Biodiesel from oilgae, biofixation of carbon dioxide by microalgae: A solution
to pollution problems

Ayhan Demirbas

⇑

Sirnak University, Dean of Engineering Faculty, Sirnak, Turkey

a r t i c l e

i n f o

Article history:
Received 2 September 2010
Received in revised form 15 December 2010
Accepted 18 December 2010
Available online 8 January 2011

Keywords:
Microalgae
Oilgae
Biodiesel
Biofixation
Global warming
Environmental impacts

a b s t r a c t

Algae containing 30–75% of lipid by dry basis can be called oilgae. All microalgae species produce lipid
however some species can contain up to 70% of their dry weight. Microalgae appear to be the only source
of renewable biodiesel that is capable of meeting the global demand for transport fuels. Biodiesel produc-
tion by using oilgae is an alternative process in contrast to other procedures not only being degradable
and non-toxic but also as a solution to global warming via reducing emission gases. Algae-based technol-
ogies could provide a key tool for reducing greenhouse gas emissions from coal-fired power plants and
other carbon intensive industrial processes. Because algae are rich in oil and can grow in a wide range
of conditions, many companies are betting that it can create fuels or other chemicals cheaper than exist-
ing feedstocks. The aim of microalgae biofixation of CO

2

is to operate large-scale systems that are able to

convert a significant fraction of the CO

2

outputs from a power plant into biofuels.

Ó 2011 Elsevier Ltd. All rights reserved.

1. Introduction

Depletion of world petroleum reserves and the impact of envi-

ronmental pollution of increasing exhaust emissions have lead to
the search for suitable alternative fuels for diesel engines

[1–3]

.

Much attention has been paid to biodiesel production from vegeta-
ble oils and animal fats; however, less attention has been paid to
the aquatic algal biomass despite its high productivity. Use of bio-
diesel from oilgae is a promising alternative to solve air pollution
problems. Algae-based technologies could provide a key tool for
reducing greenhouse gas emissions from coal-fired power plants
and other carbon intensive industrial processes

[4–13]

.

To achieve environmental and economic sustainability, fuel

production processes are required that are not only renewable,
but also capable of sequestering atmospheric carbon dioxide
(CO

2

). Second generation microalgal systems have the advantage

that they can produce a wide range of feedstocks for the produc-
tion of biofuels. Biodiesel is currently produced from oil synthe-
sized by conventional fuel crops that harvest the sun’s energy
and store it as chemical energy. This presents a route for renewable
and carbon-neutral fuel production. However, current supplies
from oil crops and animal fats account for only approximately
0.3% of the current demand for transport fuels

[14–25]

.

A variety of biolipids can be used to produce biodiesel. These

are: (a) virgin vegetable oil feedstock; rapeseed and soybean oils

are most commonly used, though other crops such as mustard,
palm oil, sunflower, hemp and even algae show promise; (b) waste
vegetable oil; (c) animal fats including tallow, lard, and yellow
grease; and (d) non edible oils such as Jatropha, Neem oil, castor
oil, and tall oil. Biodiesel development can be found in 28 countries
among which Germany (21%), USA (17%), and France (13%) are the
largest producers of biodiesel fuel in the world in 2008. In 2008 the
world production of biodiesel fuel was about 13.9 million ton

[26,27]

.

Increasing biofuel production on arable land could have severe

consequences for global food supply. In contrast, producing biodie-
sel from algae is widely regarded as one of the most efficient ways
of generating biofuels and also appears to represent the only cur-
rent renewable source of oil that could meet the global demand
for transport fuels

[28]

.

Vegetable oils are a renewable and potentially inexhaustible

source of energy with energy content close to diesel fuel. On the
other hand, extensive use of vegetable oils may cause other signif-
icant problems such as starvation in developing countries. Forest
and agricultural education, science and modern technology leads
in the solving the problems of global food resources

[10–13,29–

34]

. The vegetable oil fuels were not acceptable because they were

more expensive than petroleum fuels. Starvation becomes an
important problem around the world. To cope with this problem
it is important that use of productive and cultivated land for food
instead of fuel production

[35–42]

.

Billions of years ago the earth atmosphere was filled with

CO

2

. Thus there was no life on earth. Life on earth started with

0306-2619/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:

10.1016/j.apenergy.2010.12.050

⇑

Tel.: [phone]; fax: [phone].
E-mail address:

[e-mail]

Applied Energy 88 (2011) 3541–3547

Contents lists available at

ScienceDirect

Applied Energy

j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / a p e n e r g y

Cyanobacterium and algae. These humble photosynthetic organ-
isms sucked the atmospheric CO

2

and started releasing oxygen.

As a result, the levels of CO

2

started decreasing to such an extent

that life evolved on earth. Once again these smallest organisms
are poised to save us from the threat of global warming

[27]

.

Algae are theoretically very promising source of biodiesel. Cur-

rently considerable attention has been focused on production of
biofuels from algal biomass. Biodiesel via transesterification of al-
gal oil or oilgae has been found to be a promising method for the
recovery of energy present in algae. Huang et al.

[43]

provided

an overview of the biodiesel production by microalgal biotechnol-
ogy, including the various modes of cultivation for producing
oilgae.

Algae can grow practically in every place where there is enough

sunshine. Microlgae, like corn, soybeans, sugar cane, wood, and
other plants, use photosynthesis to convert solar energy into
chemical energy. They store this energy in the form of oils, carbo-
hydrates, and proteins. Microalgae provide advantage for usage of
unfertile lands, inefficient for agriculture, for biodiesel production
instead of using productive lands for food production. Some algae
can grow in saline water. The most significant different of algal oil
is in the yield and hence its biodiesel yield. Oil productivity of
many microalgae is higher than the best oil producing crops.
According to some estimates, the yield (per acre) of oil from algae
is over 200 times the yield from the best-performing plant/vegeta-
ble oils

[44]

. Microalgae are the fastest growing photosynthesizing

organisms. They can complete an entire growing cycle every few
days.

Industrial reactors for algal culture are open ponds, photobior-

eactors and closed systems. Different species of algae may be bet-
ter suited for different types of fuel. Algae can be a replacement for
oil based fuels, one that is more effective and has no disadvantages.
This lipid oil can be used to make biodiesel for cars, trucks, and air-
planes

[9,12,17,28,39,43,45–50]

.

Most current research on oil extraction is focused on microalgae

to produce biodiesel from algal oil. Algal oil processes into biodie-
sel as easily as oil derived from land-based crops. Algae biomass
can play an important role in solving the problem between the pro-
duction of food and that of biofules in the near future. The idea of
using microalgae to produce fuel is not new, but has received re-
cent renewed attention in the search for sustainable energy. Bio-
diesel produced from microalgae is being investigated as an
alternative to using conventional crops, such as rapeseed: microal-
gae typically produce more oil, consume less space and could be
grown on land unsuitable for agriculture. Using microalgae as a
source of biofuels could mean that enormous cultures of algae
are grown for commercial production, which would require large
quantities of fertilizers

[9,12,17,51–57]

.

Microalgae have gained much attention due to their high nutri-

tional value, high-value chemicals such as pigments and vitamins,
high growth rate as compared to higher plants, and the ability to
utilize light energy. In addition, microalgae have many bioactive
compounds. For example, dried microalgae could be used as
high-protein feeds for animals such as shrimp and fish

[10–13]

.

Microalgae cultivation using sunlight energy can be carried out

in open or covered ponds or closed photobioreactors, based on
tubular, flat plate or other designs. Microalgae production in closed
photobioreactors is highly expensive. Closed systems are much
more expensive than ponds. However, the closed systems require
much less light and agricultural land to grow the algae

[27]

.

In order to have an optimal yield, these algae need to have CO

2

in large quantities in the basins or bioreactors where they grow.
Thus, the basins and bioreactors need to be coupled with tradi-
tional thermal power centers producing electricity which produce
CO

2

at an average tenor of 13% of total flue gas emissions. The CO

2

is put in the basins and is assimilated by the algae. It is thus a tech-
nology which recycles CO

2

while also treating used water

[27]

.

The aim of this study is biodiesel produced from oilgae is a new

sustainable energy source substituted for petroleum diesel and to
investigate the use of algae for solving global warming problem
in short term.

2. Biodiesel from oilgae

Biodiesel is a biofuel commonly consisting of methyl esters that

are derived from organic oils, plant or animal, through the process
of transesterification. The biodiesel transesterification reaction is
very simple:

Triglyceride þ 3Methanol ƒƒƒƒ!

Catalyst

Gycerine

þ 3Methyl EstersðBiodieselÞ

ð1Þ

An excess of methanol is used to force the reaction to favor the

right side of the equation. The excess methanol is later recovered
and reused.

Biodiesel has received much attention in recent years. Biodiesel

is the best candidate for diesel fuels in diesel engines. Biodiesel
burns similarly to petroleum diesel as it concerns regulated pollu-
tants. On the other hand biodiesel probably has better efficiency
than gasoline. Biodiesel fuel has better properties than petro-diesel
fuel; it is renewable, biodegradable, non-toxic, and essentially free
of sulfur and aromatics

[10]

.

Typical raw materials of biodiesel are rapeseed oil, soybean oil,

sunflower oil and palm oil. Beef and sheep tallow and chicken fat
from animal sources and cooking oil are also sources of raw mate-
rials. Commonly accepted biodiesel raw materials include the oils
from soy, canola, corn, rapeseed, and palm. New plant oils that
are under consideration include mustard seed, peanut, sunflower,
and cotton seed. The most commonly considered animal fats in-
clude those derived from poultry, beef, and pork

[58]

.

Serious problems face the world food supply today. Food versus

fuel is the dilemma regarding the risk of diverting farmland or
crops for liquid biofuels production in detriment of the food supply
on a global scale. Biofuel production has increased in recent years.
The rise in world oil prices led to a sharp increase in biofuels pro-
duction around the world. Some commodities such as corn, sugar
cane, and vegetable oil can be used either as food, feed or to make
biofuels.

Table 1

shows comparison of some sources of biodiesel

[59]

.

High oil species of microalgae cultured in growth optimized

conditions of photobioreactors have the potential to yield 5000–
15,000 gallons of microalgal oil per acre per year. Algae biomass
can play an important role in solving the problem between the pro-
duction of food and that of biofules in the near future

[59]

.

Microalgae contain lipids and fatty acids as membrane compo-

nents, storage products, metabolites and sources of energy. The
most significant distinguishing characteristic of algal oil is its yield
and hence its biodiesel yield. According to some estimates, the
yield (per acre) of oil from algae is over 200 times the yield from
the best-performing plant/vegetable oils

[60,61]

. They can com-

plete an entire growing cycle every few days. Different algae spe-
cies produce different amounts of oil. Microalgae are very
efficient solar energy converters and they can produce a great vari-
ety of metabolites

[62]

.

A selection of algae strains with potential to be used for the pro-

duction of oils for biodiesel is presented in

Table 2 [59–73]

. A ma-

jor current problem for the commercial viability of biodiesel
production from microalgae is the low selling price of biodiesel.
Biodiesel from microalgal oil is similar in properties to the stan-
dard biodiesel

[43]

.

3542

A. Demirbas / Applied Energy 88 (2011) 3541–3547

The algae that are used in biodiesel production are usually

aquatic unicellular green algae. This type of algae is a photosyn-
thetic eukaryote characterized by high growth rates and high pop-
ulation densities. Under good conditions, green algae can double its
biomass in less than 24 h. Additionally, green algae can have huge
lipid contents, frequently over 50%

[59,74]

. This high yield, high

density biomass is ideal for intensive agriculture and may be an
excellent source for biodiesel production.

There are three well-known methods to extract the oil from al-

gae: (1) Expeller/press, (2) solvent extraction with hexane and (3)
supercritical fluid extraction. A simple process is to use a press to
extract a large percentage (70–75%) of the oils out of algae. Algal
oil can be extracted using chemicals. The most popular chemical
for solvent extraction is hexane, which is relatively inexpensive.
Supercritical fluid extraction is far more efficient than traditional
solvent separation methods

[75–80]

.

The lipid and fatty acid contents of microalgae vary in accor-

dance with culture conditions. Algal oil contains saturated and
monounsaturated fatty acids. The fatty acids were determined in
the algal oil in the following proportions: 36% oleic (18:1), 15% pal-
mitic (16:0), 11% stearic (18:0), 8.4% iso-17:0, and 7.4% linoleic
(18:2). The high proportion of saturated and monounsaturated
fatty acids in this alga is considered optimal from a fuel quality
standpoint, in that fuel polymerization during combustion would
be substantially less than what would occur with polyunsaturated
fatty acid-derived fuel

[17,61]

. After oil extraction from algae, the

remaining biomass fraction can be used as a high-protein feed
for livestock

[74]

. This gives further value to the process and re-

duces waste.

2.1. Production of biodiesel from algae oils

Most current research on oil extraction is focused on microalgae

to produce biodiesel from algal oil

[10–13]

. The biodiesel from al-

gal oil in itself is not significantly different from biodiesel produced
from vegetable oils. Production of biodiesel from algae is depicted
in

Fig. 1

.

Xu et al.

[81]

used Chlorella protothecoides (a microalga) for pro-

duction of biodiesel. Cells were harvested by centrifugation,
washed with distilled water, and then dried by a freeze dryer.
The main chemical components of heterotrophic C. protothecoides
were measured as previous study

[82]

. Microalgal oil was prepared

by pulverization of heterotrophic cell powder in a mortar and
extraction with n-hexane.

Biodiesel was obtained from heterotrophic microalgal oil by

acidic transesterification.

Fig. 2

shows the process flow schematic

for biodiesel production

[81]

. The optimum process combination

was 100% catalyst quantity (based on oil weight) with 56:1 M ratio
of methanol to oil at temperature of 303 K, which reduced product
specific gravity from an initial value of 0.912 to a final value of
0.864 in about 4 h of reaction time

[81]

.

The technique of metabolic controlling through heterotrophic

growth of C. protothecoides was applied, and the heterotrophic C.
protothecoides contained the crude lipid content of 55.2%. To in-
crease the biomass and reduce the cost of alga, corn powder hydro-
lyzate instead of glucose was used as organic carbon source in
heterotrophic culture medium in fermenters. The result showed
that cell density significantly increased under the heterotrophic
condition, and the highest cell concentration reached 15.5 g/L.
Large amount of microalgal oil was efficiently extracted from the
heterotrophic cells by using n-hexane, and then transmuted into
biodiesel by acidic transesterification

[81]

.

Table 1
Comparison of some sources of biodiesel.

Crop

Oil yield
(L/ha)

Land area
needed (M/ha)

a

Percent of existing US
cropping area

a

Corn

172

1540

846

Soybean

446

594

326

Canola

1190

223

122

Jatropha

1892

140

77

Coconut

2689

99

54

Oil palm

5950

45

24

Microalgae (70% oil

of sample, by wt)

136,900

2

1.1

Microalgae (30% oil

of sample, by wt)

58,700

4.5

2.5

a

For meeting 50% of all transport fuel needs of the United States.

Table 2
Oil content of some microalgae (% dry weight).

Species

Oil content

Reference

Ankistrodesmus TR-87

28–40

[63]

Botryococcus braunii

29–75

[61,64,65]

Chlorella sp.

28–32

[61]

Cyclotella DI-35

42

[61]

Cylindrotheca sp.

16–37

[59]

Dunaliella tertiolecta

36–42

[66,67]

Hantzschia DI-160

66

[61]

Isochrysis sp.

7–33

[61,68]

Nannochloris

20–63

[59,63,69]

Nannochloropsis

31–68

[59,70]

Nitzschia sp.

45–47

[59]

Nitzschia TR-114

28–50

[71]

Phaeodactylum tricornutum

31

[61]

Scenedesmus TR-84

45

[61]

Schizochytrium sp.

50–77

[59]

Stichococcus

33(9–59)

[13]

Tetraselmis suecica

15–32

[72,60,72]

Thalassiosira pseudonana

(21–31)

[73]

Fig. 1. Block scheme of production of biodiesel from algae.

A. Demirbas / Applied Energy 88 (2011) 3541–3547

3543

2.2. Advantages and disadvantages of biodiesel from algae oil

Producing biodiesel from algae has been touted as the most effi-

cient way to make biodiesel fuel. Algal oil processes into biodiesel
as easily as oil derived from land-based crops. The difficulties in
efficient biodiesel production from algae lie not in the extraction
of the oil, but in finding an algal strain with a high lipid content
and fast growth rate that is not too difficult to harvest, and a
cost-effective cultivation system (i.e. type of photobioreactor) that
is best suited to that strain

[11–13]

.

Algal strains, diatoms, and cyanobacteria have been found to

contain relatively high levels of lipids. Oil productivity, that is
the mass of oil production per volume per day, depends on algal
growth rate and oil content of the algal biomass

[10]

.

Tables 3

and 4

show the advantages and disadvantages of biodiesel from al-

gae oil. Microalgae are good candidates for biodiesel production
because of the high oil productivity. Also microalgae have several
attractive characteristics for biodiesel production:

1. Algae are the fastest-growing plants in the world. Microalgae

have much faster growth rates than terrestrial crops.

2. Costs related with their harvesting, transportation of microal-

gae are lower than other biomass materials.

3. Microalgae are capable of fixing CO

2

in the atmosphere, thus

facilitating the reduction of increasing atmospheric CO

2

levels,

which are now considered a global problem.

4. Microalgae are easily biodegradable and they can be chemically

treated easily.

5. Algae cultivation is not complex; they can grow practically in

every place where there is enough sunshine.

3. Environmental impacts of microalgae

Algae are usually found in damp places or bodies of water and

thus are common in terrestrial as well as aquatic environments.
Like plants, algae require primarily three components to grow:
sunlight, carbon dioxide and water. Photosynthesis is an important
biochemical process in which plants, algae, and some bacteria con-
vert the energy of sunlight to chemical energy

[27]

.

3.1. Biofixation of carbon dioxide by microalgae

Biofixation of CO

2

by microalgae mass cultures represents an

advanced, climate friendly biological process that enables the di-
rect utilization of fossil CO

2

streams produced from concentrated

sources. Mitigation of GHG emissions would result from the con-
version of the algal biomass to renewable biofuels

[10–13,27,29]

.

Fossil-fuel-fired power plants contribute approximately one-

third of the total human-caused emissions of CO

2

. Fossil fuels will

remain the mainstay of energy production well into the 21st cen-
tury. However, increased concentrations of CO

2

due to carbon

emissions are expected unless energy systems reduce the carbon
emissions to the atmosphere. To stabilize and ultimately reduce
concentrations of the CO

2

gas, it will be necessary to employ car-

bon sequestration – carbon capture, separation and storage or re-
use. Carbon sequestration, along with reduced carbon content of
fuels and improved efficiency of energy production and use, must
play major roles if the nation is to enjoy the economic and energy
security benefits, which fossil fuels brings to the energy mix. The
availability of a carbon dioxide fixation technology would serve

Fig. 2. Process flow schematic for biodiesel production.

Table 3
Advantages of biodiesel from algae oil.

Rapid growth rates
Grows practically anywhere
Higher yield and oil productivity-lower cost
A high per acre yield (7–31 times greater than the next best crop – palm oil)
No need to use crops such as palms to produce oil
A certain species of algae can be harvested daily
Algae biofuel contains no sulfur
Algae biofuel is non-toxic
Algae biofuel is highly biodegradable
Algae oil extracts can be used as livestock feed and even processed into

ethanol

High levels of polyunsaturates in algae biodiesel is suitable for cold weather

climates

Can reduce carbon emissions based on where it is grown

Table 4
Disadvantages of biodiesel from algae oil.

Produces unstable biodiesel with many polyunsaturates
Biodiesel performs poorly compared to it is mainstream alternative
Relatively new technology

3544

A. Demirbas / Applied Energy 88 (2011) 3541–3547

as insurance in case global warming causes severe restrictions on
carbon dioxide emissions

[27,29,37,83,84,31,38,85]

.

Integrated processes in wastewater treatment and aquaculture

were indicated as near-term applications of this technology. Micro-
algae applications in greenhouse gas mitigation could come
through the development of wastewater treatment and aquacul-
ture processes that combine their waste treatment features with
reduction in greenhouse gas emissions and biofuels production.

The greatest potential for microalgae biofixation processes is in

developing countries, which should be included in any future
development of this technology. The ultimate objective of microal-
gae biofixation of CO

2

is to operate large-scale systems that are

able to convert a significant fraction of the CO

2

outputs from a

power plant into biofuels. Biofixation of CO

2

using photosynthetic

organisms has been looked at as a way to stop or slow down the
effects of global warming.

Fig. 3

shows the carbon cycle, biofix-

ation, and main steps of algal biomass technologies.

3.2. Reduction of emissions by biodiesel fuels

Cost of producing microalgal biodiesel can be reduced substan-

tially by using a biorefinery based production strategy, improving
capabilities of microalgae through genetic engineering and ad-
vances in engineering of photobioreactors

[59]

. Genetic and meta-

bolic engineering are likely to have the greatest impact on
improving the economics of production of microalgal diesel

[86]

.

Table 5

shows the emissions of biodiesel (B20 and B100) and

same model compression–ignition (diesel) vehicles

[10]

. The prop-

erties of biodiesel and diesel fuels, in general, show many similar-
ities, and therefore, biodiesel is rated as a realistic fuel as an

alternative to diesel. The conversion of microalgal oil into methyl
esters through the transesterification process approximately re-
duces the molecular weight to one-third, reduces the viscosity by
about one-seventh, reduces the flash point slightly and increases
the volatility marginally, and reduces pour point considerably

[27]

.

4. Conclusion

Biodiesel produced from oilgae is a new sustainable energy

source substituted for petroleum diesel. Producing biodiesel from
algae has been touted as the most efficient way to make biodiesel
fuel. Large amount of oilgae biomass could be cultivated in photo-
bioreactors but a favorable assessment of the economics of produc-
tion is necessary to establish. Cultivation of oilgae biomass in open
ponds, especially in sunny and temperate region, could be very
economic. Biofixation of carbon dioxide (CO

2

) by microalgae mass

cultures represents an advanced, climate friendly biological pro-
cess that enables the direct utilization of fossil CO

2

streams pro-

duced from fossil fueled-power plants. Oilgae could be not only a
solution for renewable energy production but also a solution for
CO

2

problem causing global warming. Oilgae could be the only

quick solution for solving global warming problem in short term.

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Vehicle or engine

Fuel

Emissions, g/km

NO

x

CO

CH

PM

SO

x

Peugeot Partner

B100

2.05

9.37

0.54

2.68

0

Peugeot Partner

B20

1.86

17.73

1.32

4.71

0.004

Renault Kangoo

B100

2.23

9.22

0.49

3.06

0

Renault Kangoo

B20

1.92

17.36

1.26

5.63

0.003

Dacia Pickup

B100

2.15

9.42

0.56

2.59

0

Dacia Pickup

B20

1.91

18.29

1.35

4.63

0.005

A. Demirbas / Applied Energy 88 (2011) 3541–3547

3545

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