Microalgae the potential source for biodiesel production

Based on their size algae are divided in to two broad groups, these are Macroalgae and Microalgae. Macroalgae, which commonly called sea weeds are multi cellular algae; some of its species could grow up to 50 meters in diameters. On the other hand Microalgae are microscopic algae. Depending on the particular species both macroalgae and microalgae can grow in fresh water, sea water and seawages. Difference in size is not the only difference between these two groups, they also differ in the form of the compound they store in their cells. Macroalgae mainly store carbohydrates in their cells for energy source, but microalgae store mainly Triacylglycerol in their cells for energy source. Triacylglycerol is the major feedstock in biodiesel production. Therefore for their higher Triacylglycerol content in their cells, microalgae are considered the potential source for biodiesel production.

Microalgae also have other qualities, to be named the number one choice for biodiesel production:

1. They have very fast rate of growth and reproduction than macroalgae and other oil crops. They can be ready to be harvested with in just a few days.
2. They are microscopic and lives in aggregates so they allow different designs of photobioreacors and ponds.
3.  They can grow easily on seawages and utilizes their nutrients from the seawage water.
4. Two types of products can be produced from microalgae these are ethanol and biodiesel.
5. Carbon dioxide from coal power plants and flue gases can be utilised. Flue gases contain in addition to carbon dioxide,  hydrogen nitride, sulphides, sulphur dioxide and other gases. Microalgae utilises the CO2 for photosynthesis, and the other gases as nutrients.
6. Microalgae purifies waste water which comes out from factories and farms such as fertilizers, iron, manganese, zinc, chromium, nickel, cadmium and cobalt. One famous microalgae used for such purpose is Chlorella vulgaris which purifies wastewater from metals.
7. And most of all microalgae have very high Triacylglycerol content which could reach up to 54% in dry weight basis.

Microalgae are classified in to four groups these are Diatoms, Green algae, Golden brown algae and Blue green algae. In total there are more than 200,000 species of microalgae. Although the number of spices of microalgae is so vast, only a few are used for biodiesel purpose. Those microalgae produced for biodiesel production are highly oleogenic producing more than 40% of oil per dry weight basis. Some of the species of microalgae which are growen for biodiesel purpose are Nannochloropsis spp (54%), Botryococcus spp (54%), Nitzschia spp (47%), Botryococcus braunii, Dunaliella salina, Spirulina spp, Dunaliella spp, Scenedesmus spp and Chlorella spp.

For optimum production of biodiesel from microalgae, artificial creation of stress such as nitrogen starvation and environmental stresses such as very high temperature and light intensity will tremendously increase the quantity and quality of the oil produced. And it is the number one strategy to increase the oil yield.

There are two major sources of CO2 these are, compressed CO2 and CO2 from power plants. Compressed CO2 is very expensive to use for large scale biodiesel production. And Injection of CO2 directly from power plants to photobioreactors and ponds have two problems, first it has very high temperature which many species of microalgae can't resist except those of Chlorella spp, and second the gas mixture in addition to CO2 contains other gases such as NO2 and SO2 in very high concentrations which is toxic for the algae. To avoid the high temprature problem the gases need to cool down and reduced to 2% concentration level before injection.

Oleaginous algae for Triacylglycerol feed stock for conversion to biofuel

Oleaginous algae are economically important algae, that have a potential to produce more than 20% of oils (mainly Triacylglycerol) per dry cell weight. Many oleaginous strains of algae for bio diesel production are now known by scientists. These strains can produce large quantities of oils. Algae has a potential to produce the highest yield of biofuel than all the other major feed stocks. Yearly yield potential of algae range from 5,000 gallons per acre to 20,000 gallons per acre, which is the greatest yield potential than even the best yielding vegetable oil producer plants, such as soy beans and palm oils. All algae species produce eleven types of oils, from this oils the one which is used as a feed stock for biofuel is Triacylglycerol. This type of oil is produced by algae mainly as a response to stress situations, for its use as storage of starch or energy. In alga farms stress situations are created by nutrients starvation, high temperature and high light intensity as the algae are aging normally. Naturally most oleaginous strains produce more Triacylglycerol while aging.

Nutrient starvation: is done by depleting the nitrogen, silicon and phosphate supply of the algae. This will cause the algae to produce more Triacylglycerol.

Temperature increase: As the temperature increase the production of Triacylglycerol also increases.

Light intensity increase: Higher light intensity increases Triacylglycerol. Light intensity is increased by exposing the algae to direct scorching sunlight.

Algae species that produces more amount of Triacylglycerol in response to stress situations are:

• All of: Green algae species
• Many of: Diatom Species
• Some of: Haptophytes, Eustigmatophytes, Chrysophytes and Xanthophytes species
• None of: Cyanobacteria or Blue Green algae species

Naturally under no stress environmental conditions Green algae, Diatoms, Haptophytes, Eustigmatophytes and Chrysophytes have an average of 26% of oil, but under stress conditions their average oil content increases significantly to 45% per dry cell weight.

The yield from oleaginous algae is much more in hundreds of fold as compaired to the yield produced from the best oil producer crops. The reason for this is due to the ability of each and every algae cells to perform a range of various physiological functions starting from CO2 fixation to Triacylglycerol production and accumulations by it self. But in crops such as soy beans this physiological functions took place in separate and specific parts of the plant such as in seeds.

These days production of biofuel is gaining increasing popularity because of different reasons.

1. Algae are easy to grow. Algae needs little attention to grow, it can grow easily in sewages, farm outlets, barren and unproductive lands, salt water and in hot dry desert climate.
2. Algae reproduce very rapidly, this will make algae production for biofuel a lot sustainable, continual and unseasonal.
3. Algae produces 7 to 30 times more yield of oils than all of the oil crops combined. In other words it has high potential of yield per hectare.
4. Ease of the use of coal power plants as CO2 source for alga culture.
5. Its use to purify seawages and drainage canals from toxic chemicals and excess fertilizers.
6. Its huge ability to reduce green house gases such as carbon dioxide.
7. For its other economically important byproduct such as pigments, cosmetic products, animal feed, food products such as proteins, carbohydrates, vitamins and omega-3.
8. Increasing new discoveries and techniques to grow algae in open ponds and phobiotoreactors. 

But there are also some serious impediments for the applicability of producing biofuel from algae. The estimated production cost is very high and most of this cost involves in setting up the centrifugal system to extract the oils and in running the system, the estimated cost could reach hundreds of millions of USD. Other minor problems include unavailability of reliable carbondioxide source, high evaporation losses,  contamination and enough water source.

Taking all the high production costs in to consideration now days, it is much more advisable to grow algae for food companies than for biofuel purpose, but biofuel production from algae have a very huge potential for the future and a lot of research are underway to slash the paralyzing cost of production. As for me the future looks greener.