HR: 1330h
AN: B32A-0374 [PDF]
TI: The Effect of Ion Adsorption on Microbial Dissimilatory Iron-Reduction and the Mobility of Adsorbed
As(V)
AU: * Meyer, B A
EM: bmeyer@unr.edu
AF: Dept. of Hydrologic Sciences, University of Nevada, Reno
MS 175, Reno, NV 89557 United States
AU: * Meyer, B A
EM: bmeyer@unr.edu
AF: U.S. Geological Survey, MS 176
University of Nevada, Reno, Reno, NV 89557 United States
AU: Stillings, L L
EM: stilling@usgs.gov
AF: Dept. of Hydrologic Sciences, University of Nevada, Reno
MS 175, Reno, NV 89557 United States
AU: Stillings, L L
EM: stilling@usgs.gov
AF: U.S. Geological Survey, MS 176
University of Nevada, Reno, Reno, NV 89557 United States
AB:
The effect of varying environmental conditions on the microbial reduction of Fe(III) and the mobility of adsorbed As(V) was
investigated by studying the kinetics of reductive dissolution of synthetic, hydrous ferric oxide (HFO) in three
batch-reactor experiments. Growth medium, containing HFO as an electron acceptor (EA) and acetate as an electron donor (ED),
was dispensed into 500-ml septum sealed serum bottles. Each bottle was inoculated with an enrichment culture (MEC) containing
an anaerobic Fe-reducing bacterium obtained from sediments at Milltown Reservoir near Missoula, MT. Each enrichment culture
grew for at least 600 hrs and exhibited both exponential and stationary growth. Microbial reduction was monitored by
measuring the production of dissolved Fe(II). Total Fe(II) was calculated by applying a Langmuir adsorption model, developed
for each growth condition, to the measured dissolved Fe(II). Total Fe(II) production was modeled by: x =
X$_{s}$(1-e$^{-ket}$)-[k$_{L}$(e$^{-ket}$)]+(k$_{L}$/k$_{e}$) where x is the total Fe(II) concentration (mM) at t, k$_{e}$ is
the exponential production rate constant (hr$^{-1}$), X$_{s}$ is the total Fe(II) concentration (mM) at the time of
transition between exponential and stationary growth, t is the time since inoculation minus lag time, and k$_{L}$ is the
stationary (linear) production rate constant (mM hr$^{-1}$).
From our experiments we learned that: 1) increasing the concentration of EA from 10-30 mM had no effect on the value of
k$_{e}$, which remained constant at 0.015 hr$^{-1}$. However, the maximum production rate, R$_{max}$ = (k$_{e}$
X$_{s}$)+k$_{L}$, did increase with increasing EA, varying from 0.014-0.031 mM hr$^{-1}$; 2) increasing the concentration of
ED from 10-30 mM had no effect on either k$_{e}$ or R$_{max}$. These values remained constant as ED increased; 3) sorption of
As(V) to the EA (in mM ratios of 1:10 and 1:30, As(V):HFO) affected R$_{max}$ but not k$_{e}$. R$_{max}$ increased with
increasing EA, as observed earlier, but its value was lower than in cultures without arsenic. In the presence of As(V),
R$_{max}$ was unaffected by increasing ED. Microbial reduction of EA did not result in the release of aqueous As(V) or
As(III). In all cases, representative blank and kill controls were run concurrent with growth experiments. No Fe(II)
production was observed in the controls.
The modeling method showed that increases in R$_{max}$, when observed, were due to an elongated exponential growth phase. We
conclude that the availability of surface sites to the culture is the controlling factor in microbial iron reduction. The
length of the exponential growth phase depends on the concentration of surface sites available for microbial reduction.
Adsorbed Fe(II) or As(V) inhibits reduction by decreasing the concentration of available surface sites. Likewise, increasing
the initial concentration of EA increases the concentration of available surface sites thus increasing R$_{max}$.
DE: 0400 Biogeosciences
SC: Biogeosciences [B]
MN: 2003 Fall Meeting