The use of flocculation for the primary concentration of microalgae is a promising low-cost strategy to harvest microalgae for bulk biomass production. However, there is a need to develop new low-cost, biodegradable and efficient flocculants. This study presents the synthesis, characterization and evaluation of highly charged cellulose nanocrystals (CNCs) for flocculation of the freshwater microalgae Chlorella vulgaris. Two different synthetic strategies were employed. First, highly charged pyridinium grafted CNCs were produced by reaction with either 4-(bromomethyl)benzoic acid (PyBnOO-g-CNCs) or 4-(1-bromoethyl)benzoic acid (PyMeBnOO-g-CNCs) and p-toluenesulfonyl chloride in pyridine. The resulting highly substituted CNCs (DS up to 0.38) were shown to be highly effective in flocculation of Chlorella, with little influence of local conditions such as pH or algal organic matter. Flocculation efficiency in terms of dosage was dependent on DS, which resulted in an optimal dosage of 0.1 mg mg−1 biomass for the highest DS species.In a second route, CNCs were grafted with imidazole (ImBnOO-g-CNCs) to allow control of CNC surface charge with pH through the use of CO2 which is already present in the algal growth medium. These CNCs had a pH-dependent surface charge with ζ-potential ranging between -16 mV at pH 11 to 15 mV at pH 4 with an isoelectric point at pH 6.5. Imidazole grafted CNCs were shown to have little influence on algal cultivation (pH 8) and be capable of up to 90 % flocculation efficiency upon lowering the pH of the growth medium to 3.5 using CO2. The present results highlight the potential of these new type of nanocellulose based flocculants for microalgae harvesting.

Cationic cellulose nanocrystals as flocculants for harvesting Chlorella Vulgaris microalgae

251st National Meeting (2016)

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