5 - Harvesting of microalgae: Overview of process options and their strengths and drawbacks

Abstract

Microalgae harvesting is a major challenge because microalgal cells are small and carry a negative surface charge and biomass concentration in cultures is relatively low. The microalgal biomass (0.05%, w/w) needs to be concentrated to a paste with 15%–25% water content. This dewatering process is ideally performed in two stages, including a first preconcentration step in combination with a second dewatering step. Microalgae are a very heterogeneous group of organisms differing in size and shape and culture conditions. Applications of microalgal biomass range from low-value (biofuels) to high-value applications (nutraceuticals). It is therefore likely that the optimal harvesting technology differs between species, culture conditions, or the final application of the biomass. Harvesting should not cause contamination of the biomass or influence biomass quality. Finally, water recycling to reduce the water footprint is an important aspect to include into the harvesting process. This chapter gives an overview of several harvesting process options with the focus on their strengths and highlighting the aforementioned aspects.