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Rajesh Banu, J. Biofuel Production Pathways by Microalga. Encyclopedia. Available online: (accessed on 12 April 2024).
Rajesh Banu J. Biofuel Production Pathways by Microalga. Encyclopedia. Available at: Accessed April 12, 2024.
Rajesh Banu, Jeyakumar. "Biofuel Production Pathways by Microalga" Encyclopedia, (accessed April 12, 2024).
Rajesh Banu, J. (2021, August 27). Biofuel Production Pathways by Microalga. In Encyclopedia.
Rajesh Banu, Jeyakumar. "Biofuel Production Pathways by Microalga." Encyclopedia. Web. 27 August, 2021.
Biofuel Production Pathways by Microalga

Using microalgae to treat wastewater as well as simultaneously produce biofuels is one of the approaches for a sustainable future. The manufacture of biofuels from microalgae is one of the next-generation biofuel solutions that has recently received a lot of interest, as it can remove nutrients from the wastewater whilst capturing carbon dioxide from the atmosphere. The resulting biomass are employed to generate biofuels, which can run fuel cell vehicles of zero emission, power combustion engines and power plants. By cultivating microalgae in wastewater, eutrophication can be prevented, thereby enhancing the quality of the effluent. Thus, by combining wastewater treatment and biofuel production, the cost of the biofuels, as well as the environmental hazards, can be minimized, as there is a supply of free and already available nutrients and water.

microalgae wastewater treatment biofuel nutrient removal

1. Introduction

From sea ice in the Arctic to microbiotic crusts in deserts, the term “algae” refers to a wide group of (mainly) autotrophic, aquatic creatures found all over the world [1][2]. Algae are usually one of two types such as macro and micro algae. Macroalgae are generally considered terrestrial plants that returned to a damp environment, according to evolutionary theory. They are classified into red, brown, and green algae and are diverse forms of multicellular eukaryotes, each with a respective evolution pathway. They have leaves and branches and may be fixed firmly [3]. Microalgae, on the other hand, are unicellular and range in size from nanometers to millimetres. Microalgae is defined by phycologists as a creature with chlorophyll and a body (thallus) that is not divided into roots, leaves (thallophytes), and stems [4]. They comprise both the prokaryotes and eukaryotes. Microalgae fix carbon dioxide more efficiently than terrestrial plants, and are widely known for capturing both atmospheric and industrial pollutants [5].
Microalgae are considered as the most successful feedstock for biodiesel synthesis due to their high photosynthetic activity, effective capture of the emitted carbon dioxide, and remarkable environmental adaptation, including high algal production [6][7][8]. Thus, algae utilize carbon dioxide, along with sunlight and water, to produce sugars through photosynthesis.
Current biofuel production from microalgal biomass is limited by a lack of dependable and cost-effective technologies for producing and harvesting algal feedstocks [9]. Muchrecent research has proposed that algal biomass production be combined with wastewater treatment and recycling to equalize the expense of fertilisers and freshwater necessary for microalgae growing [10][11][12][13]. This combination of algal biomass generation and wastewater treatment also helps to purify wastewater [14][15][16].
Algae may be harvested from the treatment facility on a regular basis and used to make biofuel. In comparison to traditional wastewater treatment technologies, simultaneous wastewater treatment and algae culture can give a more cost-effective and environmentally friendly wastewater treatment. It has been demonstrated that it is a more cost-effective method of removing biochemical oxygen demand, pathogens, phosphate, and nitrogen than activated sludge [17] (Figure 1).
Figure 1. Microalgal wastewater treatment and the application of the produced biomass.

2. Biofuel Production Pathways

2.1. Biodiesel

The triglyceride transesterification technique has been used in biodiesel production for more than 50 years [18]. During transesterification, fatty acid esters are formed when the triglycerides react with alcohol, and when the reaction is sped up by a catalyst.As the chemical processes involved in the manufacture of biodiesel are rather slow, catalysts are utilised to speed them up. Biodiesel manufacturing methods can be chemical or biotechnological, depending on the kind of catalyst used in the process. Biodiesel may be made from algal biomass in a variety of ways (including oil extraction from algal biomass) via esterification and direct transesterification of microalgae [19]. Fatty acid methyl esters (FAMEs), the chemical component of biodiesel, are usually generated in algal biodiesel processes by transesterification of algal oil with the alcohol (methanol) utilizing 98% concentrated sulfuric acid as a catalyst and n–hexane as a solvent. Extraction of oil from the microalgae without breaking their cells is a novel way in using nano catalysts for biodiesel synthesis from microalgae [20]. In situ transesterification is a promising method for avoiding oil extraction and directly converting lipids within microalgae cells to biodiesel in a single step, which might simplify biodiesel manufacturing procedures while also producing more biodiesel [21].

2.2. Biomethane

Biogas is one of the most promising biofuels, with the ability to alleviate some of the rising worries about fossil fuels, such as the energy calamity and change in the weather [22][23]. Application of microalgae have been shown to be efficient, practical, and cost-effective in biogas generation [24][25][26]. Microalgae are particularly well suited for combined nutrient removal through wastewater treatment and carbon dioxide sequestration, due to their ability to assimilate large amounts of carbon dioxide and the possibility of blending microalgal cultivation with flue gas emissions or biogas upgrading, which involves removing carbondioxide (as biogas) to increase methane percentage [27][28][29]. Microalgae cultivation at a wastewater treatment facility offers a free source of water and nutrients, while also contributing to the wastewater treatment process and allowing the recycling of vital nutrients that would otherwise be lost to the environment. The resulting microalgal biomass can subsequently be processed to extract nutrients for fertiliser production or oils for biodiesel generation. Biogas can also be produced through anaerobic digestion of residual biomass [30][31][32]. Biomethane is generated via biochemical conversion of biomass, followed by gas upgrading, or by thermochemical conversion of solid biomass through gasification, followed by gas cleaning, methanation as the process of synthesis, and biogas upgrading of the product.

2.3. Biohydrogen

The term “biohydrogen” refers to hydrogen created biologically, most typically by algae, bacteria, and archaea, either through cultivating them or from organic waste sources [33]. Hydrogen is considered as yet another sustainable energy source generated by photosynthetic organisms, with a higher energy content of about 122 kJ/g, which is nearly 2.75 times greater than that of hydrocarbon fuels [34]; due to this reason, it has been considered a viable alternative to fossil fuels and as an carrier of energy. A number of microalgae species, such as Anabaena sp. [35], Chlorella vulgaris [36], Nannochoropsis sp. [37], Chlamydomonas reinhardtii [38], Spirulina maxima [39], and Scenedesmus obliquus [36][40], are capable of generating molecular hydrogen through the photofermentative metabolism. Among the various species, Chlorella vulgaris is the most commonly used untreated substrate for hydrogen generation. Hydrogen yield acquired from various species ranged from 0.37 to 19 mL of hydrogen/g VS, and highest hydrogen yield was achieved from Chlorella vulgaris [41] and the Scenedesmus sp. [42].
Hydrogen can be produced inthree different ways such as direct biophotolysis, indirect biophotolysis (as shown in Figure 2), and hydrogen production driven by ATP. In direct photolysis biohydrogen is produced by converting water to hydrogen using solar energy through photosynthesis, and is further used as a substrate for anaerobic bacteria during dark fermentation [35]. Such fermentative reactions are typically faster and produce more hydrogen [43].
Figure 2. Biohydrogen Production through photolysis and fermentation.
In indirect photolysis, the microalga produces hydrogen in two steps. In step 1, carbon dioxide is captured through photosynthesis in the presence of solar light. In other terms, microalgae produce oxygen and build up carbon within the cells. In step 2, production of hydrogen takes place through the degradation of the accumulated carbon through anaerobic fermentation which occurs in the absence of oxygen and involves a series of complex biochemical events involving multi-enzyme systems [44][34]. Hydrogenase enzyme plays an important role in this method. As discussed earlier, it is more sensitive to oxygen, so various research is being carried out to develop hydrogenase enzyme which is not sensitive to oxygen. Closed Photobioreactors can be employed for indirect photolysis (Figure 3).
Figure 3. Closed Photobioreactors.

2.4. Bioethanol

Bioethanol is considered a substitute for conventional petroleum, as they both have the same chemical and physical properties [45][46][47]. Microalgae biomass, in particular, has lately received a lot of interest as a viable renewable source for the production of biofuels. Third-generation bioethanol made from microalgae biomass could also be an environmentally beneficial fuel. As discussed earlier, microalgae are rich in lipids, enabling it to produce biodiesel. Similarly, some species of microalgae can store large amounts of carbohydrates, such as triacylglycerol and starch, within their cells. These carbohydrates can be used as a carbon source or substrate during fermentation to generate bioethanol [48][49]. Proteins can also be accumulated within the cells, along with carbohydrates and lipids under restriction of nitrogen or starvation [50]. Microalgae breakdown the complex nitrogen molecules into protein. Variation in salinity, light intensity, and temperature can also accumulate carbohydrates. Microalgae also lack lignin, and have low hemicellulose levels, making hydrolysis and fermentation yields more efficient [51].
There are three different routes to produce bioethanol from microalgae:(i) The first route is the conventional method, in which the biomass is pretreated, hydrolyzed enzymatically, and fermented using yeast [52]. (ii) The second route operates in the dark condition, and uses metabolic pathways to redirect photosynthesis to create hydrogen, acids, and ethanol [53]. (iii)The third method is to use photofermentation, which is impossible in nature [54]. (iv) The last route necessitates the use of genetic engineering to reroute microalgae′s pre-existing metabolic pathways for more subjective and efficient bioethanol synthesis. Bioethanol production from microalgae and cyanobacteria is a viable technical advancement, as they have shown to be more productive than crops such assugarcane and corn. Light is used as an energy source by genetically engineered strains to produce bioethanol from carbon dioxide and water in a single process [55].

3. Conclusions

With the rapid pace of economic development and energy consumption, as well as the limited supply of fossil fuels and the growing need for environmental protection, more attention is being paid to the development of ecologically friendly fuels such as biofuels to resolve the conflict. Microalgae-based biofuels are one of the most promising feedstocks for the next generation of biofuels due to their capacity to produce a high amount of lipids and minimum negative environmental consequence. Algal biofuels can be used in combination with a reduction in carbon dioxide in flue gas and wastewater treatment, as well as the generation of byproducts of high value. The markets for algal biofuel already exist, and are developing, but the markets’ growth is constrained due high capital and operational costs, and also due to underdeveloped production technology. Thus, the cost of algal biofuel is increasing. Therefore, more research is to be conducted to improve the technologies used to convert biomass to biofuels, and also produce better harvesting technologies to make algal based biofuels more promising.


  1. Steinman, A.D.; Vymazal, J. Algae and element cycling in wetlands. J. N. Am. Benthol. Soc. 1996, 15, 138–140.
  2. Larkum, A. Photosynthesis in Algae; Kluwer Academic Publisher: Dordrecht, The Netherlands, 2003.
  3. Cock, J.M. Introduction to Marine Genomics; Springer: Berlin, Germany, 2010.
  4. Lee, R.E. Phycology, 4th ed.; Cambridge University Press: Cambridge, UK, 2008.
  5. Brennan, L.; Owende, P. Biofuels from microalgae—A review of technologies for production, processing, and extractions of biofuels and co-products. Renew. Sustain. Energy Rev. 2010, 14, 557–577.
  6. Packer, M. Algal capture of carbon dioxide; biomass generation as a tool for greenhouse gas mitigation with reference to New Zealand energy strategy and policy. Energy Policy 2009, 37, 3428–3437.
  7. Ren, H.-Y.; Liu, B.-F.; Kong, F.; Zhao, L.; Ma, J.; Ren, N.-Q. Favorable energy conversion efficiency of coupling dark fermentation and microalgae production from food wastes. Energy Convers. Manag. 2018, 166, 156–162.
  8. Wendt, L.M.; Kinchin, C.; Wahlen, B.D.; Davis, R.; Dempster, T.A.; Gerken, H. Assessing the stability and techno-economic implications for wet storage of harvested microalgae to manage seasonal variability. Biotechnol. Biofuels 2019, 12, 80.
  9. Christenson, L.; Sims, R. Production and harvesting of microalgae for wastewater treatment, biofuels, and bioproducts. Biotechnol. Adv. 2011, 29, 686–702.
  10. Pittman, J.K.; Dean, A.; Osundeko, O. The potential of sustainable algal biofuel production using wastewater resources. Bioresour. Technol. 2011, 102, 17–25.
  11. de Alva, M.S.; Luna-Pabello, V.M.; Cadena, E.; Ortíz, E. Green microalga Scenedesmusacutus grown on municipal wastewater to couple nutrient removal with lipid accumulation for biodiesel production. Bioresour. Technol. 2013, 146, 744–748.
  12. Prajapati, S.K.; Kaushik, P.; Malik, A.; Vijay, V.K. Phycoremediation coupled production of algal biomass, harvesting and anaerobic digestion: Possibilities and challenges. Biotechnol. Adv. 2013, 31, 1408–1425.
  13. Nayak, M.; Karemore, A.; Sen, R. Performance evaluation of microalgae for concomitant wastewater bioremediation, CO2 biofixation and lipid biosynthesis for biodiesel application. Algal Res. 2016, 16, 216–223.
  14. Prandini, J.M.; da Silva, M.L.B.; Mezzari, M.P.; Pirolli, M.; Michelon, W.; Soares, H.M. Enhancement of nutrient removal from swine wastewater digestate coupled to biogas purification by microalgae Scenedesmus spp. Bioresour. Technol. 2016, 202, 67–75.
  15. Van Wagenen, J.; Pape, M.L.; Angelidaki, I. Characterization of nutrient removal and microalgal biomass production on an industrial waste-stream by application of the deceleration-stat technique. Water Res. 2015, 75, 301–311.
  16. Gao, F.; Li, C.; Yang, Z.-H.; Zeng, G.-M.; Feng, L.; Liu, J.-Z.; Liu, M.; Cai, H.-W. Continuous microalgae cultivation in aquaculture wastewater by a membrane photobioreactor for biomass production and nutrients removal. Ecol. Eng. 2016, 92, 55–61.
  17. Green, F.B.; Bernstone, L.S.; Lundquist, T.J.; Oswald, W.J. Advanced integrated wastewater pond systems for nitrogen removal. Water Sci. Technol. 1996, 33.
  18. Chisti, Y. Biodiesel from microalgae. Biotechnol. Adv. 2007, 25, 294–306.
  19. Johnson, M.B.; Wen, Z. Production of biodiesel fuel from the microalga Schizochytrium limacinum by direct transesterification of algal biomass. Energy Fuels 2009, 23, 5179–5183.
  20. Trindade, S.C. Nanotech biofuels and fuel additives. In Biofuel’s Engineering Process Technology; IntechOpen: London, UK, 2011.
  21. Wahlen, B.; Willis, R.M.; Seefeldt, L. Biodiesel production by simultaneous extraction and conversion of total lipids from microalgae, cyanobacteria, and wild mixed-cultures. Bioresour. Technol. 2011, 102, 2724–2730.
  22. Zabed, H.M.; Boyce, A.N.; Sahu, J.N.; Faruq, G. Evaluation of the quality of dried distiller’s grains with solubles for normal and high sugary corn genotypes during dry–grind ethanol production. J. Clean. Prod. 2017, 142, 4282–4293.
  23. Ayala-Parra, P.; Liu, Y.; Field, J.; Sierra-Alvarez, R. Nutrient recovery and biogas generation from the anaerobic digestion of waste biomass from algal biofuel production. Renew. Energy 2017, 108, 410–416.
  24. Zamalloa, C.; Boon, N.; Verstraete, W. Anaerobic digestibility of Scenedesmus obliquus and Phaeodactylum tricornutum under mesophilic and thermophilic conditions. Appl. Energy 2012, 92, 733–738.
  25. Saratale, R.G.; Kumar, G.; Banu, R.; Xia, A.; Periyasamy, S.; Saratale, G.D. A critical review on anaerobic digestion of microalgae and macroalgae and co-digestion of biomass for enhanced methane generation. Bioresour. Technol. 2018, 262, 319–332.
  26. Ward, A.; Lewis, D.; Green, F. Anaerobic digestion of algae biomass: A review. Algal Res. 2014, 5, 204–214.
  27. Park, J.; Craggs, R.; Shilton, A. Wastewater treatment high rate algal ponds for biofuel production. Bioresour. Technol. 2011, 102, 35–42.
  28. Sivakumar, G.; Xu, J.; Thompson, R.W.; Yang, Y.; Randol-Smith, P.; Weathers, P.J. Integrated green algal technology for bioremediation and biofuel. Bioresour. Technol. 2012, 107, 1–9.
  29. Xu, J.; Zhao, Y.; Zhao, G.; Zhang, H. Nutrient removal and biogas upgrading by integrating freshwater algae cultivation with piggery anaerobic digestate liquid treatment. Appl. Microbiol. Biotechnol. 2015, 99, 6493–6501.
  30. Ehimen, E.; Sun, Z.; Carrington, C.; Birch, E.; Eaton-Rye, J. Anaerobic digestion of microalgae residues resulting from the biodiesel production process. Appl. Energy 2011, 88, 3454–3463.
  31. Sforza, E.; Barbera, E.; Girotto, F.; Cossu, R.; Bertucco, A. Anaerobic digestion of lipid-extracted microalgae: Enhancing nutrient recovery towards a closed loop recycling. Biochem. Eng. J. 2017, 121, 139–146.
  32. Gonzalez, L.M.; Correa, D.F.; Ryan, S.; Jensen, P.D.; Pratt, S.; Schenk, P.M. Integrated biodiesel and biogas production from microalgae: Towards a sustainable closed loop through nutrient recycling. Renew. Sustain. Energy Rev. 2018, 82, 1137–1148.
  33. Wang, J.; Wan, W. Factors influencing fermentative hydrogen production: A review. Int. J. Hydrogen Energy 2009, 34, 799–811.
  34. Argun, H.; Kargi, F.; Kapdan, I.K.; Oztekin, R. Biohydrogen production by dark fermentation of wheat powder solution: Effects of C/N and C/P ratio on hydrogen yield and formation rate. Int. J. Hydrogen Energy 2008, 33, 1813–1819.
  35. Ferreira, A.F.; Marques, A.C.; Batista, A.P.; Marques, P.A.; Gouveia, L.; Silva, C. Biological hydrogen production by Anabaena sp.—Yield, energy and CO2 analysis including fermentative biomass recovery. Int. J. Hydrogen Energy 2012, 37, 179–190.
  36. Ruiz-Marin, A.; Canedo-López, Y.; Chávez-Fuentes, P. Biohydrogen production by Chlorella vulgaris and Scenedesmus obliquus immobilized cultivated in artificial wastewater under different light quality. AMB Express 2020, 10, 1–7.
  37. Nobre, B.; Villalobos, F.; Barragán-Huerta, B.E.; Oliveira, A.; Batista, A.P.; Marques, P.; Mendes, R.; Sovova, H.; Palavra, A.; Gouveia, L. A biorefinery from Nannochloropsis sp. microalga—Extraction of oils and pigments. Production of biohydrogen from the leftover biomass. Bioresour. Technol. 2013, 135, 128–136.
  38. Batyrova, K.; Hallenbeck, P.C. Hydrogen production by a Chlamydomonas reinhardtii strain with inducible expression of photosystem II. Int. J. Mol. Sci. 2017, 18, 647.
  39. Juantorena, A.; Sebastian, P.; Santoyo, E.; Gamboa, S.; Lastres, O.; Sánchez-Escamilla, D.; Bustos, A.; Eapen, D. Hydrogen production employing Spirulina maxima 2342: A chemical analysis. Int. J. Hydrogen Energy 2007, 32, 3133–3136.
  40. Batista, A.P.; Moura, P.; Marques, P.A.; Ortigueira, J.; Alves, L.; Gouveia, L. Scenedesmus obliquus as feedstock for biohydrogen production by Enterobacter aerogenes and Clostridium butyricum. Fuel 2014, 117, 537–543.
  41. Wieczorek, N.; Kucuker, M.A.; Kuchta, K. Fermentative hydrogen and methane production from microalgal biomass (Chlorella vulgaris) in a two-stage combined process. Appl. Energy 2014, 132, 108–117.
  42. Yang, Z.; Guo, R.; Xu, X.; Fan, X.; Li, X. Enhanced hydrogen production from lipid-extracted microalgal biomass residues through pretreatment. Int. J. Hydrogen Energy 2010, 35, 9618–9623.
  43. Hallenbeck, P. Fundamentals of the fermentative production of hydrogen. Water Sci. Technol. 2005, 52, 21–29.
  44. Kapdan, I.K.; Kargi, F. Bio-hydrogen production from waste materials. Enzym. Microb. Technol. 2006, 38, 569–582.
  45. Dale, B.E. Thinking clearly about biofuels: Ending the irrelevant ‘net energy’ debate and developing better performance metrics for alternative fuels. Biofuels Bioprod. Biorefin. 2007, 1, 14–17.
  46. Demirbaş, A. Conversion of biomass using glycerin to liquid fuel for blending gasoline as alternative engine fuel. Energy Convers. Manag. 2000, 41, 1741–1748.
  47. Naik, S.; Goud, V.V.; Rout, P.K.; Dalai, A.K. Production of first and second generation biofuels: A comprehensive review. Renew. Sustain. Energy Rev. 2010, 14, 578–597.
  48. Harun, R.; Singh, M.; Forde, G.M.; Danquah, M.K. Bioprocess engineering of microalgae to produce a variety of consumer products. Renew. Sustain. Energy Rev. 2010, 14, 1037–1047.
  49. Radakovits, R.; Jinkerson, R.; Darzins, A.; Posewitz, M.C. Genetic engineering of algae for enhanced biofuel production. Eukaryot. Cell 2010, 9, 486–501.
  50. González-Fernández, C.; Ballesteros, M. Linking microalgae and cyanobacteria culture conditions and key-enzymes for carbohydrate accumulation. Biotechnol. Adv. 2012, 30, 1655–1661.
  51. Ueno, Y.; Kurano, N.; Miyachi, S. Ethanol production by dark fermentation in the marine green alga, Chlorococcum littorale. J. Ferment. Bioeng. 1998, 86, 38–43.
  52. Hernández, D.; Riaño, B.; Coca, M.; González, M.C.G. Saccharification of carbohydrates in microalgal biomass by physical, chemical and enzymatic pre-treatments as a previous step for bioethanol production. Chem. Eng. J. 2015, 262, 939–945.
  53. Magneschi, L.; Catalanotti, C.; Subramanian, V.; Dubini, A.; Yang, W.; Mus, F.; Posewitz, M.C.; Seibert, M.; Perata, P.; Grossman, A.R. A mutant in the ADH1 gene of Chlamydomonas reinhardtii elicits metabolic restructuring during anaerobiosis. Plant Physiol. 2012, 158, 1293–1305.
  54. Dexter, J.; Armshaw, P.; Sheahan, C.; Pembroke, J.T. The state of autotrophic ethanol production in cyanobacteria. J. Appl. Microbiol. 2015, 119, 11–24.
  55. Saad, M.G.; Dosoky, N.S.; Zoromba, M.S.; Shafik, H.M. Algal Biofuels: Current Status and Key Challenges. Energies 2019, 12, 1920.
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