Phototaxis and new methods for the concentration of microalgae suspensions

Algaculture has gained increased interest from both scientific and industrial communities over the last decades, due to the great potential of microalgae for bio-production (food, food dyes, omega3 acids, bioplastics, fertilizers, biofuels), as well as for pollution control and remediation.

During biotransformation processes, the microorganism population grows by converting a substrate into a product, resulting in an alteration of the culture media.

One of the biggest obstacles when scaling up algal growth processes to the industrial scale, remains the efficient concentration, filtration and separation of the microorganisms from the culture media for renewing their environment and harvesting the bio-products.

This issue becomes even more complex when considering the biofuel production process, as the microalgae population needs to be temporarily transferred from the sulfur deficient culture media, to sulfur rich conditions for regenerative purposes.

In a recent experimental study, we have shown that photo-sensitive algae could be efficiently concentrated around the center of a flow when stimulated by a light signal (see our Research News for more details).

In the present project, the aim is to further understand the hydrodynamic properties of phototactic microalgae suspensions under light stimulation, to develop a new separation/concentration method based on the light-control of algal repartition in their culture media.

Our work at LIPhy will be dedicated to the understanding of the fundamental aspects involved in the hydrodynamic phenomena at play in this system, focusing on the interactions between the algae with and without light stimulation, on the hydrodynamic diffusion processes (above illustration), and on collective and concentration effects. For that purpose, a small scale device (a few millilitre size) will be developed.

Such a fundamental study will contribute to the optimisation of the above mentioned critical separation steps, and should bring interesting solutions towards industrial applications.