Citation:

Pinto, P., S. Al-Abed, AND J. McKernan. Comparison of the efficiency of chitinous and ligneous substrates in metal and sulfate removal from mining-influenced water. JOURNAL OF ENVIRONMENTAL MANAGEMENT. Elsevier Science Ltd, New York, NY, 227(1):321-328, (2018). https://doi.org/10.1016/j.jenvman.2018.08.113

Impact/Purpose:

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, we compare the metal (Al, Cu, Fe, Cd, Mn, and Zn) and sulfate removal efficiencies of two different substrates (ligneous with wood chips, hay and manure, and chitinous with crushed crab shells were these substrates) in anaerobic column experiments. We observed that the chitinous substrate provided a longer operational period, which can be determinant in substrate selection for field reactors, because these need to operate for the longest possible period without human intervention. There are just a few published articles that compare efficiencies of different substrates and even fewer considering that chitin is one of those. This is also the second paper that we have presented on this issue, since the publication of the paper about mechanisms published in the Chemical Engineering Journal (1). This paper aims to be of relevance in MIW remediation on bioreactors design and substrate selection, which involves: the mining industry, consultants, researchers, regulatory agencies, and academia.

Description:

Mining-influenced water (MIW) remediation is challenging, not only due to its acidity and high metal content, but also due to its presence in remotely located mine sites with difficult surrounding environments. An alternative to common remediation technologies, is the use of sulfate-reducing bacteria (SRB) to achieve simultaneous sulfate reduction and metal removal in on-site anaerobic passive systems. In these systems, the organic carbon source (substrate) selection is critical to obtaining the desired effluent water quality and a reasonable treated volume. In this study, we evaluated the use of two different substrates: a chitinous product obtained from crushed crab shells, and a more traditional ligneous substrate. We put the substrates, both with and without water pretreatment consisting of aeration and pH adjustment, in anaerobic experimental columns. The treatment with the chitinous substrate was more effective in removing metals (Al, Cu, Fe, Cd, Mn, Zn) and sulfate for a longer period (458 days) than the ligneous substrate (78 days) before suffering Zn breakthrough. The reactors fed with pretreated water had longer operational periods and lower metals and sulfate concentrations in the effluent than those with untreated influent water. Zn was consistently removed to levels <0.3 mg/L for 513 days in the chitinous substrate columns, while levels <0.3 mg/L were maintained for only 140 days in the ligneous substrate pretreated column. The highest sulfate removal rates achieved in this study were in the range of 5–6 mol/m3/d for the chitinous substrate and 1–2 mol/m3/d for the ligneous substrate. Overall, the chitinous substrate proved to be more efficient in the removal of all the aforementioned metals and for sulfate when compared to the ligneous substrate. This could be the determinant when selecting a substrate for passive systems treating acidic MIW, particularly when Zn and Mn removal is necessary.

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