Seaweeds: A Promising Source for Sustainable Development - Environmental Sustainability: Role of Green Technologies - page 80

a fuel quality standpoint, in that fuel polymerization
during combustion would be substantially less
than what would occur with polyunsaturated
fatty acid-derived fuel (Sheehan et al. 1998 ). Oil
levels of 20-50 % are quite common (Chisti
2007 ; Carlsson et al. 2007 ; Demirbas 2009 ).
After oil extraction from algae, the remaining
biomass fraction can be used as a high protein
feed for livestock (Schneider 2006 ; Haag 2007 ).
This gives further value to the process and
reduces waste. Moreover, according to the bio-
diesel standard published by the American
Society for Testing Materials (ASTM), biodiesel
from microalgal oil is similar in properties to
standard biodiesel and is also more stable according
to their fl ash point values.

of higher-value products/processes are other
alternatives in reducing algal oil production costs
(Chisti 2007 ). The harvested algae then undergo
anaerobic digestion, producing methane that
could be used to produce electricity. In commer-
cial photobioreactors, higher productivities may
be possible. Typical productivity for a microalga
( Chlorella vulgaris ) in photobioreactors is
13-150 (Pulz 2001 ). Photobioreactors require ten
times more capital investment than open pond
systems. The estimated algal production cost for
open-pond system is $ 10/kg and photobioreactors
are from $ 30 to $ 70/kg. The cost of algal produc-
tion is two to three orders of higher magnitude
than conventional agricultural biomass (Carlsson
et al. 2007 ). Assuming that biomass contains 30 %
oil by weight and carbon dioxide is available at
no cost (fl ue gas), Chisti ( 2007 ) estimated the
production cost for photobioreactors and raceway
ponds at $ 1.40 and $ 1.81/L of oil, respectively.
However, for microalgal biodiesel to be competitive
with petrodiesel, algal oil should be less than $
0.48/L (Chisti 2007 ).
It is useful to compare the potential of micro-
algal biodiesel with bioethanol from sugar
cane, because on an equal energy basis, sugarcane
bioethanol can be produced at a price comparable
to that of gasoline (Bourne Jr. 2007 ). Bioethanol
is well established for use as a transport fuel
(Gray et al. 2006 ), and sugarcane is the most pro-
ductive source of bioethanol (Bourne Jr. 2007 ).
For example, in Brazil, the best bioethanol yield
from sugarcane is 7.5 m 3 /ha (Bourne Jr. 2007 ).
However, bioethanol has only ~64 % of the
energy content of biodiesel. Therefore, if all the
energy associated with 0.53 billion m 3 of bio-
diesel that the USA needs annually (Chisti 2007 )
were to be provided by bioethanol, nearly 828
million m 3 of bioethanol would be needed. This
would require planting sugarcane over an area of
111 million ha or 61 % of total available US crop
land. Recovery of oil from microalgal biomass
and conversion of oil into biodiesel are not
affected by whether the biomass is produced in
raceways or photobioreactors. Hence, the cost of
producing the biomass is the only relevant factor
for a comparative assessment of photobioreactors
and raceways for producing microalgal biodiesel.

10.1 Economics of Biodiesel

Production

There are small numbers of economic feasibility
studies on microalgae oil (Richardson et al.
2009 ). Currently, microalgae biofuel has not
been deemed economically feasible compared to
the conventional agricultural biomass (Carlsson
et al. 2007 ). Critical and controversial issues are
the potential biomass yield that can be obtained
by cultivating macro- or microalgae and the costs
of producing biomass and derived products.
The basis of the estimates is usually a discussion
of three parameters: photosynthetic effi ciency,
assumptions on scale up, and long-term cultivation
issues. For microalgae, the productivity of raceway
ponds and photobioreactors is limited by a range
of interacting issues. Typical productivity for
microalgae in open ponds is 30-50 t/ha/year
(Benemann and Oswald 1996 ; Sheehan et al.
1998 ). Several possible target areas to improve
productivity in large-scale installations have been
proposed (Benemann and Oswald 1996 ; Grobbelaar
2000 ; Suh and Lee 2003 ; Torzillo et al. 2003 ;
Carvalho et al. 2006 ). Harvesting costs contribute
20-30 % to the total cost of algal cultivation, with
the majority of the cost attributable to cultivation
expenses. Genetic engineering, development of
low-cost harvesting processes, improvements in
photobioreactor, and integration of coproduction