Liquid Biofuels from Microalgae - Production Challenges and Perspectives

Two main types of liquid biofuel will be in production in 2023: biodiesel and bioethanol. Their production has increased in recent years, thanks to the use of mature technologies such as fermentation of sugar cane, beet or corn, and transesterification of waste oil, rapeseed or soya. However, the question of the raw materials used remains. The use of mass production intrinsic to the energy sector raises land-use conflicts with the production of agricultural resources for food (e.g. rapeseed and maize), as well as the risk of deforestation (e.g. oil palm). In France, since the Grenelle Environment Forum in 2009, priority has been given to so-called 2nd or 3rd generation biofuels, which differ from 1 ^and generation biofuels (also known as agrofuels) in that they are not produced from crops traditionally used for food. 2nd generation biofuels are gradually replacing those of the 1 ^era generation, and are derived from non-edible raw materials, agricultural waste or waste products such as used cooking oils and animal fats. This path is bringing undeniable progress, with the development of processes aimed at optimizing the use of bioresources (biorefinery-type approaches) and the industrial-scale implementation of circular economy principles. However, the growing demand for biofuels raises the question of their long-term supply. By 2023, for example, the supply of used vegetable oils is already under pressure. Obligations to integrate biofuels into the various transport sectors, and civil aviation in particular, will only increase these tensions due to the very high volumes involved.

Biofuels derived from microalgae fall into the category of 3rd generation biofuels. Although microalgae can be used as food, they are not considered a primary agricultural resource. They can also be grown on non-arable land [CHV 4 030] . As with higher plants, the photosynthesis-based growth of microalgae generally requires only an input of light, mainly inorganic nutrient sources, CO ₂ and water. Some of the nutrients can be supplied through industrial effluents (CO ₂ from industrial fumes, nitrates and phosphates from wastewater), opening up possibilities in the circular economy, where microalgae are combined with industrial effluent treatment to produce biomass of interest for applications including energy. What's...