Reversible Flocculation of Microalgae using Magnesium Hydroxide
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Reversible Flocculation of Microalgae using Magnesium Hydroxide Dries Vandamme & Annelies Beuckels & Giorgos Markou & Imogen Foubert & Koenraad Muylaert
# Springer Science+Business Media New York 2014
Abstract Flocculation of microalgae is a promising low-cost strategy to harvest microalgae for bulk biomass production. However, residual flocculants can interfere in further downstream processes or influence biomass quality. In this study, a new concept is demonstrated based on reversible magnesium hydroxide flocculation, using Chlorella vulgaris and Phaeodactylum tricornutum as, respectively, a freshwater and a marine model species. We show that flocculation was induced by precipitation of magnesium hydroxide at high pH (10 to 10.5). This resulted in a magnesium content of the microalgal biomass of 5 % for Chlorella and 18 % for Phaeodactylum. After pre-concentration of the microalgal biomass by gravity sedimentation, 95 % of the precipitated magnesium hydroxide could be removed from the biomass by mild acidification (pH 7 to 8). The pH fluctuations experienced by the microalgae during flocculation/de-flocculation had no influence on biomass composition (FAME, total N and P, carbohydrates, proteins, mineral content) and on the viability of microalgal cells. Magnesium can thus be used as pH-
D. Vandamme (*) : A. Beuckels : K. Muylaert KU Leuven Kulak, Laboratory Aquatic Biology, Etienne Sabbelaan 53, 8500 Kortrijk, Belgium e-mail: [email protected] I. Foubert KU Leuven Kulak, Research Unit Food & Lipids, Department of Molecular and Microbial Systems Kulak, Etienne Sabbelaan 53, 8500 Kortrijk, Belgium I. Foubert Leuven Food Science and Nutrition Research Centre (LFoRCe), KU Leuven Kasteel parkArenberg 20, 3001 Heverlee, Belgium G. Markou Department of Natural Resources Management and Agricultural Engineering, Agricultural University of Athens, Iera Odos 75, 118 55 Athens, Greece
dependent reversible flocculant for harvesting microalgae in both marine and freshwater medium. Keywords (Micro)-algae . Coagulation . Biofuels . Biomass
Introduction Microalgae are a highly promising feedstock for production of biofuels. These unicellular microorganisms have a high areal productivity and produce biomass that is low in structural compounds like cellulose or lignin and can thus be almost entirely valorised in a biorefinery context, with the lipid fraction of the biomass being used for biodiesel production while the remaining protein-rich residue can be used as animal feed [1]. Moreover, they do not compete directly with food production by using agricultural crop area. Production of microalgae, however, is a relatively energy-intensive process. To make microalgae competitive with conventional agricultural crops, the cost and energy inputs of the production process need to be reduced by at least an order of magnitude. One of the major challenges is situated in the harvesting of the microalgae. Because microalgae cells are small (5–50 μm) and the biomass concentration in the medium is low in case of open pond c
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