Efficiency of arsenic oxidizing bacterial biofilms for arsenic contaminated drinking water treatment

In drinking water supplies, arsenic exists mostly as two inorganic forms, arsenite [As(III)] and arsenate [As(V)] which are toxic to living organisms . According to WHO recommendations, the drinking water standard was reduced from 50 to 10 µg/L and many regulatory agencies have recently accepted this new standard. Most of the existing treatment processes are effective only on arsenic anionic forms [As(V)] and not on neutral and mobile arsenic complexes. To overcome this lack of efficiency, a first oxidation step of As(III) form is necessary and is usually performed using strong oxidant or binding materials that are costly for small drinking water treatment units. An alternative to theses physico-chemical treatments is the biological treatment using As(III)-oxidising bacteria. Numerous autotrophic bacteria are able to oxidise arsenic. Among them, Thiomonas arsenivorans [4-6] is able to oxidise As(III) up to 100 mg As(III)/L and appears to be a good candidate for its known capacity to use As(III) as an energy source and carbon dioxide or carbonates as carbon source. An As(III)-oxidizing biological treatment pilot unit coupled to trapping units for As(V) removal at the outflow of the biological bioreactor was performed on site in order to study the strength of the biological process in real operating conditions. The bioreactor was previously inoculated with the autotrophic As(III)-oxidizing Thiomonas arsenivorans. Then, it has been intermittently fed with contaminated water from the drinking water well, at site temperature (15-17°C) and under downstream mode. As(III)-oxidizing biofilm development has been followed during the pilot functioning using CE-SSCP-16S (targeting the global community) and PCR-DGGE-aoxB (targeting As(III) oxidizers) fingerprinting techniques. Results showed a complete colonization of the mineral support (i.e. pozzolana) by indigenous bacteria of the groundwater to be treated. Moreover, the oxidation yield of the biological step was in the range of 54 to 100 % depending on the residence time (from 30 to 7 minutes) and the residual As concentration at the end of the complete treatment process (biological oxidation and trapping) was below 2 µg As/L. These results are thus very encouraging for an industrial application in regard to the strength and its absence of nutrients supply, except for the low amount of oxygen needed if it is not in sufficient concentration in the site water.

Impact de nanoparticules de fer zéro-valent (nZVI) sur la structure de la communauté bactérienne issue d'une eau souterraine

International audienc

Decoupling of arsenic and iron release from ferrihydrite suspension under reducing conditions: a biogeochemical model

High levels of arsenic in groundwater and drinking water are a major health problem. Although the processes controlling the release of As are still not well known, the reductive dissolution of As-rich Fe oxyhydroxides has so far been a favorite hypothesis. Decoupling between arsenic and iron redox transformations has been experimentally demonstrated, but not quantitatively interpreted. Here, we report on incubation batch experiments run with As(V) sorbed on, or co-precipitated with, 2-line ferrihydrite. The biotic and abiotic processes of As release were investigated by using wet chemistry, X-ray diffraction, X-ray absorption and genomic techniques. The incubation experiments were carried out with a phosphate-rich growth medium and a community of Fe(III)-reducing bacteria under strict anoxic conditions for two months. During the first month, the release of Fe(II) in the aqueous phase amounted to only 3% to 10% of the total initial solid Fe concentration, whilst the total aqueous As remained almost constant after an initial exchange with phosphate ions. During the second month, the aqueous Fe(II) concentration remained constant, or even decreased, whereas the total quantity of As released to the solution accounted for 14% to 45% of the total initial solid As concentration. At the end of the incubation, the aqueous-phase arsenic was present predominately as As(III) whilst X-ray absorption spectroscopy indicated that more than 70% of the solid-phase arsenic was present as As(V). X-ray diffraction revealed vivianite Fe(II)3(PO4)2.8H2O in some of the experiments. A biogeochemical model was then developed to simulate these aqueous- and solid-phase results. The two main conclusions drawn from the model are that (1) As(V) is not reduced during the first incubation month with high Eh values, but rather re-adsorbed onto the ferrihydrite surface, and this state remains until arsenic reduction is energetically more favorable than iron reduction, and (2) the release of As during the second month is due to its reduction to the more weakly adsorbed As(III) which cannot compete against carbonate ions for sorption onto ferrihydrite. The model was also successfully applied to recent experimental results on the release of arsenic from Bengal delta sediments

Impact d'un traitement au H2O2 sur la biodégradation des BTEX évaluée par fractionnement isotopique du carbone stable et abondance des gènes codant des enzymes spécifiques à la dégradation des BTEX

International audienc

Shift in Natural Groundwater Bacterial Community Structure Due to Zero-Valent Iron Nanoparticles (nZVI)

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

Selection, Instrumentation and Characterization of a Pilot Site for CO2 Leakage Experimentation in a Superficial Aquifer

AbstractCO2 geological storage is one of the options for mitigation of GHG emissions into the atmosphere. Although storage is provided for several millennia, leakage can occur. Therefore the risk that the fugitive CO2 reaches a shallow aquifer cannot be excluded [1]. That is why the consortium launched the research program CIPRES, funded by the French Research Agency, concerning the potential impacts of CO2 leakage on groundwater quality. This program includes the realization of a shallow CO2 release experiment in a carbonated aquifer and its monitoring in the saturated and unsaturated zones, the soil and the soil-atmosphere interface. The experimentation consists in drilling a well into the aquifer, injecting dissolved CO2 in water [2] and tracking its impact downstream. Prior to this experiment, a site had to be selected, instrumented and characterized.Hydrogeological target is the Paris basin chalk which is the largest French aquifer. The selected area is a large parcel, formerly cultivated in intensive monoculture but left fallow for several years, located in Catenoy (Oise) about 50km north of Paris. The geological log shows the chalk is covered by 6-7 m of sands but water table is located at 12-13 m depth, i.e. integrally in the chalk strata.The site has been equipped with 10 wells to characterize the groundwater flow (hydraulic gradient ∼5 10-3). 6 wells are aligned in the groundwater flow direction: the PZ2, planned for CO2 injection, the PZ1 located 20 m upstream and 4 monitoring wells located downstream between 10 and 60 m from PZ2. There are also 4 lateral piezometers located near (PZ7, PZ8) and far (PZ9, PZ10) from the injection site: they are dedicated to the lateral plume. These 25 m depth wells are equipped with tubing fully slotted in the chalk. Alongside, 4 wells dedicated to gas monitoring in unsaturated zone have been drilled at 11m depth.To characterize the site, the following operations were performed prior to the CO2 injection between March and September 2013:•pump test into PZ2 to estimate the hydraulic conductivity (10-3 m.s-1) and the storage coefficient (1.6%); the hydraulic conductivity is higher in the first 3 m of saturated zone (∼5 10-3 m.s-1);•hydrogeochemical baseline with monthly water analysis in each well (physicochemical parameters, major and minor ions, metallic trace elements); electrical conductivity is 714μs.cm-1 and groundwater has a calcium-bicarbonated facies with high nitrate concentration (45mg.l-1) and low-level presence of trace metals;•gas baseline with continuous O2 and CO2 measurement in vadose trough 11 m depth boreholes and measurements campaigns to determine gas concentration in the soil and gas flux on the surface;•flowmeter heatpulse logging at PZ2, PZ3 and PZ4 in static and dynamic conditions; only the area situated from 15 m to 20 m depth is productive and a vertical natural downflow is measured in PZ3 (∼1-2mm.s-1) and PZ4 (1cm.s-1); furthermore, no flow is measured from 20 to 25 m depth; this confirms the vertical anisotropy of the chalky aquifer;Following this experiments, a tracer test has been done in June 2013 from PZ2 with fluorescent tracer (amino-acid G) and a dissolved gas (He), in the way to calibrate the future CO2 injection and its monitoring. 2 m3 of water from the aquifer were pumped the day before the injection and stored in tanks. Then 2kg of tracer were dissolved and water was saturated with He. This water was injected into the PZ2 the next day during 8h. The monitoring was conducted for a month by water sampling, tracer and He analyzes. The peak of fluorescent tracer arrived at the 2nd day following injection in the PZ4 (20 m downstream) but only one week later in the PZ3 (10 m downstream), due to the site anisotropy. Low He concentrations have been detected in the unsaturated zone of PZ4 before PZ3, in correlation with tracer migration.The main result is the existence of an high aquifer anisotropy in such a small area: i) the first 3 m of the saturated zone shows a higher permeability and the last 5 m a lower one, ii) the tracer arrives quickly and with higher concentration at PZ4 located 10 m farther than PZ3. However, the dilution ratio is rather important and may induce, during CO2 leakage experimentation, a slight pH decrease at the downstream wells: in order to increase the impact of the CO2 leakage, we have therefore planned to inject a higher volume (10 m3) of CO2 saturated water

Ecologie microbienne de déchets sulfurés et biolixiviation par les bactéries endogènes pour leur stabilisation et la récupération de métaux

International audienc

Cuantificación, aislamiento e identificaciónde comunidades anaerobias amilolíticas de un manantial termomineral de paipa, boyacá

Se cuantif icaron microorganismos anaerobios termofílicos amilolíticos de un manantial termomineral en la región andina (5° 45' 69’’ N, 73° 6' 61’’ W, 2500 msnm) a través del Número Más Probable (NMP). Los recuentos microbianos de las poblaciones presentaron valores entre 1,9*102 células/100 mL y 5.8*102 células/100 mL en presencia de almidón y tiosulfato como aceptor de electrones y 1,4*102células/100 mL y 3,4*102 células/100 mL en presencia solamente de almidón. Se realizaron aislamientos microbianos a partir de las últimas diluciones positivas del NMP y se aislaron 8 cepas bacterianas denominadas P4-6, P4-7, P4-8, P4-9, P4-10, P4-11, P4-12 y P4-13. Estas cepas crecieron a temperaturas óptimas entre 60 y 65 °C, y exhibieron un metabolismo fermentativo. El principal producto de fermentación fue etanol seguido de acetato, CO2 e hidrógeno. El tiosulfato fue utilizado como aceptor externo de electrones, pero el sulfato o el hierro férrico no fue reducido. La diversidad filogenética de estas 8 cepas fue evaluada por medio de geles de electroforesis de gradiente denaturalizante (DGGE). Se analizó la secuencia del gen 16S rRNA de dos de las cepas aisladas (P4-6 y P4-9) y el análisis indicó que éstas pertenecen a la familia Thermoanaerobiaceae del dominio Bacteria. Del análisis fenotípico y genotípico se deduce que estos organismos pertenecen al género Thermoanaerobacter, y con base en el análisis de las secuencias del 16S rDNA se observa una similitud del 98% con Thermoanaerobacter italicus y Thermoanaerobacter mathranii. Palabras clave: termofilia, manantiales termominerales, anaerobiosis, Thermoanaerobacter, DGGE.The amilolytic thermophilic anaerobic microorganisms of a mineral hot spring in the Andean region (5° 45' 69’’ N, 73° 6'61’’W, 2500 m) were quantified through the Most Probable Number (MPN) technique. The microbial recounts of the populations presented values between 1.4*102cell/100 mL and 5.8*102 cell/100 mL in the presence of starch and thiosulphate as electron acceptors and 3.4*102 cel/100 mL in the presence of starch alone. Microbial isolations were conducted starting with the last positive dilutions of the MPN and 8 bacterial strains were isolated and denominated P4-6, P4-7, P4-8, P4-9, P4-10, P4-11, P4-12, and P4-13. These strains grew at optimum temperatures between 60 and 65 °C and exhibited fermentative metabolism. The main product of fermentation was ethanol followed by acetate together with hydrogen and CO2. Thiosulphate was used as external acceptor of electrons by all the isolated strains, but not sulphate or ferric iron. The phylogenetic diversity of these 8 strains was evaluated through denaturing gel gradient electrophoresis (DGGE) analysis. The sequence of the gene encoding for the 16S rRNA of two of the isolated strains (P4-6 and P4-9) was analyzed. These analyses showed that they belong to the family Thermoanaerobiaceae, domain Bacteria. From their phenotypical and genotypical characteristics, it is inferred that these organisms belong to the genus Thermoanaerobacter with similarity of 98% of the 16S rDNA with Thermoanaerobic italicus and Thermoanaerobacter mathranii. Key words: thermophile, hot springs, anaerobiosis, Thermoanaerobacter, DGGE

Efficacité de biofilms de bactéries As-oxydantes pour l'étape de traitement biologique d'eaux potabilisables arséniées

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

Dynamics of Bacterial Communities Mediating the Treatment of an As-Rich Acid Mine Drainage in a Field Pilot

Passive treatment based on iron biological oxidation is a promising strategy for Arsenic (As)-rich acid mine drainage (AMD) remediation. In the present study, we characterized by 16S rRNA metabarcoding the bacterial diversity in a field-pilot bioreactor treating extremely As-rich AMD in situ, over a 6 months monitoring period. Inside the bioreactor, the bacterial communities responsible for iron and arsenic removal formed a biofilm (“biogenic precipitate”) whose composition varied in time and space. These communities evolved from a structure at first similar to the one of the feed water used as an inoculum to a structure quite similar to the natural biofilm developing in situ in the AMD. Over the monitoring period, iron-oxidizing bacteria always largely dominated the biogenic precipitate, with distinct populations (Gallionella, Ferrovum, Leptospirillum, Acidithiobacillus, Ferritrophicum), whose relative proportions extensively varied among time and space. A spatial structuring was observed inside the trays (arranged in series) composing the bioreactor. This spatial dynamic could be linked to the variation of the physico-chemistry of the AMD water between the raw water entering and the treated water exiting the pilot. According to redundancy analysis (RDA), the following parameters exerted a control on the bacterial communities potentially involved in the water treatment process: dissolved oxygen, temperature, pH, dissolved sulfates, arsenic and Fe(II) concentrations and redox potential. Appreciable arsenite oxidation occurring in the bioreactor could be linked to the stable presence of two distinct monophylogenetic groups of Thiomonas related bacteria. The ubiquity and the physiological diversity of the bacteria identified, as well as the presence of bacteria of biotechnological relevance, suggested that this treatment system could be applied to the treatment of other AMD