Nannochloropsis and biofuels

Last updated
Oil accumulation in Nannochloropsis cultures. In red the chlorophyll, in yellow the oil. In the majority of the cells of this culture oil represents a substantial fraction of the cell volume. The picture was shot using a confocal microscope by Elisa Corteggiani Carpinelli and the method used is the same described in Corteggiani Carpinelli, E. et al., (2013) NannochloropsisMinusNitrogenNileRed.jpg
Oil accumulation in Nannochloropsis cultures. In red the chlorophyll, in yellow the oil. In the majority of the cells of this culture oil represents a substantial fraction of the cell volume. The picture was shot using a confocal microscope by Elisa Corteggiani Carpinelli and the method used is the same described in Corteggiani Carpinelli, E. et al., (2013)

Nannochloropsis is a genus of alga within the heterokont line of eukaryotes, that is being investigated for biofuel production. One marine Nannochloropsis species has been shown to be suitable for algal biofuel production due to its ease of growth and high oil content (28.7% of dry weight), mainly unsaturated fatty acids and a significant percentage of palmitic acid. It also contains enough unsaturated fatty acid linolenic acid and polyunsaturated acid (>4 double bonds) for a quality biodiesel. [1]

Contents

Conditions that lead to oil content increase

Oil productivity is defined as the oil produced by the algae per day per liter of culture, which is dependent on both growth rate and lipid content. Growth rate indicates how rapid the algae grow and lipid content indicates the percentage of dry weight that is lipid. [2] In most of the studies, these two factors are investigated independently. Under normal growth conditions, Nannochloropsis does not reach its optimal oil production. Several conditions, including stress conditions, have been reported to increase oil content in Nannochloropsis.

Nitrogen deprivation

Nitrogen is essential for algal growth. Within a cell, nitrogen is involved in synthesizing amino acids, nucleic acids, chlorophyll, and other nitrogen-containing organic compounds. [3] In a study in which 30 different microalgal strains were screened, one Nannochloropsis strain was shown to obtain 60% lipid content after nitrogen deprivation, up from 30% under normal growth conditions. [4] This strain was selected for further scale-up experiments in a photobioreactor under natural sunlight. Lipid productivity increased to 204 milligram per liter per day(mg/L/day) under nitrogen starvation conditions, almost twice as much as the 117 mg/L/day under sufficient nutrition conditions. Based on these results, a two-phase cultivation process, with a nutrient sufficient phase to rapidly increase number of cells prior to a nitrogen deprived phase to boost lipid content, was found to produce more than 90 kg of lipid per hectare per day in outdoor cultures. I, depending on sun light conditions. [4]

Carbon dioxide aeration

Algae play an important role in earth's carbon cycle. Algae generate large deposits of carbonate minerals and organic compounds that are resistant to microbial breakdown, thereby contributing to the reduction of CO2 level in the atmosphere, making the earth more habitable for other organisms. [3] The CO2 concentration also has an effect on algae growth and lipid content. In Nannochloropsis oculata, the effect of CO2 concentration on biomass production and lipid accumulation was investigated. The results showed that the lipid content of N. oculata increased from 30.8% to 50.4% upon 2% CO2 aeration. Thus, this algal strain is recommended to be grown with 2% CO2 to maximize lipid production. [5]

Blue light and Ultraviolet A (UV-A)

A light-acquisition problem exists for aquatic algae since submergence can reduce light intensity and dampen photosynthesis. For land plants, full-spectrum of sunlight, from blue to red light, is available for chlorophyll absorption. However, red light is absorbed in the few meters of water closest to the surface of an aquatic environment and the light environment beneath these few meters is mainly blue-green in quality. Algal cells are likely to be transported to such depth of water, and many have evolved a mechanism to better absorb blue-green light. [3] A Nannochloropsis species isolated from Singapore's coastal water was investigated under different light wavelengths (red, green, blue, and white) and intensities to determine the optimal condition for biomass productivity and lipid production. The maximum fatty acid yield was achieved for both phototrophic (sunlight is the only energy source) and mixotrophic (utilize both sunlight and energy from carbon source) cultures at 55.15 and 111.96 mg/L, respectively, under cell exposure to blue light (470 nm). The biomass productivity of the algae also peaked under blue light for both cultures. [6]

In another study, UV-A (320 - 400 nm) was added to the photosynthetically active light spectrum (400 - 700 nm) to culture Nannochloropsis in order to study the effect of UV-A on growth and lipid accumulation. The results showed that modulated UV-A usage can lead to an increase in growth rate. [7]

Alginate oligosaccharides

Alginate, or alginic acid, is a natural acidic linear polysaccharide derived from seaweed. It is composed of α-L-guluronate and β-D-mannuronate. Bulk alginate is widely used in the food industry and for medical purposes due to its unique characteristics such as high viscosity in aqueous solution and gel-forming property in the presence of calcium ions. Previous studies have also shown that alginate oligosaccharides may act as growth promoting agents on some plant cells. [8] The effect of an alginate oligosaccharide mixture (AOM) on N. oculata was studied. The growth rate of this alga was significantly increased by AOM. Moreover, AOM appeared to alleviate the algicidal effect of Cu2+ significantly. These results suggests that AOM can be used a growth promoting supplement for N. oculata culture. [9]

Temperature

Temp has significant impact on algal growth rate, cell size, and biochemical composition. Either in natural habitats of algae or in controlled growth systems, temperature will vary. In a study on the effect of temperature on growth rate and lipid content, temperature showed no significant relation with Nannochloropsis sp. growth rate between 15 °C and 30 °C. However, another algal species in the same study, Isochrysis galbana, showed increased growth rate as the temperature increased from 15 °C to 30 °C. In many algal species, increased lipid content is also observed under increased temperature. [10]

Culture technologies

Different culture technologies are being tested with Nannochloropsis to determine most cost-effective culture methods.

Helical-tubular photobioreactor

Tubular systems are the most widely used commercial culture systems. They are usually made of polypropylene acrylic or polyvinylchloride pipes which have small internal diameters and an air pump that generates bubbles to mix and agitate the culture. They usually use artificial light but some models use natural light. The major disadvantages of this type of system, varying among individual systems, are high space requirements, cleaning, low efficiency, low gas transfer, and hydrodynamic stress. Several other problems also occur, including growth of the algae on the tube wall leading to blockage of light, high oxygen concentration inhibition of growth, and limits on the length of the tube in single run. Coiled systems were developed mainly to improve space utilization. The main advantages are: 1) large ratio of culture volume to surface area and optimized light penetration depth; 2) easy control over temperature and contaminants; 3) easy spatial distribution of fresh air and CO2; 4) better CO2 transfer through the culture; and 5) automated sensor providing cell concentration reads. [11]

Open pond and flat-plate photobioreactor

Raceway ponds are shallow ponds between 10 and 50 cm deep. They are less expensive to build compared to photobioreactors, and have low-energy-consuming paddlewheels to mix the circulate the culture. The culture is open to the atmosphere, thus allowing liquid evaporation to stabilize the temperature. They are widely used to culture several algae and cyanobacteria. However, only limited types of microalgae can be grown in open ponds. Other disadvantages include large area required, low efficiency of light utilization, poor gas/liquid transfer, no temperature control, high risk of contamination, and low final density of culture. [12]

Flat-plates are a closed system such as helical-tubular photobioreactor. They have a flat surface screen made of glass or optical light film for the even reception of light. A study compared the cultures of Nannochloropsis sp. in open ponds and photobioreactors, tubular and flat-plate. Horizontal tubular photobioreactor was not shown to be economically viable. Both open pond and flat-plate photoreactors were proven to be feasible, given that the lipid content of biomass could be increased to 60%. However, neither system is competitive due to the low cost of petroleum. [12]

Fed-batch culture

Some algae can grow faster under mixotrophic conditions rather than under photoautotrophic conditions. Under mixotrophic conditions, both light and a carbon substrate such as sugars can provide energy for cell growth. Although adding glucose increased the growth rate of the algal culture, it also adds extra cost to algal lipid production. This needs to be further studied to determine economical feasibility. [13]

Flue gas method

A unique bio-technology-based environmental system can utilize flue gas from coal burning power plants. This method is reported to decrease the cost of algae production significantly. It also absorbs excessive CO2, thus alleviating greenhouse effect. [14]

Conversion to biodiesel or biofuel

Several different technologies were reported to convert algal culture into biofuel or biodiesel.

Direct transesterification

A direct transesterification of Nannochloropsis biomass to biodiesel production can be achieved using either microwave or ultrasound radiation. The microwave method was shown to be the simplest and most efficient method for one-stage direct transesterification. [14]

Direct pyrolysis and catalytic pyrolysis

In a recent study, Nannochloropsis sp. cells was pyrolyzed. The results showed that bio-oils obtained from catalytic pyrolysis had lower oxygen content and higher heating value than those from direct pyrolysis. The catalytic pyrolysis product mainly contained aromatic hydrocarbons. These properties make Nannochloropsis residue a very promising candidate for algal fuel production. [15]

See also

Related Research Articles

<span class="mw-page-title-main">Spirulina (dietary supplement)</span> Blue-green algal genus (cyanobacteria) used in food

Spirulina is a biomass of cyanobacteria that can be consumed by humans and animals. The three species are Arthrospira platensis, A. fusiformis, and A. maxima.

<span class="mw-page-title-main">Microalgae</span> Microscopic algae

Microalgae or microphytes are microscopic algae invisible to the naked eye. They are phytoplankton typically found in freshwater and marine systems, living in both the water column and sediment. They are unicellular species which exist individually, or in chains or groups. Depending on the species, their sizes can range from a few micrometers (μm) to a few hundred micrometers. Unlike higher plants, microalgae do not have roots, stems, or leaves. They are specially adapted to an environment dominated by viscous forces.

<span class="mw-page-title-main">Algaculture</span> Aquaculture involving the farming of algae

Algaculture is a form of aquaculture involving the farming of species of algae.

Pyrolysis oil, sometimes also known as bio-crude or bio-oil, is a synthetic fuel under investigation as substitute for petroleum. It is obtained by heating dried biomass without oxygen in a reactor at a temperature of about 500 °C (900 °F) with subsequent cooling. Pyrolysis oil is a kind of tar and normally contains levels of oxygen too high to be considered a pure hydrocarbon. This high oxygen content results in non-volatility, corrosiveness, immiscibility with fossil fuels, thermal instability, and a tendency to polymerize when exposed to air. As such, it is distinctly different from petroleum products. Removing oxygen from bio-oil or nitrogen from algal bio-oil is known as upgrading.

<span class="mw-page-title-main">Photobioreactor</span> Bioreactor with a light source to grow photosynthetic microorganisms

A photobioreactor (PBR) refers to any cultivation system designed for growing photoautotrophic organisms using artificial light sources or solar light to facilitate photosynthesis. PBRs are typically used to cultivate microalgae, cyanobacteria, and some mosses. PBRs can be open systems, such as raceway ponds, which rely upon natural sources of light and carbon dioxide. Closed PBRs are flexible systems that can be controlled to the physiological requirements of the cultured organism, resulting in optimal growth rates and purity levels. PBRs are typically used for the cultivation of bioactive compounds for biofuels, pharmaceuticals, and other industrial uses.

<i>Scenedesmus</i> Genus of green algae

Scenedesmus is a genus of green algae, in the class Chlorophyceae. They are colonial and non-motile. They are one of the most common components of phytoplankton in freshwater habitats worldwide.

Auxenochlorella protothecoides, formerly known as Chlorella protothecoides, is a facultative heterotrophic green alga in the family Chlorellaceae. It is known for its potential application in biofuel production. It was first characterized as a distinct algal species in 1965, and has since been regarded as a separate genus from Chlorella due its need for thiamine for growth. Auxenochlorella species have been found in a wide variety of environments from acidic volcanic soil in Italy to the sap of poplar trees in the forests of Germany. Its use in industrial processes has been studied, as the high lipid content of the alga during heterotrophic growth is promising for biodiesel; its use in wastewater treatment has been investigated, as well.

<i>Choricystis</i> Genus of algae

Choricystis is a genus of green algae in the class Trebouxiophyceae, considered a characteristic picophytoplankton in freshwater ecosystems. Choricystis, especially the type species Choricystis minor, has been proposed as an effective source of fatty acids for biofuels. Choricystis algacultures have been shown to survive on wastewater. In particular, Choricystis has been proposed as a biological water treatment system for industrial waste produced by the processing of dairy goods.

<span class="mw-page-title-main">Algae fuel</span> Use of algae as a source of energy-rich oils

Algae fuel, algal biofuel, or algal oil is an alternative to liquid fossil fuels that uses algae as its source of energy-rich oils. Also, algae fuels are an alternative to commonly known biofuel sources, such as corn and sugarcane. When made from seaweed (macroalgae) it can be known as seaweed fuel or seaweed oil.

<i>Nannochloropsis</i> Genus of algae

Nannochloropsis is a genus of algae comprising six known species. The genus in the current taxonomic classification was first termed by Hibberd (1981). The species have mostly been known from the marine environment but also occur in fresh and brackish water. All of the species are small, nonmotile spheres which do not express any distinct morphological features that can be distinguished by either light or electron microscopy. The characterisation is mostly done by rbcL gene and 18S rRNA sequence analysis.

<span class="mw-page-title-main">Algae bioreactor</span> Device used for cultivating micro or macro algae

An algae bioreactor is used for cultivating micro or macroalgae. Algae may be cultivated for the purposes of biomass production (as in a seaweed cultivator), wastewater treatment, CO2 fixation, or aquarium/pond filtration in the form of an algae scrubber. Algae bioreactors vary widely in design, falling broadly into two categories: open reactors and enclosed reactors. Open reactors are exposed to the atmosphere while enclosed reactors, also commonly called photobioreactors, are isolated to varying extents from the atmosphere. Specifically, algae bioreactors can be used to produce fuels such as biodiesel and bioethanol, to generate animal feed, or to reduce pollutants such as NOx and CO2 in flue gases of power plants. Fundamentally, this kind of bioreactor is based on the photosynthetic reaction, which is performed by the chlorophyll-containing algae itself using dissolved carbon dioxide and sunlight. The carbon dioxide is dispersed into the reactor fluid to make it accessible to the algae. The bioreactor has to be made out of transparent material.

Nasrin Moazami is an Iranian medical microbiologist and biotechnologist. She received her Ph.D. in 1976 from the Faculty of Medicine at Laval University. Moazami is the pioneer of biotechnology and microalgae-based fuels in Iran.

<span class="mw-page-title-main">Culture of microalgae in hatcheries</span>

Microalgae or microscopic algae grow in either marine or freshwater systems. They are primary producers in the oceans that convert water and carbon dioxide to biomass and oxygen in the presence of sunlight.

Single cell oil, also known as Microbial oil consists of the intracellular storage lipids, triacyglycerols. It is similar to vegetable oil, another biologically produced oil. They are produced by oleaginous microorganisms, which is the term for those bacteria, molds, algae and yeast, which can accumulate 20% to 80% lipids of their biomass. The accumulation of lipids take place by the end of logarithmic phase and continues during station phase until carbon source begins to reduce with nutrition limitation.

Schizochytrium is a genus of unicellular eukaryotes in the family Thraustochytriaceae, which are found in coastal marine habitats. They are assigned to the Stramenopiles (heterokonts), a group which also contains kelp and various microalgae.

<span class="mw-page-title-main">Avigad Vonshak</span>

Avigad Vonshak is a Professor Emeritus at the French Associates Institute for Agriculture and Biotechnology of Drylands at the Jacob Blaustein Institutes for Desert Research at Ben-Gurion University of the Negev, Israel.

Sammy Boussiba is a professor emeritus at the French Associates Institute for Agriculture and Biotechnology of Drylands at the Jacob Blaustein Institutes for Desert Research at Ben-Gurion University of the Negev, Israel.

<i>Chlorella vulgaris</i> Species of green alga

Chlorella vulgaris is a species of green microalga in the division Chlorophyta. It is mainly used as a dietary supplement or protein-rich food additive in Japan.

Algal viruses are the viruses infecting photosynthetic single-celled eukaryotes, algae. As of 2020, there were 61 viruses known to infect algae. Algae are integral components of aquatic food webs and drive nutrient cycling, so the viruses infecting algal populations also impacts the organisms and nutrient cycling systems that depend on them. Thus, these viruses can have significant, worldwide economic and ecological effects. Their genomes varied between 4.4 to 560 kilobase pairs (kbp) long and used double-stranded Deoxyribonucleic Acid (dsDNA), double-stranded Ribonucleic Acid (dsRNA), single-stranded Deoxyribonucleic Acid (ssDNA), and single-stranded Ribonucleic Acid (ssRNA). The viruses ranged between 20 and 210 nm in diameter. Since the discovery of the first algae-infecting virus in 1979, several different techniques have been used to find new viruses infecting algae and it seems that there are many algae-infecting viruses left to be discovered

References

  1. ↑ Gouveia, L; Oliveira (4 Nov 2009). "Microalgae as a raw material for biofuels production". J Ind Microbiol Biotechnol. 36 (2): 269–74. doi: 10.1007/s10295-008-0495-6 . PMID   18982369.
  2. ↑ Huerlimann, R; de Nys, Heimann (1 Oct 2010). "Growth, Lipid Content, Productivity, and Fatty Acid Composition of Tropical Microalgae for Scale-Up Production". Biotechnol Bioeng . 107 (2): 245–57. doi:10.1002/bit.22809. PMID   20506156.
  3. 1 2 3 Graham, L (2009). Algae. USA: Pearson. ISBN   978-0-321-55965-4.
  4. 1 2 Rodolfi, L; Chini Zittelli; et al. (1 Jan 2009). "Microalgae for oil: strain selection, induction of lipid synthesis and outdoor mass cultivation in a low-cost photobioreactor". Biotechnol Bioeng . 102 (1): 100–12. doi:10.1002/bit.22033. PMID   18683258.
  5. ↑ Chiu, SY; Kao; et al. (Jan 2009). "Lipid accumulation and CO2 utilization of N. oculata in response to CO2 aeration". Bioresour Technol. 100 (2): 833–8. doi:10.1016/j.biortech.2008.06.061. PMID   18722767.
  6. ↑ Das, P; Lei; et al. (Feb 2011). "Enhanced algae growth in both phototrophic and mixotrophic culture under blue light". Bioresour Technol. 102 (4): 3883–7. doi:10.1016/j.biortech.2010.11.102. PMID   21183340.
  7. ↑ Forjan, E; Garbayo; et al. (17 Jul 2010). "UV-A mediated modulation of photosynthetic efficiency, xanthophyll cycle and fatty acid production of Nannochloropsis". Mar Biotechnol. 13 (3): 366–75. doi:10.1007/s10126-010-9306-y. hdl: 10272/2721 . PMID   20640472.
  8. ↑ Xu, X; Iwamoto (Sep 2003). "Root growth-promoting activity of unsaturated oligomeric uronates from alginate on carrot and rice plants". Biosci Biotechnol Biochem. 67 (9): 2022–5. doi: 10.1271/bbb.67.2022 . PMID   14519996. S2CID   917424.
  9. ↑ Yokose, T; Nishikawa; et al. (Feb 2003). "Growth-promoting effect of alginate oligosaccharides on a unicellular marine microalga, Nannochloropsis oculata". Biosci Biotechnol Biochem. 73 (2): 450–3. doi: 10.1271/bbb.80692 . PMID   19202274.
  10. ↑ Sayegh, FA; Montagnes (Feb 2011). "Temperature shifts induce intraspecific variation in microalgal production and biochemical composition". Bioresour Technol. 102 (3): 3007–13. doi:10.1016/j.biortech.2010.10.011. PMID   20970325.
  11. ↑ Briassoulis, D; Panagakis; et al. (Sep 2010). "An experimental helical-tubular photobioreactor for continuous production of Nannochloropsis sp". Bioresour Technol. 101 (17): 6768–77. doi:10.1016/j.biortech.2010.03.103. PMID   20400300.
  12. 1 2 Jorquere, O; Kiperstok (Feb 2010). "Comparative energy life-cycle analyses of microalgal biomass production in open ponds and photobioreactors". Bioresour Technol. 101 (4): 1406–13. doi: 10.1016/j.biortech.2009.09.038 . PMID   19800784.
  13. ↑ Xu, F; Cai; et al. (Sep 2004). "Growth and fatty acid composition of Nannochloropsis sp. grown mixotrophically in fed-batch culture". Biotechnol Lett. 26 (17): 1319–22. doi:10.1023/B:BILE.0000045626.38354.1a. PMID   15604757.
  14. 1 2 Koberg, M; Cohen; et al. (Mar 2011). "Bio-diesel production directly from the microalgae biomass of Nannochloropsis by microwave and ultrasound radiation". Bioresour Technol. 102 (5): 4265–9. doi:10.1016/j.biortech.2010.12.004. PMID   21208797.
  15. ↑ Pan, P; Hu; et al. (Jun 2010). "The direct pyrolysis and catalytic pyrolysis of Nannochloropsis sp. residue for renewable bio-oils". Bioresour Technol. 101 (12): 4593–9. doi:10.1016/j.biortech.2010.01.070. PMID   20153636.
This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.