Microalgae: A Promising Energy Source for

Internati onal Journal of Engineering Technol ogy Science and Research IJ ETS R www.ijetsr.com ISSN 2394 – 3386 Volume 2, S pecial Issue September 2015

Microalgae: A Promising Energy Source for Sustainable Development Romanchi Rastogi, Swarnima Agarwal, Santosh Kumar Mishra* Department of Biotechnology, IMS Engineering College, Ghaziabad, UP, India Abstract: Due to industrial growth and urbanization world energy crisis is increasing. It the is need of present scenario to explore new and renewable sources of energy that is ecofriendly and economically sustainable. Microalgae have been identified as one of the major renewable energy sources having potential to replace the fossil -based fuels. Algal biodiesel are technically and economically viable and have the advantage of requiring no additional lands with minimal water and nutrient use. However, commercial productions of microalgae biodiesel have certain limitations i.e. low biomass concentration and costly downstream processes. The viability of microalgae biodiesel production can be achieved by designing advanced photobioreactors with development of low cost technologies for effective biomass harvesting and oil extraction. Industrial production of microalgal biomass can also be accomplished by improving the genetic engineering strategies with enhanced lipid content. This review focuses prima rily on various cultivation conditions for optimum biodiesel production at large scale including techniques using genetic engineering approaches for maximum yield of biodiesel. Keyword: Biodiesel, Microalgae, Biofuel, Photobioreactors

1. Introduction Biofuel are produced as a result of biological processes, that use agriculture by-product as the sole carbon source via anaerobic digestion. Although fossil fuels are still the primary source of energy for the world’s developed nations, it is agreed that these traditional sources of energy cannot continue to power humanity’s growth into the future owing to their limited availability in the nature. The decreasing supply and rising demand results in escalation of the oil prices and the cost of other fossil fuels thus making them economically unsustainable.[Aleklett et al 2010] Sustainable biofuels are a necessity to ensure a constant and secure supply of energy for individuals and industry. Advanced biofuels are essential to reduce our dependency on fossil fuels and limit our impact on the environment. 1.1 Microalgae: What are they? Microalgae are prokaryotic or eukaryotic photosynthetic microorganisms that can live in harsh conditions and grow rapidly due to their unicellular or simple multicellular structure [Mata et al 2009]. Members of the phylum Cyanophyceae, commonly known as cyanobacteria or blue-green algae are the examples of prokaryotic microalgae. The eukaryotic microalgae capable of producing biodiesel at a commercial scale belong to the phyla Chlorophyta and Bacillariophyta [Li et al 2008, Li et al 2008] and Microalgae are quite diverse in nature and having presence in all existing earth ecosystems, whether it may be aquatic or terrestrial. This class represent vast species in a wide range of environmental conditions. This has been observed that nearly more than 50,000 species of this class exist, but only a limited number of around 30,000, have been studied and analyzed for research work as well as for commercial production of valuable product [Richmond A 2004] 1.2 Biology of Microalgae Algae are recognised as one of the oldest life-forms [Rawat I .et.al 2011] . They are primitive plants (thallophytes), i.e. lacking roots, stems and leaves. Algae structures are primarily for energy conversion without any development beyond cells, and their simple development allows them to adapt to prevailing environmental conditions and prosper in the long term [Zhou W.et.al 2011].The most important classes of microalgae involved in biodiesel production are: green algae (Chlorophyta), red algae (Rhodophyta) and diatoms (Bacillariophyta). Algae can either be autotrophic or .heterotrophic; the former require only inorganic compounds such as CO2, salts and a light energy source for growth; while the latter are nonphotosynthe tic

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Romanchi Rastogi, Swarnima Agarwal, Santosh Kumar Mishra

Internati onal Journal of Engineering Technol ogy Science and Research IJ ETS R www.ijetsr.com ISSN 2394 – 3386 Volume 2, S pecial Issue September 2015

therefore require an external source of organic compounds as well as nutrients as an energy source. Some photosynthetic algae are mixotrophic, i.e. they have the ability to both perform photosynthesis and acquire exogenous organic nutrients [Falkowski PG.et.al 1997]. For autotrophic algae, photosynthesis is a key component of their survival, whereby they convert solar radiation and CO2 absorbed by chloroplasts into adenosine triphosphate (ATP) and O2 the usable energy currency at cellular level, which is then used in respiration to produce energy to support growth [Zhou W.et.al 2011, Falkowski PG.et.al 1997]. 1.3 Need of microalgal biodiesel The sustainability and utility of a fuel product depends on its environmental, economic and social impacts throughout the product's entire life cycle. The future of algae biofuels is quite bright and promising in many ways. It has become increasingly obvious that continued reliance on fossil fuel energy resources is unsustainable, owing to both depleting world reserves and the greenhouse gas emissions associated with their use. Alternate energy resources akin to first generation biofuels derived from terrestrial crops such as sugarcane, sugar beet, maize and rapeseed place an enormous strain on world food markets, contribute to water shortages and precipitate the destruction of the world’s forests. Second generation biofuels derived from lignocellulosic agricultural and forest residues and from non food crop feedstocks address some of the above problems; however there is concern over competing land use or required land use changes. Therefore, based on current knowledge and technology projections, third generation biofuels specifically derived from microalgae are considered to be a technically viable alternative energy resource that is devoid of the major drawbacks associated with first and second generation biofuels. [Durga Madhab.et.al 2013] 1.4 Advantages of microalgal biodiesel Microalgae are a diverse group of single-celled organisms that duplicate by division. High-throughput technologies can be used to rapidly evolve strains. This can reduce processes that take years in crop plants, down to a few months in algae. Algae have ability to use efficiently CO2 , and are responsible for more than 40% of the global carbon fixation. The majority of this productivity coming from marine microalgae [Spolaore P.et.al 2006][Rodolfi L.et.al 2008]. Algae can produce biomass very rapidly, with some species doubling in as few as 6 hours, and in several cases exhibiting two doublings per day [Bozbas K. 2008] Algae production strains also have the potential to be bioengineered, allowing improvement of specific traits and production of valuable co-products, which may allow algal biofuels to compete economically with petroleum[Chisti Y 2007]. Algae are among the fastest-growing plants in the world, and about 50% of their weight is oil [Huang et al 2010]. Recent research data reveals that algae are quite successful when grown using wastewater and recycled nutrients from agricultural sources [Rawat et al 2011,Woertz et al 2009, Zhou et al 2011]. Despite the hurdles to the economically viable production of biofuels from algae, these organisms still represent one of the best optional energy sources among all available energy sources. A comparative study conducted between the characteristics of biodiesel and mineral oil yielded identical results as shown in the table below. Table1: Comparison of various parameters of diesel obtained from biological sources and from mineral resources. Parameters

Diesel standard

Biodiesel standard

Microalg al Biodiesel

Specific gravity, at 25o C

0.85 (at 15.5o C)

0.88 (at 15.5o C)

0.82

Moisture Content (%)

1.61

0.05% (max.)

0.05

Free fatty acid content (%)

-

-

0.98

Kinemat ic Viscosity (mm2 /s), at 40o C

1.3-4.1

1.9-6.0

3.96

Flash point (o C)

60 to 80

100 to 170

155

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Romanchi Rastogi, Swarnima Agarwal, Santosh Kumar Mishra

Internati onal Journal of Engineering Technol ogy Science and Research IJ ETS R www.ijetsr.com ISSN 2394 – 3386 Volume 2, S pecial Issue September 2015

2. Role of Microalgae in Biodiesel production Microalgae have ability to grow almost anywhere which requiring sunlight and some simple nutrients. Although the growth rates can be accelerated by the addition of specific nutrients and by increased aeration. The importance of microalgae also increases due to the fact that all, the microalgae can be produced throughout the year and therefore, quantity of oil production exceeds the yield in comparison to best oilseed crops, e.g. biodiesel yield of 58,700 l ha -1 for microalgae containing only 30% oil by wt., compared with 1190 l ha-1 for rapeseed or Canola [Schenk P et al 2008], 1892 l ha -1 for Jatropha [chisti Y 2007], and 2590 l ha -1 for Karanj (Pongamia pinnata) [Lele S] The rapid growth potential and various species of microalgae with oil content in the range of 20–50% dry weight of biomass is the another advantage for its choice as a potential biomass. The exponential growth rates can double their biomass in periods as short as 3.5 h [Deng et al 1999]. A significant advantage to environment is that algae cultivation does not require herbicides or pesticides application which is major water pollutants [Rodolfi L et al 2008]. In addition, these can also produce valuable co-products such as proteins and residual biomass after oil extraction, which may be used as feed or as fertilizer [Spolaore P et al 2006], or may be used for bioethanol or biomethane in fermentative processes [Bozbas K 2008]. Table 2: Total productivity of microalgae in terms of lipid content and biomass. Microalg ae species

Li pi d Content

Biomass Producti vity -1

References

-1

(% by dry weight)

(g l day )

Euglena Gracilis

14-20

0.13

[17,51]

Chlorella vulgaris

14-22

0.73

[18]

Botryococcus Braunii

25-75

0.25

[21,19, 20,22]

Ankistrodesmus sp.

28-40

0.34

[22]

Nannochloropsis sp.

31-68

0.17- 1.43

[24,20]

Dunaliella tertiolecta

36-42

0.098-0.12

[26,27]

2.1 Viability assessment of microalgae Important key characteristic for determining the viability of algal species is their growth characteristics. Growth rates and maximum growth densities must be characterized in terms of real-world growth conditions rather than laboratory conditions for newly isolated strains. Life cycle assessment studies are widely accepted by researchers to gain a clear idea of the real potential of a particular product that is being investigated Lifecycle assessment (LCA) is a technique to assess environmental impacts associated with all the stages of a product's life from cradle to grave (i.e., from raw material extraction through materials processing, manufacture, distribution, use, repair and maintenance, and disposal or recycling). 2.2. Cultivation of microalgae for commercial scale biodiesel production Microalgae cultivation is the first production step in the energy production system. According to the study of characteristic and function of microalgae, some scientific microalgae cultivation methods have been concluded. Microalgae which contain at least 30% lipids content can be used for biofuel production. Microalgae during photosynthesis can absorb large amounts of CO 2 to produce sugars and oxygen. 2.2.1 Cultivation Conditions for optimum production:

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Romanchi Rastogi, Swarnima Agarwal, Santosh Kumar Mishra

Internati onal Journal of Engineering Technol ogy Science and Research IJ ETS R www.ijetsr.com ISSN 2394 – 3386 Volume 2, S pecial Issue September 2015

The growth characteristics and composition of microalgae are known to significantly depend on the cultivation conditions [Chojnacka et al 2004] There are four major types of cultivation conditions that play significant role in the growth and multiplication of cell i.e. photoautotrophic, heterotrophic, mixotrophic and photoheterotrophic cultivation [Chojnacka et al 2004]. Phototrophic cultivation: Phototrophic cultivation occurs when the microalgae use light, such as sunlight, as the energy source, and inorganic carbon (e.g. carbon dioxide) as the carbon source to form chemical energy through photosynthesis [Huang et al 2010]. The major advantage of using autotrophic cultivation to produce microalgal oil is the consumption of CO2 as carbon source for the cell growth and oil production Heterotrophic cultivation: The situation when microalgae use organic carbon as both the energy and carbon source is called heterotrophic cultivation[Huang et al 2010]. This type of cultivation could avoid the problems associated with limited light that hinder high cell density in large scale photo bioreactors during phototrophic cultivation [Huang et al 2010]. Mixotrophic cultivation: Mixotrophic cultivation is when microalgae undergo photosynthesis and use both organic compounds and inorganic carbon (CO2) as a carbon source for growth.. Microalgae assimilate organic compounds and CO2 as a carbon source, and the CO2 released by microalgae via respiration will be trapped and reused under phototrophic cultivation [Mata et al 2009]. Photoheterotrophic cultivation: Photoheterotrophism, also known as photoorganitrophy, describes the metabolism in which light is required to use organic compounds as carbon source. The photoheterotrophic and mixotrophic metabolisms are not well distinguished, in particular they can be defined according to a difference of the energy source required to perform growth and specific metabolite production. 3. Industrial production of biodiesel Microalgal lipids are mostly neutral lipids with lower degree of unsaturation. This makes microalgal lipids a potential replacement for fossil fuel. Biodiesel is a mixture of fatty acid alkyl esters obtained by of vegetable oils or animal fats. Lipid containing feedstocks are composed of 90–98% of triglycerides and small amounts of mono and diglycerides, free fatty acids (1–5%), and residual amounts of phospholipids, phosphatides, carotenes, tocopherols, sulphur compounds, and traces of water [Bozbas et al 2008]. Transesterification is a multiple step reaction, including three reversible steps in series, where triglycerides are converted to diglycerides, then diglycerides are converted to monoglycerides, and monoglycerides are then converted to esters (biodiesel) and glycerol (by-product)[Mata et al 2009]. Biodiesel production from microalgal biomass is a sequential process that consists of the cultivation, harvest, oil extraction, and conversion of algal lipids into advanced biofuels. Most common methods are expeller/oil press, liquid–liquid extraction (solvent extraction), supercritical fluid extraction (SFE) and ultrasound techniques. Large scale production of biodiesel from microalgae is a sequential process comprising of cultivation and harvesting of microalgae , their processing for crude biodiesel extraction and finally their purification to give the finished oil. Fig.1 Large scale production of biodiesel by using microalgae as sole carbon source

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Romanchi Rastogi, Swarnima Agarwal, Santosh Kumar Mishra

Internati onal Journal of Engineering Technol ogy Science and Research IJ ETS R www.ijetsr.com ISSN 2394 – 3386 Volume 2, S pecial Issue September 2015

4.Challenges and limitation in large scale biodiesel production Although growth characteristics and composition of microalgae make them promising feedstocks for biodiesel production at large scale but producing microalgae biomass is generally more expensive than growing crops. Photosynthetic growth requires light, carbon dioxide, water and inorganic salts. Temperature must remain generally within 20 to 30 °C. To minimize expense, biodiesel production must rely on freely available sunlight, despite daily and seasonal variations in light levels [Christi et al 2007]. It has been argued that growing algae in bioreactors requires fossil fuels for the building of these bioreactors and for their operational activities [Reijnders et al 2008]. The crucial economic challenge for algae producers is to discover low cost oil extraction and harvesting methods [Singh et al 2010]. 5. Recent Advances in microalgal biodiesel technology Recent scientific and research data reveals that innovations in the field of biodiesel production are mainly concerned with upstream, midstream and downstream processes. Presently the most effective methods of producing biofuels from algal feedstocks are carried out by fermentation of microalgae to bioethanol and production of biodiesel via transesterification of microalgal biomass. Membrane based processes have also come to the center of attention in various applications including alga l biomass processes due to several advantages, e.g., high efficiency under mild operating conditions, compact equipment, low operational time/energy, ease of integration with other processes, and high process scale-up capacity [Shirazi et al 2013, Bilad et al 2014, Shirazi and Kargari et al 2014a, Shirazi and Kargari et al 2014b, Shirazi et al 2015, Shirazi et al 2014]. Among the mainstream process of biodiesel production using microwave reactors also come in focus which utilizes microwave irradiation to transfer energy directly into reactants and consequently accelerate the rate of reaction [Barnard et al 2007]. Several techniques and processes were recently optimized in downstream processing including productivity and yield, its purification. Introduction of a novel soluble hybrid nanocatalyst is a promising combustion improver [Mirzajanzadeh et al 2015]. The hybrid nanocatalyst containing cerium oxide owing to the high surface area of the soluble nano-sized catalyst particles and their proper distribution along with catalytic oxidation reaction, resulted in significant overall improvements in the combustion reaction which reduces pollutants, i.e., NO x, CO, hydrocarbons, and Soot were reduced by up to 18.9%, 38.8%, 71.4%, and 26.3%, respectively. Hydrothermal conversion of wet, whole algae via hydrothermal liquefaction and carbonization has most recently drawn significant attention of scientists and researchers around the world.[Broch et al 2013] Although the application of genetic engineering to improve energy production phenotypes in eukaryotic microalgae is in its infancy, significant advances in the development of genetic manipulation tools have recently been achieved with microalgal model systems and are being used to manipulate central carbon metabolism in these organisms 6.Conclusion In the current scenario, biodiesel derived from the microalgae are the only sustainable and renewable fuel that is capable of meeting the energy demands of the world and can be considered as a substitute for fossil fuels. Microalgal biodiesel has several advantages as compared to conventional fossil fuels. With the concept of green energy gaining momentum, biodiesel provide the biggest advantage of Greenhouse gas mitigation. The primary strategies for the production of biodiesel using microalgae include the identification of the species with high oil content. The second step consists of development of efficient reactor system for optimum production of microalgae. The designing and development of efficient reactor system for microalgae culture presents a challenge due to high costs involved. The advances in this technology will be effective only if the economic challenges in upstream and downstream processing could be negated. However, despite these challenges, microalgae represent a promising feedstock for the renewable fuel source.

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7.References                .          

Aleklett, K., Hook, M., Jakobsson, K., Lardelli, M., Snowden, S., Soderbergh, B. ―The Peak o f the Oil Age – Analyzing the world oil production Reference Scenario in World Energy Outlook 2008.‖Energy Policy. 2010. Vo lu me 38(3). p. 1398-1414. Ayhan Demirbas,M. Fatih Demirbas Importance of algae oil as a source of biodiesel. Energy Conver Manag Energy Conversion and Management (Impact Factor: 4.38). 01/2011; 52(1):163-170. DOI: 10.1016/ j.enconman.2010.06.055 Azocar L., Ciudad G., Heip ieper H.J., Munoz R. and Navia R., Lipase-catalyzed process in an anhydrous mediu m with enzy me reutilization to produce biodiesel with low acid value, Journal o f Bioscience and Bioengineering, 112, 583-589 (2011) Barnard, T.M ., Leadbeater, N.E., Boucher, M.B., Stencel, L.M., Wilhite, B.A., 2007. Continuous -flow preparation of biodiesel using microwave heating. Energy Fuels. 21(3), 1777 -1781. Barupal D.K., Kind T., Kothari S.L., Lee D.Y. and Fiehn O., Hydrocarbon phenotyping of algal species using pyrolysis-gas chromatography mass spectrometry, BM C Biotechnology, 10, 1472 -6750 (2010) Bilad, M.R., Arafat, H.A., Van keleco m, I.F.J., 2014. Membrane techno logy in microalgae cultivation and harvesting: a review. Biotechnol. Adv. 32(7), 1283-1300 Bozbas K. Biodiesel as an alternative motor fuel: production and policies in the European Union. Renewable and Sustainable Energy Reviews 2008;12: 542–52 Brennan L, Owende P. Bio fuels fro m microalgae—A review of technologies for production, processing, and extractions of biofuels and co-products. Renew Sustain Energy Rev (2009), doi:10.1016/j.rser.2009.10.009 Broch, A mber, Jena, Umakanta, Kent,S. Hoekman and Langford, Joel. Analysis of Solid and Aqueous Phase Products from Hydrothermal Carbonizat ion of Whole and Lipid -Extracted Algae Energies 2014, 7, 62-79; doi:10.3390/en7010062 Chisti Y. Biodiesel fro m microalgae. Biotechnol Adv 2007; 25(3):294–306. Chojnacka, K., Marquez-Rocha, F.J., 2004. Kinetic and stoichiometric relationships of the energy and carbon metabolism in the culture of microalgae. Biotechnology 3, 21– 34 Droop, S. ―Book Review: Lee RE. 1999. Phycology. 3rd edition. Cambridge University Press. Annals of Botany 85.3 (2000): 408– 409. Web. Durga Madhab Mahapatra & H. N. Chanakya & T. V. Ramachandra Euglena sp. as a suitable source of lipids for potential use as biofuel and sustainable wastewater treatment Springer Science+Business Media Dordrec ht 2013 J Appl Phycol DOI 10.1007/s10811-013-9979-5 Deng, M.-D., and Coleman, J. R. (1999). Ethanol synthesis by genetic engineering in cyanobacteria. Appl. Environ. Microbiol. 65, 523–528. Dexter, J., and Fu, P. (2009). Metabolic engineering of cyanobacteria for ethanol production. Energy Environ. Sci. 2, 857. doi:10.1039/b811937f Hirano A, Ueda R, Hirayama S, Ogushi Y. CO2 fixation and ethanol production with microalgal photosynthesis and intracellu lar anaerobic fermentation.Energy 1997;22(2–3):137– 42. Huang, G.H., Chen, F., Wei, D., Zhang, X.W., Chen, G., 2010. Biodiesel production by microalgal biotechnology. Appl. Energ. 87, 38– 46. Lele S. Indian Green Energy Awareness Center, http://www.svlele.co m/karanj.ht m Li Y, Wang B, Wu N, Lan CQ. Effects of nitrogen sources on cell growth and lipid production of Neochloris oleoabundans. Applied Microbio logy and Biotechnology 2008; 81(4):629–36 Li Y, Hors man M, Wu N, Lan CQ, Dubois -Calero N. Biofuels fro m microalgae. Biotechnology Progress 2008;24(4):815–20 Li Y, Han D, Hu G, Dauvillee D, So mmerfeld M, Ball S, Hu Q: Ch lamydomonas starchless mutant defective in ADP-g lucose pyrophosphorylase hyper-accumulates triacylg lycerol. Metab Eng 2010, 12:387-391 Leduc S., Natarajan K., Dotzaue E., McCallu m I. and Obersteiner M ., Optimizing biodiesel production in India, Applied Energy, 86, 125–131 (2009) Mata TM, et al. Microalgae for biodiesel production and other applications: A review. Renew Sustain Energy Rev (2009), doi:10.1016/ j.rser.2009.07.020 Metting FB. Biodiversity and application of microalgae. J Ind M icrobiol 1996; 17(5–6):477–89. Miao X. and Wu Q., Biodiesel production from heterotrophic microalgal oil, Bioresource Technology, 97, 841846 (2006)

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Mirzajanzadeh, M., Tabatabaei, M., Ardjmand, M., Rashidi, A., Ghobadian , B., Barkhi, M., Pazouki, M., 2015. A novel soluble nano-catalysts in diesel–biodiesel fuel b lends to improve diesel engines performance and reduce exhaust emissions. Fuel. 139, 374- 382 Patil V., Tran K.Q. and Giselrod H. R., To wards Sustainable Production of Biofuels fro m M icroalgae: A Review, Int. J. Mo l. Sci., 9, 1188-1195 (2008) P.G. Falkowski & A mp; J.A. Raven (1997) Aquatic Photosynthesis. Pp. Viii 375. Blackwell Science, Oxford. ISBN 0-86542-387-3. Journal of Ecology J Ecology 86.3 (1998): 543–543. Web. Preparation and Optimizat ion of Biodiesel Production from Mixed Feedstock Oil Kaniz Ferdous, M. Rakib Uddin, M. Rah im Uddin, Maksudur R. Khan, M. A.Islam Radakovits R, Eduafo PM, Posewit z MC: Genetic engineering of fatty acid chain length in Phaeodactylum tricornutum. Metab Eng 2011, 12:89-95. Rawat I, Ku mar RR, Mutanda T, Bu x F: Dual ro le or microalgae: phytoremed iation of do mestic wastewater and biomass production for sustainable biofuels production. Appl Energ 2011, 88:3411-3424 Reijnders L. Do b iofuels fro m microalgae beat biofuels fro m terrestrial p lants? Trends Biotechnol 2008;26:349– 350. Rich mond A. Handbook of microalgal culture: biotechnology and applied phycology. Blackwell Science Ltd; 2004. Rodolfi L, Zittelli GC, Bassi N, Padovani G, Biondi N, Bonini G, et al. Microalgae for oil: strain selection, induction of lipid synthesis and outdoor mass cultivation in a low-cost photobioreactor. Biotechnol Bioeng 2008;102(1):100–12. Rodolfi L., Zittelli G.C., Bassi N., Padovani G., Biondi N., Bonin i G. and Tredici M.R., Microalgae for Oil: Strain Selection, Induction of Lip id Synthesis and Outdoor Mass Cultivation in a Lo w-Cost Photobioreactor, Biotechnology and Bioengineering, 102, 100-112 (2009) Schenk P, Thomas-Hall S, Stephens E, Marx U, Mussgnug J, Posten C, et al.Second generation biofuels: high efficiency microalgae for b iodiesel production. Bio Energy Res 2008; 1(1):20– 43. Shimizu Y., M icroalgal metabolites, Current Op inion in M icrobio logy, 6, 236–243 (2003) Shirazi, M.M.A., Kargari, A., Tabatabaei, M., 2015. Sweeping gas membrane distillation (SGMD) as an alternative for integration of b ioethanol processing: study on a commercial memb rane and operating parameters. Chem. Eng. Co mmun. 202(4), 457-466. Shirazi, M.M.A., Tabatabaei, M., 2014. Bio fuels, In: Sharma, U.C., Ku mar, S., Prasad, R. (Eds.), Energy Science and Technology (Vol. 6), Studiu m Press LLC, USA Shirazi, M.M.A., Bastani, D., Kargari, A., Tabatabaei, M., 2013a. Characterization of polymeric membranes for memb rane distillation using atomic force microscopy. Desalin. Water Treat. 51(31-33), 6003-6008. Shirazi, M.M.A., Kargari, A., Tabatabaei, M., 2014b. Evaluation of commercial PTFE memb ranes in desalination by direct contact membrane distillat ion. Chem. Eng. Process. Process Int ensif. 76, 16-25. Shirazi, M.M.A., Kargari, A., Tabatabaei, M., Is mail, A.F., Matsuura, T., 2014c. Assessment of atomic force microscopy for characterization of PTFE membranes for memb rane distillat ion (MD) process. Desalin. Water Treat. 1-10 Singh J, Gu S. Co mmercialization potential of microalgae for biofuels production. Renew Sustain Energy Rev. 2010;14:2596–2610 Spolaore P, Joannis-Cassan C, Duran E, Isambert A. Co mmercial applications of microalgae. J Biosci Bioeng 2006;101(2):87–96. Woertz I, Feffer A, Lundquist T, Nelson Y: Algae grown on dairy and municipal wastewater for simultaneous nutrient removal and lipid production for b iofuel feedstock. J Environ Eng 2009, 135:1115-1122. Wu S, Xu L, Huang R, Wang Q: Improved biohydrogen production with an exp ression of codon-optimized hemH and lba genes in the chloroplast of Chlamydomonas reinhardtii. Bioresour Technol 2011, 102:1616-2610. Xue F., Gao B., Zhu Y., Zhang X., Feng W. and Tan T., Pilot -scale production of microbial lipid using starch wastewater as raw material, Bioresource Technology, 101, 6092–6095 (2010) Zhou W, Li Y, Min M , Hu B, Chen P, Ruan R: Local bioprospecting for high -lipid p roducing microalgal strains to be grown on concentrated municipal wastewater for b iofuel production. Bioresour Tech nol 2011, 102:6909-6919. Zilinskas Braun G, Zilinskas Braun B. Light absorption, emission and photosynthesis. In: Stewart WDP, editor. Algal physiology and biochemistry. Oxford : Blackwell Scientific Publications; 1974

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