h(-1) L(-1) in R1 and about 45% of total As was removed in R2 for an HRT of 1 h. A first order model fitted well with the As(III) concentration evolution at the different levels in R1. At the end of the pilot monitoring, batch tests were conducted with support collected at different levels in R1. They showed that bacterial As(III) oxidation rate was correlated with the axial length of reactor, which could be explained by biomass distribution in reactor or by bacterial activity. In opposition, As(III) oxidation rate was not stable in R2 due to the simultaneous bacterial As(III) oxidation and chemical removal by zero-valent iron and its oxidant products. However, a durable removal of total As was realized and zero-valent iron was not saturated by As over 33 days in R2. Furthermore, the influence of zero-valent iron and its oxidant corrosion products on the evolution of As(III)-oxidizing bacteria diversity was highlighted by the molecular fingerprinting method of PCR-DGGE using aoxB gene as a functional marker of aerobic As(III) oxidizers.

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).

Evaluation of size exclusion chromatography (SEC) for the characterization of extracellular polymeric substances (EPS) in anaerobic granular sludges

The extracellular polymeric substances (EPS) extracted from three granular and one flocculant anaerobic sludges were characterised by size exclusion chromatography (SEC) using two serially linked chromatographic columns in order to obtain more detailed chromatograms. A Superdex peptide 10/300 GL (0.1-7 kDa) and Superdex 20010/300 GL (10-600 kDa) from Amersham Biosciences were used in series with a mobile phase at pH 7 with an ionic strength of 0.223 M (phosphate buffer 50 mM and NaCl 150 mM). A part of the EPS molecules displays hydrophobic and/or ionic interactions with the column packing. Interactions could be modified by changing the mobile phase ionic strength or polarity (addition of acetonitrile). The detection wavelength (210 or 280 nm) affects strongly the EPS chromatogram. For a sludge originating from the same type of biofilms (i.e., anaerobic granules), the differences in EPS fingerprints are mainly due to differences in the absorbance of the chromatographic peaks, linked to EPS molecules content and composition. The EPS fingerprint changes significantly when the EPS originate from another type of anaerobic sludges. In addition, EPS fingerprints were affected by the extraction method used (centrifugation only; heat and centrifugation or cationic exchange resin and centrifugation). This phenomenon was observed mainly for the largest and smallest molecules and molecules which display interactions with column packing.

Advantages of hydride generation interface for selenium speciation in waters by high performance liquid chromatography–inductively coupled plasma mass spectrometry coupling

This paper focuses on the analytical performance improvement of the coupled technique HPLC-ICPMS using on-line collision/reaction cell technology for selenium elemental and speciation analyses at the ng (Se) l(-1) level in aquatic environment. Collision/reaction cell operating parameters were optimised, resulting in selected conditions of 5.5 ml min(-1) H(2) and 0.5 ml min(-1) He mixture. The detection limits obtained were around 5 ng (Se) l(-1) for total analysis, and between 7 and 15 ng (Se) l(-1) depending on the species for speciation analysis. The capability of UV irradiation-hydride generation interfacing to increase detector sensitivity was also evaluated for speciation analysis. The detection limits obtained were in the range 2-8 ng (Se) l(-1) depending on the species. Moreover, such interface allowed to prevent bromine introduction to the ICPMS which is particularly convenient for selenium trace analysis in natural waters as (80)Se is preserved free from BrH interferences. The developed method was validated using certified water with low selenium content (TM Rain 95, NWRI, Canada) and applied to the analysis of different waters.

Extraction procedure for organotin analysis in plant matrices: optimisation and application

Analysis of organotin compounds in vegetal samples is not well documented, and no specific extraction procedure of those species from vegetal matrix can be found in the literature. In order to develop such a procedure, we have compared in a first step the performances of six extracting solutions based on HCl, CH(3)COOH, NaOH, TMAH, enzymatic mixture and ethyl ethanoate. HCl-based extraction gives the highest recoveries. The whole extraction process was then optimised by investigating the influence of all the operating parameters. The resulting method, allowed a 100% recovery of tribultyltin and triphenyltin in spiked vegetal powders, without any noticeable degradation. The optimised extraction procedure was applied to the speciation of organotins in French beans and algae. Several mug (Sn) kg(-1) of butyltins were found in algae collected in an urban treatment plant and contents up to 800 mug (Sn) kg(-1) were detected in French beans cultivated with polluted nutritive solution. These results highlight the existence of a transfer of organotins from polluted waters to plants.

Methodological approaches for fractionation and speciation to estimate trace element bioavailability in engineered anaerobic digestion ecosystems: An overview

ABSTRACT Optimal supply of trace elements (TE) is a prerequisite for microbial growth and activity in anaerobic digestion (AD) bioprocesses. However, the required concentrations and ratios of essential TE for AD biotechnologies strongly depend on prevailing operating conditions as well as feedstock composition. Furthermore, TE in AD bioreactors undergo complex physicochemical reactions and may be present as free ions, complex bound or as precipitates depending on pH, or on the presence of sulfur compounds or organic macromolecules. To overcome TE deficiency, various commercial mineral products are typically applied to AD processes. The addition of heavy metals poses the risk of overdosing operating systems, which may be toxic to microbial consortia and ultimately the environment. Adequate supplementation, therefore, requires appropriate knowledge not only about the composition, but also on the speciation and bioavailability of TE. However, very little is yet fully understood on this specific issue. Evaluations of TE typically only include the measurement of total TE concentrations but do not consider the chemical forms in which TE exist. Thus detailed information on bioavailability and potential toxicity cannot be provided. This review provides an overview of the state of the art in approaches to determine bioavailable TE in anaerobic bioprocesses, including sequential fractionation and speciation techniques. Critical aspects and considerations, including with respect to sampling and analytical procedures, as well as mathematical modeling, are examined. The approaches discussed in this review are based on our experiences and on previously published studies in the context of the “COST Action 1302: European Network on Ecological Roles of Trace Metals in Anaerobic Biotechnologies.”

Simultaneous measurement of Cr(III) and Cr(VI) in freshwaters with a single Diffusive Gradients in Thin Films device.

Few attempts have been made to sample labile chromium with the DGT passive sampler (Diffusive Gradients in Thin Films) and, currently, no single device allows the simultaneous determination of both Cr(III) and Cr(VI). In this work, a procedure based on only one device combined with innovative selective elution is evaluated to assess chromium speciation. A zirconium binding gel is used to accumulate both Cr(III) and Cr(VI). Cr(VI) is quantitatively and selectively eluted by NaOH, allowing the subsequent determination of Cr(III). Accurate quantification of both species is demonstrated in synthetic solutions for pH ranging from 4 to 6 and ionic strength ranging from 10(-3) to 5×10(-2)M. Cr(VI) quantification is altered only for [SO4(2-)]≥5×10(-3)M. The method allows successful quantification of labile Cr(III) and Cr(VI) in spiked natural water. The limit of quantification of the procedure is suitable for trace level monitoring (0.03µgL(-1) for Cr(VI) and 1µgL(-1) for Cr(III), for a one-week deployment at 20°C) and the effective capacity of the sampler (∼25µg for each Cr oxidation state) should allow long term deployments. These results highlight the potential of this new procedure for a simple and effective chromium speciation analysis in natural waters.

Adsorption of AsIII, AsV and dimethylarsinic acid onto synthesized lepidocrocite

The trapping of arsenic by zero valent iron is strongly dependant on iron by-products. Among these, lepidocrite has been scarcely studied. In this work, we studied the adsorption of two inorganic (AsIII, AsV) and one organic (dimethylarsinic acid, DMA) arsenic species onto lepidocrocite. pH influence was considered in the range 5 to 9, which corresponds to natural water pH. Langmuir model was used to simulate As adsorption isotherms. Our results showed that lepidocrocite offers high adsorption capacities: up to 0,25, 0,41 and 1 mol for AsV, DMA and AsIII could be respectively trapped per kilogram of zero-valent iron. pH influence varied from one arsenic species to another: increasing pH improve AsIII and DMA sorption whereas it has a very low effect on AsV sorption.

Transmetallation of Gd-DTPA by Fe3+, Cu2+ and Zn2+ in water: Batch experiments and coagulation–flocculation simulations

The study investigates the stability of gadolinium-DTPA complex in presence of competing metallic ions, Fe(3+), Cu(2+) and Zn(2+) using batch experiments and coagulation-flocculation simulations. High performance liquid chromatography with fluorescence detection was used for simultaneous analysis of chelate gadolinium (Gd-DTPA) and free Gd(III) ion in water. It was shown that Cu(2+) has a strong affinity for DTPA and could lead to a complete release of Gd(3+). Fe(3+) appeared also to compete strongly with Gd(3+) for DTPA binding since up to 80% of Gd-complex was dissociated under iron excess condition. Finally, zinc had a lower influence on Gd speciation: only 15% of Gd(3+) was released with addition of a 5-fold excess of Zn(2+). During coagulation-flocculation simulation, Fe(3+) was able to displace about 27% of Gd-DTPA, and no adsorption was observed onto flocs.

Influence of extraction method on size exclusion chromatography fingerprints of EPS from wastewater sludges

Extracellular polymeric substances (EPS) were separated using two serial-linked size exclusion chromatography (SEC) columns to obtain detailed fingerprints. The chromatographic profile results were influenced by the nature of biological sludge (activated sludges, anaerobic granules, anaerobic flocculated sludges). Furthermore, our results highlight that EPS fingerprints are also highly dependent on the extraction method. If physical extractions modify only the relative absorbance of the chromatographic peaks, heating during extraction induces significant modifications of the fingerprints, probably owing to better organic matter extraction efficiency as well as an increase in hydrolysis for some compounds but not for EPS extracted from anaerobic granular sludges. This confirms that thermal treatment is a proper method to extract EPS from anaerobic granular sludges. The use of chemical extraction results in major changes on the EPS fingerprints. This work demonstrates that some chromatographic peaks are due to residues from the chemical reagent (such as EDTA, glutaraldehyde) which can modify or form complexes with some EPS macromolecules. As a result, due to its sensitivity to sludge origin and/or extraction procedure, SEC appears to be a suitable tool for an accurate qualitative EPS characterization.