Dewatering and Pre-treatment

Once the microalgal culture is harvested from its cultivation system, it exists as a dilute aqueous suspension (between 0.1 and 1 wt.%) and needs to be concentrated for downstream processing. Solid-liquid separation techniques (centrifugation, filtration, flocculation) are typically used to dewater the culture up to a solid con­centration of 10 wt.% [9].

The dewatered microalgal paste then undergoes a pre-treatment step intended to enhance the efficiency of subsequent chlorophyll extraction. The pre-treatment can be performed in multiple steps or as a single process. As one alternative, the semi­wet paste is completely dried and the resulting biomass is milled into powder of uniform size. Residual water in the paste needs to be removed as it is known to act as a barrier which impedes chlorophyll transfer from the microalgal cells into the extracting solvent. As another alternative, the paste can be exposed to disruption meth­ods which destroy the microalgal cellular structures and force the release of intracel­lular chlorophylls to the surrounding medium. Exposing microalgal cells to mechanical cellular disruption methods (grinding, homogenization, and sonication) prior to sol­vent extraction has been found to increase final chlorophyll yield [28, 44, 49]. Simon and Helliwell [49] found that, without preliminary disruption, only a quarter of the available intracellular chlorophyll a can be extracted from microalgal cells.

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