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

International audienc

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.

CEReS -Co-processing of Coal Mine & Electronic Wastes: Novel Resources for a Sustainable Future

International audienceMany coal mines produce waste which causes acid mine drainage (AMD) potentially resulting in severe environmental damage. This drainage can be treated, but most wastes will continue to produce such drainage for hundreds of years. Therefore, longer term, permanent solutions are needed. At the same time, the pace of technological development means most electrical and electronic equipment becomes obsolete within a matter of years. This results in the generation of vast and growing quantities of electronic waste (e-waste) every year. Where this cannot be recycled, it must be discarded. CEReS was a 3.2 M€ RFCS-funded project comprising eight partners from five countries. It targeted the development of a co-processing approach to treat these waste streams to produce metals and other valuable products, while eliminating their environmental impact. This brings together two waste streams from opposite ends of the supply chain (for which no alternative treatment option exists); turning each into a novel resource in a single, coherent 'grave-to-cradle' process. This industrial ecology approach is key to supporting a circular economy while securing the sustainable supply of critical raw materials. The project successfully elaborated a novel co-processing flow-sheet comprising: (i) the accelerated weathering of AMD-generating coal production wastes to generate a biolixiviant; (ii) the pyrolysis and catalytic cracking of low-grade PCBs to produce hydrocarbon fuel, a halogen brine a Cu-rich char; (iii) the leaching of base metals from the char using the biolixiviant; (iv) the reuse of the stabilised coal wastes; and (v) the recovery of valuable metal while concentrating precious and critical metals into enriched substrates. These individual process units were demonstrated individually at lab-pilot scale. The data were then used to validate the entire flow-sheet in an integrated process simulator. Finally an LCA approach was used to demonstrate the environmental benefits of the CEReS process over the status quo

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

Degradation and transfer of polyacrylamide based flocculent in sludge and industrial and natural waters

International audienceFlocculants are widely used in numerous industrial domains (food-processing industry, mineral industries, chemical industries, water purification, wastewater treatment) to im-prove the solid/liquid separation in water-containing fine par-ticles. Thanks to the addition of flocculants, particles gather together and form flocs that improve the materials aggregation and wastewater clarification. At the molecular level, floccu-lants can be mineral polymers or natural organic polymers, but synthetic organic polymers constitute the main flocculants. Generally, they are anionic polyacrylamides produced by polymerisation of acrylamide and the anionic co-monomer, the sodium acrylate. Monomers are only partially eliminated during polyacrylamide preparation and remain at the state of tracks in the end product. According to Smith et al. (1996), the residual content in monomers varies between 0.05 and 5 %. Sodium acrylate presents no harmfulness like the polyacryl-amide (Stephens, 1991). However, as the acrylamide is con-sidered as a carcinogenic molecule, mutagen and reprotoxic (Molak, 1991), all polyacrylamides (PAMs) used within the European Union are required to contain less than 0.1 % (w/w) of residual acrylamide (AMD) (European Parliament 1999) unless they are classified and labelled as a category 2 carcin-ogen (European Parliament 2006). More stringent thresholds are also set depending on additional regulations covering specific uses like, for example, when PAM-based flocculants are used for the treatment of drinking water (no more than 0.05 % of residual AMD). The potential risks on environment and health are thus linked to the spreading of acrylamide and polyacrylamide degradation products in the natural environment. Two levels of spreading have to be considered: – The water: about 95 % of the polymers adsorb on th

Bioprocessing low grade copper ores - a promising alternative

International audienceThis paper presents an overview of the work performed by the BRGM team in the last 10 years on the development of bio-hydrometallurgy dedicated to the processing of low-grade copper ores from the Kupferschiefer deposits. It covers selection and adaptation of microbial consortia, optimization of process operating parameters such as solid contents, the relationship between bioleaching performance and mineralogy, testing operating parameters to overcome chalcopyrite recalcitrance, design of process options and economical assessment. The selected bacterial inoculum (autotrophic, working at 42°C) enables to achieve high Cu recovery (up to 95%). In continuous piloting tests the increase of the solid load in the pulp from 15% to 25% doesn’t affect the bioleaching efficiency despite the high and unusual Cu concentration reached in the liquor (40 g l-1). Operating at 25% solid load reduces by 2.3 the size of the leaching tanks compared to 15% solid load, which leads to a significant decreasing of the CAPEX

Bioprospecting and the Microbial Ecology of a Coal Production Waste Dump

International audienceIn order to develop an optimised coal production waste bioleaching unit, a sampling campaign was carried out on the existing waste dump. Eleven samples from various surface locations of the heap were used for enrichment cultures at three temperatures (30°C, 42°C and 48°C). Interestingly, none of the 11 cultures at 42°C grew well (low cell numbers and poor pyrite dissolution). Bioreactors inoculated with pooled enrichments showed the same results, indicating that the waste heap harboured organisms capable of growth and mineral oxidation at 30°C and 48°C but not 42°C. Analysis of the 48°C culture used for subsequent reactor tests using a variety of molecular microbiology methods (CE-SSCP, T-RFLP and high-throughput sequencing) revealed the culture was dominated by Sulfobacillus thermosulfidooxidans, Acidithiobacillus caldus and an unknown member of the Acidimicrobiaceae. Further tests at 42°C using a well-characterised bi-oleaching consortium, BRGM-KCC, performed well in initial reactors. However, during each batch the relative abundance of Leptospirillum ferriphilum decreased, and its numbers declined gradually with each subsequent subculture indicating some form of accrued inhibition. Coupled with the absence of a 42°C culture from the dump it was theorised that the waste was inhibitory to Leptospirillum spp. In order to further explore the possible reasons for the absence of Leptospi-rillum in the enrichments and bioreactors, a detailed analysis of the waste heap was undertaken using a range of geochemical and molecular biology tools. Results suggest the role of an as-yet unidentified organic carbon compound from the coal itself

Dissemination of acrylamide monomer from polyacrylamide-based flocculant use—sand and gravel quarry case study

International audienceAggregate quarries play a major role in land settlement. However, like all industrial operations, they can have impacts on the environment, notably due to the use of polyacrylamide (PAM)-based flocculants, which contain residual acrylamide (AMD), a carcinogenic, mutagenic, and reprotoxicmonomer. In this study, the dissemination ofAMD throughout the environment has been investigated in a French quarry. The presence of AMD has been determined in the process water and in the sludge, as well as in the surrounding surface water and groundwater. From the results of several sampling campaigns carried out on this case study, we can (a) confirm that the AMD contained in the commercial product is found in thequarry’s water circuit (0.41 to 5.66 μg/l); (b) show that AMD is transported to the surrounding environment, as confirmed by the contamination of a pond near the installation (0.07 to 0.08 μg/l) and the presence of AMD in groundwater (0.01 to 0.02 μg/l); and (c) show that the sludge in both the current and former settling basins containsAMD (between 4 and 26 μg/kg of dry sludge). Therefore, we demonstrated in this case study that using PAM-based flocculants leads to the release of AMD to the environment beyond the treatment plant and creates a reserve of AMD in sludge basins

Metal recovery from printed circuit boards (PCBs) by acidophilic bioleaching

International audienceDuring bioleaching, the use of bacteria allows the dissolution of metals with markedly reduced amount of reagents and mild pressure and temperature conditions, compared to usual operating conditions. In our study, acidophilic bioleaching was applied to comminuted spent printed circuit boards (PCBs). These wastes contain various metals, including precious and base metals, with concentrations that are generally higher than those found in primary resources. Some studies already demonstrated the efficiency of PCBs bioleaching but significant variations are observed between reported bioleaching rates. In the present study, a double-stage bioreactor has been designed and used in order to bioleach comminuted PCBs in continuous mode. The first stage of the continuous bioreactor was a bubble column in which the acidophilic consortium BRGM-KCC mainly composed of Leptospirillum ferriphilum and Sulfobacillus benefaciens was used to oxidize Fe(II) into Fe(III). The resulting leaching solution was employed to leach the metals contained in PCBs under mechanical stirring in the second stage of the bioreactor. Such a configuration was particularly relevant to reduce the impact of PCBs toxicity on bacterial growth and to maximize bioleaching rates. The culture was able to slowly adapt to PCBs (1% w/v). Consequently , with 48 hours residence time, main metals were dissolved with high yields : 96% Cu, 85% Zn, 73% Ni and 93% Co. When the solid concentration was increased up to 1.8%(w/v), it resulted in higher dissolution rates

Community dynamics during adaptation and upscaling of a secondary polysulfidic ore bioleaching process

International audienceWithin European research project NEMO, a bioleaching strategy was developed for efficient metal extraction from secondary ore material currently heap-leached at Sotkamo by Terrafame (Finland) that still contains several sulfidic minerals and significant amounts of valuable metals (Ni, Zn, Co, Cu). A moderately thermophilic bioleaching consortium mainly composed of Acidithiomicrobium P2 and Sulfobacillus thermosulfidooxidans was adapted to the Sotkamo heap-leaching residue, grinded below 250 µm (d80), in batch 2-L stirred tank reactors, at pH 1.7 and 55°C. Community composition was followed by t-RFLP molecular fingerprinting at various operating conditions (solid concentration, pH, process scale-up). Progressive increase of solid concentration (5%, 10%, 15% and 20% (w/v)) allowed the adaptation to high solid content, with efficient metal dissolution. Community temporal evolution was remarkably reproducible at 10% and 15% solids, with Sb. thermosulfidooxidans dominant and Acidithiobacillus caldus as minor strain while Eh increased, and Acidithiomicrobium P2 dominant over Sb. thermosulfidooxidans during stationary phase. At 20% solids, Acidithiomicrobium P2 was detected earlier and its relative abundance increased with time. A pH lower than 1.5 was detrimental to Acidithiomicrobium P2 and favoured Sb. thermosulfidooxidans that showed a better tolerance to acidification; however, no impact on metal dissolution was observed. The process was scaled-up to a 114-L continuous pilot, consisting of four stirred-tank reactors in cascade and operated at 50°C and 20% solids (d80 < 430 µm), in which dissolved metals monitoring confirmed a high metal extraction rate. The two dominant strains remained main actors, especially in primary reactor R1 and in R2, but other strains such as At. caldus and Leptospirillum ferriphilum were found, possibly favoured by a lower temperature. Community differed in R3 and R4; L. ferriphilum or At. caldus became codominant probably due to observed pH fluctuations. Efficient bioleaching of Sotkamo ore was demonstrated, as well as the resiliency and robustness of the selected moderate thermophilic consortium, in all conditions tested at laboratory and pilot scales