In a world where the need for sustainable and clean energy is more urgent than ever, biofuels derived from algae stand out as a promising solution. Algae-based biofuels represent a viable alternative to traditional fossil fuels, offering a renewable and eco-friendly energy source.
Third-generation biofuels from algae-based biomass have significant advantages over first- and second-generation biofuels due to their accessibility and versatility (Muthuraman and Kasianantham, 2023); and in the last decade, substantial scientific advances have been made to make algae biofuels an important and viable alternative to fossil fuels.
This article explores in depth what algae biofuels are, how they are produced, their benefits and challenges, as well as their potential impact on the global energy future.
What are Algae Biofuels?
Algae biofuels, also known as third-generation biofuels, are produced from various species of algae (including microalgae and macroalgae) that can be cultivated in freshwater, saltwater, or brackish water, in closed cultivation systems (photobioreactors), open systems (ponds), or hybrid systems.
Algae convert solar energy into biomass through photosynthesis, and this biomass can be processed to produce different types of biofuels, such as biodiesel, bioethanol, biohydrogen, biobutanol, and biogas.
According to Sarwan et al., (2024), biofuels are defined as: “the energy source derived from living cells through the degradation of lignocellulosic or cellulosic biomass to produce ethanol and diesel,” while “the fuels generated with the help of microorganisms through fermentation are called bioethanol and biodiesel.”
Algae-Based Biofuels
The term “algae-based biofuels” refers to any biofuel derived from algae biomass. These fuels can be liquid, such as biobutanol, biodiesel, bioethanol, and biohydrogen (Mahmood et al., 2023), or gaseous, such as biogas.
The ability of microalgae to grow rapidly with photosynthesis, carbon dioxide, and nutrients makes them ideal sources of biofuels (Neeti et al., 2023). This, coupled with an energy conversion efficiency superior to many other biomass sources, makes them an attractive option for biofuel production.
Production of Algae Biofuels
The production of algae biofuels involves several key steps, from algae cultivation to the conversion of biomass into fuel. Below is a general description of the main processes involved:
- Algae Cultivation: Algae are grown in open ponds or closed photobioreactors. Photobioreactors allow for more precise control of growth conditions and can increase productivity.
- Harvesting and Drying: Once the algae have grown sufficiently, they are harvested and dried to reduce water content. This step is crucial to increase lipid extraction efficiency.
- Lipid Extraction: Lipids, which are fats contained in algae, are extracted using chemical solvents or mechanical methods. These lipids are the raw material for biodiesel production.
- Conversion to Biofuels: The extracted lipids are converted into biodiesel through a chemical process called transesterification. Other methods may include fermentation to produce bioethanol or anaerobic digestion to produce biogas.
Mahmood et al. (2023) and Muthuraman and Kasianantham (2023) provide detailed descriptions of the production process for different types of biofuels.
Farms for Algae Biofuel Production
Algae biofuel farms are facilities dedicated to large-scale algae cultivation for biofuel production. These farms can vary in size and design, but generally include algae cultivation systems, harvesting and processing facilities, and biomass conversion units for biofuels. Algae farms can be located in coastal areas, deserts, or even on land unsuitable for conventional agriculture, making them a flexible and sustainable solution.
Benefits of Third-Generation Biofuels
Algae biofuels offer numerous environmental, economic, and social benefits:
- Reduction of Greenhouse Gas Emissions: Algae biofuels can significantly reduce CO2 emissions compared to fossil fuels. During their growth, algae absorb CO2, helping to mitigate climate change. Mehta et al. (2023) highlight that the production of bioenergy resources from microalgae has the potential to reduce GHG emissions by 4% to 5%.
- Sustainability: Algae can grow in adverse conditions and do not compete with food crops, making them a sustainable biomass source. Additionally, they can be cultivated using saltwater or wastewater, reducing pressure on freshwater resources.
- High Yield: Algae have a much higher yield per hectare than other biofuel crops. They can produce up to 30 times more energy per unit area than terrestrial crops. Moreover, algae have maximum light-use efficiency and produce between 2 to 15 times more lipids compared to other oilseed crops, such as soy and canola (Mehta et al., 2023).
- Energy Diversification: Algae biofuels contribute to the diversification of the energy matrix, reducing dependence on fossil fuels and improving energy security.
- Less Land Use: Algae can be cultivated on non-arable land, such as saltwater ponds or wastewater treatment facilities. This means they do not compete with food crops for land, which is another great advantage.
- Year-Round Production Potential: Algae can be grown year-round, regardless of climate. This means they can provide a reliable energy source, even in areas with harsh climates.
- Bioremediation: Algae can be cultivated in aquaculture or domestic effluents. Regarding this, Raven et al. (2023) and Buzek (2024) report that municipal and industrial effluents can serve as a nutrient source for algae cultivation for biofuel production. Additionally, Merino et al. (2024) highlighted the potential of using sludge from the eutrophication of a bay to produce the microalga Scenedesmus acutus for biofuel production.
Challenges of Algae Biofuels
Despite their numerous benefits, algae biofuels also face several challenges:
Production Costs
Algae biofuel production remains expensive due to high cultivation, harvesting, and processing costs. More efficient and cost-effective technologies need to be developed to reduce these costs. Maroušek et al. (2022) note that technological barriers to scaling up algae production to a commercial scale mean the hypothetical price of algae biodiesel is far from competitive (€292/100 km) compared to conventional fossil fuels (€15.6/100 km). Meanwhile, Quiroz et al. (2023) identified the optimal potential for global productivity, environmental impacts, and economic viability of algae biofuels (Scenedesmus obliquus) using validated biophysical and sustainability models. They concluded that techno-economic analysis shows that minimum algae biofuel prices of $1.89–$2.15 per liter of gasoline equivalent are possible in Southeast Asia and Venezuela.
However, as Maroušek et al. (2023) conclude, most research on microalgae biodiesel yields economically overly optimistic assumptions because it has been based on laboratory-scale experiments.
Scalability
Although algae can produce high yields, scaling them to industrial levels presents significant technical and economic challenges. Substantial investments in infrastructure and technology are required. It is important to note that the biochemical composition of algae biomass (including moisture, lipids, carbohydrates, proteins, ash concentration, and lignin content) directly impacts bioenergy generation (El-Sheekh et al., 2024).
Environmental Impact
Large-scale algae production can have environmental impacts, such as eutrophication of water bodies due to the use of fertilizers. It is crucial to implement sustainable practices and appropriate regulations to mitigate these effects.
Engine Performance
Various studies have highlighted that biodiesel leads to poor engine performance due to its low calorific value and high viscosity. However, Meraz et al. (2023) report that the inclusion of nano-additives with algae biodiesel blends improves engine performance, combustion characteristics, and calorific value.
Chemistry of Algae Biofuels
The chemistry of algae biofuels is complex and involves various chemical reactions to convert biomass into usable fuels. Below are some key aspects of the chemistry of algae biofuels:
- Photosynthesis: Algae use photosynthesis to convert sunlight into biomass, producing oxygen and glucose. This biomass is rich in lipids, carbohydrates, and proteins.
- Lipid Extraction: Lipids are extracted from algae biomass using physical or chemical methods. The extracted lipids are primarily triglycerides, which can be converted into biodiesel.
- Transesterification: This chemical process converts triglycerides into biodiesel and glycerol by reacting with an alcohol, usually methanol, in the presence of a catalyst.
- Fermentation: The carbohydrates present in algae biomass can be fermented to produce bioethanol, which can be used as fuel for internal combustion engines.
A more detailed description of the chemistry of algae biofuels can be found in the work of Alazaiza et al. (2023). Additionally, scientists at RUDN University evaluated the most efficient process for obtaining biofuels from algae.
Uses of Algae Biofuels
Algae biofuels have a wide range of applications in both the transportation sector and energy generation:
- Transportation: Biodiesel and bioethanol derived from algae can be used in vehicles without significant modifications. These fuels can be blended with fossil fuels or used directly in adapted engines.
- Energy Generation: Biogas produced from algae can be used to generate electricity and heat. Power plants using biogas can be integrated into existing energy grids, providing a renewable and reliable energy source.
- Chemical Products: In addition to fuels, algae can be used to produce a variety of chemical products, including biodegradable plastics, fertilizers, and pharmaceuticals. This adds value to algae biomass and diversifies market opportunities.
Future of Third-Generation Biofuels
The future of algae biofuels depends on overcoming current technical and economic challenges. With the support of government policies, investments in research and development, and the implementation of advanced technologies, algae biofuels have the potential to play a crucial role in the transition to a more sustainable energy economy.
Moriarty & Honnery (2024) expect continued technical progress in algae-based biofuel production, both in algae strain selection and production technology. However, the researchers warn that the difficulty in forecasting algae energy lies in anticipating similar progress rates for other competing renewable energy technologies, especially photovoltaic cells and perhaps photolysis.
On the other hand, Wołejko et al. (2023) recommend that future research should focus on maximizing the yield and quality of algae-derived biofuels while increasing their economic viability. Coşgun et al. (2023) highlight the potential of machine learning (artificial intelligence) in third-generation biofuel production, particularly in the stages of detecting and selecting suitable strains.
Conclusion
Algae could play a key role in resolving the conflict between food production and biofuel production (Mahmood et al., 2023). Algae biofuels, or third-generation fuels, represent an innovative and sustainable solution to the energy challenges of the 21st century. Although they face several challenges, their environmental, economic, and social benefits make them a promising alternative to fossil fuels. As technology advances and production costs decrease, we are likely to see broader adoption of algae biofuels, contributing to a cleaner and more sustainable energy future.
References
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