Advanced Materials Research Vols. 20-21

Abstract: This paper investigates Zn2+ and Cu2+ adsorption capability of bentonite and zeolite taken from the non-raw metallic deposits of Slovakia. Viable biomass of an Bacillus pumilus and Bacillus megaterium enhanced the efficiency of Zn2+ and Cu2+ adsorption from model solution. Initial concentration of Cu and Zn in model solutions initially containing 32.3 mg.Cu.L-1and 42.9 mg Zn.L-1 after six hours sorption and desorption at 25°C, it was observed that 1g bentonite whit bacteria inokulum was found to remove 0.195 mg Zn2+ and 0.17 mg Cu2+ from the solution and 1g zeolite was found to remove 0.088 Zn2+ and 0.051 Cu2+. The ability for Zn and Cu sorption was bentonite > zeolite. The adsorption of metal ions on bentonite and zeolite depends on pH. Between pH 4 and 6, the main mechanism is by ion exchange. In order to prevent contamination of subsoil and groundwater by leachates containing heavy metals, bentonite and zeolite are widely used as cost-effective treatments barriers. For this reason it is important to study the adsorption of metals by these materials.

Abstract: Two copper flotation tailings samples, one from the Almalyk Mining and Metallurgical Complex, Uzbekistan (sample designated AMMC) and the other from Whitehorse (WT), Yukon, Canada, were bioleached at laboratory scale. Acidophilic, iron- and sulphur-oxidizing cultures were enriched from the two tailings and these cultures were used for the testing. After 24 weeks of bioleaching in percolator columns 70-72% of the copper was leached from the AMMC tailings and 91-93% of the copper was leached from the WT tailings. The chalcopyritic nature of the copper and larger particle size of the AMMC tailings compared to the WT tailings were likely reasons that copper extraction was greater for the AMMC tailings. In-column, thiosulphate leaching of biooxidized residues yielded 90+% gold extraction for both tailings. In other testing the two cultures were subjected to an electromagnetic field during growth on ferrous iron. Compared to untreated controls, cultures subjected to the electromagnetic field oxidized iron more rapidly. Although magnetite, which exerts an electromagnetic field, was present in the AMMC tailings, there was no evidence that this magnetite had any effect on the bioleaching results. However, given the enhanced performance of the iron-grown cultures under the influence of an electromagnetic field, we believe that additional research should be performed to investigate this phenomenon

Abstract: NA-processes can be enhanced for lignite overburden dumps, using dicarboxylic acid as a feasible substrate for autochthonic sulphate reducing bacteria. Sulphate reduction with simultaneous FeS/FeS2-precipitation occurs and immobilises SO4 2-, H+ and heavy metals connected with a decrease of the acidity. The used LC-OCD, HP/LC, isotopic and other chemical analyses substantiate sulphate reduction under technical enhanced conditions too.

Abstract: The present work deals with a bioremediation study of a heavy-metal polluted harbour sediment, obtained from the Italian Adriatic Coast. Bioleaching of the sediment sample was performed with a mixed culture of acidophilic, chemi-autotrophic Fe/S oxidising bacteria. The effect of an anaerobic biostimulation pre-treatment on the extent of Cd, Cu, Zn, Ni, Pb, Hg, As, Cr extraction by bioleaching was evaluated. The biostimulation pre-treatment was intended to stimulate autochthonous sulfate reducing strains, to enhance the sulfide fraction in the sediment, to favour subsequent activity of reduced-sulfur-oxidizing bacteria in the subsequent bioaugmentation (bioleaching). The effect of the duration of anaerobic pre-treatment (21 and 30 days) in the presence and absence of 1% glucose was tested. The results obtained showed that the activity of the reducedsulfur- oxidising strains was significantly enhanced after an anaerobic pre-treatment of the sediments and showed real promise for the application of bioleaching for metal polluted sediments.

Abstract: Column experiments were carried out using contaminated geosubstrates and previously isolated Streptomyces strains from the former uranium mining area Ronneburg (Germany) to study transfer processes of heavy metals including radionuclides. Preliminary tests with comparatively low heavy metal and radionuclide contaminated surface material showed strongly elevated Mn concentrations up to 1060 #g/l after passage through inoculated columns. In contrast, the eluates of non inoculated columns showed, after a “first flush”, low Mn concentrations around 30 #g/l. Poisoned control columns showed decreasing concentrations after the “first flush” (maximum Mn release of 540 #g/l). Highest manganese release from the inoculated, non poisoned columns corresponded with strongly decreasing redox potentials (+200 to -270 mV), which probably indicates microbially catalysed manganese release through reductive processes. One of the strains isolated from the column material was identified as a potentially heavy metal resistant strain of Cupriavidus metallidurans. It showed tolerance of up to 30 mM Mn (II), however no aerobic Mn (IV) reduction processes were indicated.

Abstract: Gyöngyösoroszi is an abandoned lead-zinc sulphide ore mining area in Hungary. The diffuse pollution sources of mining origin identified in the area and the residual pollution after removal of the point sources will be subjected to combined chemical- and phytostabilisation. To select the best chemical stabiliser laboratory scale experiments were performed in microcosms. The following chemical additives were tested in various concentrations: three different fly ashes, lignite, alginite, hydrated lime, raw phosphate, iron hydroxide wastes from drinking-water treatment, red mud and the mixture of selected ones. The stabilisation of toxic metals in the soil was monitored by an integrated methodology, which combined physico-chemical analysis with toxicity testing. Based on the chemical analytical and the bacterial and plant toxicity test results, one of the tested fly ash types was the most effective: the mobile Cd and Zn concentration decreased by 50–99% in the fly ash treated contaminated soil, the bacterial and plant toxicity decreased by 30-70%, and the bioaccumulated metal amount by 70%. The combination of lignite, alginite, lime and phosphate was also efficient.

Abstract: Tetrachloroethene (PCE) is one of the grave environmental pollutants. Certain anaerobic bacteria have the ability to dechlorinate PCE as an electron acceptor for their respiration (dehalorespiration). Previously, we accumulated PCE-dechlorinating culture in the presence of Fe(III)-EDTA. In this study, we have described the regulation of dehalorespiration by electrolytic control of the Fe(II)/Fe(III) ratio using a potentiostat (electrochemical cultivation). PCE-dechlorinating culture was cultivated under H2 conditions at constant redox potentials ranging from –0.1 to –0.8 V. After electrochemical cultivation for 3 weeks, PCE-dechlorinating activity of the mixed culture varied at different redox potentials. At –0.6 V, the culture showed the highest activity and the highest ratio of Desulfitobacterium/total bacteria. Electrochemical cultivation is a useful method for regulating PCE-dechlorinating bacterium.

Abstract: The amenability of hydrolysed cellulose material to low cost sulfate reduction electron donor was examined with fluidized bed reactor (FBR) treating synthetic mine waste water. The studied cellulose material was dried Phalaris arundinacea reed, which was acid hydrolysed (1.5 w/w % H2SO4, 7 w/w % solids) at 120oC to hydrolyse polymeric materials to biodegradable monomers. The FBR was operated at 35oC, and ethanol has previously been used as the electron donor. FBR was fed with synthetic waste water (pH 4.5) containing soluble fraction of Phalaris arundinacea hydrolysate, metals (Fe and Zn) and sulfate. The switch of the electron donor from ethanol to hydrolysate was successful. The acidic influent was neutralized in the FBR by the alkalinity produced in the oxidation of Phalaris arundinacea hydrolysate. The main oxidation product of the soluble hydrolysate was acetate, which accumulated in the FBR during overloading. The percent sulfate reduction remained in the range of 40-95 %. The highest obtained hydrogen sulfide production was 0.91 g L-1d-1 at a hydraulic retention time (HRT) of 9 h, while highest sulfate reduction was 8.4 g L-1d-1 (HRT 8 h). Iron and zinc precipitated in the FBR, and highest metal precipitation rates were 1.14 g Fe L-1 d-1 and 30 mg Zn L-1d-1 (HRT 8 h). The electron donor load was measured as soluble chemical oxygen demand (CODs), and highest CODs removal rate was 2.13 g L-1d-1 (HRT 9 h) and CODs percent oxidation 92 % (HRT 10 h). Soluble Phalaris arundinacea hydrolysate was found to be a suitable electron donor for sulfate reducing FBR and mine waste water treatment. The soluble fraction of Phalaris arundinacea hydrolysate was used very efficiently by sulfate-reducing bacteria (SRB). Additionally, batch bottle assays showed that SRB-enrichment also used solid, dried Phalaris arundinacea as electron donor for sulfate reduction (total sulfide yield 340 mg L-1 in 14 days). The results of sulfate reduction and iron precipitation are shown in figures 1 A-B.

Abstract: Microbial biofilms produce electrochemical interactions with metal surfaces by following a wide variety of different electron exchange pathways. Reviewing the mechanisms identified in the biocorrosion of steels leads us to distinguish direct and indirect mechanisms for biofilm-catalysed cathodic reactions. Indirect mechanisms are due to the production of metal oxides or hydrogen peroxide (aerobic corrosion) or metal sulphides (anaerobic corrosion), which further react with the metal surface. Direct mechanisms involve adsorbed biocompounds, generally enzymes or their active sites, which catalyse the cathodic reduction of oxygen for aerobic biocorrosion or the proton/water reduction in anaerobic processes. Recent studies dealing with the role of hydrogenases in anaerobic corrosion have shed light on the important role of phosphate species via so-called cathodic deprotonation. Advances in the development of microbial fuel cells have also resulted in new concepts, mainly for oxidation processes. Some microbial cells have been shown to be able to produce their own electron mediators. Others can transfer electrons directly to electrodes through membrane-bound electron shuttles or achieve long-range transfer through conductive pili.