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Mechanisms and Effectivity of Sulfate Reducing Bioreactors Using a Chitinous Substrate in Treating Mining Influenced Water
Al-Abed, S., P. Pinto, J. McKernan, E. Feld-Cook, AND S. Lomnicki. Mechanisms and Effectivity of Sulfate Reducing Bioreactors Using a Chitinous Substrate in Treating Mining Influenced Water. Chemical Engineering Journal. Elsevier BV, AMSTERDAM, Netherlands, 323:270-277, (2017). https://doi.org/10.1016/j.cej.2017.04.045
Mining influenced water (MIW) remediation is still one of the top priorities for the agency because it addresses the most important environmental problem associated with the mining industry and that affects thousands of communities in the U.S. and worldwide. In this paper, the MIW bioremediation mechanisms are studied for a very particular substrate: chitin. Chitin is obtained from crushed crab shells, hence its use as a substrate constitutes a beneficial use. Chitin is also a particular material to be used as a substrate due to its composition (protein, chitin polymer, and carbonates), which makes it very effective in metal removal, including recalcitrant metals like Zn and Mn. Overall, the use of chitinous materials as the bioreactor’s substrate could be considered a green solution for the MIW, because it uses all natural materials in a passive system and the generated sludge would be more stable than the sludges generated by the application of traditional technologies. There are a few published studies that utilized chitin as a bioreactor’s substrate, but this is the first study focused on the mechanisms of metal removal that includes the water chemistry, the generated gaseous phase analyses, and the characterization of the solid residues in the composition and the speciation. Particularly the speciation of the solid residues are important because they allow one to prove the formation of zinc sulfide in the bioreactors via XPS and XANES analyses. This paper would be of a great benefit for all the parties involved in decision-making and operations in MIW treatment: mining industry, consultants, researchers, regulatory agencies, and academia. They will benefit from the knowledge of the involved mechanisms and the efficiency of the substrate in metals removal.
Mining-influenced water (MIW) is the main environmental challenge associated with the mining industry. Passive MIW remediation can be achieved through microbial activity in sulfate-reducing bioreactors (SRBRs), but their actual removal rates depend on different factors, one of which is the substrate composition. Chitinous materials have demonstrated high metal removal rates, particularly for the two recalcitrant MIW contaminants Zn and Mn, but their removal mechanisms need further study. We studied Cd, Fe, Zn, and Mn removal in bioactive and abiotic SRBRs to elucidate the metal removal mechanisms and the differences in metal and sulfate removal rates using a chitinous material as substrate. We found that sulfate-reducing bacteria are effective in increasing metal and sulfate removal rates and duration of operation in SRBRs. The main mechanism involved was metal precipitation as sulfides. The solid residues provided evidence of the presence of sulfides in the bioactive column, more specifically ZnS, according to XPS analysis. The feasibility of passive treatments with a chitinous substrate could be an important option for MIW remediation.
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