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Arsenic (As) is one of the main toxic elements of geogenic origin that impact groundwater quality and human health worldwide. In some groundwater wells of the Sologne region (Val de Loire, France), drilled in a confined aquifer, As concentrations exceed the European drinking water standard (10 μg L

Chlordecone (CLD) is a very persistent synthetic organochlorine pesticide found in the French West Indies. Recently published work has demonstrated the potential of zero-valent iron to dechlorinate CLD by in situ chemical reduction (ISCR) in soils under water-saturated conditions, forming mono- to penta-dechlorinated CLD transformation products. These transformation products are more mobile than CLD and less toxic; however, nothing is known about their further degradation, although increasing evidence of CLD biodegradation by bacteria is being found. The present study began with the enrichment from wastewater sludge of a CLD-transforming community which was then inoculated into fresh media in the presence of either CLD or two of the main ISCR transformation products, 10-monohydroCLD (-1Cl-CLD) and tri-hydroCLD (-3Cl-CLD). Carried out in triplicate batches and incubated at 38°C under anoxic conditions and in the dark, the cultures were sampled regularly during 3 months and analyzed for CLD, -1Cl-CLD, -3Cl-CLD, and possible transformation products by gas chromatography coupled to mass spectrometry. All batches showed a decrease in the amended substrates (CLD or hydroCLD). CLD degradation occurred with concomitant formation of a nine-carbon compound (pentachloroindene) and two sulfur-containing transformation products (chlordecthiol, CLD-SH; methyl chlordecsulfide, CLD-SCH3), demonstrating competing transformation pathways. In contrast, -1Cl-CLD and -3Cl-CLD only underwent a sequential reductive sulfidation/S-methylation process resulting in -1Cl-CLD-SH and -1Cl-CLD-SCH3 on the one hand, and -3Cl-CLD-SH, -3Cl-CLD-SCH3 on the other hand. Some sulfur-containing transformation products have been reported previously with single bacterial strains, but never in the presence of a complex microbial community. At the end of the experiment, bacterial and archaeal populations were investigated by 16S rRNA gene amplicon sequencing. The observed diversity was mostly similar in the CLD and -1Cl-CLD conditions to the inoculum with a dominant archaea genus, Methanobacterium, and four OTU affiliated to bacteria, identified at the family (Spirochaetaceae) or genus level (Desulfovibrio, Aminobacterium, and Soehngenia). On the other hand, in the -3Cl-CLD condition, although the same OTU were found, Clostridium sensu stricto 7, Candidatus Cloacimonas, and Proteiniphilum were also present at > 2% sequences. Presence of methanogens and sulfate-reducing bacteria could contribute to sulfidation and S-methylation biotransformations. Overall, these results contribute to increasing our knowledge on the biodegradability of CLD and its transformation products, helping to progress toward effective remediation solutions.

Metal(loid) soil pollution resulting from mining activities is an important issue that has negative effects on the environment (soil acidification, lack of vegetation, groundwater pollution) and human health (cancer, chronic diseases). In the context of a phytostabilization process for the bioremediation of a mine soil highly contaminated by arsenic (As) and lead (Pb), a pot experiment was set up to study the effect of plant sowing and microbial inoculation on soil properties, metal(loid) (im)mobilization in soil and accumulation in plant, and plant growth. For this, mine soil was sown with endemic metallicolous Agrostis seeds and/or inoculated with endogenous microbial consortia previously selected for their As and Pb tolerance. Agrostis was able to develop on the contaminated mine soil and immobilized metal(loid)s through metal(loid) accumulation in the roots. Its growth was improved by microbial consortium inoculation. Moreover, microbial consortium inoculation increased soil organic content and electrical conductivity, and led to an increase in soil microbial activities (linked to C and P cycles); however, it also induced a metal(loid) mobilization. In conclusion, microbial consortium inoculation stimulated the growth of endemic Agrostis plants and thus ameliorated the phytostabilization of a former mine soil highly polluted by As and Pb. This study is thus a good example of the benefits of coupling several approaches such as phytostabilization and bioaugmentation for the bioremediation of former mine contaminated sites.

International audience; Microbial mats are commonly observed in estuaries and in salt marshes but they only rarely represent a significant surface involved in salt production. In the Sečovlje salt works in Northern Adriatic, a microbial mat known as the “petola” covers the bottom of salt crystallising pans, highly influencing salt composition and salt production processes. Throughout the year the petola is subjected to numerous co-varying factors that drive changes in its structure and the microbial community. Seasonal modifications were investigated via various methods (cryo-HRSEM, XRD, elemental analysis, carbohydrate content, bacterial community structure). This study provides knowledge on microbial mat compositional characteristics and functional roles in response to seasonal variation in environmental conditions. The in situ characterisation (close-to its natural hydrated state) of the three-dimensional microstructure provides precise information about dominating filamentous cyanobacterium Coleofasciculus chthonoplastes and extracellular polymer secretion (EPS) organisation. This is the first study to address how microbial mat composition and structure, especially 3D EPS network (and microbial diversity), affects the salt production processes within a hypersaline environment.

International audience; Acid mine drainage (AMD) still represents a huge environmental problem. Technical and scientific breakthroughs are still needed to decrease environmental damages, treatment cost, and waste production associated with AMD. The feasibility of combining continuously fed anaerobic sulfate-reducing bioreactor with downstream iron oxidation step was tested, at a laboratory scale, with two types of real arsenic-rich AMD waters from the site of Carnoulès (France), that differed in acidity (pH 3.3 and 4.0), arsenic (As, 18 and 174 mg.L−1), and metal concentrations. Iron remained in solution, while up to 99% of As was precipitated as amorphous orpiment in the anaerobic sulfate-reducing bioreactor. Zinc (Zn) precipitation was also observed, up to 99%; however, the efficiency of Zn precipitation was less stable than that of As. The anaerobic bioreactor presented a stable bacterial community including a Desulfosporosinus-related sulfate reducer. When the effluents from the anaerobic process step were treated in a laboratory aerobic bioreactor, iron was oxidized efficiently. The feasibility of efficient orpiment bio-precipitation coupled with downstream iron oxidation was shown, thus opening the perspective of a low-cost combination of treatment steps for the removal of arsenic, zinc, and iron in As-rich AMDs.

International audience; Nitrate contamination of groundwater remains a major concern despite all the measures and efforts undertaken over the last decades to protect water resources. We focused on a small catchment in Brittany (France) facing nitrate pollution with concentrations over the European drinking water standard of 50 mg.L−1. This is a common situation in catchments where - supposedly effective - measures were applied for reducing the transfer of N to groundwater. At the scale of this small (~100 ha) basement aquifer, nitrate concentrations are very heterogeneous in the groundwater, sampled up to 15–20 m below the soil surface in several observation wells (hereafter referred as piezometers) and up to 110 m deep in a borehole drilled through a faulted area near the Spring (outlet of the catchment). We used complementary and robust approaches for exploring and constraining the driving parameters of nitrate transfer and distribution in groundwater. Detailed geological work and a geophysical electrical resistivity tomography survey identified the lithologies, tectonic structures and weathering layers. This highlighted a complex geological structure with several compartments delimited by faults, as well as the highly variable thickness of the weathered layer. It also illustrated the heterogeneity of the hydrosystem, some compartments appearing to be disconnected from the general groundwater flow. This was confirmed by geochemical analyses and by the mean apparent groundwater residence time based on CFCs-SF6 and noble-gas analyses, locally revealing old and nitrate-free groundwater, and very old water with a recharge temperature below than the current average temperature in the area, reflecting water dating back to the last period of glaciation (−19 to −17 ky). Nitrate isotopes clearly showed denitrification processes in a few piezometers, which was generally supported by microbiology and molecular biology results. This highlighted the presence of functional genes involved in denitrification as well as a capacity of the groundwater microbial community to denitrify when in situ conditions are favourable. This type of combined approach - covering chemistry, isotopic methods, dissolved gases, microbiological activity, geophysics and hydrogeology - appears to be indispensable for implementing the most relevant programme of measures and for accurately assessing their effectiveness, notably by considering the timeframe between implementation of the measures and their impact on groundwater quality. © 2021 Elsevier B.V.

Pyrite-bearing coal wastes are responsible of the formation of acid mine drainage (AMD), and their management to mitigate environmental impacts is a challenge to the coal mine industry in Europe and worldwide. The European CEReS project sought to develop a generic co-processing strategy to reuse and recycle coal wastes, based on removal of AMD generating potential through bioleaching. Chemolitoautotrophic iron- and sulfur-oxidizing microbial consortia were enriched from a Polish coal waste at 30 °C and 48 °C, but not 42 °C. Pyrite leaching yield, determined from bioleaching tests in 2-L stirred bioreactors, was best with the 48 °C endogenous consortium (80%), then the 42 °C exogenous BRGM-KCC consortium (71%), and finally the 30 °C endogenous consortium (50%). 16S rRNA gene-targeted metagenomics from five surface locations on the dump waste revealed a microbial community adapted to the site context, composed of iron- and/or sulfur-oxidizing genera thriving in low pH and metal rich environments and involved in AMD generation. All together, the results confirmed the predisposition of the pyritic coal waste to bioleaching and the potential of endogenous microorganisms for efficient bioleaching at 48 °C. The good leaching yields open the perspective to optimize further and scale-up the bioleaching process.

International audience; Agricultural soils can contain high arsenic (As) concentrations due to specific geological contexts or pollution. Agricultural practices, in particular fertilizer amendments, could influence As speciation and mobility, thus increasing its transfer to crops and its toxicity. In the present study, field-relevant amounts of fertilizers were applied to soils from a cultivated field that was a former ammunition-burning site. Potassium phosphate, ammonium sulfate and organic matter were applied to these soils in laboratory experiments to assess both their impact on As leaching and on As bioavailability to Lactuca sativa. Results indicate that none of the fertilizers significantly influences the speciation and quantity of mobile As, although trends showed an increase of mobility with KP and a decrease of mobility with ammonium sulfate. The most probable number of AsIII-oxidizing microbes and AsIII-oxidizing activity were strongly linked to As levels in water and soils. In the reference un-polluted soil, ammonium sulfate negatively affected AsIII-oxidizing activity. KP amendment induced a small increase of As content in plants, and the polluted soil amended with ammonium sulfate was significantly less phytotoxic than the un-amended soil. Results suggest that ammonium sulfate, the most frequently applied fertilizer on site, influences the interactions between As, microorganisms and plants.

International audience; The increasing pesticide use in agriculture involves the presence of both parent pesticides and their transformation products (metabolites) in various environmental matrices and notably groundwater. One drawback is that pesticides and metabolites (even referred to as emerging groundwater contaminants) are now known to have side effects on non-target surface and subsurface living organisms. The environmental consequence of side effects of pesticides and their metabolites on microbial ecosystems is that they can threaten the ecosystem services based on microbial activities in soil (litter degradation, plant growth, nutrient cycling, degradation of pollutants…) and groundwater (production of drinking water, nutrient cycling, degradation of contaminant…). Most studies on side effects of pesticides and their metabolites have been conducted in soils, showing main impacts on microbial abundance, presence or absence of microbial species, increase or decrease in gene expression (mainly linked to the N cycle), and increase or decrease of the functional diversity (activities linked to P, N, S, C cycles). Moreover, pesticides presence was shown to usually lead to the selection of microorganisms having the ability to degrade them. Pesticides and their metabolites impacts on soil microbiology are rather well documented, but knowledge on their side effects on groundwater microbial ecosystems is scarce. The few studies conducted in groundwater have underlined potential side effects on groundwater communities as pesticides presence could increase microbial biodiversity. The role of pesticides contamination history on pesticides impact on groundwater communities has also been underlined. In this context, the impact of two pesticides, S-metolachlor and Propiconazole, and their metabolites, ESA-metolachlor and 1,2,4-triazole, was studied on microbial denitrification, a key function for nitrate removal in groundwater. Laboratory experiments were performed with or without pesticides or metabolites at 2 and 10 µg/L. Kinetics of nitrate reduction along with nitrite and N 2 O production all suggest that S-metolachlor has no or only little impact, whereas its metabolite ESA-metolachlor inhibits denitrification by 65 % at 10 µg/L. Propiconazole and 1,2,4-triazole also inhibit denitrification (by 29-38 %) at both concentrations, but to a lesser extent than ESA-metolachlor. When inhibition occurs, substances affect the reduction of nitrate into nitrite. At the end of batch experiments, no significant change in narG and napA genes abundance was detected, suggesting an impact of pesticides at the protein level rather than on bacteria abundance. Community diversity fingerprints and Illumina sequencing indicate no major impact of pesticides on bacterial diversity except for ESA-metolachlor at 10 µg/L that induces an increase of biodiversity indices. General growth parameters such as bacterial biomass and acetate consumption suggest no impact of pesticides, except for propiconazole at 10 µg/L that partially inhibits microbial metabolism (as acetate uptake). In conclusion, pesticides and their metabolites can have side effects on microbial denitrification in groundwater at realistic environmental concentrations, and may thus affect ecosystem services based on microbial activities.

The development of biofilms on modified natural zeolites was investigated with purpose to obtain biocomposites with biodegradation activity towards pesticides MCPA (2-methyl-4-chlorophenoxyacetic acid) and glyphosate (N-(phosphonomethyl)glycine) for potential application in bioaugmentation of polluted agricultural soils. Microbial communities were selected from agricultural pesticide-contaminated soil/water samples and enriched on the basis of their ability to biodegrade the pesticides. In order to enhance affinity of microbial communities to the support material, the natural mineral zeolite was modified by nontoxic environmentally friendly cations (Li+, Na+, K+, NH4+, H+, Mg2+, Ca2+, Fe3+) by methods preserving its structure and characterised using powder XRD, surface area measurement and chemical composition analysis. Kinetics of pesticide degradation by the biocomposites was studied in liquid media. Results showed that according to zeolite modifications, the microbial activity and biodiversity changed. The best biodegradation rate of MCPA and glyphosate reached 0.12-0.13 mg/h with half-life of 16-18 h, which is considerably quicker than observed in natural environment. However, in some cases, biodegradation activity towards pesticides was lost which was connected to unfavourable zeolite modification and accumulation of toxic metabolites. High-throughput sequencing on the 16S rRNA genes of the biofilm communities highlighted the selection of bacteria genera known to metabolise MCPA (Aminobacter, Cupriavidus, Novosphingobium, Pseudomonas, Rhodococcus, Sphingobium and Sphingopyxis) and glyphosate (Pseudomonas). Altogether, results suggested that zeolites do not only have a passive role of biofilm support but also have protective and nutrient-supportive functions that consequently increase biodiversity of the pesticide degraders growing in the biofilm and influence the pesticide biodegradation rate. Byl zkoumán vývoj biofilmů na modifikovaných přírodních zeolitech za účelem získání biokompozitů s biodegradační aktivitou vůči pesticidům MCPA (2-methyl-4-chlorofenoxyoctová kyselina) a glyfosátu (N-(fosfonomethyl)glycin) pro potenciální aplikaci v bioaugmentaci znečištěných zemědělských půd. Mikrobiální společenstva byla vybrána ze vzorků půdy/vody kontaminované zemědělskými pesticidy a obohacena na základě jejich schopnosti biodegradovat pesticidy. Pro zvýšení afinity mikrobiálních společenstev k nosnému materiálu byl přírodní minerální zeolit modifikován netoxickými ekologicky šetrnými kationty (Li+, Na+, K+, NH4+, H+, Mg2+, Ca2+, Fe3+) metodami zachovávajícími jeho strukturu a charakterizován pomocí práškové XRD analýzy, měření měrného povrchu a analýzy chemického složení. Kinetika degradace pesticidů biokompozity byla studována v kapalných médiích. Výsledky ukázaly, že podle modifikací zeolitu se měnila i mikrobiální aktivita a biodiverzita. Nejlepší biodegradační rychlost MCPA a glyfosátu dosáhla 0,12-0,13 mg/h s poločasem rozpadu 16-18 h, což je podstatně rychleji, než je pozorováno v přirozeném prostředí. V některých případech však došlo ke ztrátě biodegradační aktivity vůči pesticidům, což souviselo s nepříznivou modifikací zeolitu a akumulací toxických metabolitů. Vysoce výkonné sekvenování na genech 16S rRNA biofilmových komunit zdůraznilo výběr rodů bakterií, o kterých je známo, že metabolizují MCPA (Aminobacter, Cupriavidus, Novosphingobium, Pseudomonas, Rhodococcus, Sphingobium a Sphingopyxis) a glyfosát (Pseudomonasate). Celkově výsledky naznačují, že zeolit nemá pouze pasivní roli podpory biofilmu, ale má také ochranné a nutričně podpůrné funkce, které následně zvyšují biologickou rozmanitost degradátorů pesticidů rostoucích v biofilmu a ovlivňují rychlost biodegradace pesticidů.

Nitrate contamination of groundwater remains a major concern despite all the measures and efforts undertaken over the last decades to protect water resources. We focused on a small catchment in Brittany (France) facing nitrate pollution with concentrations over the European drinking water standard of 50 mg.L

A turbidimetric test for rapid quantification of As(III) (detection limit of 3 mg/L, quantification range of 10–100 mg/L) in liquid growth medium was developed for assessing and monitoring microbial As(III)-oxidizing and As(V)-reducing activities. This test is based on As(III) chelation with pyrrolidine dithiocarbamate followed by spectrometric measurement of absorbance, and was validated by comparison with AAS quantification of As after As(III)/As(V) separation.

Chlorinated ethenes (CEs) are most problematic pollutants in groundwater. Dehalogenating bacteria, and in particular organohalide-respiring bacteria (OHRB), can transform PCE to ethene under anaerobic conditions, and thus contribute to bioremediation of contaminated sites. Current approaches to characterize in situ biodegradation of CEs include hydrochemical analyses, quantification of the abundance of key species (e.g. Dehalococcoides mccartyi) and dehalogenase genes (pceA, vcrA, bvcA and tceA) involved in different steps of organohalide respiration (OHR) by qPCR, and compound-specific isotope analysis (CSIA) of CEs. Here we combined these approaches with sequencing of 16S rRNA gene amplicons to consider both OHRB and bacterial taxa involved in CE transformation at a multi-contaminated site. Integrated analysis of hydrogeochemical characteristics, gene abundances and bacterial diversity shows that bacterial diversity and OHRB mainly correlated with hydrogeochemical conditions, suggesting that pollutant exposure acts as a central driver of bacterial diversity. CSIA, abundances of four reductive dehalogenase encoding genes and the prevalence of Dehalococcoides highlighted sustained PCE, DCE and VC degradation in several wells of the polluted plume. These results suggest that bacterial taxa associated with OHR play an essential role in natural attenuation of CEs, and that representatives of taxa including Dehalobacterium and Desulfosporosinus co-occur with Dehalococcoides. Overall, our study emphasizes the benefits of combining several approaches to evaluate the interplay between the dynamics of bacterial diversity in CE-polluted plumes and in situ degradation of CEs, and to contribute to a more robust assessment of natural attenuation at multi-polluted sites.

International audience; Microbial transformation of arsenic species and their interaction with the carbon cycle play a major role in the mobility of this toxic metalloid in the environment. The influence of simple or complex organic substrates on arsenic bio-oxidation was studied using two bacterial strains: one – the arsenivorans strain of Thiomonas delicata – is able to use AsIII as sole energy source; the other, Herminiimonas arsenicoxydans, is not. Experiments were performed at two AsIII concentrations (75 and 2 mg/L). At 75 mg/L As, for both strains, expression of aioA gene decreased when yeast extract concentration was raised from 0.2 to 1 g/L. At 2 mg/L As, the presence of either yeast extract or simple (succinate or acetate) organic substrates in the medium during bacterial growth decreased the AsIII-oxidation rate by both strains. When added specifically during oxidation test, yeast extract but not simple organic substrates seems to have a negative effect on AsIII oxidation. Taken together, results confirm the negative influence of simple or complex organic substrates on the kinetics of microbial AsIII oxidation and suggest that this effect results from different mechanisms depending on the type of organic substrate. Further, for the first time, the influence of a complex organic substrate, yeast extract, on aioA gene expression has been evidenced.

In bioleaching processes using autotrophic bacteria, CO2 is the carbon source for the growth of the microorganisms and its availability is dependent on gas mass transfer. The objective of this study was to investigate the demand in CO2 in complex copper concentrate bioleaching operations and to optimize CO2 supply. Batch tests in 2L-stirred reactors at 10%w/v solid load were performed to study the need for CO2-supplementation and to determine the adequate CO2 partial pressure in the gas inlet. The results show that Fe oxidation (and thus microbial activity) is delayed when air is injected without CO2-supplementation. CO2-supplementation improves leaching kinetics since Cu dissolution rate increases from 84 mg/L/h with air solely to 120 mg/L/h when CO2 is added to air. The study proposes also a methodology to determine G/L transfer components and to asses CO2 limitations in the system. It shows that the microorganisms are not only sensitive to the transfer rate of CO2 from the gas to the liquid phase, but also to the availability of CO2 in solution.

Kupferschiefer-type ore represents an important source for base metals and several studies concerning the bioleaching of black shale ores and Cu concentrates have been carried out with focus on various microbial communities and processing parameters. However, the incomplete dissolution of chalcopyrite remains a key issue for copper ore bioleaching improvement and requires further investigations in order to ensure an optimal control of the process for upscaling. Our study clearly showed that bioleaching tests are characterized by two separate phases with a distinct optimal temperature. A distinct effect of the temperature on the copper recovery and the advantage of temperature ramp in order to enhance copper bioleaching and chalcopyrite dissolution were demonstrated.

International audience; The use of oxygen enriched air is a common practice in high-temperature bioleaching tests (> 70°C) to overcome oxygen solubility limitation and reduced the energy costs of the process. Air is usually preferred in medium and low-temperature operations mainly for technical and economic constraints. Nevertheless, under high-sulfide loading conditions - high-grade metal sulfide concentrates and high solids concentration - the microbial and chemical demand for oxygen is significantly increased during the bioleaching process. If not satisfied, this high oxygen demand might limit the oxidation efficiency. Therefore it requires the injection of large amounts of air. Sparging with oxygen enriched gas instead of air may offer an interesting alternative process option to improve gas transfer in the bioleaching reactor and to provide an adequate oxygen supply in order to satisfy the oxygen demand. It might be useful to develop innovative alternative to the classical stirred tank reactor (STR) technology. However, the use of such conditions can lead to much higher dissolved oxygen (DO) concentrations than those encountered with air. Very few papers have been devoted to the study of the optimal range of DO concentrations for bioleaching processes. Most of them reported an inhibitory effect of DO concentrations above 5 ppm. The purpose of this study was to investigate the influence of DO on the bioleaching efficiency under oxygen-enriched atmosphere in 21 L stirred tank reactor at 42°C. Bioleaching experiments were performed in continuous mode with sulfide-rich tailings wastes composed mainly of pyrite (51%) and quartz using the “BRGM-KCC” bacterial consortia. The solid load was close to 20% (w/w). Using various oxygen supply conditions (partial pressure, gas rate), the DO concentration in the reactor varied between 4 and 17 ppm. For a DO ranging from 4 to 13 ppm, a good bacterial oxidizing activity was observed and the sulfide dissolution efficiency increased with the DO concentration. It is assumed that this improvement of the bioleaching efficiency was linked to an increase of the oxygen transfer rate from the gas phase to the liquid phase rather than a direct effect of the DO level. When the DO concentration reached 17 ppm a significant decrease of the microbial activity and consequently of the oxygen consumption was noticed. These results show that there is a critical value above which the DO concentration is detrimental to the activity of the bioleach microorganisms present in the “BRGM-KCC” consortia but this value is much higher than the one usually mentioned in the literature.

International audience

International audience; The burning of chemical weapons in the 1926–1928 period produced polluted technosols with elevated levels of arsenic, zinc, lead and copper. During an eight-month mesocosm experiment, these soils were submitted to two controlled environmental changes, namely the alternation of dry and water-saturated conditions and the addition of fragmented organic forest litter to the surface soil. We investigated, by sequencing the gene coding 16S rRNA and 18S rRNA, (1) the structure of the prokaryotic and eukaryotic community in this polluted technosol and (2) their response to the simulated environmental changes, in the four distinct layers of the mesocosm. In spite of the high concentrations of toxic elements, microbial diversity was found to be similar to that of non-polluted soils. The bacterial community was dominated by Proteobacteria, Acidobacteria and Bacteroidetes, while the fungal community was dominated by Ascomicota. Amongst the most abundant bacterial Operational Taxonomic Units (OTUs), including Sphingomonas as a major genus, some were common to soil environments in general whereas a few, such as organisms related to Leptospirillum and Acidiferrobacter, seemed to be more specific to the geochemical context. Evolution of the microbial abundance and community structures shed light on modifications induced by water saturation and the addition of forest litter to the soil surface. Co-inertia analysis suggests a relationship between the physico-chemical parameters total organic carbon, Zn, NH4+ and As(III) concentrations and the bacterial community structure. Both these results imply that microbial community dynamics linked to environmental changes should be considered as factors influencing the behavior of toxic elements on former ammunition burning sites.

A field-pilot bioreactor exploiting microbial iron (Fe) oxidation and subsequent arsenic (As) and Fe co-precipitation was monitored during 6 months for the passive treatment of As-rich acid mine drainage (AMD). It was implemented at the Carnoules mining site (southern France) where AMD contained 790-1315 mg L-1 Fe(II) and 84-152 mg L-1 As, mainly as As(Ill) (78-83%). The bioreactor consisted in five shallow trays of 1.5 m(2) in series, continuously fed with AMD by natural flow. We monitored the flow rate and the water physico-chemistry including redox Fe and As speciation. Hydraulic retention time (HRT) was calculated and the precipitates formed inside the bioreactor were characterized (mineralogy, Fe and As content, As redox state). Since As(III) oxidation improves As retention onto Fe minerals, bacteria with the capacity to oxidize As(III) were quantified through their marker gene aioA. Arsenic removal yields in the pilot ranged between 3% and 97% (average rate (1.8 +/- 0.8) X 10(-8) mol L-1 s(-1)), and were positively correlated to HRT and inlet water dissolved oxygen concentration. Fe removal yields did not exceed 11% (average rate (7 +/- 5) X 10(-8) mol L-1 s(-1)). In the first 32 days the precipitate contained tooeleite, a rare arsenite ferric sulfate mineral. Then, it evolved toward an amorphous ferric arsenate phase. The As/Fe molar ratio and As(V) to total As proportion increased from 0.29 to 0.86 and from similar to 20% to 99%, respectively. The number of bacterial aioA gene copies increased ten-fold during the first 48 days and stabilized thereafter. These results and the monitoring of arsenic speciation in the inlet and the outlet water, provide evidences that As(III) oxidized in the pilot. The biotreatment system we designed proved to be suitable for high As DMA. The formation of sludge highly enriched into As(V) rather than As(III) is advantageous in the perspective of long term storage.

International audience; Toxic and persistent contaminants in groundwater are technologically difficult to remediate. Remediation techniques using nanoparticles (NPs) such as nZVI (Zero-Valent Iron) are applicable as in situ reduction or oxidation agents and give promising results for groundwater treatment. However, these NP may also represent an additional contamination in groundwater. The aims of this study are to assess the impact of nZVI on the nitrate-reducing potential, the abundance and the structure of a planktonic nitrate-reducing bacterial community sampled in groundwater from a multicontaminated site. An active nitrate-reducing bacterial community was obtained from groundwater samples, and inoculated into batch reactors containing a carbon substrate, nitrate and a range of nZVI concentrations (from 0 to 70.1 mg Fe.L-1). Physical (pH, redox potential), chemical (NO3- concentrations) and biological (DNA, RNA) parameters were monitored during 1 week, as well as nZVI size distribution and mortality of bacteria. Nitrate-reducing activity was temporally stopped in the presence of nZVI at concentrations higher than 30 mg L-1, and bacterial molecular parameters all decreased before resuming to initial values 48 h after nZVI addition. Bacterial community composition was also modified in all cultures exposed to nZVI as shown by CE-SSCP fingerprints. Surprisingly, it appeared overall that bacteria viability was lower for lower nZVI concentrations. This is possibly due to the presence of larger, less reactive NP aggregates for higher nZVI concentrations, which inhibit bacterial activity but could limit cell mortality. After 1 week, the bacterial cultures were transplanted into fresh media without nZVI, to assess their resilience in terms of activity. A lag-phase, corresponding to an adaptation phase of the community, was observed during this step before nitrate reduction reiterated, demonstrating the community's resilience. The induction by nZVI of modifications in the bacterial community composition and thus in its metabolic potentials, if also occurring on site, could affect groundwater functioning on the long term following nZVI application. Further work dedicated to the study of nZVI impact on bacterial community directly on site is needed to assess a potential impact on groundwater functioning following nZVI application.

In 2008, as part of a feasibility study for radioactive waste disposal in deep geological formations, the French National Radioactive Waste Management Agency (ANDRA) drilled several boreholes in the transposition zone in order to define the potential variations in the properties of the Callovo&ndash, Oxfordian claystone formation. This consisted of a rare opportunity to investigate the deep continental biosphere that is still poorly known. Four rock cores, from 1709, 1804, 1865, and 1935 m below land surface, were collected from Lower and Middle Triassic formations in the Paris Basin (France) to investigate their microbial and geochemical composition. Rock leachates showed high salinities ranging from 100 to 365 g&middot, L&minus, 1 NaCl, current temperatures averaging 65 &deg, C, no detectable organic matter, and very fine porosity. Microbial composition was studied using a dual cultural and molecular approach. While the broad-spectrum cultural media that was used to activate microbial communities was unsuccessful, the genetic investigation of the dominant 16S rRNA gene sequences revealed eight bacterial genera considered as truly indigenous to the Triassic cores. Retrieved taxa were affiliated to aerobic and facultative anaerobic taxon, mostly unknown to grow in very saline media, except for one taxon related to Halomonas. They included Firmicutes and &alpha, &beta, and &gamma, Proteobacteria members that are known from many subsurface environments and deep terrestrial and marine ecosystems. As suggested by geochemical analyses of rocks and rock leachates, part of the indigenous bacterial community may originate from a cold paleo-recharge of the Trias aquifer with water originating from ice melting. Thus, retrieved DNA would be fossil DNA. As previously put forward to explain the lack of evidence of microbial life in deep sandstone, another hypothesis is a possible paleo-sterilisation that is based on the poly-extremophilic character of the confined Triassic sandstones, which present high salinity and temperature.

International audience; Many studies are now focusing on bioleaching methods to recover metals from WEEE. The efficiency of this process is highly dependent on microorganisms but also on the solid-liquid-gas mass transfer, which is controlled by the reactor design. In this study, bioleaching of comminuted spent printed circuit boards (PCBs) was performed in a stirred tank reactor operated in batch mode and in a double-stage continuous bioreactor. The metal dissolution kinetics were compared. The first stage of the continuous bioreactor was a bubble column in which a BRGM-KCC acidophilic consortium comprising Leptospirillum ferriphilum and Sulfobacillus benefaciens was used to oxidise Fe(II) into Fe(III). The resulting liquor was used to leach out metals contained in PCBs in the second stage of the bioreactor with mechanical stirring. The use of two distinct stages allowed the bacteria to adapt gradually to the PCBs and reach high dissolution yields, i.e. 96% Cu, 73% Ni, 85% Zn and 93% Co when 1% (w/v) PCB scraps were added into the bioleaching reactor, with a hydraulic residence time of 48 hours. By using the double-stage bioreactor, the concentration of PCB scraps could be increased up to 1.8% (w/v) without reducing bioleaching performance. Biomass concentration in the second stage and adaptation of the microorganisms to the toxicity of the metals were sufficient for only the second stage to be used. Under these conditions, the dissolution kinetics were stable, even when iron was provided only by the comminuted PCBs.

International audience; Arsenic removal consecutive to biological iron oxidation and precipitation is an effective process for treating As-rich acid mine drainage (AMD). We studied the effect of hydraulic retention time (HRT)-from 74 to 456 min-in a bench-scale bioreactor exploiting such process. The treatment efficiency was monitored during 19 days, and the final mineralogy and bacterial communities of the biogenic precipitates were characterized by X-ray absorption spectroscopy and high-throughput 16S rRNA gene sequencing. The percentage of Fe(II) oxidation (10-47%) and As removal (19-37%) increased with increasing HRT. Arsenic was trapped in the biogenic precipitates as As(III)-bearing schwertmannite and amorphous ferric arsenate, with a decrease of As/Fe ratio with increasing HRT. The bacterial community in the biogenic precipitate was dominated by Fe-oxidizing bacteria whatever the HRT. The proportion of Gallionella and Ferrovum genera shifted from respectively 65 and 12% at low HRT to 23 and 51% at high HRT, in relation with physicochemical changes in the treated water. aioA genes and Thiomonas genus were detected at all HRT although As(III) oxidation was not evidenced. To our knowledge, this is the first evidence of the role of HRT as a driver of bacterial community structure in bioreactors exploiting microbial Fe(II) oxidation for AMD treatment.

International audience; In bioleaching processes using autotrophic bacteria, carbon dioxide (CO2) is the carbon source for the growth of the microorganisms and its availability is dependent on gas mass transfer. The objective of this study was to investigate the demand in CO2 in complex sulfidic copper (Cu) concentrate bioleaching operations and to optimise CO2 supply. Batch tests in 2 l-stirred reactors at 10%w/v solid concentration were performed to study the need for CO2-enrichment and to determine the adequate CO2 partial pressure in the gas inlet. The results show that ferrous iron (Fe(II)) oxidation, and thus microbial activity, is delayed when air is injected without CO2-enrichment; the carbonates present in the solid are not sufficient to provide the CO2 required for the activity of Fe oxidising bacteria. CO2-enrichment improves leaching kinetics since the copper dissolution rate increases from 84 mg L−1 h−1 with air solely to 120 mg L−1 h−1 when CO2 is added to air. A CO2 enrichment influences both the composition of the bacterial community and the abundance of the bioleaching species. This study proposes also a methodology to determine gas/liquid transfer components and to assess CO2 limitations in the system. It shows that the microorganisms are not only sensitive to the transfer rate of CO2 from the gas to the liquid phase, but also to the availability of CO2 in solution.

International audience; Ferric iron is a low-cost oxidant frequently used in hydrometallurgy and is particularly suitable to leach various metals from printed circuit boards (PCBs). This paper presents the use of the BRGM-KCC acidophilic consortium to generate ferric iron solution in a bubble column run in continuous mode. The influence of influent ferrous iron concentration, ranging from 1 to 9 g L −1 on the bio-oxidation rate was studied in the presence of a solid support. The impacts of the quantity of solid support, the hydraulic residence time (HRT), the culture medium and the type of support were established. Stable performance was achieved over an extended period with a Fe 2+ oxidation rate of 1400 mg L −1 h −1. Cryogenic scanning electron microscopy was used to observe the attachment of cells on the solid support in different operating conditions and showed that the clogging of the solid support with jarosite precipitates influenced its colonization by the microorganisms and the stability of the bioprocess. The operating conditions, and especially the influent ferrous iron concentration and nutritive medium composition , also influenced the structure and the abundance of the microbial community.

Primary copper sulfides, such as chalcopyrite, represent the most important copper resource and are currently mainly exploited by pyrometallurgy. Bioleaching is considered as environmental-friendly and economic alternative, and the technical feasibility of stirred tank reactor (STR) bioleaching of copper ore concentrates using acidophilic, iron- /sulfur-oxidizing microorganisms was proven. In case of copper concentrates from Kupferschiefer-type ore the copper recovery at temperatures suitable for moderately thermophilic acidophiles was, however, incomplete due to inefficient chalcopyrite dissolution. The presented study therefore aimed to enhance chalcopyrite dissolution by decoupling of growth and bioleaching activity of the acidophiles. This was achieved by a controlled temperature increase in laboratory bioreactor experiments with copper concentrate from Kupferschiefer-type ore. Total cell number and microbial activity monitoring allowed to define three stages of the bioleaching process: (i) growth phase, (ii) bioleaching phase and (iii) resting phase. The total residence time was close to seven days, according to copper recovery and iron oxidation activity. Experiments at constant temperatures (42 °C, 48 °C, 50 °C) and a controlled temperature increase at the end of the growth phase of 42/46 °C, 44/48 °C and 46/50 °C, showed that metal recovery was enhanced by incremental temperature increase and resulted in a lower redox potential. Copper recovery was improved from originally 86% to 97% by only 4–8 °C temperature increase. Mineralogical analysis confirmed an almost complete absence of chalcopyrite in the residues after the 46/50 °C bioleaching experiments. These results indicate a distinct temperature effect on copper recovery. The study defines parameters to make STR bioleaching of chalcopyrite-rich ores more efficient and economically feasible and ensures an optimal control of the process for upscaling.

Arsenic in agricultural soils may represent a risk for crop quality and surrounding water resources. In the frame of AgriAs project, “Evaluation and management of Arsenic contamination in agricultu ...