title: Treatment of acid rock drainage using a sulfate-reducing bioreactor with zero-valent iron.
abstract: This study assessed the bioremediation of acid rock drainage (ARD) in flow-through columns testing zero-valent iron (ZVI) for the first time as the sole exogenous electron donor to drive sulfate-reducing bacteria in permeable reactive barriers. Columns containing ZVI, limestone or a mixture of both materials were inoculated with an anaerobic mixed culture and fed a synthetic ARD containing sulfuric acid and heavy metals (initially copper, and later also cadmium and lead). ZVI significantly enhanced sulfate reduction and the heavy metals were extensively removed (>99.7%). Solid-phase analyses showed that heavy metals were precipitated with biogenic sulfide in the columns packed with ZVI. Excess sulfide was sequestered by iron, preventing the discharge of dissolved sulfide. In the absence of ZVI, heavy metals were also significantly removed (>99.8%) due to precipitation with hydroxide and carbonate ions released from the limestone. Vertical-profiles of heavy metals in the columns packing, at the end of the experiment, demonstrated that the ZVI columns still had excess capacity to remove heavy metals, while the capacity of the limestone control column was approaching saturation. The ZVI provided conditions that enhanced sulfate reduction and generated alkalinity. Collectively, the results demonstrate an innovative passive ARD remediation process using ZVI as sole electron-donor.
authors.affiliation: Department of Chemical and Environmental Engineering, University of Arizona, P.O. Box 210011, Tucson, AZ 85721, USA.
authors.forename: Pedro
authors.initials: P
authors.lastname: Ayala-Parra
authors.affiliation: Department of Chemical and Environmental Engineering, University of Arizona, P.O. Box 210011, Tucson, AZ 85721, USA.
authors.forename: Reyes
authors.initials: R
authors.lastname: Sierra-Alvarez
authors.affiliation: Department of Chemical and Environmental Engineering, University of Arizona, P.O. Box 210011, Tucson, AZ 85721, USA. Electronic address: jimfield@email.arizona.edu.
authors.forename: James A
authors.initials: JA
authors.lastname: Field
mesh_terms: D001419:Bacteria / Q000378:metabolism; D019149:Bioreactors; D006863:Hydrogen-Ion Concentration; D007220:Industrial Waste; D007501:Iron / Q000737:chemistry*; D019216:Metals, Heavy / Q000737:chemistry; D010084:Oxidation-Reduction; D012722:Sewage; D013431:Sulfates / Q000737:chemistry / Q000378:metabolism; D013464:Sulfuric Acids / Q000737:chemistry; D014874:Water Pollutants, Chemical / Q000737:chemistry / Q000378:metabolism
chemical_list: D007220:Industrial Waste; D019216:Metals, Heavy; D012722:Sewage; D013431:Sulfates; D013464:Sulfuric Acids; D014874:Water Pollutants, Chemical; D007501:Iron; C033158:sulfuric acid
keywords: Anaerobic; Bioremediation; Copper; Heavy metal; Permeable reactive barrier