Biomedical Engineering Reference
In-Depth Information
phases. Maximum biomass concentration,
K
, ranges from 369 mg l
-1
for
Chlorella vulgaris
to
604 mg l
-1
for
Scenedesmus obliquus
. The pH increased from 6.4-6.5 to 7.2-7.7, after about
190 h operation, as observed in Figure 3. As it could be expected, algae species growing
faster are those presenting the highest pH variation, which is clearly visible for C
hlorella
fusca
, by comparing Figure 3 with Figure 2.
7.8
7.6
7.4
7.2
7.0
6.8
Chlorella Fusca
Chlorella Vulgaris
Scenedesmus acutus
Scen edesm us o blíquus
6.6
6.4
6.2
0
50
100
150
200
250
Ti m e ( h )
Figure 3. pH evolution over time for each alga (T = 24.6 ºC; pH = 6.5).
4.2. Experiments with Different Initial pH Values (T = 20.8
o
C, pH = 6.5 and
pH = 7.9)
4.2.1. Effect of pH
The influence of the initial pH on algal growth was investigated, although maintaining
the temperature at a lower value than in the previous experiments. The initial pH was kept
around 6.5 in some experiments, whereas in others it was increased up to 7.9. Figure 4 shows
the experimental and predicted growth curves obtained and the parameters μ,
K
and
n
0
,
determined by fitting the logistic equation to the experimental results.
As indicated by
K
values, there is no significant growth of biomass when the initial pH was
adjusted to around 7.9: the highest
K
value is ≈ 54 mg l
-1
for
Scenedesmus obliquus
, whereas for
Chlorella vulgaris
is only ≈ 3 mg l
-1
. The maximum biomass concentration follows the same
order as for pH = 6.5:
Scenedesmus obliquus
>
Chlorella fusca
>
Scenedesmus acutus
>
Chlorella vulgaris
. The specific growth rate of biomass μ
is also reduced by about 50% for all
species, when compared to the values obtained at initial pH = 6.5.
In the experiments performed at a temperature of 20.8 ºC and initial pH = 6.5, it was
obtained an increase in pH of around 0.5 after about 230 h incubation. Starting with a pH =
7.9, no visible alterations were visible during the same operating time. At higher pH values,
