Advanced Materials Research Vols. 20-21

Abstract: Acid drainage waters generated in the uranium deposit Curilo, Bulgaria, were treated by means of different passive systems such as natural and constructed wetlands, alkalizing limestone drains, permeable reactive multibarriers and a rock filter, used separately or in different combinations. The waters had a pH in the range of about 2 – 4 and contained radionuclides (uranium, radium), heavy metals (copper, zinc, cadmium, lead, nickel, cobalt, iron, manganese), arsenic and sulphates in concentrations usually much higher than the relevant permissible levels for waters intended for use in agriculture and/or industry. The water flow rate through the individual systems was different and not stable, and varied in the range approximately from 0.02 to 1.5 l/s. Efficient removal of pollutants was achieved by means of these systems during the different climatic seasons, even during the cold winter months at water and ambient temperatures close to 0 oC. The removal was due to different mechanisms but microbial sulphate reduction, biosorption by living and dead plant biomass and chemical neutralization played the main roles.

Abstract: In order to remediate three sites in the vicinity of a non-ferrous industrial site, where groundwater was historically contaminated with metals, the best available technique should be selected. Because the groundwater contained high concentrations of metals and high sulphate concentrations (up to 2000 ppm), the feasibility of sulphate reduction and subsequent metal immobilization due to metal sulphide precipitation was examined in the lab before selecting an appropriate remediation technology. Because of the very high metal concentrations in the groundwater and their potential toxic effects on microbial life chemical reagents were also evaluated for immobilization of the metals in situ. The first site (site 1) was characterized by a contamination of Zn (500ppm-3ppm) up to a depth of 130 m-bg. A screening for inducibility of biological activity was performed at two depths – 30 m-bg (below ground) and 65 m-bg -- using microcosm experiments containing both aquifer solids and groundwater. Different electron-donors were selected including pure chemical agents such as lactate and waste products such as molasses and glycerol. Glycerol resulted in the most efficient metal and sulphate removal after about 106 days. Extremely high Zn concentrations were found in the groundwater of the second site (site 2), i.e., up to about 2000 ppm. Similar lab tests applied for site 1 were performed, but in addition chemical agents (NaS2 and CaSx) were used. Whereas the sulphide containing chemical agents immediately resulted in low Zn concentrations in the groundwater, it took >140 days before biological sulphate removal started. Glycerol, lactate and molasses resulted in efficient Zn removal. Site 3 was characterized by relative shallow contamination (<10 m-bg) of mainly Co (30-300 ppm), and containing typical sulphate concentrations in the range of 300-1200 ppm. Rapid microbial sulphate reduction (within 50 days) was induced in the tests containing nutrient-amended lactate, cheese whey and soy oil.

Abstract: Soluble manganese (Mn(II)) can cause nuisance and occasionally toxicity problems, both in surface and ground waters and in domestic water supplies. Many mine drainage waters contain highly elevated concentrations (often >100 mg l-1). Current systems for remediating mine waters, although effective for other metals, are often inefficient at removing manganese. This paper describes the development of self-sustaining, low-cost bioreactors that can be used in situ for passive removal of manganese from mine waters and other contaminated water courses of pH >4. A prototype bioreactor, set-up using Mn(IV)-coated pebbles from a fresh-water stream, was tested over one year and shown to be effective in removing Mn(II) from 10 to <0.25 mg l-1. Two species of fungi and one bacterial species were isolated from this system as Mn(II)-oxidizers. The fungi were identified as belonging to the order Pleosporales (Ascomycetes), and one was related (98 % 18S rRNA gene sequence identity) to a known Mn(II)-oxidising fungus. The bacterial isolate was closely related to the α-proteobacterium, Bosea thiooxidans. T-RFLP analysis showed that one or both of the fungal isolates were the dominant eukaryotes in the bioreactor community.

Abstract: For the treatment of acid mine water an in-situ pilot plant with a self-sufficient energy supply and remote data transmission was tested in acidic pit lake 111, a small lake in the Lusatian mining district in Germany. In this paper the design of the enclosure-bioreactor in-lake system, the mode of operation of a three-stage treatment process by the use of anaerobic fixed film reactors and the results of treatment are shown.

Abstract: The efficiency of natural wetlands for entrapment and concentration of aqueous uranium (U) was investigated in former uranium mining regions in the eastern part of Germany. Hydrogeochemical analyses of sediments, plants, surface and pore waters from selected small-sized wetlands show that U is predominantly accumulated in an environment where sulfate reduction is insignificant. From soil sequential extraction it is known that the bulk of U is retained in moderately labile forms, predominantly as organically bound or acid soluble phases (“specifically adsorbed”). Uranium could be identified by SEM/EDX, indicating that biosorption of U as cation or complex is important. However, the highest U concentrations prevail in Al-rich, inorganic agglomerates of colloidal phases. These agglomerates are as well very often non-specifically adsorbed to organic matter (plant debris, microorganisms) in the soils, promoting indirect biosorption of U.

Abstract: The work consists on the study of a sulphur–oxidizing bacteria (At. thiooxidans) immobilisation over polyurethane foam and the integration of two continuous processes: the solubilization of heavy metals by acidic medium generated by sulphur-oxidizing bacteria and the subsequent precipitation of metals as sulphides with H2S biologically generated by sulphate-reducing bacteria (Desulfovibrio sp). At. thiooxidans was satisfactory immobilised over polyurethane foam and added to a column reactor. Acidic medium generated was added to a column with 50 g of an artificial contaminated sand (85 mg Cr(III), 20 mg Ni(II), 200 mg Zn(II)). The effluent of this step was collected in a reservoir tank, in which H2S from sulphate-reducing reactor was included to carry out the precipitation of metals. After 2.4 l of acid medium was passed through the column, it was observed that 14.6% of Cr(III), 26.7% of Ni(II) and 90.5% of Zn(II) were solubilized. The leachate was treated with 2.2 l of reducing medium, and 2.2% Cr(III),54% Ni(II) and 28% Zn(II) were precipitated.

Abstract: The formation and treatment of acid mine drainage is the biggest environmental problems relating to mining and processing activities in the worldwide. Various methods are used for the sulphates and heavy metals removal from acid mine drainage in the world, but any of them is universal. Main aim of the paper is the interpretation of chemical and biological-chemical methods for the metals and sulphates removal from acid mine drainage sample. The chemical method is based on the sulphates precipitation by the sodium aluminate in combination with the calcium hydrate. The biological-chemical method is based on the application of sulphate-reducing bacteria (SRB). A sample of acid mine drainage from the abandoned and flooded deposit of Smolník located in Slovak republic was used in this study.

Abstract: An experimental plot consisting of alkaline soil heavily polluted with heavy metals (copper, zinc, cadmium) was treated in situ by stimulating the activity of the indigenous soil microflora, which contained different metal-solubilizing microorganisms. This was achieved by adding to the soil solid biodegradable organic substrates (cow manure, plant compost, straw), zeolite saturated with ammonium phosphate and aqueous solution containing acetate, lactate and magnesium chloride. An efficient removal of the above-mentioned heavy metals was achieved via the drainage water and their residual contents in the soil decreased to below the relevant permissible levels within 18 months of treatment. The metals were solubilized mainly as complexes with the organic acids added by the irrigating water solutions or secreted by the indigenous heterotrophic microorganisms. The effluents containing dissolved metals were efficiently treated by means of a wetland constructed near to the experimental plot.

Abstract: Column experiments investigated the stabilization of waste rock from Ljusnarsberg mine in Kopparberg, Sweden. In order to inhibit the generation of acidic leachate from the waste rock, biosludge and a Ca carbonate – rich residue from the paper industry were mixed with the sulfidic mine waste. The results of the column experiments indicate that the stabilization of the waste rock with the reactive amendments succeeded in maintaining a near – neutral pH in the waste rock leachate, compared to a pH 3 leachate from untreated waste rock. Copper and Zn concentrations in leachate from the untreated waste exceeded 100 mg/L, while these metals were detected at concentrations less than 0.1 and 1 mg/L, respectively, in the leachate from the treated wastes. This study indicates that the stabilization of acid – generating waste rock with biosludge and Ca carbonate residues is effective in preventing the generation of acid mine drainage; the treatment is expected to continue until the reactive amendments are exhausted.