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Abstract:

Microalgae are a promising source of biomass for the production of, amongst others, food, feed and biofuels. Large scale production of microalgae for these applications however is not feasible due to a high production cost. The main factor for this cost is the expensive harvesting due to the small cells (2-5 µm) and low cell concentration in the cultivation medium (<5 g/L). Currently energy intensive techniques such as centrifugation and ultrafiltration have to be used. Flocculation has been proposed as a method to reduce the energy and cost requirements. Conventional flocculants such as metal salts and synthetic polymers can contaminate the biomass, so there is a growing interest in the use of bio-based polymers. Chitosan is a biopolymer derived from chitin and already extensively investigated for flocculation in wastewater treatment and for microalgae. It is very efficient for the flocculation of fresh water microalgae, but less so for marine microalgae due to coiling of the flexible polymer chain in the high ionic strength medium. Literature is undecided of the feasibility of flocculation of marine microalgae with chitosan and little to no information is available regarding the flocculation mechanism. During this project we attempt to clarify on this issue. Cellulose-based flocculants have been introduced recently. Cellulose nanocrystals (CNCs) are considered interesting for flocculation of marine microalgae thanks to its rigid crystalline backbone, which prevents coiling. CNCs can easily be modified with cationic grafts which allows for efficient interaction with the negative algal cells. More research is required on the flocculant and micraolgal properties in order to gain full understanding of the flocculation mechanism. This will allow us to create a fully bio-based, efficient flocculant.