Therefore, a bio-refinery is a facility that contributes biomass conversion processes and tools to produce fuels and chemicals from biomass. Concept of bio-refinery is equivalent to the petroleum refinery, which harvests numerous fuels [ 13 ]. Energy is essence of life. Broadly, it is defined as the ability to do work or the ability to cause alteration, such as manufacturing molecules or moving substances. Potential energy can be believed of as kept energy. Chemical energy, in the bonds among atoms in a molecule, is a form of potential energy.
Kinetic energy can be believed of as free energy, and is commonly linked with motion. Heat dynamic motion of molecules and movement of large objects such as ourselves are formulae of kinetic energy. There are many forms of energy, including: chemical, electrical, gravitational, mechanical, nuclear, radiant and thermal energy.
The official SI unit for energy is the joule J ; energy can also be measured in calories or British thermal units Btu [ 14 ].
In physics, energy is a property of objects which can be transferred to other objects or converted into different forms [ 15 ]. Entirely of the many forms of energy are exchangeable to other types of energy. In physics, there is a widespread law of conservation of energy which states that energy can be neither produced nor be damaged; however, it can alterated from one shape to another. Energy conversion includes creating electric energy from heat energy by way of a steam turbine, or by lifting against gravity which led to mechanical work on the object and accumulations gravitational potential energy in the object.
If the object falls to the ground, gravity does mechanical work on the object which converts the potential energy in the gravitational field to the kinetic energy liberated as heat on impact with the ground. Living organisms want available energy to stay alive, such as the energy humans get from food. In reverse to the recent definition, energeia was a qualitative philosophical theory, broad sufficient to include ideas such as gladness and pleasure. The law of energy conservation was also first recommended in the early 19th century, and put on to any isolated system.
It was discussed for some years whether heat was a physical substance, dubbed the caloric, or simply a physical quantity, such as momentum. In , James Prescott Joule open the theory of energy conservation, formalized largely by William Thomson Lord Kelvin as the field of thermodynamics.
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Thermodynamics assisted the quick advance of clarifications of chemical processes by Rudolf Clausius, Josiah Willard Gibbs and Walther Nernst. The whole energy of a system can be divided in different ways. It may be too suitable to discriminate gravitational energy, thermal energy, numerous kinds of nuclear-powered energy which use capacities from the nuclear force and weak force , electric energy from the electric field and magnetic energy from the magnetic field between others.
Energy is converted into the same amount of energy in other forms, mostly light energy and thermal energy. Thermal energy is energy of microscopy constituents of matter, which may include both kinetic and potential energy. Potential energies are frequently measured as positive or negative depending on whether they are greater or less than the energy of a specified base state or configuration such as two interacting bodies being infinitely far apart. Energy is the power we use for transportation, for heat and light in our homes and for the manufacture of all kinds of products.
We use the most types of energy which originates from fossil fuels, for instance, natural gas, coal and petroleum. Uranium is considered as nonrenewable source, but it is not a fossil fuel. It is changed to a fuel and undergoes the nuclear power plants. As soon as these normal resources are used up, they are gone forever. The process of meeting these fuels can be dangerous to the biomes from which they originate.
Fossil fuels are set through a process named burning for create energy. Burning liberates pollution, such as sulfur dioxide and carbon monoxide which can result in acid rain and global warming. Renewable energy resources can be used over and over again. Renewable resources contain wind, geothermal energy, solar energy, hydropower and biomass.
That resource generates much less pollution, both in gathering and production, than nonrenewable sources. The sun produces the solar energy. Some people use solar panels on their homes to convert sunlight into electricity. Dams and rivers generate hydropower. When water flows through a dam it activates a turbine, which runs an electric generator.
Biomass includes natural products such as wood, manure, corn and algal biomass of living organisms which used as energy source. Biomass, a renewable energy source, is organic matter resulting from living, or newly living organisms. It can be used as a source of energy and it most ultimately pointed to plant-based materials which are not used for feed, and are specially named lignocellulosic biomass. Biomass can either be used in a straight line throughout burning to create heat such as forest residues and municipal solid waste, or indirectly after converting it to various types of biofuel.
Conversion of biomass to biofuel can be summarized by different methods which are generally classified into: thermal, chemical and biochemical methods [ 11 ]. Biomass is considered the simply source of fuel for domestic use in several developing countries even today. Biomass is entire biologically created matter based in hydrogen, carbon and oxygen.
The assessed biomass yield in the world is Even today, wood remains the largest biomass energy source [ 22 ]; examples include forest residues such as dead trees. Wood energy is derived by using lignocellulosic biomass second-generation biofuels as fuel. Depending on the biomass source, biofuels are divided generally into two main groups. First-generation biofuels are resulting from origin such as corn starch and sugarcane. Sugars existing in the biomass are fermented to yield bioethanol, which can be used immediately in a fuel to yield electricity or act as a flavor to gasoline [ 23 ].
Second-generation biofuels use non-food-based biomass sources, for instance, municipal waste and agriculture. These biofuels are often composed of lignocellulosic biomass, which is not edible and is a low-charge waste for several industries. Although being the favored substitute, except the second-generation biofuel neither yields an inexpensive production nor achieved by technological issues. These issues appear essentially due to chemical slowness and building inflexibility of lignocellulosic biomass [ 24 ]. Energy derived from biomass is projected to be the largest non-hydroelectric renewable resource of electricity in the US between and by Energy Information Administration [ 25 ].
There is research involving algae as non-food source can be yielded at rates of times those of other kinds of land-based agriculture, for example, soy and corn. As soon as gathered, it can be fermented to yield biofuels, for example, ethanol and methane, in addition to hydrogen and biodiesel [ 26 ]. Resources of biomass include primary, secondary and tertiary. The first one primary biomass resources consisted directly by photosynthesis process and are income directly from the land.
They contain permanent short-rotation woody crops and herbaceous crops, the seeds of oil crops and remains produced from the collecting of forest trees and agricultural crops. Secondary biomass resources result from the processing of primary biomass resources such as agricultural by-product field crop residues and water vegetation algae, seaweeds, etc. Algae used as third generation of biofuels production. This generation of biofuels is advanced and is based on biological. Microalgae are prokaryotic or eukaryotic photosynthetic organisms. Indeed, they can grow quickly in fresh or salt water due to their unicellular or simple multi-cellular building structure.
Because of their simple cellular structure, they are very capable converters of solar energy. As the cells of microalgae grow in aqueous suspension, they have efficient access of water, CO 2 and other nutrients [ 29 ]. Microalgae are one of the oldest living organisms in our planet and have more than , species. Microalgae can grow in wastewater, thus giving it the ability to address treatment, utilization and disposal concerns [ 9 ]. Also, it can be grown in arid and semi-arid regions with poor soil quality, with a per hectare yield estimated to be many times greater than that of even tropical oil seeds [ 9 ].
Microalgae can be considered as a sustainable energy source of next generation biofuels [ 31 ]. Microalgae are able to create oil along the year. Microalgae produce oil is more compared to conventional crops. Microalgae yield 15— times greater oil for biodiesel production than traditional crops.
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Biodiesel yield from algal lipid is distinguished with a high biodegradable and non-toxic. Microalgae can cultivate in high amounts arrived to 50 times greater than that of switchgrass, which is the more growing terrestrial crop. Microalgae can complete the whole growth cycle in limited days by way of photosynthesis process that alters sun energy into chemical energy.
They grow in fresh water, seawater, wastewater or non-arable lands [ 5 ]. The cultivation of microalgae needs less water than other energy oil crops. Production of biodiesel from microalgae can fix CO 2. Microalgae cultivation has a higher CO 2 mitigation rate between Microalgae cultivation can use phosphorus and nitrogen as nutrients from wastewater resources. Therefore, microalgae can provide the additional advantage for wastewater bioremediation.
Furthermore, microalgal biodiesel can decrease the liberation of NO x. Microalgae yield significant by-products for instance H 2 , ethanol, biopolymers, carbohydrates, proteins, beautifying products, animal feed, enricher, biomass remains, etc. Improvement of microalgae does not need stimulant for growth.
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The warming value of microalgal biodiesel is greater than that of the other terrestrial plants. Algal biomass is a renewable resource that has the potential to supply a limited portion of international energy needs [ 36 ].
Biofuel - Wikipedia
Preference toward microalgae is due largely to its less complex structure, fast growth rate and high-oil content for some species This characteristics of the strain should be taken into consideration. There are greater than , types of algae, with varying ratios of three main types of molecule: protein, oils and carbohydrates. Types of algae great in carbohydrates in addition to oils create starches that can be liberated then fermented into ethanol; the residual proteins can be converted into animal grains [ 1 ]. Research into algae for the mass-production of oil is mainly focused on microalgae organisms capable of photosynthesis that are less than 0.
In the end of eighteenth century, Robert Koch was one of the first scientists focused on the isolation of microorganisms in pure culture, followed by Sergei Winogradsky who initiate the field of microbiology and he was responsible for the first isolation of microorganism. There are four main techniques for obtaining unialgal isolates: spraying, streaking, serial dilution and single-cell isolations [ 37 ]. Spraying and streaking are useful for single-celled, colonial or filamentous algae that will grow on an agar surface; cultures of some flagellates may also be founded by these methods.
A lot of flagellates and in addition to other forms of algae, must be separated by single-organism isolations or serial-dilution procedures. Spraying procedure, a stream of air is utilized to diffuse algal cells from a mixture onto the surface of a petri plate having solidified medium with agar for growth. Hold a pipette in both hands; the tip end is caught with a forceps so that the glass near the tip is within the flame of a Bunsen burner gas flame.
The pipette is held in the flame only until the glass becomes marginally soft. This is determined by testing for flexibility by moving the tip with the forceps. Then the pipette is removed from the flame and pulled out straight or at an angle so that there is a bend. You can differ the diameter of the fine pulled tip by altering the speed of pulling. You would need a fine diameter tip if you are trying to separate very small algae, but a bigger diameter tip is necessary for large cells.
Addition of antibiotics to the growth medium is necessary to prevent growth of cyanobacteria and other bacteria, while addition of germanium dioxide will inhibit diatoms growth. Treatment of culture, isolated algae, by an extensive washing procedure via one or more antibiotics is called axenic culture. Resistant stages such as zygotes or akinetes can be treated with bleach to kill epiphytes, and then planted on agar for germination.
Two basic alternatives for microalgae cultivation exist and their relative merits are the basis of ongoing debate. Microalgae cultivation using sunlight energy can be carried out in open ponds, covered ponds or closed photobioreactors, based on tubular, flat plate or other designs [ 38 ]. If this commitment is followed through and subsidies are removed, a fairer market in which algae biofuels can compete will be created. In , the U. House of Representatives passed a legislation seeking to give algae-based biofuels parity with cellulose biofuels in federal tax credit programs. This policy constitutes an amendment to the Federal property and administrative services act of and federal defense provisions in order to extend to 15 the number of years that the Department of Defense DOD multiyear contract may be entered into the case of the purchase of advanced biofuel.
Federal and DOD programs are usually limited to a 5-year period . The European Union EU has also responded by quadrupling the credits for second-generation algae biofuels which was established as an amendment to the Biofuels and Fuel Quality Directives . With algal biofuel being a relatively new alternative to conventional petroleum products, it leaves numerous opportunities for drastic advances in all aspects of the technology. Producing algae biofuel is not yet a cost-effective replacement for gasoline, but alterations to current methodologies can change this.
The two most common targets for advancements are the growth medium open pond vs. Below are companies that are currently innovating algal biofuel technologies. Founded in , Algenol Biofuels is a global, industrial biotechnology company that is commercializing its patented algae technology for production of ethanol and other fuels. Algenol's technology produces high yields and relies on patented photobioreactors and proprietary downstream techniques for low-cost fuel production using carbon dioxide from industrial sources.
Blue Marble Production is a Seattle-based company that is dedicated to removing algae from algae-infested water. This in turn cleans up the environment and allows this company to produce biofuel. Rather than just focusing on the mass production of algae, this company focuses on what to do with the byproducts.
This water is then pumped back into their system. The gas produced as a byproduct of algae will also be recycled by being placed into a photobioreactor system that holds multiple strains of algae. Whatever gas remains is then made into pyrolysis oil by thermochemical processes. Not only does this company seek to produce biofuel, but it also wishes to use algae for a variety of other purposes such as fertilizer, food flavoring, anti-inflammatory, and anti-cancer drugs.
Solazyme is one of a handful of companies which is supported by oil companies such as Chevron. The effect is the production of triglycerides that are almost identical to vegetable oil. Solazyme's production method is said to produce more oil than those algae cultivated photosynthetically or made to produce ethanol. Oil refineries can then take this algal oil and turn it into biodiesel, renewable diesel or jet fuels. The Nimitz also used gallons of HRJ5 jet biofuel. Sapphire Energy is a leader in the algal biofuel industry backed by the Wellcome Trust, Bill Gates' Cascade Investment, Monsanto, and other large donors.
Diversified Technologies Inc. This technology, called Pulsed Electric Field PEF technology, is a low cost, low energy process that applies high voltage electric pulses to a slurry of algae. This alternative method to intracellular extraction has shown the capability to be both integrated in-line as well as scalable into high yield assemblies. The Pulse Electric Field subjects the algae to short, intense bursts of electromagnetic radiation in a treatment chamber, electroporating the cell walls. The formation of holes in the cell wall allows the contents within to flow into the surrounding solution for further separation.
PEF technology only requires microsecond pulses, enabling a high-throughput approach to algal extraction. Origin Oils Inc. This system utilizes low energy lights in a helical pattern, enabling each algal cell to obtain the required amount of light. Each lighting element in the bioreactor is specially altered to emit specific wavelengths of light, as a full spectrum of light is not beneficial to algae growth.
This bioreactor also addresses another key issue in algal cell growth; introducing CO 2 and nutrients to the algae without disrupting or over-aerating the algae. This process takes the CO 2 and other nutrients, fractures them at extremely high pressures and then deliver the micron sized bubbles to the algae. This allows the nutrients to be delivered at a much lower pressure, maintaining the integrity of the cells. Proviron is a Belgian microalgae company that also operates in the United States. The company has been working on a new type of reactor using flat plates which reduces the cost of algae cultivation.
At AlgaePARC similar research is being conducted using 4 grow systems 1 open pond system and 3 types of closed systems. The company intends to team with some industrial partners to create a pilot plant using this process to make biofuel in industrial quantities. Qeshm Microalgae Biorefinery Co. QMAB's original pilot plant has been operating since , and has a 25, Litre capacity.
The main product of their microalgae culture is crude oil, which can be fractioned into the same kinds of fuels and chemical compounds.
Integrating Algae with Bioenergy Carbon Capture and Storage (ABECCS) Increases Sustainability
From Wikipedia, the free encyclopedia. Main article: Biodiesel. Main article: Butanol fuel. Main article: Vegetable oil refining. Main article: Aviation biofuel. Main article: Algaculture. See also: Culture of microalgae in hatcheries. Main article: Algal nutrient solutions. Main article: Wastewater treatment facility. Main article: Algae fuel in the United States. See also: List of algal fuel producers. Renewable energy portal Energy portal. Current Opinion in Biotechnology. Current status and potential for algal biofuels production PDF. IEA Bioenergy Task Renewable and Sustainable Energy Reviews.
Bioresource Technology. Archived from the original PDF on 27 February Gas 2. Retrieved 10 June Applied Energy. Energy Policy. Journal of the Royal Society Interface. The Washington Post. The Chatham Daily News. Archived from the original on 11 October Retrieved 18 June Retrieved 14 February Biomass Magazine. Retrieved 15 November Retrieved 5 August Forschungsdienst Sonderheft. Berichte der Deutschen Botanischen Gesellschaft. Large-scale culture of Chlorella. In: Brunel J. Prescott eds The culture of algae. Charles F.
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Algal culture. From laboratory to pilot plant. Algae for Biofuels and Energy. Retrieved 3 April Dunahay, J. Benemann, P. A look back at the U. Department of Energy's Aquatic Species Program — biodiesel from algae. Energy Conversion and Management. Applied Biochemistry and Biotechnology. Biofuels, Bioproducts and Biorefining. Doughman, Srirama Krupanidhi, Carani B. Sanjeevi Current Diabetes Reviews. Journal of the American Dietetic Association. Retrieved 20 January Retrieved 11 June Biotechnology Advances.
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Retrieved 26 March Thus, establishing the feasibility of algal biofuel production regardless of energy input will be an important step in providing the platform for optimization, and also for establishing promising lines for future research. This is essentially what has happened with first-generation biofuel where, despite the concerns over food prices, land use and so on, it has led to the development of infrastructure, policies, and know-how Scott et al.
Microalgae can contribute a significant portion of the renewable fuels that will be required by the Renewable Fuels Standard described in the Energy Independence and Security Act of the United States National Research Council a. Many different paths are possible to produce biofuel out of algal biomass. Continued research into strain or community of strain selection to maximize lipid content should continue, with emphasis on strains already noted for their high lipid content and growth rates, such as Nannochloropsis , Phaeodactylum, and Chlorella. Cultivation of algal biomass in both raceway ponds and PBRs comes with advantages and disadvantages, which are often not compatible with the next down process of harvesting.
PBRs show promise for minimizing resource waste and maximizing lipid content, but their increased cost makes them even more prohibitive than raceway ponds. On the other hand, raceway ponds end up with dilute biomass, which makes the harvesting very expensive. While several methods for extraction and processing are available, some are more promising than others are. The economics and sustainability of a viable algal-based fuel and chemical platform will depend upon a close integration of cultivation and conversion.
Hydrothermal liquefaction has shown to be a very promising possibility for such integration. With a low energy and chemical requirements as well as few processing steps, hydrothermal liquefaction could lead the way in biodiesel extraction methods. This form of extraction and processing could also allow coproducts to boost the potential profits from algal biomass. Algae could prove to be the biomass feedstock of the future beside the sugar. A spike in petroleum costs could cause algae to become economically feasible sooner rather than later. Continuing research and development are valuable due to the potential gains that can be made from both an energy production and an environmental protection standpoint.
The ability of algae to build a sustainable food—energy—water nexus, by treating wastewater, while simultaneously producing renewable energy and high-value chemicals, without interfering with the food supply chain is a promising aspect that could play into decision to commercialize algal-based biorefinery in the near future.
An attempt to get a working industrial scale plant, even with the notable economic infeasibility could also prove extremely valuable, as more information could be gained by such a venture, than is currently available and would not be obtained through research pathways. A large scale of sustainable algal-based biofuels and bioproducts system needs careful integration of biology, ecology, and engineering. This will ensure that careful assessment of the energy balances and ecological constraints are exercised despite the lack of real-economic data from a large-scale operation under prevailing ecological constraints.
Also requisite is the development of high-lipid-producing strains optimized with metabolic engineering under regional ecological conditions. However, integration of biology, ecology and engineering requires an effective collective effort of real-field experimentation that creates considerable challenges. For example, with metabolic engineering and nutrient starvation, quality and yield of lipid as well as high-value chemicals may be adjusted to have a positive impact of feasibility, regardless of energy input.
JA contributed in the processes such as biological systems, algal cultivation, and algal strains. SU: literature search on economics, preparation of some of the tables and figures, and preparing Additional file. YD: engineering analysis, ecological systems, chemical processes, and economic analysis, preparation of some of the tables and figures. PB: biological systems, algal cultivation and harvesting, and biochemical systems. WR: biological systems, algal strains, and biochemical systems. All authors read and approved the final manuscript. Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Skip to main content Skip to sections. Advertisement Hide. Download PDF. Bioresources and Bioprocessing December , Cite as. Integration of biology, ecology and engineering for sustainable algal-based biofuel and bioproduct biorefinery. Open Access. First Online: 30 November Despite years of concerted research efforts, an industrial-scale technology has yet to emerge for production and conversion of algal biomass into biofuels and bioproducts. The objective of this review is to explore the ways of possible integration of biology, ecology and engineering for sustainable large algal cultivation and biofuel production systems.
Beside the costs of nutrients, such as nitrogen and phosphorous, and fresh water, upstream technologies which are not ready for commercialization both impede economic feasibility and conflict with the ecological benefits in the sector. Focusing mainly on the engineering side of chemical conversion of algae to biodiesel has also become obstacle. However, to reduce the costs, one potential strategy has been progressing steadily to synergistically link algal aquaculture to the governmentally mandated reduction of nitrogen and phosphorous concentrations in municipal wastewater.
Recent research also supports the suppositions of scalability and cost reduction. Noticeably, less is known of the economic impact of conversion of the whole algae-based biorefinery sector with additional biochemical and thermochemical processes and integration with ecological constraints. This review finds that a biorefinery approach with integrated biology, ecology, and engineering could lead to a feasible algal-based technology for variety of biofuels and bioproducts.
Open image in new window. The type and quantity of lipids accumulated saturated, polyunsaturated fatty acids, glycolipids, and triacylglycerol depends on the microalgae species and the growth conditions. Nutrient N or P deficiency and high radiation can cause considerable increase in saturated and monosaturated fatty acids, which are mainly associated with storage of triglyceride acids TGA in microalgae.
When light irradiance is low, mainly phospholipids and glycolipids, which are polar lipids and associated with cell membranes, are synthesized Hu et al. Symbol Common name Systematic name Structure Mp. Also shown are lipid contents in nutrient deficient media, notably N and Silicon S , which have been shown to affect lipid content Nrel The dominant strains of algae that are commonly found in wastewater ponds include Euglenia, Scenedesmus, Selenastrum, Chlorella , and Actinastrum.
They are able to strip nutrients and organic matter from wastewater, grow rapidly, and produce a significant level of oil Lyon et al. It also has the potential to supply algal farms with a large source of non-potable water, which does not compete with municipal or conventional agricultural needs.
Linking algal growth with water remediation also makes biofuel production more tenable by offsetting the high costs of wastewater treatment. A synergistic model for an algae-based biofuel production coupled with the bioremediation of municipal and agricultural wastewaters addresses several economic bottlenecks to earlier algal systems and promotes value-added products, including a high-quality effluent in addition to biodiesel to improve the economic feasibility of algal biofuels Lyon et al.
Use of wastewaters for cultivation of microalgae can also substantially reduce the cost of production and reduce the requirement for freshwater. Optimum resources for algal cultivation Open ponds are cost-effective system and there is an important role for aquatic ecologists to help improve the operation and performance of the engineered biosystems for algal biomass cultivation Smith and Mcbride Contamination Because of potential invasions by other species from the local and regional environment, contamination of open-pond systems will be certain during long-term continuous operation.
Community of species Carefully screened mixed species communities, for example, the presence of heterotrophic flagellates micrograzers may enhance nutrient availability and, thus, may increase microalgal yield. Frequency of algal crop harvesting The cost of resource per unit volume of algal production increases with dilution rate as each algal cell contains a cell quota of essential chemical elements such as carbon, nitrogen and phosphorus.
Algal-based biofuel and bioproduct processes Allnutt and Kessler reviewed some of the most promising microalgae biomass growth technologies for sustainable microalgae production. Following growth, the algae undergo harvesting, extraction, and various conversion processes of esterification, anaerobic fermentation, gasification, pyrolysis, and hydrothermal liquefaction. The number and intensity of post harvesting processes depend on the desired product and will have positive impact on the feasibility of algal-based productions Ferrell and Sarisky-Reed ; Halim et al.
While there are many advantages for the PBRs, the major drawback is the high cost, which ranges from nearly threefold to an order of magnitude higher than raceway pond systems Richardson et al. This increased cost is mainly due to the additional expense of the materials needed for construction, as well due to cooling and pumping needs. However, it is worth noting that improved reactor design could help to mitigate some of these costs and greatly improve the outlook of PBR use in industry Dillschneider and Posten Reactor type Advantages Disadvantages Raceway Lower capital cost Lower annual cost Risk of contamination Lower productivity Photobioreactors: tubular, helical, tubularvertical, flat panel, cuboidal, stirred tank, air lift, bubble column tubular Effective light use Little risk of contamination More controlled environment Higher productivity and cell densities High gas transfer coefficients Easy CO 2 supply Lower land use Lower water loss Estimated 2.
Centrifugation and sedimentation may be costly for the production of biofuel and bioproducts. Allnutt and Kessler discussed the historical approaches and recent advances while comparing and contrasting the different methods with an engineering estimate of comparative costs. First, the algae must be concentrated by means of filtration, centrifugation, and flocculation Mercer and Armenta Following this step, the algae may need to be dried, milled or pretreated in some other way such as microwaving, chemical treatment or milling to improve lipid extraction Harun et al.
Flocculation may be a cost-effective method Vandamme et al. Natural settling and centrifugation Jorquera et al. Harvested via flocculation Lardon et al. Harvested via flocculation Liu and Ma 3. Primary dewatering Resurreccion et al. Primary dewatering Frank et al. Bennion et al.
Jorquera et al. Primary dewatering.
Microwave-assisted extraction may reduce the cost of dewatering and extracting of dry algae. As heat is produced, water vapor formed within the cell ruptures the cell wall increasing the extraction yield Bahadar and Bilal Khan ; Balasubramanian et al. However, at scale-up, the cost may be limiting factor for this application.
Rarefaction and compression waves induced by the ultrasound above audible frequency, e. Ultrasound-assisted extraction can be cost effective and reduce the extraction time compared with conventional mechanical disruption, since the cavitation by the ultrasonic wave can rupture the cell wall and help improve the solvent extraction Mercer and Armenta ; Metherel et al. A sudden drop in osmotic pressure can similarly burst wet algae cells and can increase lipid recovery up to two times with polar and non-polar solvent, depending on the cell wall properties Mercer and Armenta ; Yoo et al.
Enzymatic treatment to disrupt cell walls of wet algae is also a promising alternative. This method causes minimal damage to lipid and hydrocarbons, but requires long cycle time and dependent on the strains being disrupted Ghasemi Naghdi et al. In contrast, the application-free nitrous acid HNO 2 —N, renewable chemical is another example of a pretreatment method that can lead to oxidative damage of cellular molecules prior to extraction, thus reducing the final quality of the fuel Bai et al.
Aqueous pores in the cell walls can be created by applying a pulsed electric field in the cells. This increases mass transfer and hence improves the lipid extraction Sommerfeld et al. Supercritical CO 2 extraction can also be used as an alternative and green solvent to extract triglyceride acid TGA and other lipids faster. However, the cost of technique is very high Bahadar and Bilal Khan Santana et al. Sahena et al. Extra unit operations are not needed Sahena et al.
During solvent removal operations, these polar substances form polymers, which lead to discoloration of the extract No such possibility exists since CO 2 is highly selective and no chance of polar substances forming polymers exists Sahena et al. Fischer—Tropsch synthesis is another well-known indirect chemical process for producing biofuel from biosyngas containing mainly CO and H 2 and produced from gasification of a biomass. The energy return on investment EROI is an important measure to determine the energy efficiency of the algae biofuels.
Energy ratio greater than unity refers to a positive energy balance and should be achieved. EROI values for algal biofuels are generally lower than unity.
Ketzer et al. The wide variation of EROI results from 0. Several useful life cycle assessment LCA studies are available that assess the energy balance and environmental impacts of large-scale algae-to-energy systems. However, these studies are theoretical because there is no full-scale commercial algae cultivation system in operation and comparing different life cycle analysis with one another is difficult.
Most of the reviewed LCA studies focus on the energy balance and greenhouse gas GHG emissions to determine the sustainability of algae-to-energy production. Data for allocation-related questions would be valuable for LCA for systems with complex interdependencies and with multi inputs and outputs, and recycle streams. Stochastic tools such as Monte Carlo analysis can be used for estimating a range of output values from a series of input variables.
Minimizing the possible subjective system boundary interpretation of data can similarly be achieved through performing sensitivity analyses to quantify the interdependency between inputs and outputs of individual and combined processes. Beside the economics analysis, sustainability metrics should also be an integral part of the feasibility analysis in a multi-criteria Pugh decision matrix Matzen et al. Sensitivity analysis Especially, the accumulated effects of the parameters for cultivation, harvesting, extraction may be useful for cost assessment Davis et al.
BioBreak model One method for estimating the economic viability of biofuels is the biofuel breakeven model or bioBreak.