title: Spatial impacts of inorganic ligand availability and localized microbial community structure on mitigation of zinc laden mine water in sulfate-reducing bioreactors.
abstract: Sulfate-reducing bioreactors (SRBRs) represent a passive, sustainable, and long-term option for mitigating mining influenced water (MIW) during release. Here we investigate spatial zinc precipitation profiles as influenced by substrate differentiation, inorganic ligand availability (inorganic carbon and sulfide), and microbial community structure in pilot-scale SRBR columns fed with sulfate and zinc-rich MIW. Through a combination of aqueous sampling, geochemical digests, electron microscopy and energy-dispersive x-ray spectroscopy, we were able to delineate zones of enhanced zinc removal, identify precipitates of varying stability, and discern the temporal and spatial evolution of zinc, sulfur, and calcium associations. These geochemical insights revealed spatially variable immobilization regimes between SRBR columns that could be further contrasted as a function of labile (alfalfa-dominated) versus recalcitrant (woodchip-dominated) solid-phase substrate content. Both column subsets exhibited initial zinc removal as carbonates; however precipitation in association with labile substrates was more pronounced and dominated by metal-sulfide formation in the upper portions of the down flow columns with micrographs visually suggestive of sphalerite (ZnS). In contrast, a more diffuse and lower mass of zinc precipitation in the presence of gypsum-like precipitates occurred within the more recalcitrant column systems. While removal and sulfide-associated precipitation were spatially variable, whole bacterial community structure (ANOSIM) and diversity estimates were comparatively homogeneous. However, two phyla exhibited a potentially selective relationship with a significant positive correlation between the ratio of Firmicutes to Bacteroidetes and sulfide-bound zinc. Collectively these biogeochemical insights indicate that depths of maximal zinc sulfide precipitation are temporally dynamic, influenced by substrate composition and broaden our understanding of bio-immobilized zinc species, microbial interactions and potential operational and monitoring tools in these types of passive bioreactors.
authors.affiliation: Colorado School of Mines, Department of Civil and Environmental Engineering, 1500 Illinois St., Golden, CO 80401, USA.
authors.forename: Dina M
authors.initials: DM
authors.lastname: Drennan
authors.affiliation: Colorado School of Mines, Department of Civil and Environmental Engineering, 1500 Illinois St., Golden, CO 80401, USA; Swedish University of Agricultural Sciences, Department of Forest Mycology and Plant Pathology, Box 7026, 75007 Uppsala, Sweden.
authors.forename: Robert
authors.initials: R
authors.lastname: Almstrand
authors.affiliation: Colorado School of Mines, Hydrologic Science and Engineering Program, 1500 Illinois St., Golden, CO 80401, USA; Freeport McMoRan Inc., 1600 Hanley Blvd., Oro Valley, AZ 85737, USA.
authors.forename: Jeffrey
authors.initials: J
authors.lastname: Ladderud
authors.affiliation: Freeport McMoRan Inc., 1600 Hanley Blvd., Oro Valley, AZ 85737, USA.
authors.forename: Ilsu
authors.initials: I
authors.lastname: Lee
authors.affiliation: Colorado School of Mines, Department of Civil and Environmental Engineering, 1500 Illinois St., Golden, CO 80401, USA.
authors.forename: Lee
authors.initials: L
authors.lastname: Landkamer
authors.affiliation: Colorado School of Mines, Department of Civil and Environmental Engineering, 1500 Illinois St., Golden, CO 80401, USA.
authors.forename: Linda
authors.initials: L
authors.lastname: Figueroa
authors.affiliation: Colorado School of Mines, Department of Civil and Environmental Engineering, 1500 Illinois St., Golden, CO 80401, USA; Colorado School of Mines, Hydrologic Science and Engineering Program, 1500 Illinois St., Golden, CO 80401, USA. Electronic address: jsharp@mines.edu.
authors.forename: Jonathan O
authors.initials: JO
authors.lastname: Sharp
mesh_terms: D019149:Bioreactors / Q000382:microbiology; D008906:Mining; D013431:Sulfates / Q000737:chemistry; D014867:Water; D015032:Zinc / Q000737:chemistry*
chemical_list: D013431:Sulfates; D014867:Water; D015032:Zinc
keywords: Bioimmobilization; Microbial diversity; Mining influenced water; Spatial distribution; Sulfate-reducing bacteria; Zinc-sulfide