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.

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

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

ISCR treatment of chlordecone contaminated soils : effect of soil structure

International audienc

Caracterisation de la distribution et du comportement metabolique de la microflore indigene dans un profil de sol

* INRA Unite Regionale de Documentation, B.V. 1540, 21034 Dijon Cedex Diffusion du document : INRA Unite Regionale de Documentation, B.V. 1540, 21034 Dijon Cedex Diplôme : Dr. Ing

Caractérisation de la distribution et du comportement métabolique de la microflore indigène dans un profil de sol

Not availableLa 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 dégradatio

Mise en evidence et etude de l'activite d'une communaute microbienne degradant le 2,4-D

National audienc

Reassessement of the Kec coefficient of the fumigation-extraction method in a soil profile

International audienc

Adsorption of AsIII, AsV and dimethylarsinic acid onto synthesized lepidocrocite

International audienceThe 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 (As-III, As-V) 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 1mol for As-V, DMA and As-III could be respectively trapped per kilogram of zero-valent iron. pH influence varied from one arsenic species to another: increasing pH improve As-III and DMA sorption whereas it has a very low effect on As-V sorpti

Remediation by chemical reduction in laboratory mesocosms of three chlordecone-contaminated tropical soils

International audienceChlordecone (CLD), a highly persistent organochlorine pesticide commonly encountered in French West Indies (FWI) agricultural soils, represents a major source of contamination of FWI ecosystems. The potential of chemical reduction for remediation of CLD-contaminated soil has been investigated in laboratory pilot-scale 80 kg mesocosms for andosol, ferralsol, and nitisol from FWI banana plantations. Six cycles consisting of a 3-week reducing phase followed by a 1-week oxidizing phase were applied, with 2 % (dw/dw) DaramendA (R) (organic plant matter fortified with zero valent iron) added at the start of each cycle. Complementary amendments of zero valent iron and zinc (total of 3 % dw/dw) were added at the start of the first three cycles. After the 6-month treatment, the CLD soil concentration was lowered by 74 % in nitisol, 71 % in ferralsol, and 22 % in andosol. Eleven CLD-dechlorinated transformation products, from mono- to penta-dechlorinated, were identified. None of them accumulated over the duration of the experiment. Six of the seven ecotoxicological tests applied showed no difference between the control and treated soils. The treatment applied in this study may offer a means to remediate CLD-contaminated soils, especially nitisol and ferralsol