The global increasing demand of fuel for various industrial activities has led the scientists to look for the alternative sources of fuels. In the recent past a much emphasis has been given to the feed stock based fuels. Different types of biomass have been identified as the potential source of fuels. Biomass includes various types of wastes e.g. agricultural wastes, sugarcane bagasse, municipal wastes, food wastes; energy crops e.g. edible as well as non edible seeds and plants. These feed stock derived fuels are collectively called as 1st and 2nd generation biofuels. But the need for more alternate and sustainable sources of fuel does not end here. As well as the increasing population and the food demand of the world has generated a “Food v/s Fuel” debate thus questioning the sustainability of the feedstock based biofuels. The answer to this debate can be given by using “Algae” as the raw material for biofuel production.
Algae are diverse group organisms that ranges from microscopic single cellular (Microalgae) to macroscopic multicellular (Seaweed or Macroalgae) organization with autotrophic mode of nutrition. Under optimal conditions algae has ability to accumulate significant amount of lipids (in some case upto 50% of their dry weight). There are other multiple benefits as well that has attracted researchers and entrepreneurs round the world .These aspects are: 1) high per-acre productivity, 2) non-food based feedstock resources, 3) use of otherwise non-productive, non-arable land, 4) utilization of a wide variety of water sources (fresh, brackish, saline, marine, produced, and wastewater), 5) production of both biofuels and valuable co-products, and 6) potential recycling of CO2 and other nutrient waste streams. Thus making algae based biofuel one of the most sustainable biofuels.
Biodiesel Production from Microalgae and Macroalgae:
Microalgae produce lipids by the metabolism. Under optimal conditions of their growth the amount of lipid produced is less (approx. 5%-20%).But under suboptimal conditions such as starvation , nitrogen limitations ,temperature change, algae change their lipid biosynthetic pathway and the yield of lipid produced is increased ( approx. 20%-50%). These lipids produced are mainly in the form of TAG (Tri Acyl Glycerol) which is converted into Fatty Acids by treating it with methanol (chemical transesterification reaction) or by enzymatic conversions. This fatty acid produced can be used as the fuel. As well as genetic engineering of the algal strains can also be done to increase the yield. Hydrogen is another fuel that is produced using the algal stock.
Whereas Macroalgae is seaweed, the fuel production strategy in them is different from that of the microalgae. Seaweeds have high starch content. The fuel is produced using the help of microbes by carrying out fermentation under anaerobic conditions. The type of fuel produced is also different as it comprises of ethanol, butanol etc. The yield of the fuel can be increased by genetic engineering in the metabolic pathways of the microbes used as the inoculums.
Apart from such benefits, biofuel production from algae is not free from challenges. The major monetary and technological challenges in the field are: 1) Harvesting and drying alone accounts for 20-30 per cent of the total production cost. 2) Extraction of oil from algal biomass on a large scale is difficult. 3) The existing techniques are very costly for the large scale production.
Algal Biorefineries: A sustainable refinery concept:
The biorefinery concept is akin to today’s petroleum refineries, which produce multiple fuels and products (petrochemicals) from petroleum. The various petrochemicals produced from the refineries find their applications in various industries, e.g. plasticizers, vegetable oil extraction, paints and anti-corrosive substances, and many more. The production of these petrochemicals makes the refinery process more profitable as well as practical.
The concept of algal biorefinery is to explore the possibility of producing biofuels from commercially grown alga at a large scale. Compounds like proteins, carbohydrates, lipids, and other valuable components, e.g. pigment, anti-oxidants, fatty acids, vitamins are produced by algae as a result of their metabolic activities. Thus a wide array of products can be formed from the algae These products range from the fuels, food supplements and nutrients for human, livestock feed and fine organic chemicals for pharmaceuticals (omega-3 fatty acid , ecosapentanoic acid , etc.).