Biodiesel From Algae Is It Feasible Biology Essay

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As the threat of fossil fuel depletion is nearing the search for alternative renewable resources has never been greater. Algae are simple photosynthesising unicellular/milticellular organisms which produce high levels of lipid. There is a great interest involving microalgae and biodiesel production due to their high oil content, there are numerous methods to cultivate, extract and process the biomass produced. The leading cultivation methods are raceway ponds and photobioreactors, although the photobioreactor is the leading system. Raceway ponds are less efficient as they are open system meaning evaporation of the batch biomass is possible as well as contamination with other microorganisms, possibly some which feed on algae. The method of which biodiesel is produced is through transesterification, this involves triacylglycerols (TAGs) and alcohol to form fatty acid methyl esters (biodiesel) and glycerol. The methods to extract the biomass are as follows flocculation, centrifugation, filtration and finally dehydration. In comparison with plants grown for biodiesel suck as rapeseed, palm or soy, algae produce much higher content per land area unit and flourish in aqueous environments therefore would not be in competition with land crops grown for food.

2. Introduction

These days petroleum and diesel are used more than ever to satisfy the world's demand. Oil reserves are drying up quickly and there is increasing demand to find alternatives to fossil fuel. Fossil fuels are also a problem as they create green house gases such as CO2, NO2 and methane polluting the environment, which increase the rate of global warming along with depleting forests resulting in destruction of habitats. With growing interest in biofuel many different ways of extraction from different sources has arisen with oil made from plants, animal fats or recycled fats. Most recently microalgae have been a hot topic for researchers; it is found that algae are a low cost alternative which produces higher yields of oil in comparison with crops and seeds. In this article this topic will be discussed in further detail and whether biodiesel from algae is feasible.

2.1 Background Theory

Interest in algae in use for commercial purposes has been under research for many years. One of the first large-scale cultivation of Chlorella, in the 1960's was produced in Japan by Nihon Chlorella. Interest in biodiesel specifically began in the 1970's during the first oil crisis. In the Unites States the National Renewable Energy Laboratory (NREL) using the Aquatic Species Program (ASP) began funding programs involving research into renewable fuels. This project lasted for many years (1978-1996) until it was terminated due to lack of funds. In these experiments the lipid production biochemistry and physiology of microalgae were studied to obtain knowledge about their composition. The final conclusion deducted was at low costs biodiesel from microalgae is feasible, however to receive high yields much more research and development in the area must be investigated. [1]

3. Classification of Algae

Algae can be classified in the paraphyletic group as a large group of organisms from different phylogenetic groups. Similar to plants in many ways but differ in the fact they are very simplistic unicellular/multicellular organisms. Mostly microscopic, some species such (e.g. seaweed) reach vast sizes up to 50m and grow in seawater or freshwater and generally damp, moist or wet conditions. Algae contain a membrane bound nucleus and encompass chloroplasts therefore can photosynthesise. Algae produce more oxygen than plants are important factor in the food chain, many small species such as shrimp feed on them therefore they are at the bottom of the food chain. Excluding Cyanobacteria (prokaryotic) most algae are eukaryotic. They were considered eukaryotic until recently were moved their cell structure resembles that of bacteria and they photosynthesise in the cytoplasm rather.[2, 3, 4]

3.1 Algae Phylum

The main algae phyla are Cyanophyta (blue green algae/ Cyanobacteria), Rhodophyta (red algae), Chrysophyceae (golden algae), Phaeophyceae (brown algae) and Chlorophyta (green algae) other phyla include Bacilloriophyta (diatoms), Dinophyta (Dinoflagellates), Haptophyta, Prochlorophyta etc. [5, 6]

3.2 Strain Efficiency

The optimum strain would be able to produce efficient biomass (high oil content) and fast growth rate and a temperature between 20 - 30oC. The problem that occurs with this is algae that grow at a fast pace usually produce low oil content about 30%, taking only a couple of hours to divide. Algae producing high oil content of 80% grow at a slow pace possibly up to 10 days and divide only once during that period. A technique enabling algae to grow efficiently and produce high oil content is nutrient starvation such as nitrogen starvation, although this is also slows growth.

Table 1 - [21]

Optimum storage triacylglycerols TAG(s) chain length would preferably need to be fully saturated or monounsaturated, as this increases oxidative stability (storage stability) and combustion performance of the oil, they should contain chain length of myristic or oleic acid C14 to C18 respectively. Fatty acids with medium to long chain length with saturated or monosaturated double bonds are ideal however algae containing these chain lengths are either slow growing strains or difficult to grow. [8, 9]

Researchers nowadays are looking into methods to produce efficient algae strains and one way is through genetic modification. It would be valuable to be able to control chain length of fatty acids as well as double bond formation, and it can be achieved through genetic engineering. Assays carried out on Chlamydomonas reinhardtii in Roessler Et. All and Dunahay explore how genes can be extracted from algae within the same phylogenetic group and introduced into C. reinhardtii. [8, 9, 10]

3.3. Chlamydomonas reinhardtii

The diatom Cyclotella cryptica has been utilised to examine how a recombinant gene can be expressed in a host cell. The synthesis of fatty acids in the cell is controlled by Acetyl-CoA Carboxylase (ACCase), therefore in Roessler Et. all's research this was the target gene to be extracted. The gene was removed from C. cryptica and cloned using polymerase chain reaction (PCR). [8, 9, 10]

The host used was Chlamydomonas reinhardtii, the method involves the removal of the cell wall by enzymatic digestion (autolysin - cell wall degrading enzyme) leaving protoplasts. As the cell is now exposed, in order for the DNA to be absorbed the cell could be treated with electroporation or polyethylene glycol. This is a difficult procedure and sometimes unsuccessful, some strains contain sporopollenin which is resistant to enzymatic digestion. [8, 9, 10]

A method to agitate the cell is DNA- coated gold particles, the way in which they are placed in the cell is through pressurised helium gas (biolistics). Another method is through agitation of C. reinhadtii with silicone carbide fibres (SiC). This combined with rapid multiplication of algal exponential growth could potentially give rise to a species which is perfect for biodiesel production. [8, 9, 10]

3.4 Species Used for Biomass Production

The most common species used are the Chlorella species, other popular algae utilised are Chlamydomonas reinhardtii, Hematococcus pluvialis, Arthrospira (Spirulina) platensis etc. The table below gives examples of these. [1]

Table 2 -[21]

4. Photosynthetic Algae

The diagram below shows a quick overview of photosynthesis, using the two photosystems in photosynthesising algae:

Fig 1 - [7]

The overall reactions of photosynthesis are:

Net: (By 8 quanta)

Eqn 1 -[11]

4.1 Photosynthetic Pigments

Blue-Green Algae

The blue - green algae evolved from bacteria hence they are prokaryotic, nowadays are classed as bacteria due to this. Their main photosynthetic pigment is chl a absorbing at 680 nm in the red and 440 nm in the blue region. They are contained in the thylakoid membrane (lamellae) in the cytoplasm. Major additional pigments are phycocyanin (absorbing at 626nm), allophycocyanin (absorbing at 650nm) and phycoerythrin. [11]

4.1.1 Red Algae

Red algae contain the xanthophyll Lutein, also phycoerythrin and this enables the absorption of green light in deep water hence algae in deeper waters naturally will have more phycoerythrin present. Phycoerythrin absorbs at 500, 540 and 566 nm and chl a at 440 and 670 nm the combination of these pigments allows a greater scale of wavelengths in the visible part of the spectrum to be covered. [11]

4.1.2 Brown Algae, Diatoms and Dinoflagellates

These obtain chl a, chl c, the xanthophylls: - fucoxanthin in brown algae, diatoms and peridinin in dinoflagellates. Both xanthophylls absorb at 490 nm and chl c around 460 and 640 nm. Although there is a 40nm shift of peridinin and fucoxanthin when in their native state, possibly being attached to a protein. [11]

4.1.3 Green Algae and Higher Plants

The pigments contained in green algae and higher plants are chl a, chl b and chl c, chl b having a blue absorption of 470 nm and red absorption of 650 nm. Unlike the other classifications of algae these do not obtain specialised pigments in order to absorb light in the region of 500 and 600 nm, therefore reflecting those wavelengths and appearing green. The major xanthophyll is lutein and small amounts of violaxanthin and neoxanthin. [11]

4.3 Chlorophyll Content

Table 1 - The distribution of photosynthetically active pigments in different algae/ plants:











Major Xanthophyll













Brown, Diatoms










Green, Higher Plants








Violaxanthin; Vaucheriaxanthin

Table 3 - [11]

4.4 Taxonomy

Fig 2 - [6]

5. Biomass Production

The production of biomass requires, light for photosynthesis, carbon dioxide, nutrients and inorganic salts. Usually contained in the growth medium for microalgae the nutrients needed are, phosphorus (P), nitrogen (N), iron and in some cases silicone. This is based from the elements that compose the algal cell, the minimal nutritional requirements can be roughly determined using the molecular formula of algae biomass, CO0.48H1.83N0.11P0.01. The algae depend on light energy so light needs to be freely available disregarding seasonal variations. CO2 needs to be constantly fed into the system during the daytime about 100 tonnes of algal biomass fixes around 183 tonnes of CO2. Fresh medium must be circulated through the system only during the daytime and at the same time the same quantity of biomass removed. The algal biomass must always be mixed even during the night time to prevent segmentation which slows down the rate of biomass production [12]

6. Oil Production

6.1 Transesterification

Biodiesel is produced through the process of transesterification (alcoholysis). This is the reaction between a triglyceride and an alcohol in the presence of a catalyst to form glycerol and esters. This takes place step by step, firstly the triglycerides are converted to diglycerides then following monoglycerides and finally to glycerol.



MAG + CH3OH ) à Glycerol + R3COOCH3

Eqn 2 - [26]

Usually used for the alcohol is methanol as it is cheap and produced from this are methyl esters. As this reaction is in equilibrium to ensure a greater yield of methyl esters excess ethanol must be used, 6mol, for each mole of triglyceride used in industry, this ensures 98% yield of esters on the basis of weight. The catalysts which can be used in the reaction include acids, bases and lipase enzymes, however lipase enzymes are high-priced therefore not appropriate for industrial use. In industrial processes alkali is applied as it is 4000 times faster than acid catalysed reactions. Alkali's currently used are sodium hydroxide (NaOH) and potassium hydroxide (KOH) at a concentration of 1% by weight of oil, sodium methoxide is a better catalyst and is increasingly utilised. The reaction conditions at atmospheric pressure at 60oC (as methanol boils at 65oC) and is approximately 1hr and 30mins long. In order to prevent saponification, the alcohol and oil must be dry and the oil must contain a minimum amount of free fatty acids. The methyl esters are then isolated by the removal of glycerol and methanol with repeatedly washing with water [12, 14, 15]

Eqn 3 - [1]

6.2 Supercritical Transesterification

Transesterification of TAG(s) with an alcohol is usually heterogeneous. This reaction utilises methanol as well as supercritical conditions, instead of a two liquid phase reaction due to the conditions triacylglycerols have been subjected to a single homogenous phase this speeds up the reaction. An alcohol molecule attacks the carbonyl of the TAG. The hydrogen bonding decreases form pressure therefore methanol becomes a free monomer, fatty acid methyl ester and diglycerides are formed, further transesterification of diglyceride forms methyl esters and monoglyceride and the final step monoglyceride forms methyl ester and glycerol. [14]

7. Cultivation Processes

7.1 Raceway Pond

This is a closed loop circulating channel system where this is about 0.3m deep which allows for light to penetrate to the bottom of the pond for maximum algal growth. The algae nutrients are fed continuously at the paddlewheel, (located at the beginning of the raceway) keeps the algae biomass circulating at all times. The raceway is built from concrete or compact earth and lined with white plastic. This loop continues in a circle until reaching the paddlewheel again,

Fig 4 - [12] where behind it, the harvest is collected. [12, 16]

To maintain constant temperature, cooling can only be done through evaporation. This causes a problem as CO2 is lost through evaporation and the algal biomass is poorly mixed. Other problems involved are unwanted algae and microorganisms that feed on algae. Although raceway ponds are cheaper and are easily maintained the algal productivity is not that efficient in comparison with photobioreactors [12, 16]

7.2 Photobioreactors

Tubular photobioreactors

These are usually tubular, transparent plastic circular photobioreactors. These allow growth of single celled species of microalgae and produce large quantities of biomass. The

Fig 5 - [12]

width of the tubes are around 0.1m or less in diameter, this is done in order for light to penetrate through the tubes completely allowing for maximum cultivation of the microalgae. The micro-algal broth is prepared in a reservoir called the degassing column this is then circulated through the tubular panels then back to the reservoir. The arrangement in which the tubes are organised is horizontally lined on the ground.

Fence-like Photobioreactors

The fence-like solar collectors are lined parallel opposing one another. The solar tubes are oriented from north to south and the ground underneath is painted white or covered with white sheets of plastic this is performed to increase reflectivity enabling higher percentage of light to reach the tubes.

Fig 6 - [12]

Helical Photobioreactor

Other methods of organising the tubes may be around a supporting frame and the tubes coil around this forming a helical photobioreactor, these are used for cultivation of a small amount of biomass. [12, 16]

In order for the photobioreactor to function efficiently a constant source of light must be applied during daylight hours, this can be created through artificial light rather than depending on fluctuations from sunlight. It is more costly however to use this method, although it has been used in large-scale production. [12, 16]

In photobioreactors there are two types of pump that prevent sedimentation of algae in the solar tubes. The first is a mechanical pump, providing a turbulent flow therefore may damage the biomass, the second is an airlift pump which is the gentler option and has been proven to be a success. The mechanical pump is flexible in comparison with the airlift pump, the airlift pump requires a supply of air. The photobioreactors must be cleaned periodically to prevent sedimentation. [12, 16]

Oxygen is formed in the photobioreactors can be as much as 10g of O2 m-3min-1 which is problematic as the saturated O2 slows down photosynthesis and at higher concentrations combining with light intensity can cause photo-oxidative damage to the cells. The way to remove the excess oxygen is to bubble air through the broth. This must be done at certain intervals the length of the tubes are limited and cannot be longer than 80m in length depending on the system, e.g. light intensity, concentration of oxygen upon entry in the photobioreactor and amount of algae cultivated. [12, 16]

CO2 is also fed into the solar tubes through the degassing column pH is an indicator of how much CO2 is required. PH controllers measure changes in pH and where increased, CO2 is fed into the system. [12, 16]

Even with photobioreactors loss by evaporation through respiration of algae still occurs and cooling of the system is needed day and night. This can be done by applying heat exchangers placed in the degassing chambers or in the tubular loop and another method is to spray water on the tubes, which has proved to be a useful method in dry climates. [12, 16]

To compare both systems, photobioreactors are much more efficient in producing a greater amount of biomass. When recovery of algae after cultivation is made, either through filtration and centrifugation that recovered from photobioreactors is 30 times the biomass concentration than that of raceway ponds [12, 16]

7.3 Extraction

Suitable harvesting methods to extract biomass and recover this from the culture include sedimentation, centrifugation, filtration, ultra-filtration and flocculation. Most commonly used step is flocculation which collects the algae cells and increases surface area which enables sedimentation, centrifugation and filtration. Another method of collection is with filter presses however this is better when used for cultivation of larger microalgae. To prevent the rupture of cell walls and destruction of cells the gentler methods to recover biomass is filtration or ultra-filtration(although are costly). [1, 19]

Dehydration of biomass is effective as increases shelf life, current methods of dehydration are spray-drying, drum-drying, freeze-drying and sun drying. As algal biomass is wet, sun drying is ineffective, the same applies for spray drying. After dehydration the cells must be disrupted and this can be done through mechanical methods (cell homogeniser, bead mills, ultrasound, autoclave and spray drying) and non-mechanical methods (freezing, organic solvents and osmotic shock and acid, base enzyme reactions). For lipids solvent extraction is applied through Lyophilisation (breaks cells and turns to powder), this makes extraction easier and with less degradation of the dry biomass. Solvents used to extract the Fig 7 - [1] fatty acids are hexane-ethanol which successfully extract 96%. [1, 19]

8. Biodiesel Content and Acceptability

In order to be used as an efficient transport fuel or for other applications biodiesel should be composed of saturated or monosaturated fatty acids, therefore the lower the amount of polyunsaturated fatty acids the higher the quality fuel. Oil from microalgae usually contain four or more double bonds, two common examples are eicosapentaenoic acid (EPA, C20:5n-3), and docosahexaenoic acid (DHA, C22:6n-3), EPA containing 5 and DHA 6 double bonds. The reason this is a problem is that the double bonds in unsaturated fatty acids are reactive and susceptible to oxidation (auto-oxidation) whilst in storage and become prone to forming peroxides, therefore high oxidative stability is equal to long term storage stability. Oxidation causes the chemical decomposition of oil and degradation of biodiesel. [12, 13, 17 ,18]

A test to measure unsaturation levels is the Iodine Value (IV), it measures per 100g of oil the amount of Iodine absorbed, since the unsaturated bonds are sensitive to iodine, the higher the iodine value the greater amount of unsaturated fatty acids present. A Peroxide Value is used to measure the amount of ROOH present this method is used in the food industry to measure the rancidity (oxidation of oils). [12, 13, 17, 18]

In terms of regulations set in EU (Standard EN 14214), most microalgal oils would not comply due to their high levels of unsaturation, these standards require the IV not to exceed 120/130g of iodine per 100g of oil. There is a 12% (mol) value of the amount of linolenic acid methyl esters present in biodiesel in the EN14214 regulations, linoleic (C18:3n-6) and linolenic (C18:3n-3) acid have a much higher oxidative stability in comparison with DHA and EPA due to lower unsaturated fatty acid levels, but are still under restrictions in the EU in biodiesel oil. There is a way to remove double bonds in fatty acids and this is through the partial catalytic hydrogenation of the oil, e.g. production of margarine from vegetable oils. [12, 13, 17 ,18]

Table 4 - [21]

8.1 Power Plant CO2 Utilisation

Operating photobioreactors is costly, including expenses of building and running the system the cost of nutrients and CO2 will also need to be incorporated. In order to reduce this value flue CO2 from power plants provides the solution. Other pollutants such as NOx and SOx can also be recycled and applied as nutrients.

A system design given by Brune Et. all, suggests a hypothetical estimation of the costs which would be involved in utilising power plant CO2. The scenario presents a semibase-load (output of power plant over a period of time) with an electrical production of 18h/day in 8 months. The electrical capacity is 50MW hence giving 216 million kMh/ season. The generated CO2 from this is calculated to be 30.3million kg-C/ season, with such a high quantity of CO2 the power plant presents enough CO2 for a photobioreactor to utilise. For CO2 to be used successfully it depends on several factors, the rate of CO2 transfer from power plant to reactor and the amount of algae grown each time CO2 is madee. CO2 transfer ranges from 85-95% and even lower reducing to 60-80% .There a high recovery value of 15-50% of algal carbon. If the overall production of biomass from algae is on average 20g-m2/day at a CO2 efficiency of 70% and including 30.3 million kg-C/season (126,450 kg-C/day) of CO2 the production of algae will be: [20]

(126,450 kg-C/day)(2g VS/g-C)(0.70) = 177,030 kg-VS/ day

X (240 days) = 42.4million kg-VS/season [20]

Flue CO2 flow rate (at 6% CO2) is around 322,000 kg/h. Algal productivity, assuming the average cell completes a full cycle in 3 days, is 20g VS/m2 -day or carbon fixation of 10g-C/m2 -day. To culture the algae the surface area therefore is:

(176,030 kg-VS/day)(1,000 g/kg) / ((20 g VS/m2 -day) x (10,000 m2/ha)) = 880 ha (2,147 acres) [20]

The 880 ha can be placed as 4 photobioreactors made of 220 ha. The system hypothesised by Brune Et. all shows that power plants generate 126,450 kg-C/day enough to produce 4 photobioreactor systems of 880ha. However the cost to build these especially with such a large surface area would be very high-priced and impractical. The electrical capacity to operate the facility must also be considered. [20]

9. Economic Value

9.1 The World's Situation

The International Energy Agency (IEA) reported the world's primary energy, which is considered to be fossil fuels as they provide 84% of the world's overall demand, will grow by 55% from 2005 to 2030 annually at rate of 1.8%. In reports from energy and capital a drastic increase of up to 60% will hit by 2025. Two of the biggest consumers are China and India with annual growth rate amounting to 7.5% and 5.5% respectively. If policies do not change by 2030 there will be an increase of 60% greater demand for oil, both China and India account for 45% of this. At the rate fossil fuels will be exhausted in around 45 years time. [21, 22]

9.2 Consumption Costs

According to Chisti(2007) if it is assumed CO2 is not included in the cost, the expense for producing a kilogram of biomass is $2.95 for photobioreactors and $3.80 for raceways. If the biomass contained 30% oil by weight a litre of oil would therefore amount to roughly $1.40 for photobioreactors and $1.81 for raceways. Oil recovery costs amount are important as these save expenses and contribute 50% to the cost of the final recovered oil. In the US during 2006, if taxes and distribution are excluded the price of petrodiesel was $0.49/L (73% crude oil, 27% refining). Biodiesel produced from palm oil

Table 5 - [12]

costs $0.66/L amounting to a total of 35% extra cost in comparison with petrodiesel. For biodiesel from palm oil to compete with petrodiesel the cost of biodiesel should be $0.48/L the same logic applies to biodiesel produced from algae. This requires the $2.80 current production costs to decrease to $0.48. [12]

Byung-Hwan Um states that trials in ideal conditions fast-growing micro-algae yield 1800-2000 gallons/acre annually of oil, whereas soybean 50 gallons, rapeseed 130 gallons and ~650 gallons palm oil. The land required to harvest algae is minimal since land area of photobioreactors or raceway ponds are much smaller in comparison with that of crops and surface area of cultivation is larger as solar panels are compact. The microalgae would not be competing with food crops as they are grown in aqueous conditions and it is possible to cultivate algae in sewage and water treatment plants. Oil produced from 20-40M acres of land could replace entire US supply of imported oil therefore allowing for 450M acres for food production. Algal biodiesel can be produced using photobioreactors at $4.54 per gallon. However this would have to drastically reduce to £1.81 per gallon (2006) in order to compete with petrodiesel. This is taking into account that 71% of the costs are from starting materials and refining of fuels. [8, 24]

9.3 Industrial Costs

To compare the two processes of extraction, the cost to operate raceway ponds annually is much less compared with that of photobioreactors, photobioreactors are complex and sophisticated systems which require in the range of $60-100/m2. The total cost per annum per hectare (ha) of a photobioreactor closed system is $200,000. The comparison of expenses for open pond system is $125,000 - $150,000 per hectare per annum consequently the photobioreactor costs more to operate. [23]

10. Future Prospects

Companies currently researching biodiesel from microalgae and perfecting culture techniques include ExxonMobil, Solazyme, GreenFuel Technologies, Solix and Livefuels. Possible future prospects would be to identify the optimum therefore a strain of algae with fast exponential growth rate, high lipid content and light saturation factor could be engineered. Of course the trouble with this model would be the damage that this strain could impose on the environment and could potentially harm the eco-system and niches of microorganisms within it. The research into low cost photobioreactors must be delved into further, as well as lower costs to operate the system. Further development should be conducted into utilising flue CO2 from power plants as well as the application of nutrients from wastewater systems this area is of vast importance with the potential to reduce pollution and GHG. [23]

11. Conclusion

Biodiesel from algae seems to be a very promising area with constant new R&D in this field. Algae have high oil content, photosynthesise rapidly producing large quantities of biomass in a short amount of time making them ideal for biodiesel production. Algae can survive in harsh conditions and are not high maintenance they may simply obtain nutrients from wastewater and CO2 from flue gas. They have been successfully cultivated at a large scale by raceway ponds and photobioreactors and in competition with biodiesel from plants they produce a higher content of oil without competing with crops grown for food.The cost to build and operate this machinery is expensive and currently for algal oil from raceway ponds are estimated to be $1.40, photobioreactors at $1.81 per L and $2.80 for oil recovery from lower cost biomass, excluding the cost for CO2. The cost for petrodiesel in 2006 was $0.49/L. If potentially there is an increase in production of biomass to 100,000t the cost per kilogram would reduce to $0.47 and $0.60 for photobioreactors and raceways respectively. However currently petrodiesel is still the easiest and cheapest option to produce and sell fuel. Biodiesel from microalgae is feasible although not cost effective at present, it has the potential to replace fossil fuels therefore research into cutting the cost of building photobioreactors is required also the cost of CO2 and nutrients. The cost of CO2 and nutrients could potentially be made through the use of flue gas from power plants and nutrients such as nitrogen at wastewater plants or the use of low-cost fertilisers. This will also reduce the amount of green house gases released in the atmosphere reducing pollution and the rate of global warming. [1]