Lipid Identification and Extraction Techniques - Biotechnological Applications of Microalgae - page 92

the lipid composition. Hence, it is necessary to determine the fatty acid profiles of
extracted algal lipids for suitability in biodiesel production and assess the fuel qual-
ity. It is essential for biodiesel derived from microalgal oil to meet ASTM (2008) or
EN (2003) biodiesel standards for ensuring fuel quality.
7.3 OIL EXTRACTION
The mass production of microalgae can be achieved through raceway ponds or pho-
tobioreactors. The feasibility of biodiesel production from algae is totally depen-
dent on the technologies used in the downstream processing of algae. Downstream
processing of algae involves dewatering, drying, oil extraction, biofuel production,
and by-product utilization. Dewatering of algae is an energy-consuming process
that requires a high capital investment for equipment. There is a greater possibility
of quick spoilage of the harvested biomass slurry (5% to 15% dry solids) under hot
climatic conditions due to its high moisture content (Brennan and Owende, 2010).
The harvested slurry must be dewatered and dried quickly after harvesting. Drying
is an important process in the downstream process that enhances biomass shelf
life and lipid recovery efficiency. The process employed for oil extraction from
dried algae is similar to that of oil extraction from oil seeds. In order to achieve
economically viable algal oil-based biodiesel production, the technical feasibility
must be thoroughly studied; that is, downstream technologies/processes must be
optimized.
The oil content of dried algal biomass varies from 20% to 50% oil by weight and
can be increased by optimizing growth parameters (Hu et al., 2008). Before com-
mencing oil extraction from microalgae, it must be dewatered and dried to remove
the moisture. The present oil extraction techniques applicable for wet/dry algae bio-
mass have limitations due to technical barriers, difficulty in scaling-up, high cost
investment, and extraction efficiency (Cooney et al., 2009). The choice of oil extrac-
tion technology depends on the moisture content, quantity to be treated, quality of
the end-product, extraction efficiency, safety aspects, and cost economics. The main
outputs from the oil extraction process are oil and oil cake. The extracted oil can
be used for biodiesel production with/without pretreatment, depending on the qual-
ity of the oil. The actions involved in the oil extraction process are (1) breaking the
algae cell walls, (2) freeing the oil, and (3) separating out the oil and oil cake. The
most common methods used for the oil extracted from algae biomass are mechanical
press, solvent extraction, and supercritical fluid extraction. The methods employed
for oil extraction from microalgae are depicted in Figure 7.1.
7.3.1 M eChaniCal e xtraCtion
In the case of mechanical extraction, the feedstock (oil seed or algae biomass) is
subjected to high pressure for rupture and release of the oil. The added advantages
of mechanical extractions are that (1) no chemicals are used for extraction, (2) the
process is free of chemicals in the products, and (3) the product is safe for storage.
The major drawbacks of mechanical extraction are an inadequacy in complete lipid
recovery from the feedstock, and the high energy inputs.