Environmental Engineering Reference
In-Depth Information
NaCl concentrations. Takagi et al. (
2006
)
observed that
Dunaliella
cells grown in concen-
trations of >1.0 M NaCl show increased biomass,
but there is no signifi cant effect on biomass in a
concentration of <1.0 M NaCl. However, intra-
cellular lipid and triglycerides were higher (67
and 56 %) in saltwater species grown in 1.0 M
NaCl; the same species grown in 0.5 M NaCl
accumulates a low lipid content (60 and 40 %).
However, these physico-chemical treatments
could also favor the synthesis of polar lipids like
phospholipids or glycolipids associated with cell
walls of the microalgae; such lipids are less
interesting for biodiesel production (Nagle and
Lemke
1990
).
high lipid contents, lower triglycerides clearly
indicated that the species is ineffi cient for use as
a biodiesel feed stock.
Nannochloropsis
has the ability to accumulate
60 % of lipids and if the culture is mixed with
2 % CO
2
, the biomass yield is ~0.48 g/L/d
(Vunjak-Novakovic et al.
2005
; Chiu et al.
2009
).
These results indicate that the
Nannochloropsis
species have a potential use as biofuel feedstock,
whereas the average lipid content and biomass
yield of
Nannochloropsis
species is low when
compared with
Schizochytrium limacinum
,
Ch.
emersonii
and
Ch. protothecoides
. The lipid
accumulation of
Chaetoceros calcitrans
,
Neochloris oleoabundans
, and
Scenedesmus
obliquus
is very low (Natrah et al.
2007
; da Silva
et al.
2009
). Even under nitrogen-defi cit condi-
tions,
N. oleoabundans
is able to accumulate
37 % of lipid/dry weight, and the biomass yield is
in the range of 0.05-0.09 g/L/d (Pruvost et al.
2009
). These results show that the algae are
unproductive as biofuel feedstocks.
7
Microalgal Lipid
and Biomass Productions
The medium composition is an important factors
for increased microalgal growth and lipid pro-
duction. Microalgae require inorganic nutrients
in the form of carbon, nitrogen, and phosphorous
for growth (Suh and Lee
2003
; Brennan and
Owende
2010
; Sathasivam and Juntawong
2013
).
The growth medium of microalgae generally
consists of macronutrients like nitrogen, phos-
phate, and a metal chelator. Iron is generally a
micronutrient, and low concentrations of iron in a
form that can be assimilated are essential for
microalgae growth. In a nutrient-rich medium,
Chlorella
sp. are known to grow fairly. The
growth of various species of
Chlorella
in
Watanabe media containing 1.25 g/L KNO
3
was
demonstrated by Illman et al. (
2000
). Changes in
culture conditions may lead to changes in meta-
bolic pathways and result in the production of
neutral lipids (Singh et al.
2011
). Sometimes
nutrient-rich media may cause nutrient toxicity,
with lethal results (Watanabe et al.
2000
). The
well known microalgae and the medium used for
their growth, biomass, and lipid productivity
have been quoted from various literature.
Stephenson et al. (
2010
) tested
Ch. emersonii
and
Ch. protothecoides
and achieved the highest lipid
and biomass yield. Even though
Ch. vulgaris
and
Ch. minutissima
are capable of accumulating
8
Global Scenario of Algal
Biofuels
The growth of algae is motivated around the
world (Piccolo
2009
), and the large-scale algal
biofuel companies throughout the world are
listed in Table
3
. Even though algae oil produc-
tion has increased worldwide, the biggest algae
investment in the EU is the £26 million in the
public sector funded by the UK Carbon Trust. In
2009, the Carbon Trust launched a new £8 mil-
lion research program called 'Algae Biofuels
Challenge' (ABC) (
http://www.carbontrust.co.
schallenge.htm
). Later, the Scottish government
launched a £6 million EU project called
'BioMara'. In 2007, a Spanish renewable energy
company, Aurantia and Green Fuel Tech of
Massachusetts (USA) formed a partnership
through a $US92 million project to produce
algae oil.
According to Piccolo (
2009
), countries with a
coastline near the Mediterranean Sea region
(roughly between 45°N and 30°N) are the best
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