Microalgae are generally assumed to achieve much higher areal productivities than agricultural crops. Microalgal biomass is poor in lignocellulose and rich in lipids and proteins, making it a valuable feedstock for biofuels or animal feed production.So far, however, the production cost of microalgae is still high and production is only economically feasible for high-value applications such as food supplements, natural pigments or poly-unsaturated fatty acids. To be able to use microalgae for low-value applications such as feed or fuel production or even wastewater and flue gas treatment, the production cost has to be reduced by at least an order of magnitude. Due to the small size of the algal cells and their relatively low concentration in the culture medium, cost-efficient harvesting of the microalgal biomass from the culture broth is a major challenge. A significant reduction in the cost of microalgal biomass production will require cost-efficient methods for harvesting microalgae. If the microalgae could be preconcentrated by coagulation-flocculation and gravity sedimentation prior to centrifugation, the energy demand for harvesting could be strongly reduced. We studied 3 types of flocculation both for freshwater and marine microalgal species
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