Scale-up of a low energy striless photobioreactor using phototaxis and motile microalgae

INTERNSHIP OFFER

Master 1/Master 2 (5 - 6 months)

Scale-up of a low energy striless photobioreactor using phototaxis and motile microalgae

Keywords: Motile microalgae, Chlamydomonas Reinhardtii, motility, phototaxis, mass transfer (CO₂), image processing.

INTRODUCTION

Microalgae possess diverse biotechnological potential: they can harness solar energy and extract the necessary carbon from atmospheric CO₂ to perform certain biotransformations and produce value-added compounds. However, one of the main obstacles to their large-scale use is the cost of harvesting them, with relatively low-density cultures (0.5 to 4.0 g dry matter/L), and sometimes also the operational costs of the cultivation systems.

This internship is part of a project aimed at developing a new biotechnology for the energy-efficient cultivation and harvesting of microalgae. In this technology, mixing and harvesting operations will be carried out by controlling "phototaxis": a phenomenon of locomotion of an organism guided by light stimuli. This physiological characteristic is specific to several species of motile algae, including the alga Chlamydomonas Reinhardtii. This alga, approximately 10 µm in diameter, uses its two flagella and stigma to detect the presence and intensity of light, swim, and modulate its distance from the light source.

Our most recent study [1] suggests that controlling phototactic movement can both (i) provide access to nutrients, particularly dissolved CO₂, and (ii) be used for cell harvesting. This technology could offer several advantages, such as eliminating mechanical agitation and thus reducing energy consumption for mixing and harvesting operations. Indeed, mechanical agitation, or even agitation by aeration in large volumes, such as ponds, can be very costly and poorly controlled.

INTERNSHIP TASKS

The first proof of concept of a bioreactor agitated by phototaxis only considers very small reaction volumes, not exceeding 50 ml [1]. The main task of the intern will be to test the feasibility of the concept on a larger scale (1L or more). In particular, he/she will have to:

• Finalize the construction of an experimental setup (~1L) for the culture of algae whose agitation will result from the control of the phototaxis of the microalgae Chlamydomonas Reinhardtii,
• Adapt this setup to observe and analyze the operation of the reactor by image acquisition and processing,
• Experimentally test the limits of the bioreactor in terms of biomass production and CO₂ absorption (mass transfer) in the case of an agitation controlled by phototaxis,
• Observe and describe the possible bioconvective phenomena characteristic of the reactor and identify the parameters governing these phenomena.
• Develop a simplified mathematical model (0D or 1D) describing the movement and growth of biomass in the bioreactor.