Microalgae and Cyanobacteria Industrial Production

Photosynthetic micro-organisms such as microalgae and cyanobacteria are gaining ground in many application sectors. Thanks to the specificity of photosynthetic metabolism compared with heterotrophic micro-organisms (bacteria, yeast), and to a high level of biodiversity, the potential applications are wide-ranging. Photosynthetic micro-organisms are used for (i) the solar production of bioenergies (lipids for use as biodiesel or biokerosene, sugars as a source of bioethanol or biomethane, hydrogen by water biophotolysis, etc.), (ii) the production of biofuels (bioethanol, bioethanol, etc.) and (iii) the production of biofuels (bioethanol, bioethanol, etc.).), (ii) the production of natural molecules of interest (pigments and polysaccharides for cosmetics and nutraceuticals, omega-3 proteins and lipids for food, synthons for green chemistry, etc.) or (iii) the depollution of gaseous effluents (CO ₂ from smoke) or liquids (nitrates, phosphates, metals from wastewater) with the associated production of a plant biomass with multiple outlets.

Because of the particular needs of photosynthetic growth, however, the industrial production of microalgae and cyanobacteria requires dedicated technologies radically different from the bioreactors conventionally used in the fermentative industry. These photo-processes must enable photosynthetic growth based on the assimilation, thanks to captured light, of inorganic nutrients (CO ₂ or hydrogen carbonates) and minerals (nitrates, phosphates, etc.). Depending on operating constraints and objectives, the cultivation process is to be selected from a wide panel of technological solutions ranging from extensive open systems (lagoon-type) to intensified, closed systems (photobioreactor-type) and using either solar energy or an artificial light source.

This technological diversity results in a wide range of performance levels, depending on the level of control and optimization applied. However, these technologies are governed by a set of specific rules that have now been tried and tested. These rules make it possible to propose rational approaches for engineering missions involving forecasting the performance of a given technology, designing intensified technologies with very high productivity levels, and optimizing the operation of given production units to maximize performance.

This article sets out to present the essential elements of this engineering approach, as well as the main concepts involved. In the first part, the general principles of microalgae and cyanobacteria cultivation will be discussed. The various factors affecting photosynthetic growth will be presented. In the second part, the fundamental principles...