Environmental Engineering Reference
In-Depth Information
of the curve (Fig. 16.2) reveals that as concentration increases, uptake in-
creases rapidly only at low concentrations. At high substrate concentra-
tions, the maximal rate of uptake is approached. Values for
K
s
vary widely
among and within algal taxa (Table 16.1) and may even vary among indi-
vidual cells as they become adapted to surrounding nutrient concentra-
tions. Values of
V
max
can be a useful physiological indicator (Zevenboom
et al.,
1982). For example, organisms existing in low-nutrient environments
tend to have low values of
K
s
and those in areas with high nutrient avail-
ability have high values of
V
max
. Larger cells have greater values for
V
max
and
K
s
than small cells (Suttle
et al.,
1988). A calculation with this equa-
tion is presented in Example 16.1.
When an organism takes up nutrients, it cannot always immediately
use them for growth. Organisms that are under nutrient stress are able to
take up nutrients at very high rates upon transient exposure to high nutri-
ent concentrations but are not able to sustain growth rates proportional to
this uptake. This high uptake is a selective advantage when nutrients are
scarce because pulses of nutrients can be stored. Such consumption in ex-
cess of growth requirements is called
luxury consumption
. Enough phos-
phorus can be stored in the form of the polymer polyphosphate through
luxury consumption for several cell divisions (Healy and Stewart, 1973).
0.04
V
max
= 0.04
0.03
1/2 V
max
0.02
A
K
s
=0.1
0.01
0.0
0.5
1.0
1.5
2.0
S (mg L
-1
)
1.0
max
= 1
0.8
0.6
0.4
Q
0
=0.1
B
0.2
0.0
0.0
0.5
1.0
1.5
2.0
Q (mg/g)
0.010
max
= 0.01
0.008
0.006
0.004
C
0.002
K
s
=0.1
0.000
0.0
0.5
1.0
1.5
2.0
S (mg L
-1
)
FIGURE 16.2
Graphical representation of equations used to describe nutrient uptake and
assimilation: (A) Michaelis-Menten, (B) Droop, and (C) Monod relationships.
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