40 Biogeochemistry of Water, Sediments, and Interfaces

Tuesday, 17 April 2018
1:30 PM - 5:30 PM
Room 250/252

INVESTIGATING FE(III)-REDUCING MICROBIAL ACTIVITY UNDER 100% CARBON DIOXIDE HEADSPACE

Paper number: 40-3
Program: Theme Sessions
Time: 2:10 PM – 2:30 PM

Authors

Abstract

CO2 sequestration aims to use CO2 for enhanced oil recovery or to inject into confined subsurface reservoirs for geologic storage. The effect of increased CO2 on subsurface microbial communities is unknown. Microorganisms can influence groundwater chemistry and potentially impact the efficacy of C­O2 sequestration. This work is part of an ongoing investigation aimed at understanding the potential for microorganisms to affect biogeochemical cycling in naturally high CO2 systems. Previously, Fe(III)-reducing bacteria (FeRB) from aquifers with naturally high CO2 were enriched under a 100% CO2 headspace. We evaluated the ability of these FeRB enrichments to impact solid and aqueous phase Fe transformations.

FeRB cultures and controls (in triplicate) were cultured in anoxic seawater media with synthetic ferrihydrite and organic acids as electron acceptor and donors, respectively. Incubations were performed under 100% CO2, at 37°C for 82 days, and in the presence of resazurin as a redox indicator. Over time, aqueous Fe(II), aqueous total Fe [Fe(II+III)], and HCl-extractable Fe(II) [Fe(II)HCl] were measured using a ferrozine assay. Color changes and mineralogy were also monitored.

Cultures showed visible evidence of Fe(III) reduction in 7 days, indicated by a dark mineral substrate. Chemical measurements showed that Fe(III) reduction peaked at 16 days. No Fe(III) reduction was observed in control bottles. In culture bottles, aqueous Fe(II) initially increased along with increasing Fe(II)HCl concentrations. A decrease in aqueous Fe(II) soon followed, decreasing to below detection. Mineralogical data indicated the initial presence of ferrihydrite (Fe2O3•H2O), followed by siderite (FeCO3) precipitation (observed at day 16), which indicates sequestration of CO2 into a solid phase. These results indicate Fe(III)-reducing bacteria native to high CO2 accumulation sites can impact the geochemistry of their environment and enhance sequestration through mineral formation.

Geological Society of America Abstracts with Programs. Vol. 50, No. 4

doi: 10.1130/abs/2018NC-312850

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