cultivation and harvesting of micro-algae for bio-fuel...
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Indian Journal of Geo Marine Sciences
Vol. 46 (09), September 2017, pp. 1731-1742
Review Paper
Cultivation and harvesting of micro-algae for bio-fuel Production –
A review
R. Dineshkumar, R. Narendran & P. Sampathkumar*
Centre of Advanced Study in Marine Biology, Faculty of Marine Sciences Annamalai University, Parangipettai-608 502, India.
[Email: [email protected]]
Received 08 December 2015 ; revised 30 October 2016
Although micro-algal biomass can be ‘energy rich’, the growth of algae in dilute suspension at around 0.02–0.05 % dry
solids poses considerable challenges in achieving a viable energy balance in micro-algal biofuel process operations. Similarity in
density of the algal cells to the growth medium, the negative surface charge on the algae and the algal growth rates which require
frequent harvesting compared to terrestrial plants. Micro-algae are harvested by a number flocculation, flotation, centrifugation
and filtration or a combination of any of these. This paper reviews the various methods of harvesting and dewatering micro-algae
for the production of biofuel. There appears to be no one method or combination of harvesting methods suited to all micro-algae
and harvesting method will have a considerable influence on the design and operation of both upstream and downstream
processes in an overall micro-algal biofuel production process.
[Keywords: Microalgae, biodiesel, transestrification, renewable energy]
Introduction
Deficiency of fossil fuels may result in
global famine as technological development,
including modern agriculture advance, is
predominantly petrol dependent1. Renewable
fuel sources are permanently searched for,
especially ones suitable for transportation. One
of the resources is products originating from
living organisms (animals, plants and micro-
organisms). Fuels from these sources are called
biofuels. The review explores the opportunities
for energy products encompassing both fresh
and marine habit microalgae. This paper also
discusses the variety of algal resources and their
environment along with the mass production
systems that have been demonstrated for use, as
well as algae mass cultivation.
Biodiesel
The choice of raw material is a critical
factor contributing to the final cost of biodiesel
and accounts for 50-85% of the total cost of the
fuel. Therefore, to minimize the cost of this
biofuel, it is important to assess the raw material
in terms of yield, quality, and the utilization of
the by-products2. A positive aspect of the
production of biodiesel from microalgae is the
area of land needed for production. For example,
to supply 50% of the fuel used by the
transportation sector using palm oil, which is
derived from a plant with a high oil yield per
hectare, would require 24% of the total
agricultural area available in the country. In
contrast, if the oil from microalgae grown in
INDIAN J. MAR. SCI., VOL. 46, NO. 09, SEPTEMBER 2017
photo bioreactors was used, it would require
only 1-3% of the total cultivation area3.
Biochemical composition of the algal
biomass can be manipulated through variations
in the growth conditions, which can significantly
alter the oil content and composition of the
micro organism. Biodiesel produced from
microalgae has a fatty acid composition (14 to
22 carbon atoms) that is similar to the vegetable
oils used for biodiesel production4. Biodiesel
produced from microalgae contains unsaturated
fatty acid and is composed of a mixture of
microalgae genera, Chlorella sp., Euglena sp.,
Spirogyra sp., Scenedesmus sp., Desmodesmus
sp., Pseudokirchneriella sp., Phormidium sp.
(cyanobacteria), and Nitzschia it can exhibit
various fatty acid profiles.
Introduction of algae as biodiesel feedstock
Microalgae are prokaryotic or
eukaryotic photosynthetic microorganisms that
can grow rapidly and live in extreme alkaline
conditions due to their unicellular or simple
multicellular structure. Examples of prokaryotic
microalgae are Cyanobacteria (Cyanophyceae)
and eukaryotic microalgae are green algae
(Chlorophyta) and diatoms (Bacillariophyta)5.
They are, not just aquatic but also terrestrial,
representing a big variety of species living in a
wide range of environmental conditions. It is
estimated that more than 50,000 species exist,
but only a limited number, of around 30,000,
have been studied and analyzed. Previous
studies reported that, in order to not compete
with edible vegetable oils, the low cost and
profitable biodiesel should be produced from
low cost feed stocks such as non edible oils,
used frying oils, animal fats, soap stocks and
greases6.
However, the available quantities of
waste oils and animal fats are not enough to
match the demands for biodiesel. Thus transition
to second generation biofuels, such as
microalgae, can also contribute to a reduction in
land requirements due to their presumed higher
energy yields per hectare as well as to their non
requirement of agricultural land. Additionally,
biodiesel needs to have lower environmental
impacts and ensure the same level of
performance of existing fuels. It is still on its
infancy despite it’s the growing interest. A large
investment in research and development and
correct policies and strategies are still needed,
for all stages of the biofuels value chain, from
raw materials production to delivery and final
consumption. Among the various possibilities,
currently being investigated and implemented at
pilot scale or even at industrial scale concerns
potential feed stocks, as well as the potential of
the microalgae. Since microalgae cultivation is
not directly linked to human consumption, they
should have a low space requirement for its
production.7 have described that the microalgae
reproduce using photosynthesis to convert sun
energy into chemical energy, completing an
entire growth cycle every few days.
Moreover, they can grow almost
anywhere, requiring sunlight and some simple
nutrients, although the growth rates can be
accelerated by the addition of specific nutrients
and sufficient aeration8; Different microalgae
species can be adapted to live in a variety of
environmental conditions. Thus, it is possible to
find species best suited to local environments or
specific growth characteristics, which is not
possible to do with other current biodiesel feed
stocks (e.g. soybean, rapeseed, sunflower and
palm oil). They have much higher growth rates
and productivity when compared to conventional
forestry, agricultural crops, and other aquatic
plants, requiring much less land area than other
biodiesel feed stocks of agricultural origin, up to
49 or 132 times less when compared to rapeseed
or soybean crops, for a 30% (w/w) of oil content
in algae biomass 9. Therefore, the competition
for arable soil with other crops, in particular for
human consumption, is greatly reduced by
microalgae cultivation. 10
suggested that genetics
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is one of the factors that affect the microalgae
lipid and biomass productivity. Thus, it is
important to choose species that have the
potential for commercialization. Chlorella
achieved the highest average lipid and biomass
yield among the tested algae, specifically
Chlorella emersonii and C. protothecoides.
Although C. vulgaris and C. minutissima are
capable of producing high lipid content
however, the triglycerides content is low, thus
these species are inefficient as biodiesel feed
stocks 11
.
Microalgae can provide feedstock for
several different types of renewable fuels such
as biodiesel, methane, hydrogen, ethanol, etc.
Algae biodiesel contains no sulfur and performs
as well as petroleum diesel, while reducing
emissions of particulate matter, CO,
hydrocarbons, and SOx. 10,12
reported that for the
past 50 years, extensive research has been
performed on microalgae and how they can be
used in a wide variety of processes to
manufacture many practical and economically
important products. The first large scale culture
of microalgae started in the early 1960s in Japan
by Nihon Chlorella with the culture of
Chlorella. Interest in using microalgae for
renewable energy increased in 1970s during the
first oil crisis (Fig 1).
Fig. 1: Potential fuels from microalgae.
Isolation of algae
2Studied the isolation of pure culture of
green algae from the soil. 13
obtained pure culture
of algae by washing, centrifugation by
antibiotics by dilution and plating by UV
irradiation or by combination of all these. There
are four major techniques for obtaining unialgal
isolates are streaking, spreading, serial dilution
and single cell isolate. Studied the Nile red
staining is used to screen the microalgae for the
presence of lipids droplets in the cells14
. Niles
red can be applied to algal cell and it does not
dissolve in the lipids. 15
Stated that the first to
isolate free living Chlorella and Scenedesmus in
allegedly pure culture of other algae, including
Cyanobacteria and Diatoms.
Cyanobacteria and other algae have a
wide range of pigmented compounds, including
carotenoids, chlorophyll and phycobiliproteins
which consist of timer with two subunits (a, b)
of pigmented poly peptide16
. Some species of
microalgae such as Spirulina standout in this
context by presenting biomass with excellent
nutritional characteristics. The most group of
algae are obligatory in other word they are
entirely depended on their photosynthetic
apparatus for their metabolic needs using
sunlight as energy source and CO2 as carbon
source to produce the carbohydrate and ATP17
.
Spirulina is a spiral filament generally found in
fresh water consists of 60%-70% protein in dry
weight. Protein elements consist of 18 types of
amino acid, several vitamins such as vitamin A,
B, E and K, minerals and fatty acids necessary to
the body. Blue green algae S.maxima were
maintained in the zarrouk medium a standard
synthetic medium, containing 2.5 g/l sodium
nitrate as the nitrogen source (Zerrouk. 1966).
Scenedesmus is one of the most
common freshwater genera; however, the
extremely diverse morphologies found among
species make identification and understanding of
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their mechanisms difficult. While most species
are found across the world, certain species exist
only in local populations such as S. intermedius
and S. serratus. The formation of colonies as
opposed to unicellularity is dependent on a
number of factors. A higher proportion of
unicellular organisms were found at high light
intensities and high temperatures, suggesting
that at higher growth rates these organisms
prefer to be non-colonized (Fig 2).
Fig. 2: Taxonomy of some algae species potentially useful
for biodiesel production.
Growth Requirements of Microalgae
The biochemical composition of
microalgae can be affected by such factors as
growth rate, environmental conditions, and life
cycle18
. Microalgal growth and chemical
composition are mainly controlled by light,
temperature, available carbon dioxide, pH, and
nutrients (Other factors, such as salinity, can be
of vital importance to some species. Growth
medium must provide sufficient nutrients for
microalgal growth. 19
found that the quality and
quantity of lipids within the cells can vary as a
result of changes in growth conditions
(temperature and light intensity) or nutrient
media characteristics (concentration of nitrogen,
phosphates and iron). 20
reported that while
many microalgae strains naturally have high
lipid content (20-70% on dry weight basis), it is
possible to increase the concentration by
optimizing the growth determining factor such
as the control of nitrogen level light intensity,
temperature and salinity21
, CO2 concentration
and harvesting procedure22
had studied that not
only organic carbon or substrate (a carbon
source such as sugars, proteins and fats),
vitamins, salts and other nutrients (nitrogen and
phosphorous) are vital for algal growth, but also
equilibrium between operational parameters
(oxygen, CO2, pH, temperature, light intensity,
product and by product removal). CO2 is also
involved in the regulation of pH and carbon
balance. Some algae are capable of growing in
extreme conditions of pH. Studies revealed the
effect of changes in pH alters on lipid
metabolism in non-extremophiles. Alkaline pH
stress resulted in TAG accumulation and a
decrease in membrane lipid in Chlorella spp.
Light
The use of monocultures is required in various
microalgal applications and controlled
cultivation systems. This requirement has
favored the development of closed photo
bioreactors. Efficient utilization of light is one of
the major challenges in microalgal
biotechnology, especially when an increase in
the biomass yield is desired22
. It has been
recognized that environmental factors such as
temperature, light, nutrients, affect the lipid
composition of algae23
. Some researchers used
continuous light for culturing
Botryococcusbraunii, 24
as well as Chlorella sp. 25
other researchers applied dark and light
photoperiod for growing Chlorella sp. To
provide dark and light photoperiod in the
system, air lift bioreactor stirred tank photo
bioreactor and other types or photo bioreactor
were employed.
pH
The pH of the culture medium is one of
the important factors in algal cultivation. pH of
medium for algae growth is usually neutral or
slightly acidic, mainly to avoid precipitation of
several major elements. The algae exhibit a clear
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dependency on pH of the growth medium and
different species vary greatly in their response to
pH26
. The pH of algal cultures can be influenced
by various factors such as composition and
buffering capacity of the medium, amount of
CO2 dissolved temperature (which controls CO2
solubility) and metabolic activity of the algal
cells. pH increases during the day to values up to
10, mainly because of the depletion of the anions
NO3- and of CO2 formed in the medium and the
excretion of OH- ions
27. One of the common
effects observed in culture media having pH
values above 9, is the precipitation of several
calcium salts, i.e. carbonates, phosphates and
sulphates, leading to nutrient deficiencies and
growth retardations or even algal flocculation,
induced by the precipitating minerals. Optimum
pH for most cultured algal species ranges
between 7 and 9, with the optimum pH being
8.2-8.7. Complete culture collapse due to the
disruption of many cellular processes can result
from failure to maintain an acceptable pH. In the
case of high intensity algal culture, the addition
of carbon dioxide allows correction for
increased pH, which may reach limiting values
of pH during algal growth 28
.
Temperature
The optimum temperature to grow
Scenedesmus sp. is between 20-40°C (Sanchez
et al., 2008). Christov et al. (2001) studied
Scenedesmus sp. at temperatures of 15 to 36°C
and found at lower temperatures, the chlorophyll
and protein levels were reduced, while levels of
carotenoids, saccharides, and lipid were
increased. They also observed an increase of
30% of the sugars and lipids at extreme
temperatures (36°C).
Scientists are looking for algae that
show good thermo stability at high temperatures.
They have interest in the effect of growth
temperature on chemical and fatty acid
compositions of tropical microalgae
species29
.The effect of temperature exerts on
biochemical reactions and how it affects the
biochemical composition of algae, makes
temperature one of the most important
environmental factors 20
.
Nutrients
Nutrients are inorganic or organic
compounds other than carbon dioxide and water,
used for growth whose presence in the cell is
necessary for cellular function. Some algae
require specific organic compounds synthesized
by other organisms. However, many algae
require only inorganic nutrients, and it is likely
that these algae could be used as feedstock for
biomass fuel production. Limiting nutrients to
algae are nitrogen, phosphorus, silica (for
diatoms) and iron 30
.
Carbon sources
As for microalgae grown on the
heterotrophic mode, experiments using diverse
sources such as molasses, acetic acid and
hydrocarbons (such as n-heptadecane) have been
evaluated and shown to work at different
concentrations. To determine the availability of
using microalgae as carbon di-oxide
sequestration option, CO2 fixation rates of the
test microalgae were studied. The maximum
CO2 fixation rate was shown by mixed algae
sample which could be the combined result of
all the algae species present in the sample 31
.
The increased lipid accumulation has
been observed during the stationary stages of
growth, which is in accordance with the earlier
studies 32
. Nitrogen limitation result in lower
photosynthetic carbon fixation for protein
synthesis evident from the carbohydrate to
amide ratio, consequently stocking carbon in the
form of lipid or carbohydrates, depending on the
species 33
.
Algae growths in waste water treatment
ponds contribute mainly through dissolved
oxygen production and nutrient assimilation and
there are already being used by many waste
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water facilities as bioremediation agent. In waste
water stabilization ponds, the algae produce
oxygen from water as a by- product of
photosynthesis. This oxygen is used by the
bacteria and they bio-oxidize the organic
compounds in the waste water. An end product,
carbon di oxide is fixed into cell carbon by the
algae during photosynthesis34
. Mixotrophy is
growth in which CO2 and organic carbon are
assimilated simultaneously and hence, both
respiratory and photosynthetic metabolism have
to operate concurrently 35
.
Nitrogen
After carbon, nitrogen (N) is the most
important nutrient contributing to the production
of biomass. The nitrogen content in the
microalgae biomass can range from 1% to more
than 10% and depending on its supply and
availability, it can vary between different groups
(e.g. low in diatoms) and within a particular
species 36
. Discoloration of the cells is a frequent
response to nitrogen limitation due to a decrease
in chlorophyll content and an increase in
carotenoids, as well as the accumulation of
organic carbon compounds such as
polysaccharides and certain oils like
polyunsaturated fatty acids (PUFAs)37
. Nitrogen
is mostly supplied as nitrate, but often ammonia
and urea are used, both displaying similar
growth rates 38
.
Many microorganisms tend to prefer
ammonia as a nitrogen source, and the
assimilation of either nitrate or ammonia is said
to be related to the pH of the growth media 39
. A
drop on pH can be observed when ammonia is
used as the only source of N, especially during
active growth owing to the release of H+ ions.
An increase in pH is observed when nitrate is
used as the only N source 40
. Ammonia loss due
to volatilization is an important factor to be
considered when deciding whether to supply
either one.
Urea can be considered another
attractive source of nitrogen 41
reported that the
microalgae fed with a combination of urea and
sodium nitrate had the highest ash-free dry
biomass content with a yield of 4.15 ± 0.38 g
L⁻1. The urea molecule contains a carbon atom
as well as two nitrogen atoms. This carbon atom
is released as CO2 when urea is utilized and
presumably, it is available for photosynthetic
assimilation. Therefore, urea has the potential of
providing both the nitrogen and 1.5 to 10 % of
the carbon requirement10
reported the
heterotrophic cultivation of Chlorella
protothecoides in various N sources for lipid
production.
The lipid content, lipid class
composition and the proportion of the various
fatty acids in a microalgae vary according to the
environmental or culturing variables such as
light intensity growth phase photoperiod and
nitrogen concentration. Most critical nutrient
affecting lipid metabolism in microalgae is
nitrogen limitation42
, nitrogen limitation leads to
a decrease in protein content in both freshwater
algae and diatom. Cell size for nutrient limited
cultures were significantly smaller than the non
–limited cells43
. Previous studies have
demonstrated that lipid content in some
microalgae increase during different cultivation
conditions such as nitrogen deprivation.
Phosphorus
Phosphorus is essential for growth in many
cellular processes such as energy transfer and
during the biosynthesis of nucleic acids.
Orthophosphate is the preferred form in which it
is provided to algae and its uptake is said to be
energy dependant 44
. In spite of the fact that
algal biomass contains less than 1% phosphorus
(P), it usually becomes one of the most
important growths limiting factors in algal
culture 45
. This happens because P binds easily
to other ions (e.g. carbonate and iron) resulting
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in its precipitation. Insolubility of the resulting
phosphate makes this essential nutrient
unavailable for algal uptake46
. Supply of P also
influences the composition of the produced
biomass. Similar effects to the ones obtained in
algae grown under nitrogen starvation, such as
the tendency to accumulate large amount of
lipids, with a decreased amount of proteins,
chlorophyll and nucleic acids content have been
reported on phosphate deficient cultures47, 48
,
reported that the very high concentration of cell
lipid tend to be coupled with low biomass
particularly induced by environmental stress
such as N and P limitation.
Other macro and micronutrients
Sulfur, potassium, sodium, iron,
magnesium, calcium and trace elements like
boron, copper, manganese, zinc, molybdenum,
cobalt, vanadium, and selenium are also
important in algal nutrition 49
. Silicon, present in
the cell walls of many algal groups especially in
diatoms, is an important component where it
constitutes an essential nutrient for their growth
and production. Silicon limitation, which is
prone to happen, can also lead to the
accumulation of secondary metabolites, such as
lipids. Experiments conducted with silicon-
deficient cells of Cyclotella cryptic (a diatom
species that accumulates lipids under non-
growing conditions) indicated that lipid
accumulation occurs as a function of both
increased partitioning of newly photo-
assimilated carbon into lipids and slow
conversion of non-lipid compounds.
Utilization of sewage by algal sp
It was reported that the algal growth
rates and nutrient uptake were found to be high
and equivalent to value from algae grown on
municipal wastewater51
. It is defined that
Chlorella minutissima which was identified in
waste water oxidation ponds in India52
. Waste
water was shown to be low enough in toxins and
had enough P and N to support algal growth of
microalgae, Chlorella saccharophila able to
grow particularly well on the untreated waste
water50
. They also reported that the potential for
some industrial waste waters in providing
resources for the generation of significant algal
biomass came from the analysis of waste water
from carpet mill effluent. The earlier researcher
suggested that a more practical approach for
algae biodiesel production is to utilize
wastewater for algae propagation 34
.
The use of waste water for algal and
biofuel production would ensure sustainability in
terms of (a) biofuel production (b) nutrient
removal and remediation of wastewater and (c)
mitigation of GHGs. Thus, the development of
renewable clean algal biofuel fosters sustain-
ability and helps in maintaining the
environmental quality. Waste water which is
produced from various industries can also be a
source of feed for the algae to grow and hence,
play a dual faction i.e., nutrient removal and
biofuel production. The effluent from the
secondary treatment unit of domestic waste
water treatment plant is used for large scale
cultivation of microalgae for biofuel production.
The best suitable method for cultivation of algae
in the waste water is open pond way reactor for
biofuel production 23
.
The effluent from the secondary
treatment unit of domestic waste water treatment
plant is used for large scale cultivation of
microalgae for biofuel production and observed
the inhibition in the growth of microalgae at the
initial stage due the presence of high nutrient
and the other factors present in sewage as
nutrient medium. Various sp of Chlorella and
Scenedesmus can provide very high (>80%) and
many cases almost complete removal of
ammonia, Nitrate and total P from secondary
treatment waste water indicating the potential of
microalgae for tertiary sewage treatment. Many
of these experiments were performed under
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INDIAN J. MAR. SCI., VOL. 46, NO. 09, SEPTEMBER 2017
laboratory based batch culture condition with the
microalgae showing high growth rates over the
batch growth period. Some unicellular green
microalgae species are particularly tolerant to
sewage effluent condition; most notably those of
the Chlorella and Scenedesmus genus and so
most studies have examined the growth of these
species52
. Microalgae are effectively able to
grow in wastewater conditions through their
ability to utilize abundant organic carbon and
inorganic N and P in the waste water.
It is stated that the Chlorella vulgaris
immobilized in alginate pellets placed in a
fluidized bed column could effectively remove
approximately 80% of the ammonia content and
70% of the total P contentment in a sewage
culture35
. It is reported that Scenedesmus
immobilized in alginate sheets could effectively
remove ammonia and orthophosphate from
secondary treated effluent54
. Algae species
Chlorella was widely applied for waste water
treatment and had proven abilities of removing
N, P and chemical oxygen demand (COD) with
different retention times ranging from 10 to 40
days. Further same researches reported that 55%
P removal from agro industrial waste water by
Chlorella. 45
Stated that the algae based
treatments have been found to be as efficient at
removing P from waste water as compared to
chemical treatment. 55
Studied the Chlorella
kesslerii able to uptake only 8-20% of P under
the light and dark cycle for PO4 concentration of
10mg. 56
Reported that recovered N and P rich
algal biomass can be used as a low cost fertilizer
or as animal feed. Activated algal process to
treat waste water and found that it was able to
remove 80-88% of BOD, 70-82% of COD, 60-
70% of N and 50-60% of P with a retention
period of 15 days56,57
reported that the growth
potential and the N and P scavenging ability was
examined in micro algal strains grown under
secondary treated sewage effluent.
Collection of biomass
Harvesting, thickening and dewatering is a key
step in the production of algal biofuel is
harvesting and dewatering of the algal biomass
before extraction. The high cost of harvesting
and dewatering presents major challenges to the
development of commercially viable
microalgae-based biofuel. It is reported that for a
process to be suitable for very large volumes of
biomass 47
. As microalgae vary greatly in those
properties, which affect harvesting processes
(e.g., size, surface charge, resistance of cell to
breakage, compressibility etc.) between species
and with growth phase the biomass recovery
processes must be tailored to the species of
microalgae and the growth system. As very large
amounts of water are used in microalgae culture
the medium which still contains nutrients, must
also be able to be recycled after cell harvesting.
The harvesting, thickening and
dewatering of microalgae cultures have been
extensively reviewed 18, 29, 36
. Key properties of
microalgae which influence their separation are:
(a) shape: [rods, spheres or chains or filaments],
(b) size: [generally between 2 and 30 μm], (c)
specific weight: [1.05–1.1], (d) surface charge:
[usually negative]. Microalgal cultures to be
harvested usually contain between 0.2 to 2 g L−1
solids and for lipid extraction a concentration of
at least 20 g L−1
solids is required. Filamentous
algae such as Spirulina can be harvested by
filtration, but almost all of the algae under
consideration as a source of biofuels (e.g.,
Nannochloropsis or Chlorella) are unicellular
and too small for effective filtration.
Centrifugation is very energy intensive (Mohn,
1988) and not practical for the large volumes for
algal biofuel production. Sedimentation is also a
possibility, but it is time-consuming .
The most commonly considered
processes are flocculation followed by flotation
or by settling as the first step. Flocculation is the
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first stage in the bulk harvesting process to
aggregate the cells, so increasing their effective
particle size and thus easing subsequent
centrifugation, filtration or sedimentation steps.
Flocculation can be achieved by the use of
inorganic flocculants such as alum 19
or organic
flocculants such as or starch, although the cost
of these flocculants is substantial. The flocculant
used must be compatible with the need to
recycle the water back to the growth system
without complex pretreatment of this recycled
water.
Lipid extraction
Lipids are mostly hydrophobic
molecules (e.g., neutral lipids) which interact
with relatively non-polar solvents such as ethyl
ether, chloroform and benzene, while membrane
associated polar lipids require polar solvents
such as ethanol and methanol to disrupt the
hydrogen bonding and electrostatic forces
between the lipids and proteins 59
studied that
the most common laboratory methods for lipid
extraction are the Soxhlet extraction (usually
with n-hexane as solvent), and the Folch, Bligh
and Dyer methods which use chloroform and
methanol in varying ratios as solvents. Because
of the toxicity of methanol and chloroform and
the fact that chloroform extracts more than just
saponifiable lipids (e.g., pigments and other
lipids and non-lipid contaminants), methods
using other alcohols such as ethanol, 1-butanol
and isopropanol are being developed to replace
the methanol. Other combinations of co-solvents
also have been proposed for the extractions of
lipids from microalgae are hexane/ethanol, and
hexane/ isopropanol. 60
It is also studied that the
hexane system, the hexane and alcohol will
readily separate into two separate phases when
water is added, thereby improving downstream
separations. Furthermore, the combination of
ethanol and hexane at a 5:1 v/v ratio in a 2-step
extraction procedure reduces the solvent
requirement for the same amount of biomass by
approximately 10-times compared to the
chloroform/methanol extraction procedure.
Conclusion
In spite of many advantages of biodiesel
production from algae, there are a lot of
limitations blocking its real competition with
petroleum derived diesel. Production costs seem
the most substantial problem. Out of all
recognized methods of microalgae production,
the culture in photo bioreactors seems the most
favorable for biodiesel production, however the
costs are discouraging. Investments cost of
whole plant is one of the major limiting factors.
It seems that small modular systems and outdoor
Raceway pond cultivation system may be an
attractive solution with positive economical
rationale. Algae production plant should also be
integrated with other existing installation like
sewage treatment, biogas and power
cogeneration plant. Co-localization these
production processes results in lowered
operating and investments costs. Also, such a
waste treatment and the biofuel-energy centre
generate a number of additional by-products that
can be sold on or used for self-consumed.
The most energy-efficient method of
harvesting or of producing feasible energy from
micro-algae may depend on harvesting and oil
extraction method. Major challenge of
commercializing micro-algal biofuel has a
considerable influence on the design and
operation of both upstream and downstream
processes in an overall micro-algal biofuel
production process.
Algae derived biodiesel is ecofriendly
which in the case of petroleum shortage may
replace petro diesel. However, the biodiesal
derived from algae is very cost-effective.
Presences of alternative technologies of fuels
production are optimistic in the face of
discussion about petroleum stock out.
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INDIAN J. MAR. SCI., VOL. 46, NO. 09, SEPTEMBER 2017
Acknowledgements
Authors are thankful to Dean and
Director, Centre of Advanced Study in Marine
Biology, Faculty of Marine Sciences, Annamalai
University, Parangipettai, India for providing
necessary lab facilities. The first author is
grateful to the University Grants Commission –
Rajiv Gandhi National Fellowship, Government
of India for the financial assistance (Name of the
Awardee: R. Dineshkumar) with UGC Circular
No. F1-17.1/2015-16/RGNF-2015-17-SC-TAM-
4190 in January, 2016.
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