Potential use of biochar, compost and iron grit associated with Trifolium repens to stabilize Pb and As on a multi-contaminated technosol.

Vegetation cover can be used in the phytomanagement of polluted areas by adding value to abandoned sites and reducing the dispersion of pollutants by erosion. Appropriate amendments, that allow both efficient plant growth and the immobilization of contaminants in the soil must be chosen in order to optimize the efficiency of this process. We used a mining technosol mainly contaminated by arsenic (1068 mg kg-1) and lead (23387 mg kg-1) to study the effect of three amendments (biochar, compost and iron grit) on (i) physico-chemical properties of the soil and soil pore water, (ii) metal(loid) mobility, bioavailability and bioaccessibility (CaCl2 and Simple Bioaccessibility Extraction Test (SBET)), and (iii) the capability of Trifolium repens to germinate and grow. All the amendments used increased the pH and electrical conductivity of the SPW, resulting in a 90% decrease in the concentration of lead in the soil pore water (SPW). We also demonstrated a decrease in Pb phytoavailability. The amendments allowed the establishment of a plant cover, although the addition of iron grit alone did not allow any clover germination. For the Pontgibaud technosol, the combination of the three amendments resulted in a significant decrease in As and Pb concentrations in clover tissues, mainly in the aerial organs. The amendments also made it possible for some of them to halve the phytoavailable fraction of arsenic. However, for compost, both the As concentrations in the SPW, and the bioavailable fraction of As increased. All the amendments used had contrasting effects on the bioaccessible fractions of metal(loid)s. The most efficient amendment combination was the addition of 5% biochar and 5% compost.

A field-pilot for passive bioremediation of As-rich acid mine drainage.

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 Carnoulès mining site (southern France) where AMD contained 790-1315 mg L-1 Fe(II) and 84-152 mg L-1 As, mainly as As(III) (78-83%). The bioreactor consisted in five shallow trays of 1.5 m2 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 ±â€¯0.8) ✕ 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 ±â€¯5) ✕ 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 ∼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.

Influence of organic matters on AsIII oxidation by the microflora of polluted soils.

The global AsIII-oxidizing activity of microorganisms in eight surface soils from polluted sites was quantified with and without addition of organic substrates. The organic substances provided differed by their nature: either yeast extract, commonly used in microbiological culture media, or a synthetic mixture of defined organic matters (SMOM) presenting some common features with natural soil organic matter. Correlations were sought between soil characteristics and both the AsIII-oxidizing rate constants and their evolution in accordance with inputs of organic substrates. In the absence of added substrate, the global AsIII oxidation rate constant correlated positively with the concentration of intrinsic organic matter in the soil, suggesting that AsIII-oxidizing activity was limited by organic substrate availability in nutrient-poor soils. This limitation was, however, removed by 0.08 g/L of added organic carbon. In most conditions, the AsIII oxidation rate constant decreased as organic carbon input increased from 0.08 to 0.4 g/L. Incubations of polluted soils in aerobic conditions, amended or not with SMOM, resulted in short-term As mobilization in the presence of SMOM and active microorganisms. In contrast, microbial AsIII oxidation seemed to stabilize As when no organic substrate was added. Results suggest that microbial speciation of arsenic driven by nature and concentration of organic matter exerts a major influence on the fate of this toxic element in surface soils.

Characterization of Halanaerocella petrolearia gen. nov., sp. nov., a new anaerobic moderately halophilic fermentative bacterium isolated from a deep subsurface hypersaline oil reservoir : New taxa: Firmicutes (Class Clostridia, Order Halanaerobiales, Halobacteroidaceae, Halobacteroides).

An anaerobic, halophilic, and fermentative bacterium, strain S200(T), was isolated from a core sample of a deep hypersaline oil reservoir. Cells were rod-shaped, non-motile, and stained Gram-positive. It grew at NaCl concentrations ranging from 6 to 26% (w/v), with optimal growth at 15% (w/v) NaCl, and at temperatures between 25 and 47°C with an optimum at 40-45°C. The optimum pH was 7.3 (range 6.2-8.8; no growth at pH 5.8 and pH 9). The doubling time in optimized growth conditions was 3.5 h. Strain S200(T) used exclusively carbohydrates as carbon and energy sources. The end products of glucose degradation were lactate, formate, ethanol, acetate, H(2), and CO(2). The predominant cellular fatty acids were non-branched fatty acids C(16:1), C(16:0), and C(14:0). The G + C mole% of the DNA was 32.7%. Phylogenetic analysis based on the 16S rRNA gene sequence revealed that strain S200(T) formed a distinct lineage within the family Halobacteroidaceae, order Halanaerobiales, and was most closely related to Halanaerobaculum tunisiense DSM 19997(T) and Halobacteroides halobius DSM 5150(T), with sequence similarity of 92.3 and 91.9%, respectively. On the basis of its physiological and genotypic properties, strain S200(T) is proposed to be assigned to a novel species of a novel genus, for which the name Halanaerocella petrolearia is proposed. The type strain of Halanaerocella petrolearia is strain S200(T) (=DSM 22693(T) = JCM 16358(T)).

Biological attenuation of arsenic and iron in a continuous flow bioreactor treating acid mine drainage (AMD).

Passive water treatments based on biological attenuation can be effective for arsenic-rich acid mine drainage (AMD). However, the key factors driving the biological processes involved in this attenuation are not well-known. Here, the efficiency of arsenic (As) removal was investigated in a bench-scale continuous flow channel bioreactor treating As-rich AMD (∼30-40 mg L-1). In this bioreactor, As removal proceeds via the formation of biogenic precipitates consisting of iron- and arsenic-rich mineral phases encrusting a microbial biofilm. Ferrous iron (Fe(II)) oxidation and iron (Fe) and arsenic removal rates were monitored at two different water heights (4 and 25 mm) and with/without forced aeration. A maximum of 80% As removal was achieved within 500 min at the lowest water height. This operating condition promoted intense Fe(II) microbial oxidation and subsequent precipitation of As-bearing schwertmannite and amorphous ferric arsenate. Higher water height slowed down Fe(II) oxidation, Fe precipitation and As removal, in relation with limited oxygen transfer through the water column. The lower oxygen transfer at higher water height could be partly counteracted by aeration. The presence of an iridescent floating film that developed at the water surface was found to limit oxygen transfer to the water column and delayed Fe(II) oxidation, but did not affect As removal. The bacterial community structure in the biogenic precipitates in the bottom of the bioreactor differed from that of the inlet water and was influenced to some extent by water height and aeration. Although potential for microbial mediated As oxidation was revealed by the detection of aioA genes, removal of Fe and As was mainly attributable to microbial Fe oxidation activity. Increasing the proportion of dissolved As(V) in the inlet water improved As removal and favoured the formation of amorphous ferric arsenate over As-sorbed schwertmannite. This study proved the ability of this bioreactor-system to treat extreme As concentrations and may serve in the design of future in-situ bioremediation system able to treat As-rich AMD.

Biological treatment of gold ore cyanidation wastewater in fixed bed reactors.

The treatment of a cyanidation effluent containing thiocyanate, free cyanide, and complexed cyanide was continuously performed for a period of 6 months. Activated carbon, pozzolana, and a mixture of pumice stone and zeolite were tested as supports in fixed bed reactors. Activated carbon adsorbed the different forms of cyanide. In contrast, the other supports did not remove any pollutants from the effluent during an adsorption experiment. All supports successfully allowed fixation of bacteria. More than 90% of the thiocyanate was biologically decomposed into NH4+, CO2 and SO4(2-), even when increasing the feed flow-rate and the pollutant concentrations. Free and complexed cyanides were eliminated, probably through a combination of precipitation and biological degradation. The oxidation of ammonium into nitrate was only performed by the activated carbon-containing column and with the more diluted feeding. The nitrification process was inhibited in all reactors when the cyanide concentrations and feed flow-rates were increased.

Chromate reduction at low sulphate concentration in hydrogen-fed bioreactors.

Aimed at developing a bioremediation process to treat Cr(VI)-bearing water at low sulphate concentration in order to reduce excess sulphide production, the highly toxic, mutagenic, and soluble Cr(VI) was reduced to the less toxic and insoluble Cr(III) in 2-litre fixed-bed reactors inoculated with the sulphate-reducing bacterium (SRB) Desulfomicrobium norvegicum, capable of performing direct enzymatic Cr(VI) reduction. H2 was used as the electron source. The fixed-films were developed on three different supports: a PVC cross-flow material, a pozzolana, and a ceramic granulate. The phased experiments began with a progressive increase of the Cr(VI) concentration in the feed to the column reactors, followed by a progressive decrease of the sulphate concentration. Inhibition by Cr(VI) was less pronounced with pozzolana than with the other supports; when the pozzolana column was fed with a medium containing 100 mg l(-1) Cr(VI) and only 250 mg l(-1) sulphate, the lowest residence time that could be applied for complete Cr(VI) reduction was 16 h. The molar ratio between the sulphate and Cr(VI) reduction rates was decreased down to 1.5, suggesting that indirect reaction with HS was not the sole mechanism of Cr(VI) reduction.

Reduction of chromate by fixed films of sulfate-reducing bacteria using hydrogen as an electron source.

The ability of sulfate-reducing bacteria (SRB) to reduce chromate, Cr(VI), was evaluated using fixed-film growth systems and H2 as the electron source. A main objective of the experiment was to distinguish between direct enzymatic reduction and indirect reduction by hydrogen sulfide, in order to subsequently verify and control the synergy of these two mechanisms. In batch experiments with the sulfate-reducing consortium CH10 selected from a mining site, 50 mg l(-1) Cr(VI) was reduced in 15 min in the presence of 500 mg l(-1) hydrogen sulfide compared to 16 mg l(-1) reduced in 1 h without hydrogen sulfide. Fixed films of a CH10 population and Desulfomicrobium norvegicum were fed-batch grown in a column bioreactor. After development of the biofilm, hydrogen sulfide was removed and the column was fed continuously with a 13-mg l(-1) Cr(VI) solution. Specific Cr(VI) reduction rates on pozzolana were close to 90 mg Cr(VI) h(-1) per gram of protein. Exposure to Cr(VI) had a negative effect on the subsequent ability of CH10 to reduce sulfate, but the inhibited bacteria remained viable.

Monitoring of a pyrite-oxidising bacterial population using DNA single-strand conformation polymorphism and microscopic techniques.

The single-strand conformation polymorphism (SSCP) technique was used to study the evolution of a bacterial consortium during the batch oxidation of a cobaltiferous pyrite in two types of bio-reactor: a bubble column and a classical stirred tank. Sequencing 16S rDNA revealed the presence of three organisms affiliated to Leptospirillum ferrooxidans, Acidithiobacillus thiooxidans and Sulfobacillus thermosulfidooxidans, respectively. Attempts were made to determine the proportions of bacteria attached to solid particles or freely suspended in the medium using a combination of PCR-SSCP and a microscopic technique. Ac. thiooxidans-related bacteria were dominant in the liquid during the early phase of the batch, but were later supplanted by L. ferrooxidans-related bacteria. L. ferrooxidans-related organisms were always in the majority on the solids. The growth of S. thermosulfidooxidans-related bacteria seemed to be favoured by the bubble-column reactor.

An arsenic(III)-oxidizing bacterial population: selection, characterization, and performance in reactors.

AIMS: To select an autotrophic arsenic(III)-oxidizing population, named CASO1, and to evaluate the performance of the selected bacteria in reactors. METHODS AND RESULTS: An As(III)-containing medium without organic substrate was used to select CASO1 from a mining environment. As(III) oxidation was studied under batch and continuous conditions. The main organisms present in CASO1 were identified with molecular biology tools. CASO1 exhibited significant As(III)-oxidizing activity between pH 3 and 8. The optimum temperature was 25 degrees C. As(III) oxidation was still observed in the presence of 1000 mg l(-1) As(III). In continuous culture mode, the As(III) oxidation rate reached 160 mg l(-1) h(-1). The CASO1 consortium contains at least two organisms - strain b3, which is phylogenetically close to Ralstonia picketii, and strain b6, which is related to the genus Thiomonas. The divergence in 16S rDNA sequences between b6 and the closest related organism was 5.9%, suggesting that b6 may be a new species. CONCLUSIONS: High As(III)-oxidizing activity can be obtained without organic nutrient supply, using a bacterial population from a mining environment. SIGNIFICANCE AND IMPACT OF THE STUDY: The biological oxidation of arsenite by the CASO1 population is of particular interest for decontamination of arsenic-contaminated waste or groundwater.