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Ecofuel conversion technology of inedible lipid feedstocks to renewable fuel 241

brown with a greenish tinge. Attempts are being made to enable extraction at lower
temperature (less than 60°C) to produce crude RBO with good refining properties.
However, this process requires a longer time to extract lipids from rice bran.
Regarding the world paddy production in 2017, the estimated potential yield of
crude RBO is about 70 million tons if all the rice bran produced in the world is to
be harnessed for oil extraction [33a]. It is estimated that currently less than 10 million
tons of crude RBO are produced with the bulk being of industrial grade, which means
that 85% of the rice bran available in the world is not being utilized for oil extraction.
One of the best ways for the potential utilization of RBO is the production of biodiesel
(BD) and bioactive compounds [4–8].

9.2.2 Microalgae
Microalgae have been suggested as a promising biodiesel feedstock and have been
called the third-generation feedstock. Microalgae are either prokaryotic or eukaryotic
microorganisms growing through photosynthesis [3, 34]. Microalgae have a simple
cell structure and their growth requires light, carbon dioxide, water, and nutrients
(phosphorus and nitrogen as major nutrients). Photosynthetically, microalgae can con-
vert those necessities into energy and use that in cell development. The major chem-
ical constituents of microalgae are lipids, proteins, and carbohydrates with different
compositions that are stored in the microalgae cell. The great flexibility and adaptabil-
ity of microalgae to grow in diverse environments mean that they use less arable land
than terrestrial plant, and therefore competition with agriculture for food production
can be avoided. The growth rate of microalgae is 5–10 times faster than conventional
food crops. Moreover, high lipid productivity is the main reason why microalgae can
be used as an alternative feedstock of biodiesel. Microalgae can have 15–300 times the
lipid productivity of common oil crops and lipid accumulation of microalgae can be
more than 50% under exhaustion of nutrients [3, 15, 34–38]. Minor constituents of
microalgae are pigments such as phycobiliproteins, chlorophylls, and carotenoids,
which can be used in industries such as pharmaceuticals, food, and cosmetics [37,
39]. Microalgae-based biodiesel production commercially combines several pro-
cesses working simultaneously, namely cultivation, harvesting/dewatering, and con-
version of biodiesel [26].
Cultivation conditions such as light, carbon dioxide, temperature, pH, and nutrients
affect the characteristics of microalgae. Light provides energy for photosynthesis and
microbial growth. Carbon dioxide is a carbon source of microalgae cell development
[38]. In order to reduce the cost of the carbon source, flue gas can be used as an alter-
native carbon source; 1.8kg of CO 2 can produce 1kg of microalgae biomass [35]. The
temperature and pH of the growing culture are maintained in appropriate conditions to
support microbial growth. The major nutrients needed are phosphorus and nitrogen;
however, utilization of inorganic nutrient sources can cause pollution in water. There-
fore, applying wastewater in microalgae cultivation is an alternative because it usually
contains phosphorus and nitrogen nutrients. Not only supplying nutrients for micro-
algae growth, using wastewater can also reduce contaminants in wastewater. How-
ever, unknown constituents, imbalance of composition, and toxic compounds may