June 24, 2025

Microalgae As Biofuel: Unlocking The Potential of Nature’s Tiny Powerhouses

1. Introduction

 Over the past few years, worldwide consumption of energy has been steadily rising as a result of growing urbanisation and industrialisation [3]. The main energy source is still traditional fossil fuels such coal, oil, and natural gas [34]. Utilising sustainable and renewable energy sources, such as wind, solar, tidal hydropower, and biomass, is necessary to address the world’s expanding energy needs.

Advanced renewable fuels known as algal biofuels are created using a variety of conversions techniques from algae feedstock. The feedstock’s high photosynthetic capacity is attributed to its high oil content. The initial generation of biofuels, which often employ edible feedstocks including corn, soyabeans, wheat, sunflower oil, and palm oil, may put food and fuel sources in competition.

[43]. Since second-generation biofuels are mostly produced from non-edible materials like switchgrass, straw, and food waste, they are more sustainable than first-generation biofuels. However, both land and water have limitations because of grain availability [37].

Based on their size and physical characteristics, algae are frequently classified as either macroalgae or microalgae. Seaweeds, also known as macroalgae, are observable to the naked eye and are made up of a large number of cells. Microalgal species, which are only visible under a microscope, are much more important in the area of micro-nanomedicine than macroalgae [56]. Microalgae can grow in saline-alkaline soil, saltwater, wastewater, and food waste. Because they can produce more biomass than terrestrial plants when given limited resources, they are essential sources of biomass for third and fourth generation biofuels.

 [36], [33], [57].

Because they can directly convert solar energy into biomass, algae are a type of organism having one or more cells that are classified as highly effective biofuel sources based on physical and ecological characteristics [41], [23]. They are also important producers in aquatic environments. From photosynthesis, algae create organic molecules.

2.Benefits and potential of microalgae as a biofuel source

Compared to terrestrial plants, the biomass of algae contains more lipids and proteins. Algae’s shorter generation times, higher photosynthetic efficiency, and less cultivation space make them an attractive feedstock for the production of biofuels and bio-based goods [16], [48]. Microalgae are a third-generation biofuel with substantial promise for the manufacture of biofuels because of their quick development, high biomass yield, and diverse lipid and carbohydrate contents. Biodiesel, bio gas, bio gasoline, and bio-methane are some of the valuable biofuels produced by algae.

Algal oils are used to make biodiesel and algal carbohydrates are used to make bioethanol.  Fuel oil or methane can be produced from the leftover biomass. Eico-sapentaenoic acid (EPA), docosahexaenoic acid (DHA), bio-control agents, protein supplements, fertilisers, and animal feed can all be made from the leftover material from the manufacturing of biofuel. Biofuel is a renewable fuel that functions in engines similarly to petroleum but emits fewer sulphur and particle pollutants, claim [24].

3. Microalgae cultivation technique

In accordance with the species and developing environment, algae can include a wide range of unique macromolecules, such as proteins, lipids, and carbohydrates. Algal cell membranes are made of lipids, which are molecules with lengthy carbon chains. Algae are frequently grown in photobioreactors and raceway ponds, that can be covered or open.

3.1 Open Pond system

The main design factors for an open pond are light penetration, mix efficiency, residence time and gas/liquid mass transfer. The open ponds are mixed using a hand paddle as well as a paddle wheel-driven motor. Undisturbed ponds, which are easy to build and coated with plastic films at a depth of less than half a metre, grow slowly because of environmental conditions [6]. Raceway ponds, circular pond tanks, closed ponds and huge shallow ponds are the most popular types. Among the main features of open systems is their use of atmospheric CO2. The position of the open system is important since it affects the amount of sunshine. They usually also feature a rotating arm to make sure the culture is continuously agitated [10]. Compared to closed systems that need infrastructure, operation, and maintenance requirements, open ponds are less expensive [5]. Invasion of non-cultivated algae species, fungal development, and contamination of specific microalgal species are the primary drawbacks of such open systems [55]. Open pond systems account for roughly 98% of the total production of algal biomass, and due to the rapid growth rate of microalgae, they can produce 15–20 tonnes of dry biomass per hectare annually. High-yielding types of algae may have an oil content of 50–60% in their dry mass.

3.2 Closed systems (photobioreactors (PBRs))

According to Lee et al. (2016), photobioreactors are highly controlled, high-yield devices designed to provide optimal stirring and high light accessibility. The most common design for photobioreactors is tubular, but they can also be flatter plate, cylindrical, or column-shaped [10]. It encourages a chosen strain to grow under ideal circumstances, including those related to light, temperature, pH, etc.

Photobioreactors with light-emitting diodes can achieve up to 100 gm/m2/h of efficiency. Access to natural sunlight enables photosynthesis and the formation of algae on materials composed of clear acrylic or glass [27]. The primary disadvantage of these controlled facilities is their cost.

 [9]. These bioreactors prevent contamination from bacteria, fungi, and algae species that are not native to the area. It minimizes evaporation, better dissipate heat, nutrients and allows for continuous parameter monitoring [25]. According to Adeniyi et al. (2018), there are additional difficulties such as oxygen buildup, overheating, scaling up difficulties, bio-fouling, and gradual cell death.

4. Algal harvesting

The technique of harvesting involves removing algal cells from their medium without compromising the water content [35]. Numerous studies have found that the cost of harvesting accounts for at least 20% of the total cost of producing microalgal biomass [13]. A variety of methods, such as flocculation, flotation, centrifugation and precipitation, have been employed to harvest algal biomass.

5. Extraction methods for microalgae lipids

Lipid extractions from microalgae can be used to make biodiesel. Proteins and carbs make up the majority of the residues from lipid extraction. However, the process of fermentation of carbohydrates such as starch and other sugars can yield ethanol.

As a crucial stage in the transesterification process, ethanol production can speed up the extraction of oil needed to make biodiesel. In the oil transesterification process, ethanol and sodium ethoxide act as catalysts [48], [15].


Many strains of microalgae have varied compositions and structures, therefore the production of microalgal biodiesel depends on how well and economically lipid extraction works. For the purpose of producing biodiesel on a wide scale, a more effective and economical lipid extraction technique is required. Additionally, the complex and inflexible cell walls of microalgae can be broken down by a variety of mechanical, chemical, and enzymatic treatments, which facilitates solvent penetration and lipid extraction [29], [44].

To get the optimum lipid extraction, choosing the right solvent is essential. Hexane, chloroform, diethyl ether, benzene, methanol, acetone, ethanol, ethyl acetate, and alcohol are examples of polar solvents that can be utilised for extraction [28]. The selective extraction technique can be used to directly convert wet algal paste into jet fuel utilising hexane, ethanol, and Pt/Meso-ZSM-5 as a catalyst [30].

Biomass cells are freeze-dried using N-dimethylcyclohexylamine, although distillation uses a lot of energy for these cells. A variety of solvents with varying volume-to-volume (v/v) ratios, including dichloroethane/ethanol, hexane/isopropanol, chloroform/methanol, and acetone/dichloromethane, can be used to chemically extract lipids. Different species have different levels of permeability, or the ability to pass through the cell membrane and its thickness. Choosing the appropriate solvent is therefore essential to increasing the productivity of lipid extraction. Long-chain lipids are directly secreted into the growth medium by the microalga Botryococcus braunii. There is no question that long-chain hydrocarbons are present in the recovered lipids. This strategy’s benefit is that it can easily and affordably convert long-chain hydrocarbons into biodiesel.

Being able to recover all of the lipids from microalgae to 100% is what makes the soxhlet extraction process the most popular. A combination of methanol and chloroform as a solvent appears to produce more lipid extract than hexane extraction, according to certain studies’ findings. Methanol and chloroform can be used to extract polar and neutral lipids, whereas hexane exclusively dissolves non-polar lipids. To extract lipids more effectively while using less solvent and energy, a more viable strategy combines mechanical and solvent-free extraction techniques with enzymatic processes [42].

6. Environmental impact and sustainability

The environmental impact of algae-based biofuels is usually negligible or nonexistent. The process of making biofuels can, in fact, be connected to various environmental applications such wastewater treatment, energy or heat production, CO2 removal through bio-fixation, biofertilizer use, food production, medical care, and animal feed. When it comes to lowering greenhouse gas emissions, algae are the most environmentally benign fuel source [51]. The European Union Renewable Energy Directive (RED) recommended obtaining up to 15% of energy from renewable sources in order to significantly reduce greenhouse gas emissions to 20% by 2050 [45], [54]. This requirement was accepted since liquid fuels were responsible for 36% of CO2 emissions in 2012 [50] and might reach 45,000 mega tonnes by 2040 [20]. Renewable energy is predicted to surpass traditional energy sources by 2070 [2].

Fossil fuels currently supply 80% of the energy needed annually, making them the primary energy sources [4]. Due to the development of other forms of renewable energy like geothermal, wind, solar, and biomass, the use of fossil fuels has significantly decreased, even if highly industrialised countries like the USA, Germany, Japan, and China still use them [17], [40]. Clean, renewable marine biomass may be the ideal alternative energy source because the production of biofuels from plants such as maize, sugar cane, and sugar beets has detrimental consequences on the environment, society, and economy (soil fertility, biodiversity, and freshwater use). Fossil fuel shortages lead to greenhouse gas emissions and climate change [19].

7. Challenges of algal biofuel

8. Conclusion

Compared to other photosynthetic organisms, microalgae grow quickly, making them an exciting prospect for the production of biofuel. It is possible to grow them on non-arable soil by using wastewater as a nitrogen source. With the help of efficient, reasonably priced harvesting techniques and fuel from microalgae cultivation techniques, algae-based fuels have the ability to satisfy long-term global fuel demands.

They are thought to be among the most affordable, sustainable, renewable, and eco-friendly ways to address food security and climate change. However, due to the lack of effective, reasonably priced harvesting mechanisms from this organism and the limitations of present culture techniques, additional research is needed to create more biofuel from microalgae than is now feasible.

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