Biomedical Engineering Reference
In-Depth Information
Light intensity values ranged from 2000 to 3000 lux (32-48 µE m
-2
s
-1
). Twist et al. [6,
29], Minowa and Sawayama [30] used similar values, 40, 30 and 40-60 µE m
-2
s
-1
,
respectively.
A second set of experiments was carried out to evaluate the effect of pH on microalgae
growth rate. Experiments performed with buffered culture medium at pH ≈ 8 were compared
with experiments where initial pH = 6.5. All the operating conditions were as before, except
temperature, which was around 20.8
±
1.8ºC.
500
Chlorella Fusca
Chlorella Vulgaris
Scenedesmus Acutus
Scen edesm us Obliquus
450
400
350
300
250
200
150
100
50
0
0
50
100
150
200
250
Ti m e ( h )
Figure 1. Microalgal growth as a function of time. (T = 24.6 ºC; pH = 6.5).
To study the effect of the addition of Cr(VI), pre-defined volumes of metal stock solution
were added simultaneously to 2000 ml-glass flasks containing 1500 ml of each algal culture
once a density of 100 000 cells ml
-1
was reached. Experiments with Cr(VI) concentrations of
0, 1, 5 and 25 mg l
-1
(50 mg l
-1
for
Chlorella fusca
culture) were carried out at room
temperature approximately constant: 21.6±1.1, 22.4±0.6, 21.0±0.71 and 21.0±0.3 ºC (mean ±
standard deviation) for
Chlorella fusca
,
Chlorella vulgaris
,
Scenedesmus acutus
and
Scenedesmus obliquus
cultures
,
respectively. No pH corrections were performed. An
Erlenmeyer flask containing only sterile culture medium was submitted to the same operating
conditions, for each set of experiments, and used as blank to correct optical density
measurements over time. Daily samples were collected both in test and control flasks for pH,
biomass (optical density) and total, dissolved and suspended organic carbon.
Flocculation properties of algal cultures were evaluated through settling tests. Initial
optical densities were compared with those of the supernatants after a 6 h-settling period.
