It relates to long-term degradation in the availability of petroleum. On an average, human utilizes fossil fuels which results in the release of 29 gigatonnes CO each year.
This critical situation has led to the emergence of an eco-friendly, alternative fuel biodiesel. According to United States Environmental Protection Agency, the volume requirement of the biomass based diesel in is 1. This, combined with growing demand, significantly increases the worldwide prices of petroleum derived products.
Most important concerns are the availability and price of liquid fuel for transportation [ 3 ]. In recent years, the use of biofuels has shown manifold global growth in the transport sector due to the policies concentration on achieving energy conservation and the avoidance of excess or extremes of GHG greenhouse gases emissions [ 4 ]. The 1st generation biofuels which are extracted from oil crops like rapeseed oil, sugarcane, sugar beet, and maize [ 5 ] including vegetable oils and animal fat using conventional technology have attained profitable levels of production [ 6 ].
But the use of 1st generation biofuels has raised questions and controversies due to their impact on the global food market and food security [ 7 ]. For example, the demand for biofuels may impose additional pressure on natural resource base, with potentially harmful surrounding and social concerns [ 8 ].
Energy shortage refers to the crisis of energy resources to an economy. There has been a massive uplift in the global demand for energy in recent years as a result of industrial development and population growth.
Since the early s, the demand for energy, especially from liquid fuels, and limits on the rate of fuel production have created such a stage leading to the current energy crisis.
The cause may be overconsumption, aged infrastructure, choke point disruption or crisis at oil refineries, and port facilities that confine fuel supply. In this paper, we have focused on addressing the global oil shortage by replacing nonrenewable source of oil reservoir by evergreen renewable natural source, algae oil. Microalgae cover unicellular and simple multicellular microorganisms, including prokaryotic microalgae that are cyanobacteria chloroxybacteria and eukaryotic microalgae for example, green algae chlorophyta , and diatoms bacillariophuta.
Unlike other biodeisel corps microalgae does not require herbicides or pesticides [ 13 ], microalgae also produce beneficial coproducts such as proteins and residual biomass after oil extraction, which can be used as feed or fertilizer or can be fermented to produce ethanol or methane [ 14 ]; the oil yield, can be significantly increased by varying growth conditions to modulate biochemical composition of algal biomass [ 15 ].
They also produce beneficial coproducts such as proteins and residual biomass after oil extraction, which can be used as feed or fertilizer or can be fermented to produce ethanol or methane [ 16 ]; the oil yield can be significantly increased by varying growth conditions to modulate biochemical composition of algal biomass [ 17 ].
The algal biofuel technology includes selection of specific species for production and extraction of valuable co-products [ 18 ]. The algaes are bioengineered for achieving advanced photosynthetic efficiencies through continued development of production system [ 19 ]. Challenges include, only single species cultivation techniques which are developed so far and are recommended to follow globally, but mixed culture may yield more algae oil than mono culture [ 20 ].
Algae oil may be less economically which includes techniques such as water pumping, CO 2 transmission, harvesting and extraction [ 21 ]. Fatal compounds such as NO x and SO x are produced in high concentrations as fuel gases, which are not environmental friendly [ 22 ]. Microalgae are sunlight-driven cell factories that transform carbon dioxide to potential biofuels, foods, feeds, and high-value bioactive.
In addition, these photosynthetic microorganisms are useful in bioremediation applications and as nitrogen fixing biofertilizers.
This review focuses on microalgae as a potential basis of biodiesel. The idea of using microalgae as a source of fuel is not novel, but it is now taken seriously because of the increasing price of petroleum and, more significantly, the emerging issues about global warming and greenhouse effect that is associated with incinerating fossil fuels.
Thus, several companies are involved in the production of algal fuel in order to decrease global warming and greenhouse effect. Biodiesel is an established fuel. In the United States, biodiesel is produced mainly from soybeans [ 23 ]. Other origins of commercial biodiesel include canola oil, animal fat, palm oil, corn oil [ 24 ], and waste cooking oil. Microalgae offer several different kinds of renewable biofuels [ 25 ]. The yields of different oil producing feedstock can be explained, as shown in Table 1.
The feedstock is not available for the biodiesel production as it is unethical to use these cash crops for fuel while the world is witnessing food shortage. The primary cause for global food shortage may be due to overconsumption, overpopulation, and overexploitation.
Peak oil is the point where maximum extraction of petroleum is reached, after which the rate of production enters decline stage [ 28 ]. The invention of new fields, the development of new production techniques, and the misuse of eccentric supplies have resulted in productivity levels, which endure to increase.
Peak oil is often confused with oil depletion; peak oil is the point of maximum extraction, while depletion indicates the period of falling in production and supply. Rapeseed and soybean oils are most commonly used, mostly in U.
They also can be obtained from Pongamia , field pennycress, Jatropha, and other crops such as mustard, jojoba, flax, sunflower, palm oil, coconut, and hemp. Several companies in various sectors are piloting research on Jatropha curcas , a poisonous shrub-like tree that produces seeds, considered by many to be a feasible source of biodiesel feedstock oil [ 30 ]. Vegetable oil is an alternative fuel source for diesel engines and for heating oil burners.
The viscosity of the vegetable oil plays an important role in the atomization of fuel for engines designed to burn diesel fuel; otherwise, it causes improper combustion and causes engine collapse. The most important vegetable oils used as fuel are rapeseed oil also known as canola oil, which is mostly used in the United States and Canada. In some places of the United States, the use of sunflower oil as fuel tends to increase [ 31 ].
Some island nations use coconut oil as fuel to lower their expenses and their dependence on imported fuels. The annual vegetable oil recycled in the United States, as of , was in excess of 11 billion liters 2. If all those 11 billion liters could be recycled, it could replace the energy equivalent amount of petroleum [ 32 ].
Other vegetable oils which can be used as fuel are cottonseed oil, peanut oil, and soybean oil [ 31 ]. Animal fats are the by-product of meat production and cooking.
These include tallow, lard, yellow grease, chicken fat, and the by-products of the production of omega-3 fatty acids from fish oil [ 33 ]. Oil yielding Plants like Salicornia bigelovii , a halophyte, is harvested using brackish water in coastal areas where conventional crops are not feasible to be grown.
The oil from Salicornia bigelovii equal to the yields of soybeans and other oilseeds grown by freshwater irrigation [ 34 ]. Multifeedstock biodiesel facilities produce high standard animal-fat based biodiesel. Currently, a 5-million-dollar plant is being built in the USA, with the objective of producing Sludge refers to the unused, semisolid material left from industrial wastewater or sewage treatment processes.
It can also refer to the settled suspension obtained from drinking water treatment and other industrial processes. Sludge is generally produced by a poorly designed or defective ventilation system, low engine operating temperatures or the presence of water in the oil.
The sewage-to-biofuel field process is developing interest from major companies like Waste Management and startups like InfoSpi, which are challenging that renewable sewage biodiesel can become modest with petroleum diesel on price [ 35 ]. Algae fuel or algal biofuel is another form of fossil fuel that uses microalgae as its source of natural deposits [ 36 ].
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This produces biodiesel and glycerin byproducts. After the oil is removed from the algae there is a lot of solid material, known as biomass. This leftover biomass, can be used to create another algae based fuel product, bioethanol which is ethanol from biomass. The carbohydrate content of the biomass can be converted into sugars.
This can be accomplished through fermentation with yeast, giving off carbon dioxide, which can be recycled back into the growing process of the algae. Then the sugars continue to ferment into ethanol. Also, in the case where the algae still contains the original oil in the biomass, decay can be initiated in order to rupture cell walls, releasing the carbohydrates, then followed by fermenting figure 3.
Algae are organisms that grow in aquatic environments and use light and carbon dioxide CO 2 to create biomass. There are two classifications of algae: macroalgae and microalgae. Macroalgae, which are measured in inches, are the large, multi-cellular algae often seen growing in ponds. These larger algae can grow in a variety of ways. The largest multicellular algae are called seaweed; an example is the giant kelp plant, which can be more than feet long.
Microalgae, on the other hand, are measured in micrometers and are tiny, unicellular algae that normally grow in suspension within a body of water. Microalgae have long been recognized as potentially good sources for biofuel production because of their relatively high oil content and rapid biomass production. Microalgae grow very quickly compared to terrestrial crops; the practice of algal mass culture can be performed on non-arable lands using non-potable saline water and waste water.
Thus, use of microalgae as an alternative biodiesel biofuel feedstock is gaining increasing interest from researchers, entrepreneurs, and the general public.
Because the bulk of the natural oil made by microalgae is in the form of tricylglycerol Figure 1 , which is the right kind of oil for producing biodiesel, microalgae are the exclusive focus in the algae-to-biodiesel arena. In addition to biodiesel, microalgae can also be used to generate energy in several other ways. Some algal species can produce hydrogen gas under specialized growth conditions. The biomass from algae can also be burned similar to wood or anaerobically digested to produce methane biogas to generate heat and electricity.
Algal biomass can also be treated by pyrolysis to generate crude bio-oil. Microalgae grow quickly and contain high oil content compared with terrestrial crops, which take a season to grow and only contain a maximum of about 5 percent dry weight of oil, Chisti, They commonly double in size every 24 hours. During the peak growth phase, some microalgae can double every three and one-half hours Chisti, Oil content of microalgae is usually between 20 percent and 50 percent dry weight, Table 1 , while some strains can reach as high as 80 percent Metting, ; Spolaore et al.
This is why microalgae are the focus in the algae-to-biofuel arena. Most microalgae are strictly photosynthetic — that is, they need a light and carbon dioxide as energy and carbon sources. This culture mode is usually called photoautotrophic.
Some algae species, however, are capable of growing in darkness and using organic carbons such as glucose or acetate as energy and carbon sources. This culture mode is termed heterotrophic.
Due to high capital and operational costs, heterotrophic algal culture is hard to justify for biodiesel production. In order to minimize costs, algal biofuel production usually relies on photoautotrophic culture that uses sunlight as a free source of light. Phototrophic microalgae require light, carbon dioxide, water, and inorganic salts to grow. The growth medium must contribute the inorganic elements that help make up the algal cell, such as nitrogen, phosphorus, iron, and sometimes silicon Grobbelaar, For large-scale production of microalgae, algal cells are continuously mixed to prevent the algal biomass from settling Molina Grima et al.
However, up to one-quarter of algal biomass produced during the day can be lost through respiration during the night Chisti, A variety of photoautotrophic-based microalgal culture systems are available. For example, the algae can be grown in suspension or attached on solid surface. Each system has its own advantages and disadvantages.
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