Dehydration of biomassHarvesting ge

Dehydration of biomass
Harvesting generally results in a 50- to 200-fold concentration of algal biomass. The harvested biomass slurry (5–15% dry solids) must be processed rapidly, or it can spoil within a few hours in a hot climate. The specific postharvest processing necessary depends strongly on the desired product. Dehydration or drying of the biomass is commonly used to extend the shelf-life of the biomass especially if biomass is the final product. Drying methods that have been used for microalgae include spray drying, drum drying, freeze-drying and sun drying. Spray drying, freeze-drying and drum drying of β-carotene-rich Dunaliella all produce satisfactory results in terms of the uniformity of the biomass powder and stability of β-carotene in the biomass (Ben-Amotz and Avron, 1987).

Spray drying is the method of choice for high-value products (>$1000 ton−1), but it can cause significant deterioration of some algal components such as pigments. The expense of drying can be a significant impediment to producing microalgal biomass powder for use in food and feeds. Freeze-drying, or lyophilization, has been widely used for drying microalgae in research laboratories; however, freeze-drying is too expensive for use in large-scale commercial recovery of microalgal products. In some cases, solvent extraction of dry biomass has proved much more effective for recovery of intracellular metabolites than the extraction of wet biomass.

Intracellular products such as oils can be difficult to solvent extract from wet biomass (Belarbi et al., 2000) of undisrupted cells, but are extracted readily if the biomass has been freeze-dried. Lipids have been extracted directly from freeze-dried biomass of Isochrysis galbana (Molina Grima et al., 1994).