Oil recovery from algal
biomass and then conversion of oil to biodiesel is not affected by the method
of biomass production, whether it is produced in raceways, photo-bioreactors or
open ponds. Therefore, actual factor responsible for the cost determination is
cost of producing biomass for comparative analysis of photo-bioreactors,
raceways or open ponds for producing microalgal diesel.

The estimated production
cost of a kilogram of microbial biomass is $2.95 and $3.80 for
photo-bioreactors, raceways and open ponds, respectively (Chisti, 2007; Molina
Grima et al. 2003). If we increase the biomass production annually, then the
production cost per kilogram reduces similarly, due to economy of scale. If the
biomass contains 30% oil by weight, then the cost of biomass for producing a
liter of oil would be approximately like $1.40 and $1.81 for photo-bioreactors,
raceways and open ponds, respectively. Low cost biomass enhances the cost of
oil approximately to $2.80/L. This means that the recovery process of oil
contribute about 50% to the cost of finally recovered oil.

The cost of biodiesel
depends upon the cost of biomass produced. To make algal diesel competitive in
the market with petro diesel, then it requires reduction in the cost of
production of algal oil from about $2.80/L to $0.48/L (Chisti, 2007). The cost
is reduced significantly to $0.72, if the algal biomass produced in
photo-bioreactors or raceways contains 70% oil instead of 30% by weight. These
reductions in the cost are attainable with adopting strategic objective.

Microalgal oils can surely
replace petroleum as a source of hydrocarbon feedstock. This will happen only
if microalgal oil needs to be sold at a price which is roughly somewhat related
to the price of crude oil. For example, if the price of crude oil is
$80/barrel, then price of microalgal oil should be $0.55/L to economically substitute
for crude petroleum. In this example we assume the energy output of algal oil
is 80% as compared to 100% of crude petroleum. Overall production cost of algal
oil in current cultivation systems is a critical issue of concern (Benemann,
2008; Ullah et al. 2014)). The current commercial algal production is in very
small scale and inefficient, so to make the process efficient and cheap,
technological advances will be required to overcome this gap. Along with this
research and development activities will be required in large scale to mass
culture algae for maximizing oil productivity and harvesting them cheaply which
would reduce the production cost of algal biomass to an acceptable level. 



This chapter suggests that
production of biodiesel from microalgae is technically feasible. This is the
only renewable biodiesel that can potentially replace transport fuels derived
from petroleum. Economics of microalgal biodiesel production needs improvement
to make it competitive with petrodiesel, and the level of improvement necessary
to achieve this is attainable by using technology advancement. Overall, the
practical feasibility of a production system centers on the key properties of
the selected algae strain, which indicates a need for species screening, as
well as research on optimizing culture conditions and production systems.
Low-cost microalgal biodiesel production requires improvements to algal biology
through genetic and metabolic engineering. Biorefinery concept and advances in
photobioreactor engineering will further cut down the production cost. Keeping
in view of larger productivity than raceways, tubular photobioreactors are
likely to be used in producing much of the microalgal biomass required for
making biodiesel in terms of net energy balance. However, productivity values
changes and are significantly lower as compared to heterotrophic production.
Photobioreactors provide controlled environmental conditions that can be
utilized to produce highly productive microalgae and to achieve good yield of
oil in a year. Harvesting of algal biomass during production accounts for the
highest proportion of energy input, but currently, there are no standard
techniques available for harvesting. Adaptation of technologies which are
already available and use in the food and wastewater treatment area may provide
required possible solutions. This chapter also suggests that both
thermochemical liquefaction and pyrolysis appear to be the most technically and
practically feasible approaches after extraction of oils from algae for
conversion of biomass to biofuels.


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