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and degradation.
1
Kinzelbach
et al
.
2
developed the aerobic-anaerobic mass
transport model in which oxygen, nitrate, organic carbon and bacteria
growth in liquid, solid, and biophases are included. Lensing
et al
.
3
included
the effect of inter-phases mass transport related to the bacteria-mediated
biochemical reactions. Schafer
et al
.
4
,
5
examined the effect of decrease of
organic carbons consumed by bacteria on the biochemical mass transport.
The inclusions of sulfur reducing and methane yielding processes were con-
sidered important in the modeling of the extremely reduced aquifer condi-
tions. The authors developed the algorithm of ion exchange reactions for
the major cation such as Ca
2+
,Mg
2+
,K
+
,Na
+
, and the dissolved Mn
2+
and Fe
2+
, which are yielded by the biochemical reactions by bacteria, con-
sidering the possible contribution on the cation exchange process.
6
,
7
This
effect should be significant for the situation in a coastal aquifer where the
intruded seawater region resides for a long time compared to the freshwa-
ter above the mixing zone between the fresh and seawater. For example,
Snyder
et al
.
8
reported that the reduced environment of Mn
2+
and Fe
2+
plays an important role in determining the geochemical properties in a
coastal aquifer, where the bacteria mediated biochemical reactions would
take place.
In the present paper, objecting the ion exchange processes by six cations
such as Na
+
,K
+
,Ca
2+
,Mg
2+
,Mn
2+
,andFe
2+
, the consumptions of
dissolved oxygen (DO) and nitrate caused by aerobic bacteria and the
reduction of manganese oxidize and iron hydroxide were studied through
the laboratory experiment infiltrating seawater into the alluvial soil. The
numerical simulation model including the above mentioned chemical species
in the bio-, liquid-, and solid phases were also evaluated. By conducting a
sensitivity analysis for the model parameters, several significant properties
in the mass transport were obtained. This study, particularly, focuses on
the iron behavior, because iron oxide abundantly exists in nature, iron is
common redox element and has much effect on redox mechanism.
2. Mult-icomponent Solute Transport Model
Figure 1 illustrates the conceptual model of the reactions considered in
this research. The reactions to be discussed herein are the cation exchange,
bacteria-mediated biochemical processes as well as the convection and dis-
persion. The bacteria-mediated process is assumed to take place in the
biophase. Arrows in the figure depict the possible mass transport between
the different phases.
