Biomedical Engineering Reference
In-Depth Information
values were 0.002 to 0.02 g L −1 d −1  biomass, 0.2 to 5.4 mg L −1 d −1  lipid, and 11% to
23% lipid dry cell weight (Chen et al., 2011). Twenty-one other phototrophic spe-
cies had a range of biomass production rates from 0.02  to 0.53  g L −1 d −1 , 0.2  to
178.8 mg L −1 d −1  lipid, and 5.1% to 67.8% lipid dry cell weight. Calculation of lipids
on a cell basis also varied from 0.068 to 29.11 pg cell −1 (Huerlimann et al., 2010).
The data on lipid variations given by Chisti (2007), Khan et al. (2009), Harun
et al. (2010), Basova (2005), Huerlimann et al. (2010), Mata et al. (2010), Malcata
(2010), and Chen (2011) summarized in Table 13.3 show that wide inter- and intra-
specific variations in lipid levels as percent dry cell weight exist. For example, the
lowest (6%) was in Scenedesmus dimorphus (Gouveia and Oliveira, 2009), com-
pared to 75% in Botryococcus braunii (Chisti, 2007) and 77% in Schizochrtrium
sp. (Chisti, 2007). Gouveia and Oliveira (2009) reported a wide range of values
within the same species: 11% to 55% in Scenedesmus obliquus , 14% to 56% in
Chlorella vulgaris , 23% to 55% in Chlorella protothecoides, and 35% to 65% in
Neochloris oleoabundans. Chisti (2007) reported 25% to 75% in Botryococcus
braunii . These variations could be attributed to variations in the physiological
state of the cells; marked differences in the lipid were noticed in cultures har-
vested in logarithmic, late logarithmic, and stationary phases of Nannochloropsis
sp., Isochrysis sp., Tetraselmis sp., and Rhodomona s sp. (Huerlimann et al., 2010).
Results of Chiu et al. (2009) corroborate that lipids vary with the phase of growth
of the alga Nannochloropsis oculata ; lipids were 30.8% in log phase cultures,
39.7% in early stationary phase, and 50.4% in stationary phase cells (Chiu et al.,
2009). In Nannochloropsis sp., the lipid as percent dry cell weight ranged from
21.6  to 60 (Rodolfi et  al., 2008; Chiu et  al., 2009), and their production rates
correspond to 30 mg L −1 d −1  and 86.3 mg L −1 d −1 , respectively. Sturm and Lamer
(2011), based on energy evaluation from wastewater algal biomass production,
concluded that if the lipid in dry biomass from the field is less than 10%, com-
pared to 50% to 60% in laboratory-scale reactors, it would be better to use the
biomass as a combustible source of viable energy.
13.6 BIOCHEMICAL MANIPULATION: HIGHER YIELDS
Chemical manipulations of algae are reflected in their biochemical constituents.
Nitrogen starvation increased lipid production from 117 to 204 mg L −1 d −1 ( R o d o l i
et al., 2008). By manipulating the nutrients in Scenedesmus obliquus , up to 58.3%
lipid was attained, which was five- to tenfold higher than controls (Mandal and
Mallick, 2009). It is of interest to note that carotenoids increased only in Dunaliella
salina as the salinity increased (Gómez et  al., 2003; Coesel et  al., 2008). The
carotenoid levels (mg L −1 ) corresponded to 6.9, 10.8, and 12.9 mg L −1  in Provosoli
medium of 1 M, 2 M, and 3 M sodium chloride (NaCl), respectively; in an arti-
ficial medium, they were more pronounced and were 8, 12.9, and 29.5 mg L −1  in
1 M, 2 M, and 3 M NaCl, respectively. Takagi et al. (2006) showed that the salt
content of the medium could also be a stressor in Dunaliella . In the initial stages
of cultures, when the NaCl was increased from 0.5 M (equivalent to seawater) to
1.0 M, lipid increased by 67%; when mid- or late-log phase cultures were subjected
to a similar stress, cellular lipid increased to 70%. So while harvesting cells for
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