Abstract: Obligate autotrophic and acidophilic characteristics of iron oxidizing bacteria were exploited to prevent or attenuate the generation of AMD. Inhibition of iron oxidizing bacteria growth was performed by variation of growth medium by increasing pyrite concentration (substrate inhibition), by addition of limestone (inhibition by pH increase) and olive pomace (inhibition by organic compounds). Preliminary pyrite bioleaching tests showed the ability of the available inoculum to oxidize the mineral. Inhibition tests of batch growth were performed according to full factorial design with three factors (pyrite, limestone and olive pomace). Experimental data denoted a strong inhibition in all the operating conditions, except the case when larger pyrite concentrations were used. In particular, limestone is a strong inhibitor and inhibition by olive pomace may be related to the antioxidant properties of polyphenols. Interactions among operating conditions were specifically assessed by analysis of variance.
Abstract: Acid Mine Drainage (AMD) from voluminous sulfide-bearing wastes contributes to the environmental burden of mineral processing. To diminish burden and its time frame of risk, the disposal of sulfidic waste materials is re-examined through the valuable distinction between reactive or active gangue materials contributing to AMD generation and largely unreactive passive gangue. In an example process for disposal of tails from mineral sulfide beneficiation, a proof of concept is provided for inclusion of a non-selective sulfide float preceding or following selective separation of the desired mineral sulfide. The environmental benefit of subsequent reduction of sulfide in the tailings from 3.7 to 0.2% on AMD generation potential is quantified through a combination of methodologies including MPA, ANC, NAPP, NAG and microbial testing. Sulfide reduction from 4 to 1% reduces AMD generation. Further reduction below 1% S yields diminishing returns. The environmental benefit of separating ‘active’ and ‘passive’ gangue material prior to disposal is shown, and the reduced active gangue fraction determined through material balance.
Abstract: This study investigated the influence of culture conditions on the dominant metabolic pathways and resultant reaction stoichiometry, using chemostat cultures. The kinetic properties (max and Ks) under conditions dominated by either lactate oxidation or lactate fermentation were determined. These properties were used to simulate the competition between lactate fermentation and oxidation. Sulphate reduction and lactate utilisation were determined across residence times of 1 to 5 d and feed sulphate concentrations of 1.0 to 10.0 g l-1. Assuming lactate limitation, results revealed a lower maximal growth rate max of 0.2 h-1 and a higher affinity for lactate characterised by Ks of 0.6 g l-1 for the lactate oxidisers (SRB) than the lactate fermenters. The latter were characterised by a max of 0.3 h-1 and Ks of 3.3 g l-1. Modelling of the competition between lactate fermenters and lactate oxidisers illustrated that lactate oxidisers compete more effectively for lactate under conditions of low lactate concentration (≤5 g l-1) and high sulphide concentration (0.5 g l-1). On the other hand lactate fermenters outcompete the oxidisers under conditions of higher lactate concentration (>5 g l-1). Findings from this study show that in order to optimise BSR system, an understanding of the impact of physicochemical conditions on the metabolic dominance is critical.
Abstract: Biosulfidogenesis (the generation of hydrogen sulfide by microorganisms) in acidic liquors was investigated using two metabolically-distinct bacteria. One was a novel acidophilic sulfate-reducing bacterium (isolate CL4) that grew at pH 3.0 and above using glycerol as electron donor, and the other was the type strain of Acidithiobacillus ferrooxidans which was grown at pH 2.5 using hydrogen (derived from dissolution of metallic iron) as electron donor and elemental sulfur as electron acceptor. Both bacteria were grown in pH-controlled bioreactors. Isolate CL4 mediated the selective precipitation of zinc in situ, while the At. ferrooxidans bioreactor operated as an off-line system, generating hydrogen sulfide that precipitated copper in a separate reaction vessel. The potential of using acidophilic sulfidogens for the selective recovery of metals from acidic waste streams is discussed.
Abstract: . The historical hard coal mining area of the districts of Zwickau and Lugau/ Oelsnitz in Saxonia (Germany) is a source of heavy metals and arsenic polluting the adjacent ground- and surface waters. Heavy metals and metalloids like Zn, Cd, Ni, Co, As and Mn are transported, partially as fine precipitates, to the adjacent river Zwickauer Mulde and with that to the river Elbe. Some of the dumps are partially older than 150 years, and some of them were remediated more than 50 years ago. Today we still can learn from the more or less successful remediation measures after some decades of application. In this paper, three different dumps are presented and differences between their remediation measures and the long-term success of it shall be pointed out. As a result, especially a sealing and covering of a dump turned out as very successful for the prevention of AMD generation. A further utilization of such a remediated and revegetated area is possible, or it can be “given back” to the nature. In contrast, a revegetation without covering results in a long-term AMD-generation of such a mining dump site.
Abstract: Important groups of microbes were investigated in three hard coal mining dumps in Saxonia/ Germany. In the particular dumps, different chemophysical and geochemical conditions are existing, depending on the kind of remediation up to six decades ago. Thiobacillus denitrificans, iron and sulfate reducers, and general aerobic heterotrophs and fungi were counted by MPN and CFU methods. Samples were taken from drilling cores in different depths out of the dumps, from seepage-, surface- and ground waters and from sediments. Similarities and significant differences were found between the microbial populations of the three dumps, depending on the appropriate environmental conditions. As a result, enhanced counts of T. denitrificans were detected at all three sites, originating from fertilizers (agricul-ture, gardens) and atmospheric precipitations. Sulfate reducers and aerobic heterotrophic microorganisms are suited indicators for the ongoing biogeochemical processes in the dumps
Abstract: Large sites with a low contamination of metall(oid)s were in the past a problem for remediation measures – the “traditional” processes were too expensive for an application on such expanded areas. Phytoremediation can be an alternative for such low contamination problems. In Germany, a research project is performed on this subject, in cooperation of the University of Jena and the TU Dresden. The field site is a former U mining area. Until 1991, a low grade U ore dump for sulfuric acid leaching was located on this site. After the close-down of the U mining in East Germany in 1991, the dump material was removed. Now, a phytoremediation test field is constructed on top of this site for the capture of the remained contaminants coming up by capillary forces. The paper pictures the phytoremediation in general, the research project and gives some first preliminary results.
Abstract: Indigenous microorganisms isolated from organic-rich copper-bearing black shale from the Fore-Sudetic Monocline were able to transform naturally occurring metalloporphyrins in laboratory cultures. It was also demonstrated that these bacteria can utilize synthetic metalloporphyrins as the sole energy and carbon source. The first step in metalloporphyrin biotransformation was identified as the highly effective bioaccumulation of these compounds in bacterial cells. The ability of both living and dead cells to biosorb metalloporphyrins was also confirmed. Besides contributing to the important biogeochemical role of these microorganisms in the environment, their biotransformation activities are of potential use in the bioremediation of copper tailings as well as in the recovery of metals from organic-rich black shale ore, which is not possible using traditional hydrometallurgical procedures.
Abstract: To examine the effects of organic and inorganic amendments on the degradation of petroleum hydrocarbons, we conducted a pilot-scale experiment during the winter and summer periods. Soil samples were analyzed periodically to determine the soil gas amount of volatile organic compound, carbon dioxide flux, consumption of O2 and indigenous bacterial numbers during bioremediation. The initial level of the most contaminated site (10 070 mg hydrocarbon kg-1 soil) was reduced successively to 4 800 mg kg-1 after 4 months and to 1 400 mg kg -1 after 6 months in ex-situ amended soils. The hydrocarbon-degrading microbial populations increased during the treatment as also did soil respiration. Both aerobic and methanogenic conditions appeared to be important at these sites. Methane concentration (500-23 000 ppm) and CO2 production (800-17 000 ppm) varied with the extent of contamination. The bioventing system used in this study aerated a wide area of soil. It was concluded that N and P availability within the organic and inorganic nutrients limited the biodegradation of hydrocarbon contamination. By combination of organic and inorganic amendments a 86% removal efficiency was achieved. Nutrient diffusion varied within the 3 m high decontamination biopile but was sufficient to promote bacterial proliferation in all layers.
Abstract: In the course of remedial investigations for a former gasworks site, high cyanide pollution of the soil (74.6 - 101.7 mg/kgDS total cyanide) and of the groundwater (3,840 µg/l total cyanide /approx. 300 µg/l free cyanides) were particularly problematic. Extensive investigations in the laboratory as well as in field studies finally resulted in a 2-step oxic/anoxic concept. Both the free cyanides as well as the complex bound cyanides could be biodegraded at more than 90% through a combination of H2O2-treatment (ISCO) and denitrification by in situ conditions. Furthermore a destruction of the iron cyanide complexes under fermentative conditions could be observed for the first time.