CO2 Conversion Into Thermoplastic Starch By The Microalga Chlorella vulgaris

Keywords: Microalgae, Chlorella vulgaris, Thermoplastic starch, Solar energy, Bioplastic, Carbon dioxide

Chlorella vulgaris as a photosynthetic vector for converting solar energy and CO2 into starch

Microalgae are unicellular organisms capable of rapidly adapting their metabolism to environmental conditions, which allows them to achieve both high area productivities and starch contents under natural light. While conventional photosynthetic crops such as maize and rice reach maximum starch productivities of 10 t/ha/year, this metabolic flexibility enables potential higher area productivities.

With Chlorella vulgaris, a green microalga species commonly used as a food supplement, we notably obtained a productivity of 0.43 g/L/day in total sugars (mainly starch). Based on extrapolation assumptions (150 production days per year, solar resources from Southern France, etc.), this leads to an annual area sugar productivity of over 20 t/ha/year. Beyond this potential gain in productivity, microalgae offer the advantage of not mobilizing arable land for the manufacture of thermoplastic starch.

Producing, extracting, and transforming Chlorella vulgaris starch into bioplastic

We optimized the production of Chlorella vulgaris starch under natural light at the pilot scale (180 L). During cultivation at low concentration (<1 gDM/L) over three days of nitrogen stress, approximately 3% of incident solar energy (including infrared) is converted into sugars, primarily in the form of starch.

To manufacture a bioplastic, the cells are then lysed at high pressu