Solid State Phenomena Vol. 262

Abstract: The ability of neutrophilic bacterium association to destruct thiocyanates and cyanides was found when working with oxidation of elemental and sulphide sulfur in biocake [1]. It was used for microorganisms association selection, which will oxidize thiocyanates and cyanides in liquid CIL tails of Olimpiada gold recovery plant. Originally selection occurred in laboratory reactors in periodical and later in continuous operation with thiocyanate content of 400-500 ml/l. Molasses in concentration of 0,5 g/l used as a source of carbons. After thiocyanates and cyanides stable oxidation in laboratory conditions the process was transferred to larger reactors (capacity of 2,2 m³). As a result of the research, rhodanides concentration reached 1800 mg/l. During the research rhodanides concentration was reduced from 1800 mg/l to 0,02 mg/l and cyanides concentration was reduced from 20 mg/l to 0,01 mg/l. Oxidation took 24 hours. Microbiological researches with application of molecular genetic analysis have shown that in the selected thiocyanate destructive association prevail the following strains: Pseudomonas aeruginosa, Stenotrophomonas maltophilia and Enterobacter.

Abstract: This work was done to assess the arsenate (AsV ) removal from the model solution by sorbents based on Fe-oxide. Two samples were compared in sorption properties, synthetically prepared Fe-oxide and bentonite/iron oxide (ratio 2:1). The effect of pH and initial metal ion concentration was investigated. The optimum pH for arsenic adsorption by both samples was found to be about 3.0. The adsorption increased very significantly with decreasing pH for both samples. The Fe-oxide sample achieved the maximum adsorption capacity 24,1 mg.g-1 AsV at pH 3, composite sample 14,1 mg.g -1 AsV at pH 3. The adsorption of AsV on Fe-oxide sample increased with the increasing initial metal ion concentration up to 40 mg/l and then equilibrium was established, by contrast of bentonite/Fe-oxide sample shown no significant change at this concentration range.

Abstract: The use of chemical pretreatment with 10mM EDTA to enhance the arsenic microbial mobilization was evaluated in this study. The bioleaching involved the use of the indigenous sedimentary and soil heterotrophic microorganisms, whose leaching media contained 2mM EDTA. The main objectives of using the chemical pretreatment was the removal of metal surface coatings from the iron minerals, such as Cu and Zn, which inhibited the iron microbial dissolution in the soil and sediment environment and thus increasing the mobilization of the retained As. To examine the effect of the chemical pretreatment and the biological leaching on the mobilization of Cu, Zn, and As, batch and column tests were conducted within the laboratory experiments. The removal of As and Zn from the soil and sediment was greatly enhanced by the co-treatment in the batch solution conditions than in the column percolate conditions and had negative effect only for Cu. In the batch tests, the heterotrophic bioleaching of the soil and sediment was found to have a pronounced positive effect on the extraction of As and Zn.

Abstract: Biological sulfate reduction represents an alternative and sustainable option to reduce the high sulfate load, precipitate heavy metals and neutralise the acidity associated with acid rock drainage (ARD). Sulfate-reducing enrichment cultures have been developed on simple and complex electron donors from several environmental samples and used to inoculate three reactor configurations, namely a continuous stirred tank bioreactor, up-flow anaerobic packed bed reactor and a linear flow channel reactor, with varying degrees of biomass retention provided by carbon microfibres and polyurethane foam. These matrices are included to enhance microbial attachment and colonisation, allowing for the decoupling of hydraulic retention time and biomass retention time. The bioreactor systems are operated under increasingly stringent conditions through the reduction in the hydraulic residence time. The biological sulfate reduction performance and the biomass concentration of planktonic, matrix-attached and matrix-associated communities are routinely monitored. This investigation makes use of biomass quantification of the planktonic community and, following detachment, the matrix-associated community to investigate the resultant microbial communities in these reactor systems. Evaluation of these mixed microbial communities, and their link to process performance, provides an opportunity to impact the design and operation of pilot- and industrial-scale bioprocesses.

Abstract: Gallium (Ga) is a critical element for the electronic industry, however, its long-term supply is not assured. Thus, the recovery of Ga from industrial wastewaters is important. Selective sorption is a recommended technology for the recovery of Ga from industrial wastewaters, however, selective sorbents are elusive. Desferrioxamine B (DFOB), a hydroxomate siderophore that is known to be highly selective towards Fe³⁺, is tested for its ability to complex Ga. This study demonstrated that DFOB forms 1:1 complex with Ga and the maximum Q_e-Ga is 124.4 mg of Ga complexed per g of DFOB. Further, the complexation mechanism of Ga³⁺ and Fe³⁺ with DFOB is similar, as indicated by NMR, suggesting that the selectivity of DFOB towards Fe³⁺ will be extended to Ga³⁺ as well. Thus, DFOB seems to be a suitable candidate for the sorption of Ga from industrial wastewaters.

Abstract: Arsenic contamination is considered as a global environmental problem. This metalloid is known to be carcinogenic in some forms, and is mostly found in the environment as arsenate As (V) and arsenite As (III). Several chemical methods have been established for decontamination of arsenic from ground water including biological treatments. In the present work, the effect of the anaerobic bioreduction of soluble Fe (III) by the strain Aeromonas hydrophila on arsenic immobilization has been investigated. The tolerance of this strain to arsenic concentration and the effect of the iron concentration in arsenic immobilization have been studied. The release of ferrous ion indicated the bioreduction of iron and promoted the subsequent arsenic co-precipitation, leading to the formation of various iron-bearing minerals. This precipitate has been observed and identified by Scanning Electron Microscopy and X-ray diffraction analysis as Fe₃(AsO₄)₂(H₂O)₈.

Abstract: To research the remediation efficiency of sulfate reducing bacteria and iron reducing bacteria on heavy metals, the remediation experiments of laboratory-scale and field-scale were conducted respectively with chalcopyrite tailings and 3 hectares lead-zinc sulfides mine tailings. The ion concentration of exudate was determined using inductively coupled plasma atomic emission spectroscopy, and key bacterial strains were investigated by real-time PCR. The laboratory-scale experiment of chalcopyrite tailings indicated pH of exudate rose to neutral, penetration time of exudate significantly increased, redox potential and dissolved iron notably decreased, and black metal sulfides were formed during remediation by sulfate reducing bacteria and iron reducing bacteria. The field-scale lead-zinc sulfides mine tailings remediation results indicated that the concentration of dissolved heavy metals in exudate decreased, and the growth of both moss and plants were promoted.

Abstract: Arsenic is an abundant element associated with a wide range of minerals and a major contaminant in metallurgical wastewater. For the immobilization of arsenic, iron arsenate in the very stable mineral scorodite (FeAsO₄ 2H₂O) is the preferred route. Microorganisms of the natural iron cycle living at pH below 2 and high temperatures can conduct the oxidation of ferrous iron with oxygen, which is not feasible chemically at these extreme conditions. Remarkably, at similar acidic conditions and high temperature these microorganisms can also carry out the oxidation of arsenite (As(III)) to arsenate (As(V)). Using these intrinsic features of the microorganisms, we have investigated the role of a thermoacidophilic mixed culture in the oxidation of As(III) and precipitation of (As(V) in the form of scorodite from a synthetic wastewater containing 6.7mM of As(III) and 0.5%Wt pyrite as main iron Fe(II) source. The results indicate that As(III) was completely oxidized from the synthetic wastewater in the presence of pyrite and scorodite was formed only in presence of the mixed culture at a Fe/As:1.3. This is a combination of biological oxidation and biocrystallisation accomplished to the presence of pyrite not only as the main energy source for the microorganisms, but as catalyst in the As(III) oxidation reaction.

Abstract: Rhodococcus erythropolis S43 is an actinobacterium isolated from an arsenic-contaminated soil sample, collected from an old smelter site, including an arsenic smelter, in Germany. This strain has unique features as compared to the other members of the species, namely resistance to elevated concentrations of arsenic. Here, we present the microbiological features and genomic properties of this biotechnologically relevant strain. The 6,812,940 bp draft genome is arranged into 264 scaffolds of 848 contigs. It possesses 62.5% of CG content and comprises 6,040 coding sequences and 49 tRNA genes. Bioinformatic genome analysis showed the presence of arsenic-resistance genes. A complete ars operon was found containing the arsACDR cluster coding for ArsA (efflux pump ATPase), ArsC (arsenate reductase), ArsD (chaperone) and ArsR (ars operon regulator). Our results show that the arsC mRNA level significantly increased in response to arsenite and arsenate exposure, suggesting its involvement in the arsenic resistance phenotype of strain S43. In addition, this strain showed to have a plethora of genes coding for proteins involved in oxidative-stress response, including catalase, super-oxide dismutase, glutathione peroxidase-related genes, thioredoxin and thioredoxin reductase, suggesting it is highly tolerant to oxidative conditions. Finally, genes for radiation resistance, biodesulfurization, and oil and phenol degrading pathways were also detected. Altogether this data make R. erythropolis S43 a good candidate microorganism for bioremediation of highly contaminated environments and other industrial applications.

Abstract: The potential utility of mesophilic/moderately thermophilic acidophiles was investigated for immobilization of arsenic (As) as scorodite (FeAsO₄·2H₂O) at moderate temperatures (35–45 °C). Here, the acid-tolerant mesophile Thiomonas cuprina Hö5 and acidophilic moderately thermophile Acidimicrobium ferrooxidans ICP were selected as As (III)- and Fe (II)- oxidizers, respectively. Due to a difference in their optimal growth pHs, a 2-step reaction consisting of the 1st As (III) oxidation step followed by the Fe (II) oxidation + precipitation step was studied. In our previous study, the optimal [Fe (II)]_ini/[As (III)]_ini molar ratio for bioscorodite formation at 70 °C was shown to be around 1.4. However, setting the same molar ratio at moderate temperatures (35-45 °C) resulted in formation of unstable amorphous ferric arsenate. Lowering the ratio to ≤ 1.0 led to precipitation of crystalline bioscorodite with > 90% As (III) removal at 45 °C.