Algae-Mediated Carbon Dioxide Sequestration for Climate Change Mitigation and Conversion to Value-Added Products - Biotechnological Applications of Microalgae - page 166

TABLE 11.2
Comparison of Some Biodiesel Sources

Crop Oil Yield (L ha −1 y −1 )

Corn 172

Soybean 446

Canola 1,190

Jatropha 1,892

Oil palm 5,950

Microalgae a 136,900

Microalgae b 58,700

a 70% oil (by wt.) in biomass.
b 30% oil (by wt.) in biomass.
Source: Adapted from Chisti (2007) and Mata et al. (2010).

The oil content in microalgae can exceed 80% by weight of dry biomass (Spolaore
et al., 2006). The biofuel production potentials of various algal strains reported are
summarized in Table 11.3. Depending on the species, microalgae produce many
different kinds of lipids, hydrocarbons, and other complex oils. Hexadecanoic acid
methyl ester (16:0), palmitoleic acid methyl ester (16:1), octadecanoic acid methyl
ester (18:1), and stearic acid methyl ester (18:0) are some of the major FAMEs found
to be suitable for biodiesel production derived from microalgal lipids (Dayananda
et al., 2007; Francisco et al., 2010; Fulke et al., 2010). Using microalgae to produce
biodiesel will not compromise the production of food, fodder, and other products
derived from crops (Griffith and Harrison, 2009). The strain Botryococcus braunii ,
however, grows slowly and produces about 30% to 73% hydrocarbons under labora-
tory conditions (Dayananda et al., 2006; 2007; 2010).
For cost-effective commercial biodiesel production, appropriate strain selection
according to the suitability for site of cultivation and local environmental conditions
is imperative (Sheehan et al., 1998; Griffith and Harrison, 2009; Chanakya et al.,
2012). The key challenge for microalgal biodiesel production is the screening and
selection of microalgal species that can maintain a high growth rate with high lipid
content in addition to a high metabolic rate (Griffith and Harrison, 2009). The spe-
cies that are metabolically rigorous can tolerate high concentrations of salt, CO 2 ,
high alkalinity, and high temperature; and have the ability to grow and replicate
under nutritional stress by altering their metabolic pathways—these are the species
that are found to be most promising in this regard (Verma et al., 2010). Nitrogen limi-
tations have been found to enhance lipid accumulation in the microalgae (Griffith
and Harrison, 2008). Yeesang and Cheirsilp (2011) studied the effect of nitrogen
deprivation and iron (Fe 3+ ) enhancement with higher light intensity on lipid con-
tent. They observed an increase in lipid content from 25.8% to 35.9% (Yeesang and
Cheirsilp, 2011). The findings of Liu et al. (2008) also confirmed that lipid content
in C hlorella vulgaris increased by three- to sevenfold when the growth medium was
supplemented with 0.012 mM Fe 3+ .