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Procedia Engineering 105 (2015) 763 – 768

6th BSME International Conference on Thermal Engineering (ICTE 2014)

Third generation biofuel from Algae

Firoz Alam, Saleh Mobin and Harun Chowdhury*
School of Aerospace, Mechanical and Manufacturing Engineering, RMIT University, Melbourne, 3083, Australia

Abstract

The use of liquid fossil fuel as an energy source has long been considered unsustainable and most importantly the liquid fossil
fuel will be diminished by the middle of this century. In addition, the fossil fuel is directly related to environmental degradation
and greenhouse emission. Biofuel produced from plants, animals or algae products can offer an alternative to reduce our
dependency on fossil fuel and assist to maintain healthy global environment. Micro-algae is becoming popular candidate for
biofuel production due to their high lipid contents, ease of cultivation and rapid growth rate. This paper reviews the current state-
of-the-art of biofuel from algae as a renewable energy source.

©©2015
2015TheThe Authors.
Authors. Published
Published by Elsevier
by Elsevier Ltd.
Ltd. This is an open access article under the CC BY-NC-ND license
Peer-review under responsibility of organizing committee of the 6th BSME International Conference on Thermal Engineering
(http://creativecommons.org/licenses/by-nc-nd/4.0/).
(ICTE 2014).
Peer-review under responsibility of organizing committee of the 6th BSME International Conference on Thermal Engineering (ICTE 2014)

Keywords: Biofuel, microalgae, biodiesel, bioethanol, renewable energy.

1. Introduction

The growing concern surrounding the continued use of fossil fuels and rapid depletion of fossil fuel reserves,
global climate change, rising crude oil price and environmental degradation have forced governments, policymakers,
scientists and researchers to find alternative energy sources. The biofuel production from renewable sources is
widely considered to be one of the most sustainable alternatives to fossil fuels and a viable means for environmental
and economic sustainability. The biomass of currently produced biofuel is human food stock, which is believed to
cause the shortage of food and worldwide dissatisfaction especially in developing nations.

* Corresponding author. Tel.: +61 3 99256103; fax: +61 3 99256108.

E-mail address: harun.chowdhury@rmit.edu.au

1877-7058 © 2015 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license
(http://creativecommons.org/licenses/by-nc-nd/4.0/).
Peer-review under responsibility of organizing committee of the 6th BSME International Conference on Thermal Engineering (ICTE 2014)
doi:10.1016/j.proeng.2015.05.068
764 Firoz Alam et al. / Procedia Engineering 105 (2015) 763 – 768

Microalgae are currently being promoted as an ideal third generation biofuel feedstock because of their rapid
growth rate, greenhouse gas fixation ability (net zero emission balance) and high production capacity of lipids (fat).
They also do not compete with food or feed crops, and can be grown on non-arable land and saline water. Biofuels
are generally referred to solid, liquid or gaseous fuels derived from organic matter [1]. The classification of biofuels
is shown in Fig. 1 [2].

Biofuels

Primary Biofuels Secondary Biofuels

Natural Biofuel 1st Generation Biofuels 2nd Generation Biofuels 3rd Generation Biofuels

P roduc ed from Bioethanol produc ed from Bioethanol & Biodiesel Biodiesel produc ed from
- F irewood, plants - W heat, barley, c orn produc ed from - M ic roalgae
- W ood c hips - P otato, s ugarc ane, beet - C as s ava, jatropha - M irc obes
- F ores t - O il s eeds (s oybeans mis c anthus
- A nimal was te c oc onut, s unflower - S traw, gras s , wood
- Landfill gas rapes eed
- C rop res idues - A nimal fat, us ed
c ooking oil

Fig. 1. Biofuel production sources (biomasses) (adapted from [2, 12]).

The first generation biofuels possess notable economic, environmental and political concern as the mass
production of biofuel requires more arable agricultural lands resulting in reduced lands for human and animal food
production. Moreover, production process of first generation biofuels is also responsible for environmental
degradation. Therefore, enthusiasms about first generation biofuels have been demised. As first generation biofuels
are not viable, researchers focused on second generation biofuels. Because of the second generation biofuels
production process requires expensive and sophisticated technologies, the biofuel production from the second
generation is not profitable for commercial production [2, 4]. Therefore, the researchers focused on third generation
biofuels. The main component of third generation biofuels is microalgae as shown in Fig. 1. It is currently
considered to be a feasible alternative renewable energy resource for biofuel production overcoming the
disadvantages of first and second generation biofuels [1- 2, 5, 16]. Microalgae can provide several different types of
renewable biofuels. This includes methane [6], biodiesel [9] and bio-hydrogen [29]. There are many advantages for
producing biofuel from algae as microalgae can produce 15 to 300 times more biodiesel than traditional crop on area
basis [2]. The harvesting cycle of microalgae is very short and growth rate is very high [2, 15]. Moreover, high
quality agricultural land is not required for microalgae biomass production [3].

2. Biofuel Production from Microalgae

Microalgae are single-cell microscopic organisms which are naturally found in fresh water and marine
environment. There are more than 300,000 species of micro algae, diversity of which is much greater than plants [3].
Microalgae are generally more efficient converters of solar energy comparing to higher plants. In addition, because
the cells grow in aqueous suspension, they have more efficient access to water, CO2, and other nutrients [2, 5]. The
current biofuel yields from various biomasses are shown in Table 1. The table clearly shows huge potential of
microalgae compared to other biomasses.
 Firoz Alam et al. / Procedia Engineering 105 (2015) 763 – 768 765

Table 1. E-Portfolio types based on features and purposes (adapted from http://scu.edu.au/teachinglearning/index.php/79).
Oil Yields Litre/Hectare/Year Barrels/Hectare/Year
Soybeans 400 2.5
Sunflower 800 5
Canola 1,600 10
Jathropha 2,000 12
Palm Oil 6,000 36
Microalgae 60,000 – 240,000 360 – 1,500

The oil contents of various microalgae in relation to their dry weight are shown in Table 2. It is clear that several
species of microalgae can have oil contents up to 80% of their dry body weight. Some microalgae can double their
biomasses within 24 hours and the shortest doubling time during their growth is around 3.5 hours which makes
microalgae an ideal renewable source for biofuel production [7].

Table 2. Oil contents of microalgae [7].

Name of microalgae (% dry wt)
1 Botryococcus braunii 25 - 75
2 Chlorella sp. 28 - 32
3 Crypthecodinium cohnii 20
4 Cylindrotheca sp. 16 - 37
5 Dunaliella primolecta 23
6 Isochrysis sp. 25 - 33
7 Monallanthus salina 20
8 Nannochloris sp. 20 - 35
9 Nannochloropsis sp. 31 - 68
10 Neochloris oleoabundans 35 - 54
11 Nitzschia sp. 45 - 47
12 Phaeodactylum tricornutum 20 - 30
13 Schizochytrium sp. 50 - 77
14 Tetraselmis sueica 15 - 23

3. Microalgal Biomass Production

Producing microalgal biomass is generally more expensive and technologically challenging than growing crops.
Photosynthetic growth of microalgae requires light, CO2, water and inorganic salts. The temperature regime needs to
be controlled strictly. For most microalgae growth, the temperature generally remains within 20°C to 30°C. In order
to reduce the cost, the biofuel production must rely on freely available sunlight, despite daily and seasonal variations
in natural light intensities [7, 17-20]. Growth medium must provide the inorganic elements that constitute the algal
cell. Essential elements include nitrogen (N), phosphorus (P), iron (Fe) and in some cases silicon (Si).
Microalgae is grown in various aquatic environments, such as fresh and marine water, municipal waste waters,
industrial waste waters and animal waste waters as long as there are adequate amounts of carbon (organic or
inorganic), N (urea, ammonium or nitrate), and P as well as other trace elements are present [30]. Sea water
supplemented with commercial nitrate and phosphate fertilizers and a few other micronutrients are commonly used
for growing marine microalgae [31]. Waste waters are unique in their chemical profile and physical properties as
compared with fresh and marine waters. Recent researches indicated the great potential of mass production of algal
766 Firoz Alam et al. / Procedia Engineering 105 (2015) 763 – 768

biomass for biofuel and other applications using wastewaters. However, wastewater based algae cultivation still
faces with many uncertainties and challenges including variation of wastewater composition due to source,
infrastructure, weather conditions, and pre-treatment methods, improper nutrient ratios (e.g., C/N and N/P), high
turbidity due to the presence of pigments and suspended solid particles which affects light transmission, and the
presence of competing microflora and toxic compounds, and accumulation of growth inhibiting compounds which is
worsened if water is recycled and reused [30].
There are different ways microalgae can be cultivated. However, two widely used cultivation systems are a)
suspended cultures, including open ponds and closed reactors, and b) immobilized cultures, including matrix-
immobilized systems and biofilms. The most common large scale production systems in practice are high rate algal
ponds or raceway ponds. Raceway ponds are open and shallow with paddle wheel to provide circulation of the algae
and nutrients. Raceways are relatively inexpensive to build and operate, but often suffer low productivity for various
reasons [5, 32]. Tubular photobioreactors are the only type of closed systems used at large scale production of algae
[5].
The photoreactor system can be sub-classified as: a) vertical photoreactor, b) flat or horizontal photoreactor, and
c) helical photoreactor. The helical photoreactor is considered the easiest to scale up production. Compared to open
ponds, tubular photobioreactors can give better pH and temperature control, better protection against culture
contamination, better mixing, less evaporative loss and higher cell densities [32]. However, each system has relative
advantages and disadvantages. One of the significant challenges of using raceways and tubular photobioreactors is
biomass recovery. This challenge has been mitigated to an extent by immobilized cultures or attached algal
processes [33]. Algal biofilms could play a large role in overcoming the major challenges to production and
harvesting of microalgae. If enough surface area is provided, algae biofilm growth can be more than suspended
growth. More details about these cultivation systems can be found in [2-3, 7].

4. Algae Harvesting Methods

Various methods are currently used for harvesting algae, which includes chemical based, mechanical based,
biological based and to a lesser extent, electrical based operations However, various combinations or sequence of
these methods are also commonly in use. The cell size of algae is very small. Therefore, chemical flocculation is
often performed as a pre-treatment to increase the particle size of algae before using another method such as
flotation to harvest the algae. In mechanical based process, centrifugation process, which is the most reliable and
rapid method, is used for recovering suspended algae. In electrical based method, negative charge properties of algal
cells are used for separating the cells. These cells can be concentrated by the movement in an electric field [34].

5. Biofuels Production Processes from Microalgae

A number of ways the microalgae biomass can be converted into energy sources which includes: a) biochemical
conversion, b) chemical reaction, c) direct combustion, and d) thermochemical conversion. Fig. 2 illustrates a
schematic of biodiesel and bioethanol production processes using microalgae feedstock [10, 12]. Depending on the
microalgae species, in addition to biofuel production, other compounds may also be extracted, with valuable
applications in different industrial sectors [2, 8, 10, 21-28]. The production of biofuel is a complex process. A
schematic of biofuel production processes from microalgae is shown in Figure 3. However, these processes are
complex, technologically challenging and economically expensive.

6. Discussion

The environmentally concerned nations have put emphasis on the use of renewable energy in transport and other
sectors. A percentage of renewable energy can be extracted from biofuels. As the second generation biofuels is
mainly produced from raw materials (biomasses) that compete with the feedstock of higher vertebrates (human and
animal), the 3rd generation biofuels generated from microalgae which do not compete with our feedstock can be
well utilised. The biofuels produced from microalgae are generally carbon neutral. The burning process of biofuel
 Firoz Alam et al. / Procedia Engineering 105 (2015) 763 – 768 767

produces CO2 which is in turn consumed by the algae in biomass production. Hence the process is carbon neutral
and is a viable alternative to fossil fuels.
Nevertheless, a number of challenges remain in biofuel production. At present research is going on to identify the
most promising algae species that can be mass produced in order to make biomass production commercially viable.
The biomass production methods (i.e., photobioreactor system and open air (pond) system) also need further
research for making algal production economically and environmentally sustainable. Current harvesting process
using centrifugation (mechanical), chemical flocculation, biological or electrical methods creates challenges for
recovering the suspended algae. All these processes are still relatively costly [13, 16-27].

Photobiological
Hydrogen Hydrogen
Production

Biomechanical Bioethanol
Fermentation
Conversion Acetone, Butanol

Anaerobic Methane,
Digestion Hydrogen

Gasification Syngas
Thermochemical
Bio-oil, Charcoal,
Conversion Pyrolysis Syngas
Microalgal
Liquefaction Bio-oil
Biomass
Chemical
Transesterification Bio-oil
Reaction

Direct Power
Bio-oil
Combustion Generation

Fig. 2. Biofuel production processes from microalgae biomass, adapted from [2, 11-12]

Light

Nutrients Cell Disruption

Microalgae Lipids & Free Transesterification
Harvesting Drying
CO2 Cultivation & Oil Extraction Fatty Acids

Starch &
Biodiesel
Proteins
Water Culture Recycle

Starch
Fermentation Distilation
Hydrolysis

Bioethanol

Fig.3. Biodiesel and Bioethanol production processes from microalgae, [2, 12]

Biofuel production from algae biomass can be commercially viable if algal by-products are optimally utilised.
The oil part of algae biomass is around 30% and the remaining 70% is algae by-product. This by-product can be
utilised as nutrients for feedstock (animal, fish, etc.), pharmaceutical ingredients, cosmetics, toiletries and fragrance
products [13, 23-27].

7. Conclusion

Biofuel offers a true supplement to fossil if high yielding algae species can be identified, advanced production
and harvesting methods are employed, and innovative drying and oil extraction processes are utilised. Given the
current state-of-art, the biofuel cannot be a full replacement of fossil fuel at least in short-term.
768 Firoz Alam et al. / Procedia Engineering 105 (2015) 763 – 768

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