Review of metal sulphide precipitation

Bacteria of the sulphur cycle: An overview of microbiology, biokinetics and their role in petroleum and mining industries

Biological sulfate reduction is increasingly replacing chemical unit processes in mining biotechnology. Sulfate reducing bacteria (SRB) can be used for treating ground- and surface waters contaminated with acid mine drainage (AMD), and for recovering metals from wastewater and process streams. Biologically produced H2S precipitates metals as metal sulfides, while biogenic bicarbonate alkalinity neutralizes acidic waters. This paper reviews various passive and active SRB-based alternatives as well as some process design aspects, such as reactor types, process configurations, and choices of substrates for sulfate reduction. The latest developments of using various low-cost substrates together with new bioprocess designs are increasing the uses and applications of SRB-based bioreactors in AMD control and selective metal recovery.

Sulfate Reduction Based Bioprocesses for the Treatment of Acid Mine Drainage and the Recovery of Metals

Sulfate reduction at low pH to remediate acid mine drainage.

The biocathode of a microbial fuel cell (MFC) offers a promising potential for the reductive treatment of oxidized pollutants. In this study, we demonstrated biological Cr(VI) reduction in the cathode of a MFC and identified putative Cr(VI) reducing microorganisms. The MFC was continuously monitored for Cr(VI) reduction and power generation. Acetate was provided to the anode compartment as substrate and bicarbonate was added to the cathode compartment as the sole external carbon source. The contribution of biomass decay and abiotic processes on Cr(VI) reduction was minimal, confirming that most of the Cr(VI) reduction was assisted by microbial activity in the cathode, which utilizes electrons and protons generated from the oxidation of acetate in the anode compartment. Relatively fast Cr(VI) reduction was observed at initial Cr(VI) concentrations below 80 mg/L. However, at 80 mg Cr(VI)/L, Cr(VI) reduction was extremely slow. A maximum Cr(VI) reduction rate of 0.46 mg Cr(VI)/g VSS.h was achieved, which resulted in a current and power density of 123.4 mA/m(2) and 55.5 mW/m(2), respectively. The reduced chromium was nondetectable in the supernatant of the catholyte which indicated complete removal of chromium as Cr(OH)(3) precipitate. Analysis of the 16S rRNA gene based clone library revealed that the cathode biomass was largely dominated by phylotypes closely related to Trichococcus pasteurii and Pseudomonas aeruginosa, the putative Cr(VI) reducers.

Biological Chromium(VI) Reduction in the Cathode of a Microbial Fuel Cell

Treatment by sulfate-reducing bacteria of Chessy acid-mine drainage and metals recovery

The ability of sulfate-reducing bacteria (SRB) to reduce chromate, Cr(VI), was evaluated using fixed-film growth systems and H2 as the electron source. A main objective of the experiment was to distinguish between direct enzymatic reduction and indirect reduction by hydrogen sulfide, in order to subsequently verify and control the synergy of these two mechanisms. In batch experiments with the sulfate-reducing consortium CH10 selected from a mining site, 50 mg l−1 Cr(VI) was reduced in 15 min in the presence of 500 mg l−1 hydrogen sulfide compared to 16 mg l−1 reduced in 1 h without hydrogen sulfide. Fixed films of a CH10 population and Desulfomicrobium norvegicum were fed-batch grown in a column bioreactor. After development of the biofilm, hydrogen sulfide was removed and the column was fed continuously with a 13-mg l−1 Cr(VI) solution. Specific Cr(VI) reduction rates on pozzolana were close to 90 mg Cr(VI) h−1 per gram of protein. Exposure to Cr(VI) had a negative effect on the subsequent ability of CH10 to reduce sulfate, but the inhibited bacteria remained viable. Journal of Industrial Microbiology & Biotechnology (2002) 28, 154–159 DOI: 10.1038/sj/jim/7000226

Reduction of chromate by fixed films of sulfate-reducing bacteria using hydrogen as an electron source.

A biological method for the reduction Cr(VI), using sulphate-reducing bacteria (SRB), was tested in 2-L then 20-L fixed-bed reactors, with H2 as a low-cost and clean substrate. The systems were inoculated with Desulfomicrobium norvegicum, that proved to be particularly efficient for direct Cr(VI) enzymatic reduction. The bacterial reduction was efficient when some SO2−
4 was provided in the feeding, in order to allow their growth and to combine the direct enzymatic reduction to the indirect chemical reduction by dissolved H2S. The Cr(VI)/SO2−
4, ratio in the influent was adjusted in order to avoid excess sulphide production. A real polluted groundwater and an industrial electroplating effluent were treated in the 20-L pilot plant.

Chromate (CrO 2- 4 ) Reduction in Groundwaters by Using Reductive Bacteria in Fixed-Bed Bioreactors

Aimed at developing a bioremediation process to treat Cr(VI)‐bearing water at low sulphate concentration in order to reduce excess sulphide production, the highly toxic, mutagenic, and soluble Cr(VI) was reduced to the less toxic and insoluble Cr(III) in 2‐litre fixed‐bed reactors inoculated with the sulphate‐reducing bacterium (SRB) Desulfomicrobium norvegicum, capable of performing direct enzymatic Cr(VI) reduction. H2 was used as the electron source. The fixed‐films were developed on three different supports: a PVC cross‐flow material, a pozzolana, and a ceramic granulate. The phased experiments began with a progressive increase of the Cr(VI) concentration in the feed to the column reactors, followed by a progressive decrease of the sulphate concentration. Inhibition by Cr(VI) was less pronounced with pozzolana than with the other supports; when the pozzolana column was fed with a medium containing 100 mg 1‐1 Cr(VI) and only 250 mg 1‐1 sulphate, the lowest residence time that could be applied ...

D. Morin

Papers

Treatment by sulfate-reducing bacteria of Chessy acid-mine drainage and metals recovery

Reduction of chromate by fixed films of sulfate-reducing bacteria using hydrogen as an electron source.

Chromate (CrO 2- 4 ) Reduction in Groundwaters by Using Reductive Bacteria in Fixed-Bed Bioreactors

Chromate Reduction at Low Sulphate Concentration in Hydrogen-Fed Bioreactors