Sustainable electron donor amendments with potential for faster and less expensive mine waste (bio)remediation

Authors: Finneran, KT Download Paper Open access courtesy of:

DOI https://doi.org/10.36487/ACG_repo/2315_073

Cite As:
Finneran, KT 2023, 'Sustainable electron donor amendments with potential for faster and less expensive mine waste (bio)remediation', in B Abbasi, J Parshley, A Fourie & M Tibbett (eds), Mine Closure 2023: Proceedings of the 16th International Conference on Mine Closure, Australian Centre for Geomechanics, Perth, https://doi.org/10.36487/ACG_repo/2315_073



Abstract:
Metals and metalloids from mine waste present a unique set of challenges for in situ or ex situ remediation. Ionic strength, pH, and metal/metalloid concentration are outside of typical ranges encountered in freshwater environments, and because of this combined biological-chemical remediation can be inefficient, expensive, or completely ineffective. Many microbial remediation processes for mine waste are predicated on stimulating microbial Fe(III) and/or Mn(IV) reduction, because these cells influence the combined microbial-chemical processes that: a) directly reduce toxic metals/metalloids, b) increase the pH to precipitate non-redox-active metals, and c) generate biogenic-reactive ferrous iron to chemically reduce toxic metals/metalloids. Stimulating these cells requires engineered amendments of electron donor(s). The problem is that the current commercially available “long-term, slow-release” electron donor(s) are derived from soybean oil and are purely lipid based. Lipids are exceedingly poor electron donor(s) for microbial metal reduction, and as such the use of lipid electron donors has failed many more times than it has been successful, and it is an extremely expensive technology. In addition, lipids can saponify during in situ process with calcium and magnesium ions, and partially fermented lipid combined to form a wax that impedes wells and groundwater flow. These electron donor(s) have been used commercially merely because good alternatives that are “long-term” have not been developed. We have developed a technology based on amendment of novel electron donor(s) derived from animal co-products, which far outperform conventional electron donors for stimulating metal reduction. These co-products are comprised of waste generated in the animal rendering process such as feathers or bone. This technology will lead to faster remediation times at considerably lower cost. Batch incubations with aquifer material and/or sediments were designed and run to mimic in situ conditions. The rendered animal co-product electron donors stimulated simultaneous fermentation, Fe(III) reduction, and alternate metal/metalloid reduction via combined microbial-chemical processes, while emulsified vegetable oil generated primarily methane. Data suggest the protein content and nitrogen released accelerated metal reduction, and it is the protein content that promoted the rapid onset of metal-reducing microbial activity, while the remaining animal (not soybean) lipid content sustained it. Price per ton of these electron donors is in the USD 1000 – USD 1300 range, while similar lipid based amendments are in the USD 6,000 to USD 7,000 per ton range. This is a more effective and more cost efficient technology for metal/metalloid mine waste remediation.

Keywords: bioremediation, metals, metalloids, electron donor, site remediation

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