HR: 0800h
AN: B21B-0887    [Abstracts]
TI: THE ROLE OF MICROBIAL Fe (III) REDUCTION IN THE CLAY FLOCCULATION
AU: * Kim, J
EM: jkim@nrlssc.navy.mil
AF: Naval Research Lab., Seafloor Sciences Branch, Stennis Space Center, MS 39529 United States
AU: Furukawa, Y
AF: Naval Research Lab., Seafloor Sciences Branch, Stennis Space Center, MS 39529 United States
AU: Dong, H
AF: Department of Geology, Miami University, Oxford, OH 45056 United States
AU: O'Reilly, E
AF: Naval Research Lab., Seafloor Sciences Branch, Stennis Space Center, MS 39529 United States
AU: Daulton, T
AF: Naval Research Lab., Seafloor Sciences Branch, Stennis Space Center, MS 39529 United States
AU: Newell, S
AF: Naval Research Lab., Seafloor Sciences Branch, Stennis Space Center, MS 39529 United States
AB: This study was undertaken to investigate the changes in flocculation properties of ferruginous smectite particles (Nau-1), including settling velocity, aggregate size, and floc architecture as a result of microbial reduction in the smectite structure. Dissimilatory iron reducing bacterium, Shewanella oneidensis MR-1 was inoculated with lactate as the electron donor and Fe(III) in smectite as the sole electron acceptor for 3, 12, 24, and 48 hours in an anaerobic chamber. Two controls were utilized; the first was identical to the experimental treatments except that heat-killed cells were used (nonreduced control), and the second control was the same as the first except that the incubation was carried out in an aerobic environment. The extent of Fe(III) reduction for the 48-hr incubation was observed to reach up to 18 %. Neither the nonreduced control nor the aerobically inoculated sample showed Fe(III) reduction. Compared with the nonreduced control, there was a 2.7-ŸYm increase of mean aggregate size and a 30-times increase in average settling velocity in the bioreduced smectite suspensions as measured with a Micromeritics Sedigraph. The aerobically inoculated smectite showed a similar aggregate size distribution to that of the nonreduced control. Significant changes in physical properties of smectite suspensions induced by microbial Fe(III) reduction were directly measured using transmission electron microscope (TEM). Floc architecture of the bioreduced smectite reveals no open structures (pore areas) as observed in nonreduced control. The aspect ratio (thickness/length) of individual smectite particle increased from 0.11 for the nonreduced control to 0.18 for the bioreduced smectite suspensions. The effects of pH on the clay flocculation were minimal in this study because the value of pH remained nearly constant at pH=7.0 ­V 7.3 before and after the experiments. We, therefore, suggest that the increase in net negative charge caused by microbial Fe(III) reduction significantly promoted clay flocculation by increasing the electrochemical attraction in the smectite suspensions.
DE: 4825 Geochemistry
DE: 4558 Sediment transport
DE: 4802 Anoxic environments
DE: 0400 Biogeosciences
SC: Biogeosciences [B]
MN: 2004 AGU Fall Meeting