Scholarly article on topic 'Biofuel from Algae- Is It a Viable Alternative?'

Biofuel from Algae- Is It a Viable Alternative? Academic research paper on "Chemical engineering"

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{Biofuel / Microalgae / Biodiesel / Bioethanol / "Renewable energy"}

Abstract of research paper on Chemical engineering, author of scientific article — Firoz Alam, Abhijit Date, Roesfiansjah Rasjidin, Saleh Mobin, Hazim Moria, et al.

Abstract Fossil fuel energy resources are depleting rapidly 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 air pollution, land and water degradation. In these circumstances, biofuel from renewable sources can be an alternative to reduce our dependency on fossil fuel and assist to maintain the healthy global environment and economic sustainability. Production of biofuel from food stock generally consumed by humans or animals can be problematic and the root cause of worldwide dissatisfaction. Biofuels production from microalgae can provide some distinctive advantages such as their rapid growth rate, greenhouse gas fixation ability and high production capacity of lipids. This paper reviews the current status of biofuel from algae as a renewable source.

Academic research paper on topic "Biofuel from Algae- Is It a Viable Alternative?"

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Engineering

Procedia Engineering 49 (2012) 221 - 227 =

www.elsevier.com/locate/procedia

Evolving Energy-IEF International Energy Congress (IEF-IEC2012)

Biofuel from algae- Is it a viable alternative?

Firoz Alam*a, Abhijit Datea, Roesfiansjah Rasjidina, Saleh Mobinb, Hazim Moriaa

Abdul Baquic

a School of Aerospace, Mechanical and Manufacturing Engineering, RMIT University, Plenty Road, Bundoora, Melbourne, VIC 3083, Australia

b Department of Higher Education Primary Industries, Northern Melbourne Institute of TAFE (NMIT), Epping, Melbourne, VIC 3076, Australia

c Department of Mechanical Engineering Technology, Yanbu Industrial College, Yanbu Al-Sinaiyah, Saudi Arabia Elsevier use only: Revised 29th August 2012; accepted 31st August 2012

ELSEVIER

Abstract

Fossil fuel energy resources are depleting rapidly 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 air pollution, land and water degradation. In these circumstances, biofuel from renewable sources can be an alternative to reduce our dependency on fossil fuel and assist to maintain the healthy global environment and economic sustainability. Production of biofuel from food stock generally consumed by humans or animals can be problematic and the root cause of worldwide dissatisfaction. Biofuels production from microalgae can provide some distinctive advantages such as their rapid growth rate, greenhouse gas fixation ability and high production capacity of lipids. This paper reviews the current status of biofuel from algae as a renewable source.

© 2012Elsevier Ltd.... Selection and peer-review under responsibility of the RMIT University Keywords: Biofuel, microalgae, biodiesel, bioethanol, renewable energy

1. Introduction

The global climate change, rising crude oil price, rapid depletion of fossil fuel reserves, and concern about energy security, land and water degradation have forced governments, policymakers, scientists and researchers to find alternative energy sources including wind, solar and biofuels. The biofuel production from renewable sources can reduce fossil fuel dependency and assist to maintain the healthy environment 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 the developing nations. Therefore, microalgae can provide an alternative biofuel feedstock thanks to their rapid growth rate, greenhouse gas fixation ability (net zero emission balance) and high production capacity of lipids as microalgae do not compete with human and animal food crops. Moreover, they 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. These classifications are: a) Natural biofuels, b) Primary biofuels, and c) Secondary biofuels. Natural biofuels are generally derived from organic sources and include vegetable, animal waste and landfill gas. On the other hand, primary biofuels are fuel-woods used mainly for cooking, heating, brick kiln or electricity production. The secondary biofuels are

* Corresponding author. Tel.: +61-3-99256103; fax: +61-3-99256108. E-mail address: firoz.alam@rmit.edu.au.

1877-7058 © 2012 Elsevier Ltd.... Selection and peer-review under responsibility of the RMIT University doi:10.1016/j.proeng.2012.10.131

bioethanol and biodiesel produced by processing biomass and are used in transport sectors [1]. The secondary biofuels are sub classified into three so called generations, namely, a) First generation biofuels, b) Second generation biofuels, and c) Third generation biofuels based on their different features such types of processing technology, feedstock and or their development levels [2].

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

Despite having potential in producing carbon neutral biofuels, the first generation biofuels possess notable economic, environmental and political concerns. The most alarming issue associated with first generation biofuels is that with the increase of production capacity, more arable agricultural lands are needed for the production of first generation biofuel feedstock resulting in reduced lands for human and animal food production.

The increased pressure on arable land currently used for food production leads to severe food shortages, especially in developing countries of Africa, Asia and South America where over 800 million people have been suffering from hunger and malnutrition due to severe shortages of food. With the growing world's population, the demand for food is increasing while the arable land is decreasing. The intensive use of fertilizer, pesticides and fresh water on limited farming lands can reduce not only the food production capacity of lands but also cause significant environmental damage [15]. Therefore, enthusiasms about first generation biofuels have been demised. Increasing use of first generation biofuels will inevitably lead to increasing the price of food beyond the reach of the under privileged. The political consequences of this could be difficult to contain.

As first generation biofuels are not viable and receive lukewarm reception, researchers focused on second generation biofuels. The primary intention here is to produce biofuels using lignocellulosic biomass, the woody part of plants which do not compete with human food chain directly [2]. As shown in Fig. 1, main sources for second generation biofuels are predominantly agricultural residues, waste (e.g., trimmed branches, leaves, straws, wood chips, etc.) forest harvesting residues, wood processing residues (e.g. saw dust) and non-edible components of corn, sugarcane, beet, etc. However, converting the woody biomass into fermentable sugars requires sophisticated and expensive technologies for the pre-treatment with special enzymes making second generation biofuels economically not profitable for commercial production [2, 4].

Hence, the focus of research is drawn to 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]. The potential for biodiesel production from microalgae is 15 to 300 times more than traditional crops on an area basis [2]. Furthermore compared with conventional crop plants which are usually harvested once or twice a year, microalgae possess a very short harvesting cycle (1 to 10 days depending on the process), allowing multiple or continuous harvesting with significantly increased yields [2, 15]. Additionally, the microalgae generally have higher productivity than land based plants as some species have doubling times of a few hours and accumulate very large amounts of triacylglycerides (TAGs). Most importantly, the high quality agricultural land is not required for microalgae biomass production [3].

2. Biofuel Production Potential from Microalgae

Microalgae are single-cell microscopic organisms which are naturally found in fresh water and marine environment. Their position is at the bottom of food chains. Microalgae are considered to be one of the oldest living organisms in our planet. There are more than 300,000 species of micro algae, diversity of which is much greater than plants [3]. They are thallophytes - plants lacking roots, stems, and leaves that have chlorophyll as their primary photosynthetic pigment and lack a sterile covering of cells around the reproductive cells [4]. While the mechanism of photosynthesis in these microorganisms is similar to that of higher plants, microalgae are generally more efficient converters of solar energy thanks to their simple cellular structure. In addition, because the cells grow in aqueous suspension, they have more efficient access to water, CO2, and other nutrients [2, 5]. Generally, microalgae are classified in accordance with their colours. The current systems of classification of microalgae are based on a) kinds of pigments, b) chemical nature of storage products, and c) cell wall constituents [2]. Some additional criteria are also taken into consideration including cytological and morphological characters: occurrence of flagellate cells, structure of the flagella, scheme and path of nuclear and cell division, presence of an envelope of endoplasmic reticulum around the chloroplast, and possible connection between the endoplasmic reticulum and the nuclear membrane [6]. Some major groups of microalgae are shown Table 1.

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. As mentioned earlier, some microalgae can double their biomasses within 24 hours and the shortest doubling time during their growth is around 3.5 hours which make s microalgae an ideal renewable source for biofuel production [7]. The oil content and types of microalgae available at fresh water and marine water are shown separately in Tables 3 & 4.

Table 1. Major microalgae groups based on their colours

Colour Group

1 Yellow-green algae Xanthophyceae

2 Red algae Rhodophyceae

3 Golden algae Chrysophyceae

4 Green algae Chlorophyceae

5 Brown algae Phaeophyceae

6 Cyanobacteria Cyanophyceae

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

Table 3. Oil contents of microalgae grown in fresh water [adapted from 2, 7-9, 14-16]

Where grown Name of microalgae species (% dry wt)

1 Botryococcus sp. 25 - 75

2 Chaetoceros muelleri 34

3 Chaetoceros calcitrans 15 - 40

4 Chlorella emersonii 25 - 63

5 Chlorella protothecoides 15 -58

6 Chlorella sorokiniana 19 - 22

Fresh Water Algae 7 Chlorella vulgaris 5 - 58

8 Chlorella sp. 10 - 48

9 Chlorella pyrenoidosa 2

10 Chlorella sp. 18 - 57

11 Chlorococcum sp. 20

12 Ellipsoidion sp. 28

13 Haematococcus pluvialis 25

14 Scenedesmus obliquus 11 - 55

15 Scenedesmus quadricauda 2 - 19

16 Scenedesmus sp. 20 - 21

Table 4. Oil contents of microalgae grown in marine (salt) water [adapted from 2, 7-9, 14-16]

Where grown Name of microalgae species (% dry wt)

1 Dunaliella salina 6 - 25

2 Dunaliella primolecta 23

3 Dunaliella tertiolecta 18 -71

4 Dunaliella sp. 18 - 67

5 Isochrysis galbana 7 - 40

6 Isochrysis sp. 7 - 33

Marine Water Algae 7 Nannochloris sp. 20 - 56

8 Nannochloropsis oculata 23 - 30

9 Nannochloropsis sp. 12 - 53

10 Neochloris oleoabundans 29 - 65

11 Pavlova salina 31

12 Pavlova lutheri 36

13 Phaeodactylum tricornutum 18 - 57

14 Spirulina platensis 4 - 17

3. Biofuels Production Processes from Microalgae

The production of microalgae biomass for extraction of biofuels 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 biodiesel production must rely on freely available sunlight, despite daily and seasonal variations in natural light levels [7, 17-20]. 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]. As mentioned previously, microalgae provide significant advantages over plants and seeds as they: i) synthesize and accumulate large quantities of neutral lipids (20-50 % dry weight of biomass) and grow at high rates; ii) are capable of all year round production, therefore, oil yield per area of microalgae cultures could greatly exceed the yield of best oilseed crops; iii) need less water than terrestrial crops therefore reducing the load on freshwater sources; iv) cultivation does not require herbicides or pesticides application; v) sequester CO2 from flue gases emitted from fossil fuel-fired power plants and other sources, thereby reducing emission of greenhouse gas (1 kg of dry algal biomass utilise about 1.83 kg of CO2). In addition, microalgae offer wastewater bioremediation by removing of NH4, NO3, PO4 from wastewater sources

(e.g. agricultural run-off, concentrated animal feed operations, and industrial and municipal wastewaters). Their ability to grow under harsher conditions and reduced needs for nutrients, microalgae can be cultivated in saline/brackish water/coastal seawater on non-arable land, and do not compete for resources with conventional agriculture. Depending on the microalgae species other compounds may also be extracted, with valuable applications in different industrial sectors, including a large range of fine chemicals and bulk products, such as polyunsaturated fatty acids, natural dyes, polysaccharides, pigments, antioxidants, high-value bioactive compounds, and proteins [2, 8, 10, 21-28].

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

There are different ways microalgae can be cultivated. However, two widely used cultivation systems are the open air system and photobioreactor system. The photoreactor system can be sub-classified as a) tabular photoreactor, b) flat photoreactor, and c) column photoreactor. Each system has relative advantages and disadvantages. More details about these cultivation systems can be found in [2-3, 7].

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

The production of biofuel is a complex process. A schematic of biofuel production processes from microalgae is shown in Figure 3. The process consists of following stages: a) stage 1 - microalgae cultivation, b) stage 2 - harvesting, drying & cell disruption (cells separation from the growth medium), c) stage 3 - lipid extraction for biodiesel production through transesterification and d) stage 4 - starch hydrolysis, fermentation & distillation for bioethanol production. However, these processes are complex, technologically challenges and economically expensive. A significant challenge lies ahead for devising a viable biofuel production process [2, 28-30].

4. Discussion and Conclusion

Many countries including the European Union (EU) have adopted policies on certain percentage of renewable energy use for transport and other relevant sectors. In December 2008, the EU signed a directive that requires 10% of member countries' transport fuel needs to come from renewable sources (biofuels, hydrogen and green electricity) as part of EU's policy towards mitigation of climate change effect and global warming. The EU directive also obliges the bloc to ensure that biofuels offer at least 35% carbon emission savings compared to fossil fuels and the figure should rise to 50% in 2017 and 60% in 2018 [12]. However, the use of biofuels especially the biofuels' raw materials (biomasses) have caused serious debates among governments, policymakers, scientists and environmentalists as currently most commercially produced biofuels are derived from sources that compete with or belong to feedstock for human and animal consumption.

In terms of greenhouse gas emission, the biofuels produced from microalgae is generally carbon neutral. The CO2 emitted from burning biofuel is assumed to be neutral as the carbon was taken out of the atmosphere when the algae biomass grew. Therefore, biofuels from microalgae do not add new carbon to the atmosphere. Biofuels can be a viable alternative to fossil fuels on short and medium terms. Additionally, advanced biofuels made from residues or waste have the potential to reduce CO2 emissions with 90% compared to petrol/diesel.

While many years of research and development still lie ahead, if successful, algae-based fuels can help meet the world's growing demand for transportation fuel while reducing greenhouse gas emissions. However, a number of challenges remain before algae can be used for mainstream commercial applications as the uncertainty of cost constitutes the biggest obstacle. There is no doubt that research work on microalgae is still in primary stages. Currently, it is not clear that what kinds or families of algae would be most appropriate in order to produce commercially viable biofuels. Researchers are currently working on appropriate commercial cultivation processes of algae biomasses. At this point in time, there is no definitive answer to an open question if it is better to grow algae in photobioreactor system or open air (pond) system. As algae are micro-organisms of a size ten times smaller than human hair, it is a great challenge to harvest them. At present, microalgae harvestings are based on either centrifugation or chemical flocculation, which push all the microalgae together, but these processes associated with high cost [16-23].

Biodiesel or bioethanol production from algae biomass cannot be commercially viable unless by-products are optimally utilised. As mentioned earlier, the lipid or the oil part is around 30% of the total algae biomass and the remaining 70% is currently wasted which can be used as nutrients, pharmaceuticals, animal feed or bio-based products. The use of lipid as well as all by-products will allow exploring the full potential of microalgae towards sustainable environment and economy. At present, 70 -90% of the energy put into harvesting microalgae for fuel usually gets used into extracting the lipids (oil) they produce under current factory designs. It is obvious that new technologies are needed for reducing huge energy losses [13, 23-27].

Microalgae have immense potentials for biofuels production. However, these potentials largely depend on utilisation of technology, input feedstock (CO2, wastewater, saltwater, natural light), barren lands and marine environment. Based on energy content, available technology, land, it is hard to overemphasize that biofuels are a realistic short-term, but definitely not a long-term and large scale solution to energy needs and environmental challenges. Microalgae can be temporary sources of energy, and with the appropriate growth protocols they may address some of the concerns raised by the use of first and second generation biofuels.

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