Algae-based biofuel has recently become a popular renewable energy source due to its potential to produce vegetable oil and petroleum-derived fuels, like gasoline, diesel, and jet fuel. Through a process of distillation, natural oils found in certain types of algae can be isolated and used as a direct replacement for traditional petroleum-based fuels. This promising energy source could revolutionize the way we power our world.

Bio-fuel derived from algae is considered carbon-neutral as the carbon emitted from burning it is the same as the amount of carbon that was recently absorbed by the algae as food. While industry claims suggest that the GHG footprint of algae-based bio-diesel. It is 93 percent lower than conventional diesel, this does not factor in the CO₂ used in its production.

Algae-based fuel yields more energy per unit area than other bio-fuels and can be produced on land that is not suitable for other agricultural activities. Many companies have already started large-scale production of algae-based fuel and trials with airlines such as United and Qantas. These have been conducted using fuel blends of up to 40 percent algae-derived fuel. To maximize efficiency, vertical photo bio-reactors (PBRs) are now in use and can recycle up to 85 percent of the water along with excess nutrients and CO₂ (Rony, Z. I., et al. 2023).

Importance and challenges of Algal Biofuels

Algal Biofuels are gaining attention as a potential renewable alternative to traditional fuels. Algal biofuels are produced from oils extracted from microalgae, which are a form of microscopic life found in water. Algae can be grown in ponds, tanks, or bioreactors, and the oils they produce can be refined into biofuels. The use of fossil fuels is essential for the functioning of the global economy, and the energy needed for domestic as well as industrial growth. Consequently, there is a growing concentration of atmospheric CO_2, which is likely to have a significant impact on the climate of all parts of the world.

Moreover, since petroleum is a finite resource derived from ancient algae deposits, it will eventually become scarce or too expensive to recover. A variety of technologies have been explored as alternatives, and it appears that a combination of these strategies. These could potentially decrease our reliance on fossil fuels.

From 1978 to 1996, the U.S. Department of Energy funded a research project to develop renewable transportation fuels from high lipid-producing algae. Early research focused on identifying high lipid-yielding strains or detecting culture conditions, such as nutritional stress, to enhance lipid production. However, they found that high lipid production was always associated with lower biomass productivity, resulting in a lower overall lipid yield.

Subsequently, attention has shifted to cultivating conditions that promote both high biomass productivity and lipid content in the range of 20-30% (John S. et. al., 1998). Additionally, the algal feedstock is an optimal choice for bioethanol and biogas production due to its low lignin content. Thus, the current focus is on generating large amounts of algal biomass and utilizing it for cost-effective energy production, such as bioethanol, bio CNG (methane or biogas), and syngas. (Magar C. & Deodhar M. 2019)

Different fuel forms from Biofuels

Algal biofuel offers a potential alternative to conventional fossil fuels, due to its production process. By utilizing specific algae species, carbon dioxide can be converted into high carbohydrate, lipid, and hydrocarbon compositions. These compositions can then be used to produce ethanol, biodiesel, and renewable distillates. All of which are viable replacements for fossil fuels. Therefore, algal biofuel is an environmentally-friendly resource that can help reduce our dependence on non-renewable fuels.

• Biodiesel – The lipid (oily) part of the algae biomass can be extracted and converted into biodiesel through a transesterification process akin to that used for other vegetable oils.
• Biogas – It is produced as per the conventional ruminant dung-based method of biogas production in anaerobic digesters (AD). The steps involved are acid hydrolysis of algal biomass and then methanogenesis to produce methane with a low-cost biorefinery approach.
• Bioethanol – Microalgae are rich in lipids, proteins, carbohydrates, and other valuable compounds, making them ideal for bioethanol production. The carbohydrates in microalgal cells can be transformed into bioethanol through fermentation, which overcomes many of the limitations associated with conventional sources of starch. Additionally, since microalgal cells do not contain structural biopolymers such as hemicelluloses and lignin, bioethanol production is easier than with terrestrial plants.

Other Biofuel from Algae

• Butanol can be produced from whole or processed algal biomass with the help of a solar-powered biorefinery. This fuel has an energy density that is 10% lower than that of gasoline, and higher than both methanol and ethanol. Further, Clostridia fermentation of macroalgae can produce butanol and other solvents. Additionally, it can be blended with gasoline to create a renewable fuel blend.
• De-oiled biomass pyrolysis for crude oil production- The production of bio-oil and biochar through the pyrolysis of de-oiled cakes and seed cakes has been gaining attention. The study is a comprehensive analysis of investigations into the characterization of these materials. Also, the reactors and operating parameters employed were conducted. The kinetic and thermodynamic analysis of pyrolysis, the characterization of the resulting biochar, and its potential applications were also evaluated. Results showed that the average activation energy for pyrolysis of de-oiled cakes was between 98 and 162 kJ/mol. The findings suggest that biochar from de-oiled cakes has the potential for a range of emerging applications due to its high specific surface area and abundance of surface functional groups. Moreover, it was found that plasma and microwave-based reactors could be excellent options for further exploration.
• Hydrogen – Biohydrogen is the hydrogen produced by living organisms such as algae, bacteria, and archaea. It can be extracted from both cultivated sources and waste organic materials and is primarily released during microbial fermentation processes. During this process, organic matter is broken down into carbon dioxide and hydrogen. Microalgae such as cyanobacteria and green algae can not only derive biohydrogen from their photosynthetic metabolism. But can also be used as feedstock for microbial dark fermentation to produce biohydrogen.

Benefits of Algal Biofuel

• Bio-based fuel offers combustion that is carbon-neutral, meaning the amount of carbon dioxide released during combustion. The amount of CO₂ absorbed by plants used to create fuel results in net-zero CO₂ emissions.
• Biofuel could be used alongside our existing fuel sources, providing an additional option to the fuels we currently use.
• Biofuel can produce a variety of different by-products, which are similar to the hydrocarbons created from petroleum.
• Biofuel is a crop that can be grown with a high level of efficiency, providing us with an alternative energy source. That can be used to power transportation and other machinery.

The project conducted by the US DOE (Department of Energy) for screening algal species lead to turn the research towards Biomass from algal oil

In 2010, biomass-derived fuels were identified as a potential solution to reduce the US nation’s dependence. The dependence was on imported oil and the associated economic and security risks. The Energy Independence and Security Act of 2007 (EISA) set a Renewable Fuel Standard (RFS) requiring 36 billion gallons of renewable fuels. Such as advanced cellulosic biofuels and biomass-based diesel, to be sold in the U.S. by 2022. During that time along with many other biofuel options renewable Algae-based biofuels also emerged as a promising alternative. It could help the U.S. meet the EISA goals and move closer to energy independence (U.S. DOE 2010).

Since the termination of the DOE-supported Aquatic Species Program in 1996, the necessity for reducing U.S. reliance on foreign oil. And promoting environmental protection has generated a resurgence of interest in employing algae as a biofuel feedstock. The rising cost of petroleum has also contributed to this renewed enthusiasm for the development of algal feedstocks for biofuel production (U.S. DOE 2010, loc. cit.).

Well-known microalgal species for oil content and biofuel production

Microalgae include many microscopic, photosynthetic organisms that are capable of producing biomass much faster than terrestrial plants. Microalgae boast a lipid content of up to 50% in the form of triglyceride – the essential starting material for biodiesel production. With over 800,000 species, ranging from 1 to 50 µm in diameter, they offer a more efficient alternative to macroalgae. Microalgae such as brown algae, green seaweed, and red algae. Harvesting microalgae is an expensive step in process of biofuel production – accounting for up to 30% of the total cost. Transesterification is the reaction used to convert triglycerides into biodiesel. While thermochemical and biochemical processes are necessary to convert the entire biomass into biofuel. Microalgae can also be used to create multiple forms of biofuel, making them a versatile source of renewable energy.

Microalgae are divided into two main types- filamentous (Multicellular) and phytoplankton (unicellular). Three prominent families of microalgae have been identified, Chlorophyceae (green algae), Bacillariophyceae (diatoms), and Chrysophyceae (golden algae), Cyanophyceae (Blue-Green Algae). To cultivate microalgae, open ponds, and photobioreactors are used. Open ponds are often less expensive and the most used method in developing countries, but it is vulnerable to contamination. To harvest microalgae, methods such as flocculation, flotation, gravity sedimentation, filtration, electrophoresis, and filtration are used.

Oil extraction from microalgae is a key step for biodiesel production- mechanical crushing, solvent extraction, pyrolysis, sonication, autoclaving, and microwaving are some of the methods used. The fatty acids produced from microalgae oil are mainly polyunsaturated and can be prone to oxidation. Chlorella vulgaris, Chlorella protothecoides, Nannochloropsis sp., Nitzchia sp., Chlamydomonas reinhardtii, Schizochytrium sp., Scenedesmus obliques, and Neochloris oleabundans. These have been identified as good sources for biodiesel production based on quality composition and oil yield (Adewuyi, A. et al 2022).

Challenges in Algal Biomass and Biofuel Production

• Algal biomass production requires a significant amount of water and land in order to be successful and yield a productive output.
• Designing and constructing of algae cultivation system is a very complex and cost-intensive process.
• Maintenance of some stringent environmental condition for high lipid-producing microalgae strain is very essential which make the production further expensive.
• Contamination by other fastidious microorganisms and invaders, and algae grazers make mass-scale cultivation unrealistic.
• Algal biofuel technology faces major challenges associated with efficient biomass harvesting and pre-treatment at low cost. And microalgae with reduced emissions of gases and high yields with scalable co-products.
• Different products require different methods of pre-treatment; mechanical methods yield biodiesel while enzymatic and chemical methods (such as acidic hydrolysis). These are used for bioethanol production due to the need for the degradation of cellulose, hemicellulose, and starch.

(Khan, M.I., Shin, J.H. & Kim, J.D. et al 2018).

Biorefinery concept to cope with existing issues for sustainable development in the field

The news from Bloomberg about Exxon’s retreat on algal biofuel funding to the Viridos facility in Calipatria. California is an example of multiple industrial failures that happened in the last century in the field of algae-based biofuels. Though the lab scale results and initial pilot trials always seem promising when it comes to the actual continuous production of high lipid-containing algal biomass the whole system fails. This required furthermore comprehensive research to understand the reasons behind the failures and financial crunches makes it impossible. 

The way to deal with this issue has already been proposed by many experts in the field of algal biotechnology. The concept of biorefinery is the perfect way for sustainable development in this field. The Biorefinery concept aims to provide an alternative solution to current economic, environmental, and social issues. The biorefinery is to integrate analysis of the three pillars of sustainability through a life cycle sustainability assessment (LCSA). In order to ensure a “good” or “appropriated” conceptual design (Solarte-Toro, J. C., & Alzate, C. A. C. 2021).

This integrated analysis evaluates economic, environmental, and social impacts and benefits through the entire life cycle of the product. It considers the effects of one dimension on the other and covers the whole life cycle of products analyzed from different perspectives. The main users of the results of the LCSA are potential and future decision-makers, stakeholders, enterprises, and consumers. This process is intended to provide a comprehensive understanding of the product and its life cycle. Also, can be used as a tool for decision-making to create more sustainable products (Solarte-Toro, J. C., & Alzate, C. A. C. 2021 loc. cit.).

Conclusion:

Along with many other alternative conventional and non-conventional energy resources, the generation of algae-based biofuel is the need of the growing population and industrialization. Making fuel from algae is a tedious task particularly facing issues where the crucial step of technology transfer from lab to land is ceased and failed due to various obstacles. Making the whole technology self-sustainable is very important and the best way to do it is by biorefinery concept along with the generation of bio commodity options. This is especially done to generate the funding to support algae biofuel research and development.

Algae-based Biofuel is High Volume Low-Value product that will not survive until permanent and stable financial support is grown through High-Value Low Volume products of algae. Nutraceuticals, pharmaceuticals, cosmetics, health care, food, and feed from algae are revenue-generation options. Also, it will potentially support biofuel development from algae. Algae biofuel is definitely a potential option for energy in the future considering the potential of algal biomass and its growth rate but making it really is challenging. The ongoing research in the algae-based Biofuel field and large-scale trials will help to understand the future of this technology.       

References:

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Magar, Chaitanya & Deodhar, Manjushri, 2019, Construction of laboratory scale photobioreactor for sequestration of CO₂ from industrial flue gases and utilizing biomass for biofuel production, Ph. D. Thesis, Dept. of Biotechnology, K.E.T.’s V. G. Vaze College of Arts, Science and Commerce, University of Mumbai.

U.S. DOE 2010. National Algal Biofuels Technology Roadmap. U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, Biomass Program.

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Khan, M.I., Shin, J.H. & Kim, J.D. The promising future of microalgae: current status, challenges, and optimization of a sustainable and renewable industry for biofuels, feed, and other products. Microb Cell Fact 17, 36 (2018).

Solarte-Toro, J. C., & Alzate, C. A. C. (2021). Biorefineries as the base for accomplishing the sustainable development goals (SDGs) and the transition to bioeconomy: Technical aspects, challenges, and perspectives. Bioresource Technology, 340, 125626.

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Sivaramakrishnan R, Suresh S, Kanwal S, Ramadoss G, Ramprakash B, Incharoensakdi A. Microalgal Biorefinery Concepts’ Developments for Biofuel and Bioproducts: Current Perspective and Bottlenecks. International Journal of Molecular Sciences. 2022; 23(5):2623.

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