Biomedical Engineering Reference
In-Depth Information
markedly decreases. However,
K
values are significantly higher than those obtained for the
other species. For Cr(VI) = 25 mg l
-1
the algal growth is completely inhibited.
Comparing the results obtained without Cr(VI) addition (Figure 4) with those presented
in Figure 5, one can conclude that growth rates are lower in the first experiments. The
difference may be due to the higher medium volume used in the second study (1500 ml
instead of 250 ml). As light intensity over the flasks was the same, the available light for algal
growth was lower. As light is one of the most important environmental factors influencing the
growth and development of photosynthetic organisms like chlorophyceae [21], the maximum
concentration of growing algae in a continuously mixed culture is determined by the degree
of penetration of light into the culture.
4.4. Effect of Cr(VI) on Metabolites Production
Total, dissolved and suspended organic carbon was measured over time in each algal
culture. Table 4 presents the mean production of metabolites (in terms of dissolved organic
carbon) for different Cr(VI) concentrations. Dissolved organic carbon concentration is small
when compared with total organic carbon concentration. There are no indications that cellular
growth by non photosynthetic routes may have occurred. Results also indicate that an
outstanding dissolved organic carbon production due to the metal presence seems not to
occur. It is also possible to observe that
Chlorella fusca
yields the lowest dissolved organic
carbon concentration.
Table 3. Specific growth rates of biomass (
μ
) and maximum biomass concentrations (K)
obtained by fitting the experimental data to the logistic equation
Concentration of
Cr(VI) (mg l
-1
)
μ
(h
-1
)
K
(mg l
-1
)
R
2
Microalgae
Chlorella fusca
0.008
372.4
0.97756
Chlorella vulgaris
0.014
171.4
0.98586
0
Scenedesmus acutus
0.013
356.1
0.99839
Scenedesmus obliquus
0.017
603.0
0.99914
Chlorella fusca
0.015
267.9
0.93015
Chlorella vulgaris
0.015
182.7
0.99860
1
Scenedesmus acutus
0.015
313.6
0.99351
Scenedesmus obliquus
0.017
607.7
0.99973
Chlorella fusca
0.009
178.1
0.97919
Chlorella vulgaris
0
-
-
5
Scenedesmus acutus
0.009
124.0
0.98879
Scenedesmus obliquus
0.016
254.6
0.99525
Chlorella fusca (CF)
0
-
-
Chlorella vulgaris
0
-
-
25 (50 for
CF
)
Scenedesmus acutus
0
-
-
Scenedesmus obliquus
0
-
-
