Search

Authors’ original file for figure 7

Authors’ original file for figure 3

Authors’ original file for figure 2

Authors’ original file for figure 5

Authors’ original file for figure 9

Authors’ original file for figure 1

Authors’ original file for figure 6

Authors’ original file for figure 8

Authors’ original file for figure 4

L'arsenic est un métalloïde toxique dont la présence, relativement fréquente, dans les eaux et les sols est liée soit au fond géochimique, soit aux activités humaines. En ce qui concerne les eaux destinées à la consommation, la législation impose une concentration maximale en arsenic de 10 µg.L-1. Les effets nocifs de l'arsenic sur la santé humaine rendent nécessaire le développement de technologies efficaces et peu couteuse pour éliminer cet élément des eaux potables, ainsi que dans les aquifères pollués et dans les effluents miniers (Wang et Zhao, 2009). Une unité de traitement biologique d'eaux potabilisable faiblement arséniée (As< 50µg/L), couplée à une unité de piégeage de l'As en sortie du bioréacteur, a été mise en œuvre sur un site réel afin d'étudier la robustesse du bioprocédé. Un bioréacteur contenant de la pouzzolane (matériau utilisé dans les traitements d'eaux) a été préalablement ensemencé par une souche bactérienne As(III) oxydante autotrophe (Thiomonas arsenivorans) (Battaglia-Brunet et al., 2002, Michon et al., 2010 ; Wan et al., 2010) puis alimenté par l'eau issue du forage à température ambiante (15-17°C) avec un fonctionnement discontinu (asservissement de l'alimentation du bioréacteur à la pompe du forage d'alimentation en eau). Le suivi du développement du biofilm As(III) oxydant au cours du traitement biologique a été réalisé par la recherche des gènes codant pour l'ARNr 16S (diversité bactérienne totale) et ceux codant pour une arsénite oxydase (aoxB) (diversité des bactéries As(III)-oxydantes). Ce suivi a montré une colonisation rapide et stable du support minéral par des bactéries endogènes de l'eau à traiter. Le rendement d'oxydation de l'étape d'oxydation biologique est compris entre 54 et 100 % avec des temps de séjour de 30 minutes à 7 minutes qui sont comparables à des temps de séjour de techniques classiques de traitement. Les concentrations résiduelles en As en sortie du procédé complet (oxydation biologique + piégeage) sont inférieures à 1 µg/L, et qui sont donc très encourageants pour une application industrielle.

Arsenic is a common trace-level constituent of gold-quartz vein deposits in mining regions. This toxic metalloid is often present in waste material, water and soil near gold mining areas. The discharge of mining drainage water containing arsenic contributes to its dispersion in the environment. The resulting contamination of surface waters, groundwater and sediments is a matter of great public concern due to the deleterious effects of arsenic on human health. In water, arsenic exists mostly as trivalent arsenite (As (III)) and pentavalent arsenate (As(V)), both forms being toxic to living organisms. Most of the existing treatment processes are effective only on As(V) which forms anionic complexes and is therefore more easily converted into solid waste, unlike As(III) which forms mobile neutral complexes. As a consequence, the removal of arsenic from water requires a preliminary oxidation step. The chemical oxidation of As(III) by O2 is very slow (Jekel [1]), and the use of oxidant chemicals entails high operation costs (US-EPA [2]). This cost aspect could be overcome by using biological treatment with As(III)-oxidizing bacteria (Zouboulis and Katsoyiannis [3]). Arsenic oxidation capabilities of bacteria are known for a long time, since Green [4] isolated a bacteria belonging to Achromobacter in cattle dip in South Africa. Numerous studies reported isolation of heterotrophic and autotrophic bacteria able to oxidize arsenic (Philips and Taylor [5], Osborne and Ehrlich [6], Abdrashitova et al. [7], Battaglia-Brunet et al. [8]). The present study deals with a mining water drainage resulting of the digging of an exploration gallery in a gold-arsenopyrite mineralization (cherts and quartz veins). Its flow-rate varies between 10 and 30 m3 h-1 and the arsenic concentration between 10 and 500 μg L-1 for a pH close to 6.5. The water contains also high concentrations of iron (between 2 and 15 mg L-1). Both arsenic and iron concentrations are higher than the French quality standards (which are set to 100 μg L-1 for arsenic and 3 mg L-1 for iron in this kind of context), and thus, require a treatment to be removed from the effluent before discharging it in the environment. In the earlier part of the study, Battaglia-Brunet et al. [9] identified a biological As(III)-oxidizing activity in diverse micro-environments along the water stream, from the source to the discharge point. From those results, we investigated the possibilities of using this natural phenomenon for the removal of arsenic in a passive on-site treatment process based on three successive steps: (i) biological oxidation of As(III) by indigenous bacteria biofilm in a fixed-bed reactor filled with pozzolana, (ii) precipitation of iron in the form of hydroxides, (iii) adsorption of As(V) onto iron hydroxides (and/or co-precipitation of As(V) with iron). Small-scale laboratory experiments showed that the indigenous bacterial population promoted As(III) and Fe(II) oxidation in conditions close to those of the site, i.e. temperature, water composition and oxygen availability. The immobilization of the bacteria on pozzolana by the development and the maintenance of a biofilm increased oxidation rates compared to natural conditions. These results were confirmed by long-term on site pilot-scale experiments. As and Fe removal was significant and their concentrations at the pilot outlet decreased under the discharge standards. The critical operation parameters determined in the study will be used to design a treatment unit based on the biological passive process described above.

International audience; Background/Objectives. The global use of organochlorine pesticides (OCPs) such as Lindane, DDT, Dieldrin, Kepone, Chlordane and Toxaphene has resulted in long-term soil impacts at many sites. Given the potential risks to human health and the environment, some OCP-impacted sites require treatment. One example being the use of the insecticide Kepone (1,1a,3,3a,4,5,5,5a,5b,6-Decachlorooctahydro-2H-1,3,4-(methanetriyl)cyclobuta[cd]pentalen-2-one) on banana plantations until the late nineties in the French West Indies (FWI) islands (Caribbean) which has resulted in the contamination of drinking water supplies, bans on vegetables, fish and sea food consumption and commercialization, and increased occurrence of prostate cancer. As in many other cases, the "dig-and-dump" approach is not practical here due to the magnitude of the problem, access issues, and/or resource constraints. Alternatively, "bioremediation" may potentially be used to treat the soils on site, often at lower costs, and certainly in a more sustainable manner. Unfortunately, most OCPs, notably kepone, are not amenable to conventional bioremediation technologies.

La contamination de l'arsenic des eaux destinées à la consommation humaine est un problème environnemental international majeur. De nombreuses études toxicologiques ont clairement mis en évidence la nature carcinogène de l'arsenic et la recommandation du seuil maximal admissible de l'As dans l'eau de l'OMS (10 µg/L) a été suivie par l'Union européenne en 1998. La mise au point de technologies efficaces et peu couteuse pour éliminer cet élément des eaux destinées à la consommation humaine, ainsi que dans les aquifères polluées et dans les effluents miniers est ainsi rendue nécessaire. Une unité de traitement biologique d'eaux potabilisable faiblement arséniée, couplée à une unité de piégeage de l'As en sortie du bioréacteur, a été mise en œuvre sur un site réel afin d'étudier la robustesse du bioprocédé biologique en conditions réelle. Ce bioréacteur à lit fixé a été préalablement ensemencé par une culture de bactéries As(III) oxydante autotrophe (Thiomonas arsenivorans) puis alimentée par l'eau issue du forage dans des conditions de température ambiante (15-17°C). Le suivi du développement du biofilm As(III) oxydant au cours du traitement biologique, qui a été réalisé par des techniques de CE-SSCP et PCR-DGGE -aoxB, a permis de démontrer une colonisation du support bactérien par des bactéries endogène de l'eau à traiter. Le rendement d'oxydation de l'étape d'oxydation biologique est compris entre 54 et 100 % selon le temps de séjour et des concentrations résiduelles en As en sortie du procédé complet (oxydation biologique + piégeage) inférieures à 2 µg/L, qui sont très encourageants pour une application industrielle.

Les effets nocifs de l'arsenic sur la santé humaine rendent nécessaire le développement de technologies efficaces et peu couteuse pour éliminer cet élément des eaux potables, ainsi que dans les aquifères polluées et dans les effluents miniers (Wang et Zhao, 2009). La limite maximale admissible dans les eaux destinées à la consommation humaine a été fixée à 10 µg/L par l'Organisation Mondiale de la Santé. Une unité de traitement biologique d'eaux potabilisable faiblement arséniée (As< 50µg/L), couplée à une unité de piégeage de l'As en sortie du bioréacteur, a été mise en œuvre sur un site réel afin d'étudier la robustesse du bioprocédé en conditions réelle. Ce bioréacteur à lit fixé a été préalablement ensemencé par une souche bactérienne As(III) oxydante autotrophe (Thiomonas arsenivorans) (Battaglia-Brunet et al., 2002) puis alimenté par l'eau issue du forage dans des conditions de température ambiante (15-17°C). Le suivi du développement du biofilm As(III) oxydant au cours du traitement biologique, par la recherche des gènes codant l'ARNr 16S et une arsenite oxydase (aoxB), a montré une colonisation par des bactéries endogènes de l'eau à traiter. Le rendement d'oxydation de l'étape d'oxydation biologique est compris entre 88 et 100 % avec des concentrations résiduelles en As en sortie du procédé complet (oxydation biologique + piégeage) inférieures à 1 µg/L, qui sont très encourageants pour une application industrielle.

One of the main challenges of CCS technology is to estimate and control the stability of the storage zone. Among all the parameters that can be listed on that subject, the knowledge about the local biosphere effect is poor. However, its activity has been already proven to be important, especially for BECCS systems where the CO2 incoming flux contains organic compounds. Indeed, these latter might significantly enhance the interaction between the biosphere and the CO2 plume. In this context, the goal of this study is to give first insights for the quantification of the impact of CO2 front on microbial biomass that occurs in saline aquifers during carbon geological storage. A sulfate reducing bacterium (Desulfotomaculum geothermicum) was tested with sediments (carbonaceous sandstone) in a pressurized column (10 bar of CO2 and 40 bar of nitrogen) at 54°C during a percolation test in saline artificial groundwater. Different measurements were realized in order to quantify the respective metabolic activities and the spatial speciation of organic and inorganic carbon in those systems. Despite a protective effect of the mineral matrix, the results showed a high sensitivity of autotrophic microorganisms to the stress induced by few bars of CO2 and revealed that a part of this stress was mainly due to direct toxic effects. Still an equilibration is reached and appeared to moderate these effects. Biomineralization processes of carbonates were not observed for D. geothermicum during these experiments and demonstrated variations in accordance with the availability of sediments. All these results were analyzed in correlation with previous results with that strain and demonstrated the feasibility to integrate geobiological data in speciation models as regards geological exploitation processes.

Background/Objectives. The global use of organochlorine pesticides (OCPs) such as Lindane, DDT, Dieldrin, Kepone, Chlordane and Toxaphene has resulted in long-term soil impacts at many sites. Given the potential risks to human health and the environment, some OCP-impacted sites require treatment. In certain cases, the "dig-and-dump" approach is not practical due to magnitude of the problem, access issues, and/or resource constraints. Here "bioremediation" can be used to treat the soil on site, often at lower costs, and certainly with lower generation of greenhouse gases. Unfortunately, most OCPs are not amenable to conventional bioremediation technologies hence they persist over time. Approach/Activities. DARAMEND® in situ chemical reduction (ISCR) technology uniquely combines controlled-release carbon with a reduced metal such - as zero valent iron (ZVI) or zinc - to yield a highly effective material for stimulating the complete degradation (no accumulation of catabolic intermediates) of persistent organic compounds present in soil, sediment and groundwater. The term ISCR is used to define the combined effects of stimulated biological oxygen consumption (via "fermentation" of complex organic carbon sources), direct chemical reduction with reduced metals, and the corresponding enhanced decomposition reactions that are realized at the lowered redox (Eh) conditions. In brief, the ZVI oxidizes to form ferrous iron and releases electrons in the process. The organic carbon is consumed by microorganisms that are indigenous to the soil, resulting in release of additional free electrons. These electrons transferred to the OCPs result in the removal of chlorine from the compound's structure (reductive dechlorination); ultimately, complete destruction of the pesticides occurs. Most soils can be effectively treated in a reasonable time frame (e.g., from 4 to 8 weeks) using standard agricultural machinery at a price typically less than US$20 per tonne of soil treated. Results/Lessons Learned. The presentation will summarize the ISCR theory followed by case studies in the United States, Brazil and Europe. Particular emphasis will be placed on the removal of OCPs from soil at sites in Canada (34 acres impacted by DDT, DDD, and DDE) and the Caribbean (French West Indies, Kepone impacted soils - technology validation tests). For Kepone, bench-scale studies demonstrated rapid (< 2 weeks) and extensive degradation: catabolites with up to 7 Cl removed were identified by GC/MS. Mesocosm (scale-up) studies with tropical soils determined that soil type had a significant impact on process efficacy. Ecotoxicity tests and bioaccumulation studies were also considered in the evaluation of the process. Recognized technology development needs include insight into catabolite environmental fate/affect. Significant advances in the biogeochemistry of OCP degradation are anticipated from basic research on microbiology and genetics of ISCR processes.

Decrease of As authorized level in drinking waters to 10 μg.l-1 requires developing treatments with low costs. In water, arsenic is mainly found as inorganic forms: As(V) and As(III), the latter being more toxic and mobile. Water treatments are therefore more effective to remove As(V) and thus, a pre-oxidation step is generally necessary. Biological treatment using As(III)-oxidising bacteria, followed by As adsorption on Fe0 coated sand bed reactor, could be a promising treatment process. Thiomonas arsenivorans, an autotrophic bacteria isolated from a gold mine in France, was used to oxidise As(III) in fixed bed bioreactors. The objectives of this work were to study the influence of filling material (sand or Fe0-coated sand) on bacteria development and to compare performances obtained for biological oxidation in a single oxidation-adsorption reactor or in an oxidation reactor followed by an adsorption one. Experiments were carried out in three thermostated reactors (12°C). C1 was filled with sand (sieved at 1-2 mm) and 1% Fe0, C2 was identical but inoculated with Thiomonas arsenivorans and C3 was filled with sand only and inoculated. Bed volume and hydrodynamic parameters of all reactors were characterised. After inoculation of C2 and C3, the three bioreactors were continuously up-flow fed with a synthetic water containing 10 mg.l-1 As(III). This high concentration was chosen in order to favour bacteria development. During experiments, water samplings were performed at several heights along the reactors for arsenic speciation analysis using HPLC-HG-AFS. At the end of the experiment, the contents of bioreactors were collected and divided into different parts according to their height in the reactor in order to study bacterial distribution. For each collected fraction, batch experiments were performed to study kinetics of As(III) bacterial oxidation. Bacteria diversity was also analysed on these fractions by PCR-DGGE.

In drinking water supply, arsenic exists mostly as As(III) and As(V) forms which are toxic to living organisms. According to WHO recommendations, the drinking water standard was reduced from 50 to 10 μg.L-1 and many regulatory agencies have recently accepted this new standard. Most of the existing treatment processes are effective only on As(V) which forms anionic complexes unlike As(III) which forms mobile neutral complexes. As a consequence, the removal of arsenic from water requires a preliminary oxidation step of As(III) form which can be done by using Bayoxide, GEH but their cost remains high for small drinking water treatment units. This could be overcome thanks to biological treatment using As(III)-oxidising bacteria associated with As(V) adsorption process. Numerous autotrophic bacteria are able to oxidise arsenic. Among them, Thiomonas arsenivorans is able to oxidise As(III) up to 100 mg As(III).L-1 and appears to be an interesting bacterium in that it is an autotrophic bacterium which uses arsenic as an energy source and carbon dioxide or carbonates as carbon source The objectives of this work were (1) to optimise the As(III) oxidation from water drinking resources in fixed bed bioreactor and (2) to study the biofilm development during the treatment in order to improve the efficiency of the treatment. Experiments were performed in plastic bioreactors equipped with intermediate water outflows, filled with pozzolana sieved at 5-7 mm and inoculated with a culture of T. arsenivorans. Bioreactors were then continuously up-flow fed with As(III) and a synthetic water at pH 7 whose composition and temperature (12°C) are closed to that of a natural groundwater. Residence time (30 and 15 minutes) and As(III) concentrations (15 and 50 μg.l-1) were studied. Arsenic speciation and analysis was performed using GF-AAS. At the end of the experiment, bioreactors were dismantled for biolfim analysis: bacterial counting, bacterial cell viability, bacterial diversity by CE-SSCP, diversity of aoxB gene (As(III)-oxidase enzyme) by PCR-DGGE were performed on the pozzolana samples.

Not available, La distribution de la microflore dans un profil de sol ainsi que son comportement métabolique ont été caractérisés au cours de ce travail. L'installation d'un dispositif expérimental sur une parcelle cultivée de Bourgogne nous a permis de suivre les variations des facteurs physiques comme la température et la teneur en oxygène à différentes profondeurs dans le sol. Les fluctuations saisonnières de ces 2 facteurs permettent une activité microbienne aérobie jusqu'a une profondeur de 5 mètres. Nous avons mis en évidence que la microflore du sous-sol est à prédominance bactérienne. Le nombre de microorganismes aérobies est de 10^7 g-¹ sol et décroit à 10^5-10^6 g-¹ sol à partir de 60 centimètres de profondeur puis reste constant au-delà. Les mesures d'estimations de la teneur en carbone microbien (estimées par les méthodes biocidales et physiologiques) corroborent le résultat précédent. Nous avons aussi déterminé que le coefficient de conversion du carbone extrait par la méthode de fumigation-extraction en carbone microbien, Kec, variait avec la profondeur. Nos résultats montrent l'existence d'une activité microbienne aérobie diversifiée jusqu'à 5 mètres de profondeur. Toutefois, la vitesse de minéralisation des composés organiques (glucose, l'acétate, l'acide benzoïque) diminue avec la profondeur et cette diminution semble être liée à celle de la biomasse microbienne. La diminution de l'activité hétérotrophe de la microflore du sous-sol, à savoir une diminution des paramètres Vm et Km, met en évidence une adaptation des microorganismes aux conditions oligotrophes de leur environnement. Les études de dégradation des molécules xénobiotiques telles que le 2,4-D et l'atrazine dans le sous-sol montreraient la nature co-métabolique de la dégradation

International audience

National audience