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Cécile Formosa-Dague

LISBP, CNRS, Toulouse, france

Towards a better understanding of microalgae natural flocculation mechanisms to enhance flotation harvesting efficiency (scientific report)

Annual meeting: 2019

Fields-Topics: P5 Products and Technology

Type of talk: Fellows Speed Presentation

Towards a better understanding of microalgae natural flocculation mechanisms to enhance flotation harvesting efficiency (scientific report)


I studied fundamental microbiology and biotechnologies at the university Paul Sabatier of Toulouse, in France. After obtaining my master degree in 2011, I started a PhD, in 2012, at the Laboratoire d’Analyse et d’Architecture des Systèmes (LAAS-CNRS) in Toulouse. During this PhD, I have worked on important issues related to multidrug resistant microorganisms using nanobiotechnologies, more specifically Atomic Force Microscopy. Afterwards, I chose to do a postdoc in Belgium at the Université catholique de Louvain, between 2015 and 2017, in the nanobiophysics field in which I could learn to lead an original research project using a multidisciplinary approach. Indeed, during this postdoc, I had the opportunity to work on biofilm formation by bacterial pathogens, but more interestingly, I could work on my research project with scientists with different scientific backgrounds. These two research experiences led me to develop research interests in biological interfaces and their interactions with their environment or with other interfaces. To address these challenges, I develop multidisciplinary approaches, at the frontier between biology, chemistry and physics. I recently got a permanent position at CNRS.


Towards a better understanding of microalgae natural flocculation mechanisms to enhance flotation harvesting efficiency (scientific report)

Because of their important oil producing capacity, microalgae are a promising resource for biofuel production, but not only. Indeed, the potential of microalgae is even greater as they also represent an important source of biomass and molecules of interest such as carbohydrates, proteins or pigments. But currently, their industrial use is limited by the lack of efficient harvesting techniques. Harvesting consists in removing cells undamaged from their aqueous culture medium where their concentration is low, at a minimal cost. For this purpose, flotation is a promising technique, where air is transformed into bubbles rising through a microalgae suspension. As a result, microalgae cells get attached to the bubbles and are carried towards the surface. But flotation harvesting is challenging for microalgae as they do not adhere to bubbles because of their surface charge and low hydrophobicity. To enhance flotation efficiency, one possibility is to increase the microalgae particle size by adding molecules that flocculate the cells and facilitate their capture by the bubbles. However such flocculants can affect the cells and impact the quality of the products derived from the biomass; in many cases, natural flocculation thus represents an interesting alternative. There are several natural flocculation mechanisms: identifying and understanding these mechanisms could help in increasing flotation efficiency without the possible damages of synthetic flocculants.
During my AgreenSkills+ fellowship, I used a multi-scale approach, involving nanoscale biophysical experiments (atomic force microscopy imaging and force spectroscopy) and population-scale flocculation/flotation experiments to decipher auto-flocculation and bio-flocculation mechanisms in the cases of three industrially-relevant microalgae species: Phaeodactylum tricornutum, Dunaliella salina and Arthrospira platensis.
Our results showed that for both P. tricornutum and D. salina, an auto-flocculation mechanism was involved, and was mediated by an increase of pH in the medium, resulting in the precipitation of magnesium hydroxide. This precipitate flocculates the cells through a charge neutralization mechanism in the case of P. tricornutum, and through a sweeping mechanism for D. salina. As for A. platensis, our results showed that in bicarbonate-rich culture conditions, bioflocculation, mediated by extra-cellular polysaccharides, was responsible for flocculation.
The approach developed in this work, combining nanoscale and population-scale experiments, has offered the possibility to understand the molecular mechanisms of natural flocculation mechanisms in microalgae, which are key to develop efficient flocculant-free large-scale harvesting flotation processes. The next steps of the project, which will be developed in the next years thanks to an ANR funding, will focus on measuring the interactions between the cells and the bubbles, using a combination of AFM with microfluidic AFM probes (FluidFM technology), to go a step further in the comprehension of the global process of microalgae flocculation/flotation harvesting.

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