Industrial valorisation of photosynthetic microalgae

The term "microalgae" generally covers photosynthetic microorganisms from a few microns to a few tens of microns in size, growing in an aqueous environment. In addition to microalgae proper, this family includes cyanobacteria (including spirulina), which are also used industrially. Known as phytoplankton in the oceans, microalgae represent an emerging biological resource of growing industrial interest. Microalgae are particularly rich in proteins, lipids or specific molecules with strong biological activities or original functional properties, so their products of interest are varied. These, combined with surface production yields that are generally higher than for conventional agricultural resources, offer relevant alternatives, both as a new food source and as a plant-based raw material for substitutes to petro-sourced products.

Global production in 2020 is estimated at several tens of thousands of tonnes per year (in dry biomass). Today, the main use of microalgae is in the food sector, either directly in dry form or as an ingredient in food formulations. Their content is often high in original compounds, such as pigments. For this reason, they are also used in the nutraceutical, pharmaceutical and cosmetics industries, in the form of extracts enriched with molecules of interest. Over 30% of the world's microalgae production is also destined for animal feed (particularly aquaculture). This rapidly diversifying sector is witnessing the growing commercialization of products derived from microalgae. This applies in particular to global demand for polyunsaturated fatty acids and carotenoids (astaxanthin, β-carotene, lutein), which are currently highly coveted by manufacturers. Other emerging markets include bioplastics, composite materials, fine chemicals, fertilizers and 3rd-generation biofuels. Interest in microalgae also extends to the phytoremediation sector for purifying nutrients and metals from wastewater, as well as bioprocesses for recovering waste heat and carbon dioxide from industrial flue gases.

Since the 1980s, commercial production has focused on a few species of microalgae, including Arthrospira platensis and Arthrospira maxima, commonly known as spirulina (food protein, antioxidant), Haematococcus pluvialis (pigment and antioxidant astaxanthin), Chlorella sp. (food protein) and Dunaliella salina (β-carotene antioxidant). The development of the microalgae industry is closely linked to improved techniques for producing and extracting their molecules, but also to human needs and regulations, which also play a fundamental role, particularly in the food sector. Technologies for growing microalgae on a large scale, in tanks or photobioreactors (PBRs), were developed in the 1950s and have since evolved considerably. With new technologies, it is now possible...