Agriculture Reference
In-Depth Information
1.0
As(V) Transport
Windsor Soil
0.8
0.6
As(V)
Column
0.4
0.2
0.0
0
10
20
30
40
50
60
Pore Volumes (V/V
o
)
FIGURE 7.32
Experimental As(V) breakthrough curves in Windsor soil without addition of P. Solid curves
are single-component multireaction model (MRM) predictions using batch kinetic parameters.
The dashed curves depict MRM results based on nonlinear optimization. Arrows indicate
pore volumes when flow interruptions occurred.
The transport of As(V) in the presence of P is illustrated by the BTCs
shown in Figures 7.33 and 7.34. Similar to As(V), BTCs for P exhibited exten-
sive asymmetry. Nonequilibrium conditions appear dominant as indicated
by the sharp drop in P concentration as a result of flow interruption (or stop
flow). In order to describe the competitive transport of As(V) and P, a model
was developed that accounts for equilibrium and kinetics mechanisms.
Specifically, the equilibrium and kinetic adsorption equations were modi-
fied in a way similar to the competitive SRS model. The single-species simu-
lation results were further tested with the analytical solution for the two-site
nonequilibrium transport model provided by CXTFIT (Toride, Leij, and van
Genuchten, 1995).
7.8.4 Vanidate-Phosphate
Vanadium is a ubiquitous trace element in the environment and is an essen-
tial trace element for living organisms, but in excessive amounts is harm-
ful to humans, animals, and plants (Crans et al. 2004). Vanadium acts as a
growth-promoting factor and participates in fixation and accumulation of
nitrogen in plants, whereas high concentrations of vanadium may reduce
their productivity (Underwood, 1977). In soils, vanadium is derived from
parental rocks and deposits.
Search WWH ::
Custom Search