The Effect of Microbial FE(III) Reduction on Smectite Flocculation
NAVAL RESEARCH LAB WASHINGTON DC
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This study was undertaken to investigate the changes in flocculation properties of Fe-rich smectite nontronite, NAu-1 suspensions, including settling velocity, aggregate size and floc architecture associated with microbial FeIII-reduction in the smectite structure. The dissimilatory Fe-reducing bacterium Shewanella oneidensis MR-1 was incubated with lactate as the electron donor and structural FeIII as the sole electron acceptor for 3, 12, 24 and 48 h in an aerobic chamber. Two controls were prepared the first was identical to the experimental treatments except that heat-killed cells were used non-reduced 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 FeIII reduction for the 48 h incubation was observed to reach up to 18. Neither the non-reduced control nor the aerobically inoculated sample showed FeIII reduction. compared with the non-reduced control, there was a 2.7 micrometer increase in mean aggregate size and a 30-fold increase in average settling velocity in the bioreduced smectite suspensions as measured using a Micromeritics SedigraphRegistered.
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