Environmental Engineering Reference
In-Depth Information
location for algae farms. In these countries south
of the Mediterranean, the climate is warmer, and
the temperature does not drop below 15 °C
throughout the year. This kind of climate is ideal
for the growth of algae in open or closed pond
systems. These systems would perhaps be the
most suitable, effi cient, and economically feasi-
ble for the growth of algae. Many countries in the
Mediterranean basin have a large potential for
harvesting algae. Some countries like Israel have
begun to produce several strains for fuel produc-
tion and have also been harvesting algae for
medicinal purposes for decades. The southern
countries bordering the Mediterranean Sea, such
as Morocco, Algeria, Tunisia, and Egypt, are
particularly attractive because of their high tem-
peratures and huge unused desert land. In the
future, Bio3 Dakhla, an algal industry in Dakhla,
Morocco, anticipates investing billions on bio-
fuel industries and are currently producing large
amounts of Spirulina for human consumption.
However, countries like Libya, Cyprus, and
Turkey could also harvest algae on marginal land.
Although these countries do not have suffi cient
water resources, they grow algae in recycled
brackish or saline water since the algae is from a
marine source and does not require fresh water
for growth. Moreover, these countries are just
developing and could strongly benefi t from run-
ning these algal industries. Algae farming can
offer jobs for local people, and the transfer of
technologies to developing countries can only be
benefi cial (Piccolo 2009 ; Singh and Gu 2010 ).
A complete survey has been carried out for the
various aspects of algal cultivation (Edward
2009 ), including the profi les of various compa-
nies involved in the growth of algae for biofuel as
well as other applications around the world. The
classifi cation is based on various algae farming
technologies being used. The reported informa-
tion has been summarized in Table 3 . Some of
these companies are exploring suitable regions
for algae cultivation, but only a few are using
open pond systems or natural settings. Initially,
closed systems or photobioreactors (PBRs) were
proposed to cultivate algae; these bioreactors are
installed near a source of CO 2 , and thus serve an
additional purpose of carbon sequestration.
However, natural settings have the least capital
cost. So regions in which enough land is avail-
able to grow algae in open ponds without inter-
fering with the food chain are an attractive option.
9
Cultivation of Microalgae
Cultivation is the biggest part of generating
biomass from microalgae. This has been done
on an industrial scale for many years with the
help of solar energy (photoautotrophically) and
is economically feasible for large-scale produc-
tion for other uses (Borowitzka 1997 ). There
are two main cultivation systems: open pond
(raceways) and closed systems (PBRs). Each
system is infl uenced by intrinsic properties that
play a major role in feasibility, including strains
used, nutrients, costs of land and water, down-
stream process, manpower, and climatic condi-
tions (Borowitzka 1992 ).
9.1
Open Pond System
The open pond production system has been used
to cultivate algae since the 1950s (Borowitzka
1999 ). These systems can be divided into natural
waters (lakes, lagoons, and ponds) and artifi cial
systems or containers (Jiménez et al. 2003 ).
The most commonly used cultivation system is
raceway ponds. They are typically made up of
closed, loop, oval-shaped recirculation channels
(Fig. 1f ). They are generally constructed in con-
crete (Fig. 2b), but plastic-covered earth-lined
ponds have also been used (Brennan and Owende
2010 ). The plastic culture system is cheaper, easy
to operate, and more durable than closed systems
(Zeng et al. 2011 ; Rawat et al. 2011 ). Most pad-
dle wheel-driven raceway ponds are 60 cm in
depth, and the paddle wheels are helpful to mix
and circulate the culture, thus reducing the shad-
ing effect required to stabilize algae growth and
productivity (Chisti 2007 ; Brennan and Owende;
2010 ; Norsker et al. 2011 ). In continuous produc-
tion, algae broth and nutrients are introduced
near the paddle wheel to prevent sedimentation
and can be circulated through the loop to the
 
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