Geochemical, Microbiological, and Geophysical Assessments of Anaerobic Immobilization of Heavy Metals

Abstract

Bioremediation methods that precipitate contaminants in situ as solid (mineral) phases can provide cost-effective options for removing dissolved metals in contaminated groundwater. The current field-scale experiments demonstrate that indigenous bacteria can be stimulated to remove metals by injection of electron-donating substrates and nutrients into a contaminated aquifer. Groundwater at the investigation site is aerobic and contains high levels of lead, cadmium, zinc, copper, and sulfuric acid (pH = 3.1) derived from a car-battery recycling plant. During the experiments, lead, cadmium, zinc, and copper were almost completely removed by precipitation of solid sulfide phases, as pH increased from 3 to ∼5 and Eh dropped from +400 mV to −150 mV. X-ray and transmission electron microscopy (TEM) analyses of filtered material from the treated groundwater indicated the presence of newly formed nanocrystalline metal sulfides. Genetic sequencing indicated that the principal species of sulfate-reducing bacteria involved in the bioremediation process was Desulfosporosinus orientis. Geochemical modeling shows that oxidation of added substrates and subsequent bacterial sulfate reduction produced desired geochemical conditions (i.e., decreasing Eh and increasing pH) for the precipitation and sorption of metal sulfides. Geophysical survey results suggest that bioremediation lowers electrical conductance of groundwater and possibly increases the magnetic susceptibility of porous media. This study demonstrates that integrated geochemical, geophysical, and microbiological analyses, combined with theoretical modeling, can successfully track and predict the progress of subsurface bioremediation.

Experimental analysis of arsenic precipitation during microbial sulfate and iron reduction in model aquifer sediment reactors

“…This observation implies that we may be able to remediate As contamination in situ in reducing aquifers simply by injecting SO 4 2À to stimulate microbial SO 4 2À reduction (Kirk et al, 2004). Other studies have also concluded that enhancing SO 4 2À reduction may be useful for As remediation, including Rittle et al (1995), Castro et al (1999), Jong and Parry (2003), Lee et al (2005), and Saunders et al (2005), Keimowitz et al (2007). In a field test of this strategy at a naturally contaminated site in Bangladesh, Saunders et al (2008) observed a decrease in aqueous As concentration coinciding with stimulated SO 4 2À reduction.…”

Surfactants and Bacterial Bioremediation of Polycyclic Aromatic Hydrocarbon Contaminated Soil—Unlocking the Targets

“…Anaerobic degradation of PAHs in subsoils or aqueous systems may be enhanced by adding suitable electron acceptors, nutrients, and surfactants (Bach, Kim, Choi, & Oh, 2005;Providenti et al, 1993;Saunders et al, 2005). For example, amendment with sulfate, nitrate, or nitrous oxide may allow denitrification-coupled degradation to occur (Annweiler et al, 2002;Van Hamme et al, 2003).…”

The Geomicrobiology of Ore Deposits

“…At a site at Troy, Alabama, which was contaminated by Zn Cd, Pb, Cu, and sulfuric acid, Saunders et al (2005b) induced bacterial sulfate reduction by injecting sucrose and diammonium phosphate into ground water. Within 30 d, previous aer-obic ground waters had become reducing enough for sulfate reduction to commence, leading to the almost instantaneous removal of the Cu, Zn, Pb, and Cd from solution as sulfides (Fig.…”