Selective removal of transition metals from acidic mine waters by novel consortia of acidophilic sulfidogenic bacteria.
Bottom Line: Two continuous-flow bench-scale bioreactor systems populated by mixed communities of acidophilic sulfate-reducing bacteria were constructed and tested for their abilities to promote the selective precipitation of transition metals (as sulfides) present in synthetic mine waters, using glycerol as electron donor.Analysis of the microbial populations in the bioreactors showed that they changed with varying operational parameters, and novel acidophilic bacteria (including one sulfidogen) were isolated from the bioreactors.The modular units are versatile and robust, and involve minimum engineering complexity.
Affiliation: School of Biological Sciences, Bangor University, Bangor LL57 2UW, UK.Show MeSH
Related in: MedlinePlus
Mentions: The major objective with bioreactor I was to determine conditions which allowed the selective precipitation of copper sulfide from feed liquors that also contained soluble zinc and ferrous iron. The mean flow rate with this bioreactor was 49 (± 27, standard deviation) ml h−1, corresponding to a mean dilution rate of 0.021 h−1, with maximum and minimum rates of 135 and 20 ml h−1 (Fig. 1). All of the copper present in the influent liquor was precipitated in the bioreactor for the greater part of the experiment (Fig. 2). At times when soluble copper was detected in the bioreactor liquor, this was due to short‐term perturbations in the system (reflux of copper sulfate from the gas trap into the reactor, due to low nitrogen pressure) and, on each occasion, the bioreactor recovered rapidly. In contrast, none of iron in the influent liquor was retained in the bioreactor. Concentrations of iron were invariably greater than the 1 mM present in the feed water, due to: (i) dissolution of small amounts of FeS deposited during the initial commissioning of the bioreactor, and (ii) microbially and acid‐enhanced corrosion of some of the stainless steel components of the bioreactor (Dinh et al., 2004). Since separation of copper and iron as solid and liquid phases was readily achieved in bioreactor I, the main challenge was to establish conditions where copper would precipitate (as a sulfide) but zinc would be retained in solution. When the bioreactor pH was set at 3.6, > 99% of the zinc in the influent liquor was precipitated, along with the copper, within the bioreactor (Fig. 1). By progressively lowering both the bioreactor pH and the concentration of the electron donor (glycerol) in the influent liquor, it was possible to retain increasing amounts of zinc in solution. Between days 147 and 236, the bioreactor was maintained at pH 2.4, and the amount of zinc precipitated stayed reasonably stable at 47 ± 16% (23 sampling time points) even though influent glycerol concentrations was lowered from 4 to 1.5 mM during this time. However, by decreasing the bioreactor pH still further (ultimately to pH 2.2) and the influent glycerol concentration to 0.7 mM, it was possible precipitate only 8 ± 2% (nine samples) of zinc within the bioreactor, while maintaining > 99% removal of copper from solution. Analysis of the solid residue that accumulated in bioreactor I confirmed that it was predominantly copper sulfide.
Affiliation: School of Biological Sciences, Bangor University, Bangor LL57 2UW, UK.