Algae and microalgae come from freshwater and marine environments, where they grow in water or sediment. Algae and microalgae are organisms that, like land plants, perform photosynthesis, converting and sunlight into carbohydrates. Millions of species are known worldwide. In addition to carbohydrates, they also produce proteins and lipids (oils), including compounds such as enzymes, peptides, toxins, or polymers (Chowdhury 2019). Since algae grow in water, they do not require additional land resources and can even be cultivated in wastewater, simultaneously performing tertiary wastewater treatment. These characteristics make algae an attractive option for biofuel production. However, it should be noted that significant amounts of water and nutrients are required to produce substantial quantities of algae. Algae or microalgae can be produced in open ponds outdoors, in closed ponds using a CO₂ source, or in specialized transparent photobioreactors.

Photobioreactor PBR 4000 G IGV Biotech by IGV Biotech (CC BY-SA 3.0)

The most common method for large-scale algae production is open water ponds, with systems that promote the circulation of CO₂and nutrients. This method is simple but less efficient. Contaminants such as growth-inhibiting substances or unwanted algae can enter the system. Algae cultivation in photobioreactors is more complex and expensive but yields higher output and allows better process control.

Several methods can be used to extract or separate oil from algae:

• Physical pretreatments, such as grinding, microwaves, or high-pressure homogenization, disrupt the cell structure and release lipids. These methods are relatively simple to perform and do not require chemical solvents, but they can be energy-intensive and sometimes less efficient than chemical methods.
• Supercritical CO₂ extraction uses CO₂ under high pressure to dissolve the oil from algae cells. Supercritical CO₂ is an environmentally friendly solvent as it is non-toxic and easy to remove. However, this method is expensive due to the specialized equipment and high energy consumption required.
• Extraction with organic solvents (e.g., n-hexane, chloroform, benzene, diethyl ether, or ethanol) is highly efficient for oil recovery and widely used in industrial applications. However, solvents pose health and environmental risks, so they must be handled carefully and removed after production.