Cellulose-based nanocrystals as flocculants for harvesting Chlorella vulgaris

We aimed at designing novel cellulose nanocrystals (CNCs) that could serve as microalgae flocculants. In a first study, we synthesized and characterized cationic CNCs with pyridinium groups, grafted by reaction with either 4-(bromomethyl)benzoic acid ([Br][PyBnOO]-g-CNCs) or 4-(1-bromoethyl)benzoic acid ([Br][PyMeBnOO]-g-CNCs) and p-toluenesulfonyl chloride in pyridine. These two types of CNCs showed improved flocculation and separation of the freshwater alga Chlorella vulgaris, when compared to unmodified CNC. We also demonstrated that flocculation using both CNS was negatively affected by AOM. (Vandamme et al. 2015; Bioresource Technology). In a second study, we synthesized a pH-responsive CNC flocculant with imidazole functionality (pKa = 7). Imidazole was chosen as a functional group because the pKa of substituted imidazoles approximates the apparent pKa of CO2 in solution. As such, CO2 could be used for CNC protonation and flocculation initiation, while the CNC remained deprotonated under microalgae cultivation conditions. Furthermore, the modified cellulose nanocrystals showed good compatibility with the microalgae during cultivation, giving potential for the production of reversible flocculation systems. (Eyley et al. 2015; Nanoscale). These studies show that cellulose nanocrystals show great potential as a novel type of flocculant for microalgal harvesting.status: publishe