Biological Sulfate Reduction and Recovery of Elemental Sulfur from Mining Waste Waters
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Sulfate in waste waters, especially in effluents of the mining industry, is a growing concern in environmental protection. The conventional methods are limited in terms of sulfate removal efficiency, and new processes are needed for decreasing sulfate emissions to water systems. Biological removal by sulfate reduction to sulfide is one alternative for efficient sulfate removal. The possibility of combining sulfate reduction and sulfide oxidation to elemental sulfur is a comprehensive process for the removal of sulfur compounds, as well as a way to create profit from sulfate containing waste streams. This work investigates a continuous biological sulfate removal from real mine drainage with cow manure as the main carbon source and electron donor. Batch experiments for elemental sulfur recovery were also performed. The bacterial communities present in the effluents of the sulfate-reducing reactors were analysed and their influence in the process is discussed. Biological sulfate removal was tested with three upflow anaerobic sludge blanket reactors with different additional inocula. The highest stable sulfate removal efficiency was 60% with lactate as a co-substrate. Sulfide concentration in the effluents was low, but sulfide oxidation experiments indicated elemental sulfur formation, so the waste water treatment principles of this work could be applied to actual mining sites. The DNA analyses showed a wide range of bacterial groups present in the reactor effluents. The bacterial communities developed and the amount of sulfate-reducers grew during the operation. These microbial analyses allow a uniquely continuous peek inside the biological process, offering knowledge in the interactions of different bacterial groups and their effect on sulfate removal efficiency.