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1 .Back Ground:
The word biofuel means fuel that is made from biomass. Biofuel is a term used to describe biodiesel, bioethanol which is used in petrol and methane gas which is found in biogas. Fossil fuel is playing important role in today global economy and it is used to run transportation and also being used in heating and lightning purposes. The need for energy source is continuously being raised due to increasing population with each passing day and due to escalating economy. Increased use of fossil fuel has been resulting in increasing global warming and other types of pollutions due to increasing level of CO2 in atmosphere which has aroused need for some eco-friendly and renewable resource and may lower increasing pollution problem and is easily available. Algal is being used for extraction of biofuel is due to its non-toxic characteristics, biodegradability and lower net carbon cycle compared to conventional diesel fuels.(Mostafa El sheekh 2016). Micro and Macro-algae is called as third generation fossil fuel.

2. Introduction:
Now a day algal based biofuel has diverted attention of researchers. The FAO Inter Departmental
Working Group on Bioenergy established the Aquatic Biofuels Working Group (ABWG) in 2008 started their work with the objectives of innovation of the potential and sustainability of biofuel assembly from algae and fish waste in order to exchange knowledge and experiences with the objective of promoting R&D in this field. (Flammini 2010)
3. Importance of algae in biofuels:
The researcher’s attention is diverted towards cultivation of algae for extraction of energy resources is due to following characters of algae:
1. Algae resourcefully transform carbon dioxide, water and light in biomass in a system which do not essentially need agriculture plot for its cultivation.(Flammini 2010)
2. Its combustion produce less pollution and is cleaner as compared to fossil fuel and is environmentally friendlier
3. It do not require any modification for its use in diesel engines.(Mostafa El sheekh 2016)
4. Faster growth rate and higher lipid content as compared to seeded plants and having shorter generation time. They have potential to double their number within few hours and yield no less than 30 times more oil per acre than seed plants, making it referable source of biofuels.
4. Fuel Types Extracted From Algae:
The specie of algae and part of algae which is being use determine the type of fuel to be produced. Algae contain three essential ingredients: carbohydrates, proteins, natural oils. These are the key ingredients to obtain biodiesel, bioethanol, hydrogen and methane
(Weaver (2018, September 4))
Following are some fuel types extracted from algae:
4.1 Biodiesel:
Biodiesel is extracted from micro-algae. It is manufactured by using oil (lipid) content of microalgae which is processed chemically to give biodiesel (fatty acid methyl ester; FAME) and glycerol, which are then used in chemical manufacturing. Since algae contain potentially over 80% total lipids therefore, biodiesel production from algal oils has received most consideration, whereas, rapeseed plants contains about 6% lipids only. The various lipids assembly can be roused under stress conditions, e.g. inadequate nitrogen availability. Under such circumstances, biomass production is not optimum though, reducing the non-lipid part of the biomass that can be further used as a source for co-products.
4.2 Bioethanol:
Bioethanol manufactured through fermenting the carbohydrate content of algae using microbes or yeasts. . It is used as a replacement for petrol. Starch-containing feed-stocks is mainly used for the production of ethanol; some species of alga have been reported that contain about 50% of starch. Polysaccharides present in the cell wall of algae is used as a feedstock in a process analogous to cellulosic ethanol production, in addition it has a advantage that algae seldom contains lignin and their polysaccharides, are normally more simply broken down than woody biomass.
4.3 Biobutanol:
They are manufactured by fermenting carbohydrate content present in either micro-algae or macro-algae more energy content is present in them as compared to ethanol. and it is less eroding to internal combustion engines.
4.4 Hydrocarbons:
It can be produced in two ways either by treating unprocessed algae with high pressures and temperatures or by chemical conversion of microalgal oil. Hydrocarbons are produced directly in some species. They are consumed as aviation fuel.
4.5 Biogas:
It is produced by a process called as anaerobic digestion.in which energy is produced from microalgae and macro-algae by bacteria. Heat and electricity can be generated through its direct burning, or it can be purified to obtain bio-methane (which is used as a substitute to obtain natural gas in electricity generation, heating or transport). Biogas can be manufactured from unprocessed algae, or from remains left after other creates is taken out. Organic matter is transformed into biogas through anaerobic digestion that have about 60%-70% biomethane, while the remaining is mostly CO2 and it can be fed back to the algae.
Advantage: It has following advantages.
1. It uses wet biomass and the lessen the necessity of drying
2. The nutrients present in the digested biomass can be regained from the liquid and solid phase.
3. This process can be used to any unwanted biomass after withdrawal of a co-product.
4.6 Hydrogen:
Some species are present in water and produce hydrogen in anaerobic conditions. Botryococcus, one of the genus of algae is unable to yield the above said lipids rather they produce hydrocarbons having longer chains. These longer chain hydrocarbons are not proper for the production of biodiesel. As a substitute, they can be transformed through a process that is used for producing conventional fuels by the use of fossil oil. Although Botryococcus belongs to freshwater species but it is also capable to grow in saline water. It is also able to produce certain carotenoids (Banerjee, Sharma et al. 2002). Its disadvantage is comparatively sluggish growth speed..(Dr Stephen Allen 2011)
5. Cultivation of algae:
Following are the methods for cultivation of algae.
1. Open cultivation systems: Raceway pond is mainly used to cultivate algae on larger scale. It is difficult to maintain open system because of instability of ecosystems, temperature fluctuation due to climatic conditions and weather changes. Moreover, the open character of the system makes algae vulnerable to predator and growth of other species of algae that will result in competition among algae species make the cultivation difficult. Therefore extreme conditions are given in order to maintain monoculture such as high salinity (e.g. Dunaliella), high pH (e.g. Spirulina) or high nitrogen(e.g.Chlorella) water (Flammini 2010)

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2. Closed cultivation system: Much of the issues raised in open system can be lowered by constructing a closed system that is less effected by environment and these system require huge investment of money and are highly expensive, but allows a wider number of species to be cultivated normally with a higher concentration and productivity Closed systems allow for the cultivation of algal species that cannot be grown in open ponds.
3. Sea-based cultivation systems: Algae cultivation in the sea is the area of seaweed. Seaweed cultivation need large amount of work as compare to output, near shore in shallow water and often at small-scale, is common practice in parts of Asia
6. Methods to extract oils from algae:
There are various methods for extraction of oils from algae and some of them are discussed below:
1. Oils can be extracted from algae by oil press method as for olives. This is easiest and most common mean for extracting oil from algae and 75% yield of total available oil from algae can be obtain through this method
2. Hexane solvent method is another method for oil extraction., This step can yield up to 95 percent of available oil from algae when combined with the oil press method. It utilizes a two-step process.(1)To utilize the oil press method is first. (2)Then, instead of ending there, hexane is mixed with the remaining algae, it is filtered and washed to eliminate all traces of the chemical in the oil.
3. The Supercritical Fluid method is also a method for extraction. About 100% of available oil extracted by this method. Firstly CO2 is pressurized and heated to fluctuate composition into both a liquid as well as a gas. Then it is mixed with the algae which turns it completely into oil. This is least popular method because it requires large supply of algae and additional work plus work yet it yields upto100% of available oil
,
(Weaver (2018, September 4))
7. Refining:
After oil extraction, refining is done through a process called trans-esterification. Sodium hydroxide used as a catalyst and a alcohol (methanol) is added in it. This results in biodiesel fuel along with glycerol. The mixture is then refined to eliminate glycerol present in the mixture. This is universal process for extraction of oils from algae

.(Newman 2008)

8. Co-products of algae:
Food: as different types of nutrients and vitamins are present in algae, people it is also used as food. Fats, polyunsaturated fatty acid, oils are accessible in markets of Japan. Approximately 2400 tons of food is obtain in this way.
Pharmaceutical: antibiotics, antiviral or antifungal and a vast variety of other products are obtained from algal extract.
Cosmetics: For skin treatment Arthrospira and Chlorella are being used e.g. anti-aging cream, collagen synthesis in skin and also in sun protection.
Fuel Gas CO Emissions as Microalgae Nutrient: To bring forth the products of petroleum. Alga needs CO as a reactant. From usable energy, power plants are liable of 7% CO2 emission 15% CO is expelled from industries is an wealthy source for cultivation of microalgae is a competent dispatch for CO fixation.

References:
Dr Stephen Allen ( 2011). “Biofuels from Algae.” 4.

Flammini, S. v. I. a. A. (2010). Algae-based biofuels: applications and co-products FAO Environmental and Natural Resources Service Series, No. 44 – FAO, Rome 2010.

Mostafa El sheekh, A. E. F. A. (2016). Industrial Microbiology, Nova Science Publishers.
Biodiesel Production from Microalgae

Newman, S. (2008, 18 june). “How Algae Biodiesel Works.” from https://science.howstuffworks.com/environmental/green-science/algae-biodiesel2.htm.

Weaver, L. R. f. ((2018, September 4)). ” Making Biodiesel From Algae.”