Inhibition of sulfate‐reducing bacteria by metal sulfide formation in bioremediation of acid mine drainage

Abstract

Acid mine drainage (AMD) containing high concentrations of sulfate and heavy metal ions can be treated by biological sulfate reduction. It has been reported that the effect of heavy metals on sulfate-reducing bacteria (SRB) can be stimulatory at lower concentrations and toxic/inhibitory at higher concentrations. The quantification of the toxic/inhibitory effect of dissolved heavy metals is critical for the design and operation of an effective AMD bioremediation process. Serum bottle and batch reactor studies on metal toxicity to SRB indicate that insoluble metal sulfides can inhibit the SRB activity as well. The mechanism of inhibition is postulated to be external to the bacterial cell. The experimental data indicate that the metal sulfides formed due to the reaction between the dissolved metal and biogenic sulfide act as barriers preventing the access of the reactants (sulfate, organic matter) to the necessary enzymes. Scanning electron micrographs of the SRB cultures exposed to copper and zinc provide supporting evidence for this hypothesis. The SRB cultures retained their ability to effect sulfate reduction indicating that the metal sulfides were not lethally toxic to the SRB. This phenomenon of metal sulfide inhibition of the SRB has to be taken into account while designing a sulfate-reducing bioreator, and subsequently an efficient biotreatment strategy for AMD. Any metal sulfide formed in the bioreactor needs to be removed immediately from the system to maintain the efficiency of the process of sulfate reduction.

Effects of Sulfate Reduction on Trichloroethene Dechlorination by Dehalococcoides-Containing Microbial Communities

“…At the end of the experiment (day 16), the cell number ratio of strain 195 to DvH was about 1:6 in contrast to the no-sulfate control (coculture grown on lactate and TCE), where the ratio was 4.3:1, similar to previously reported ratios (34). Sulfide can precipitate metals that are necessary nutrients and hence make them inaccessible to the cells (35). In order to demonstrate that the lack of dechlorination observed in this study was due to sulfide inhibition instead of trace metal insufficiency caused by sulfide precipitation, at the end of the experiment (day 16) the headspaces of the experimental bottles were flushed for 40 min with sterilized nitrogen gas to remove sulfide, and then the bottles were re-amended with 0.5 mM TCE and 1 mM lactate.…”

Methanogens, sulphate and heavy metals: a complex system

“…Metal sulphides generally present a specific gravity of around 4, which allows their separation from biomass by gravity settling; a solution to avoid their toxicity is their removal from the sludge before they reach inhibitory concentrations. Some systems have shown to operate well, even in the presence of metal sulphides (Utgikar et al 2002, Van Houten et al 2006. Van Houten et al (2006) studied the start-up of a full-scale synthesis gas-lift reactor for treating metal and sulphate rich wastewater, and did not observe any interference from the zinc sulphide precipitates in the performance of the reactor.…”

Developments in Bioremediation of Soils and Sediments Polluted with Metals and Radionuclides – 1. Microbial Processes and Mechanisms Affecting Bioremediation of Metal Contamination and Influencing Metal Toxicity and Transport

“…The metals precipitate as highly insoluble sulfides (entrapment, nucleation and crystallisation of insoluble sulfides), e.g. ZnS, CdS, CuS, CoS, NiS and FeS White & Gadd 2000;Labrenz et al 2000;Wang et al 2001;Drzyzga et al 2002;Valls & de Lorenzo, 2002;Utgikar et al 2002;White et al 2003;Krumholz et al 2003). Sulfide precipitation is an efficient means of removing toxic metals from solution, while immobilisation in a biofilm is also an affective method to reduce the mobility of the metals, which is of value in bioremediation of anoxic sediment and wetlands Kaksonen et al 2003;Labrenz & Banfield 2004).…”