Advanced Materials Research Vols. 71-73

Abstract: Bio-beneficiation of ores through iron removal is a common technique, but not yet tested for the case of bauxite. In this study we compared the iron reducing ability of three bacterial species with and without the chelating action of EDTA. Tests were carried out using a diasporic bauxite sample containing 19.3% Fe2Ο3 in the form of hematite, goethite and chamosite. Reductive dissolution was attempted using three neutrophilic, dissimilatory Fe(III) respirators, i.e. the facultative anaerobes Shewanella putrefaciens and Ferrimonas balearica and the strict anaerobe Desulfuromonas palmitatis. Almost 25% of Fe was reduced by D. palmitatis and S. putrefaciens and 30% by F. balearica in bauxite samples. In the case of S. putrefaciens and F. balearica, Fe(III) reduction took place without addition of EDTA, but most of the biologically produced Fe(II) reprecipitated. The addition of EDTA proved to hinder the bioreduction potential for both S. putrefaciens and F. balearica. On the contrary, D. palmitatis was able to reduce Fe(III) oxides only in the presence of EDTA. Moreover, the presence of EDTA helped maintain biogenic ferrous iron in solution.

Abstract: Selective separation of pyrite from galena and quartz was achieved through microbiologically induced flotation in presence of Bacillus subtilis. B. subtilis functions as a depressant for pyrite while it promotes the flotation of galena and quartz. Bacterial extracellular protein (EP) was isolated and the protein profile of bacterial cells grown in presence and absence of minerals established.

Abstract: Pakistan is endued with 185 billion tons colossal reserves of coal, but only 7.89 % of the country total energy requirements are met by coal. Most of the Pakistani coal reserves are sub-bituminous or lignitic in nature and contain 3-12 % sulphur. Existence of sulphur compounds in coal limits its industrial application due to environmental as well as technical problems. However, coal biotechnology can emerge as panacea for upgrading the huge reserves of coal in Pakistan. In general, coal biotechnology refers to biodesulphurization, biosolubilization and biogasification of coal. NIBGE has long term interests in the field of coal bioprocessing for tapping prime resources of indigenous coal. In NIBGE, lab scale experiments for coal biodesulphurization led to 90% efficiency in sulphur removal. Heap leaching was also carried out at the level of 10 and 20 tons coal heaps with 60% sulphur removal efficiency. Furthermore, a prototype of 300 tons coal heap was set up with a local cement industry and 75% microbial desulphurization was achieved. The league of indigenously isolated chemolithotrophic bacteria was involved in coal desulphurization. On the other side, for making the best use of 175 billion tons of low rank coal reserves, coal biosolubilization and subsequent biogasification is being projected. Consequently, beneficiated coal through biotechnology is supposed to contribute in energy mix of Pakistan for providing electricity requirements of the country and saving huge oil import bills.

Abstract: Chitosan is an emblematic example of biopolymer that can be obtained from renewable resources (fungal biomass, crustacean shells…) and that can be used for binding a number of metal ions through different mechanisms (complexation, electrostatic attraction, ion pair formation). Chitosan was used for the sorption of various transition metals, from toxic (Hg(II), Cd(II), U(VI), Mo(VI), V(IV) and V(V) …) to strategic and valuable metals (Pd(II), Pt(IV), Au(III) …). However, the interactions of chitosan with metal ions are not strictly limited to environmental applications. Hence, the binding of metal ions on the biopolymer can be used for designing new materials or new applications. Some examples are reported below.

Abstract: Bioremediation can be applied for the treatment of metal/metalloid and radionuclide bearing water streams in order to immobilize the targeted species. Interactions of microbial cells with soluble targeted species may occur during the microbial metabolism and result to the reduction of their mobility and toxicity. The most important metabolically mediated immobilization processes for metal/metalloid and radionuclide species are bioprecipitation and bioreduction. Bioprecipitation includes the transformation of soluble species to insoluble hydroxides, carbonates, phosphates and sulfides as a result of the microbial metabolism. In the case of biological reduction, the cells use the species as terminal electron acceptors in anoxic environments to produce energy and/or reduce the toxicity of the cells microenvironment. These processes can be the basis of technologies for the rehabilitation of contaminated sites both for surface and groundwater aquifers, soils and industrial water streams. Such technologies are recently developed and applied both in pilot and full scale, although the related mechanisms are complicated and not always fully understood.

Abstract: Experimental plots consisting of acidic and alkaline soils heavily contaminated with radionuclides (mainly U and Ra) and non-ferrous metals (mainly Cu, Zn, Cd, Pb) were treated in situ under real field conditions using the activity of the indigenous soil microflora. This activity was enhanced by suitable changes of some essential environmental factors such as pH and water, oxygen and nutrient contents of the soil. The treatment was connected with solubilization and removal of contaminants from the top soil layers (horizon A) due to the joint action of the soil microorganisms and leach solutions used to irrigate the soils (mainly acidophilic chemolothotrophic bacteria and diluted sulphuric acid in the acidic soil, and various heterotrophs and bicarbonate and soluble organics in the alkaline soil). The dissolved contaminants were removed from the soil profile through the drainage soil effluents or were transferred to the deeply located soil subhorizon B2 where they were precipitated as the relevant insoluble forms (uranium as uraninite, and the non-ferrous metals as the relevant sulphides) as a result of the activity of the sulphate-reducing bacteria inhabiting this soil subhorizon.

Abstract: Over the past 30 years the literature has burgeoned with bioremediation approaches to heavy metal removal from wastes. The price of base and precious metals has dramatically increased. With the resurgence of nuclear energy uranium has become a strategic resource. Other ‘non-carbon energy’ technologies are driven by the need to reduce CO2 emissions. The ‘New Biohydrometallurgy’ we describe unites these drivers by the concept of conversion of wastes into new materials for environmental applications. The new materials, fashioned, bottom-up, into nanomaterials under biocontrol, can be termed ‘Functional Bionanomaterials’. This new discipline, encompassing waste treatment along with nanocatalysis or other applications, can be summarized as ‘Environmental Bionanotechnology’. Several case histories illustrate the scope and potential of this concept.

Abstract: Metallurgical processes and mining are the main source of heavy metal contamination of water sources, rivers and lakes. There are a large number of physicochemical processes that can be applied for the immobilization of heavy metals from a liquid matrix. However, many of them are not particularly desirable because their low selectivity and inefficiency when high volumes of low metal concentration liquids must be treated. In such conditions, alternative biological processes have shown to be more useful than traditional physicochemical processes. One of those processes, bioprecipitation of metal sulphides is relevant due to the possibility of forming stable solids (very low solubility) with small volumes compared with other solids. This process is mediated by a broad group of organisms called sulphate reducers that are able to catalyze, under anaerobic conditions, the reduction of sulphate with organic compounds as electron donors. In this paper, we study the effect of the presence of various heavy metals and the pH on the ability to reduce sulphate by sulphate-reducing bacteria. We compare the reduction of sulphate by a microbial community obtained from the effluent of a tannery with a strain isolated from that community. Our results showed that sulphate reduction was significantly affected by pH changes whereas the presence of heavy metals did not show a significant effect. In addition, metal precipitation by the isolated strain was similar than that produced by the community.

Abstract: The amenability of sulfate reduction at low temperature for the treatment of acid mine drainage in arctic areas was investigated with three reactor experiments. The aim of these studies was to assess the potential and determine rates of sulfate reduction at 9oC with formic acid and hydrogen as electron donors. Three different bench-scale reactor configurations were tested: fluidized-bed reactor, membrane bioreactor and gas-lift bioreactor. The reactors were inoculated with a low temperature enrichment culture of sulfate-reducing bacteria. The temperature range of sulfate reduction was studied with a temperature gradient assay. The microbial community structure of the reactors was analyzed using polymerase chain reaction - denaturating gel gradient electrophoresis (PCR-DGGE) with universal 16S rRNA gene primers and SRB specific dsrB primers. The stable sulfate reduction rates at 9oC in all the reactors ranged from 0.6 to 1.4 g SO42- L-1 d-1. The temperature gradient assay supported also by the PCR-DGGE sequence profiling indicated that the low temperature enrichment was dominated by a psychrotolerant mesophilic Desulfomicrobium sp. having their maximal sulfide production rate at 31oC.

Abstract: An integrated sulfate reducing process was used to treat Acid Mine Drainage with high concentrations of Cu2+, Fe and SO42-. The water treatment system integrated a sulfidogenic UASB bioreactor with a precipitation reactor which was used to recover copper. Sodium lactate was used as energy source. The effective volume of the UASB reactor was 2 L and the hydraulic retention time was 12.57h. In the sulphate removal reactor, sulphate was removed from 21160 to 195 mg/L with a rate of 4427.8 mg/L/d. Cu2+ and Fe was removed by biologically generated S2- and OH- from 360 and 6520 to 0.049 mg/L and less than 10 mg/L respectively. The average COD, copper and iron removal rate was 2523.2, 15.21 and 274.98 mg/L/d separately. The effluent pH reached 6.0-7.0. The results showed potential usage of this bioreactor in treating Acid Mine Drainage.