『Abstract
Far-from-equilibrium steady-state basaltic glass dissolution
rates were measured using newly developed Bacterial Mixed-Flow
Reactors (BMFR) at 25℃. Experiments were performed in aqueous
pH 4, 6, 8, and 10 buffer solutions with and without nutrients
and in: 1) the absence of bacteria, 2) the presence of 0.1-0.4
gwet/L dead Pseudomonas reactans,
and 3) in the presence of 0.9-19.0 gwet/L
live P. reactans extracted from a deep subsurface oxygen-bearing
basaltic aquifer. The BMFR allows steady-state rate measurements
at constant concentrations of live or dead bacteria. Experiments
ran for 30-60 days on a single basaltic glass powder, initially
at bacteria- and nutrient-free conditions until Si steady-state
glass dissolution was achieved. Then, in 2-4 steps, either live
or dead P. reactans were added via nutrient-rich or nutrient-free
inlet solutions, and the flux of Si and other mineral constituents
from the basaltic glass were measured until a new chemical steady
state was attained. Scanning Electron Microscope and X-ray Photoelectron
Spectroscopic techniques verified the presence of live bacteria
on the basaltic glass surfaces through biofilm formation, bacterial
dissolution imprints, and enrichment of surface layers in C and
N. The presence of either live or dead P. reactans lowers
constant pH steady-state basaltic glass dissolution rates by no
more than 〜0.5 log units which is close to combined analytical
and experimental uncertainties of the experiments. The presence
of bacteria did not cause any significant modification in trace
element release rates from dissolving basaltic glass within the
uncertainty of the measurements. Experiments in nutrient-rich
solutions yielded close to stoichiometric release of all major
elements from basaltic glass at pH 6-8 likely as a result of organic
ligand complexation with aqueous Al and Fe, which would otherwise
form hydroxy-precipitates. As the results of this work suggest,
at most, a small inhibiting effect of live or dead P. reactans
on basaltic glass dissolution rates, geochemical modeling of mineral
reactivity in basaltic aquifers likely does not require explicit
provision for the presence of heterotrophic bacteria on basaltic
glass reactivity.
Keywords: Basaltic glass; Pseudomonas reactans; Mineral-bacteria
interaction; Dissolution kinetics; Bacterial mixed-flow reactors;
CO2 sequestration』
1. Introduction
2. Theoretical background
3. Material and methods
3.1. Basaltic glass
3.2. Bacterial culture
3.3. Dissolution rate experiments in Bacterial Mixed-Flow Reactors
(BMFR)
3.4. Batch experiments performed to assess live bacteria interaction
with mineral-free solutions in the presence of mineral constituents
3.5. Analytic methods
4. Experimental results
4.1. Basaltic glass dissolution in the presence of dead bacteria
in BMFR
4.2. Basaltic glass dissolution in the presence of live bacteria
in BMFR
4.3. Element assimilation and release by bacteria cells in basaltic
glass free, closed-system batch experiments
5. Discussion
5.1. The effect of cell wall adsorption and bacterial assimilation
on mass balance calculations
5.2. Effect of nutrients and bacteria on basaltic glass element
release rates
5.3. Comparison with literature data on the effect of bacteria
on silicate minerals dissolution
5.4. Application to subsurface CO2 storage
and soil weathering
6. Conclusions
Acknowledgments
Appendix 1. Chemical composition of the inlet fluids used in the
BMFR experiments
Appendix 2. Supplementary data
References