Author:

Abstract:

The large-scale production of marine microalgae for biomass production is facing several challenges to be competitive with other renewable and non- renewable energy forms. A major challenge is harvesting, which requires solid-liquid separation of a low amount of biomass consisting of small individual cells from a large volume of marine culture medium. Flocculation based harvesting is promising, but it needs to be optimized to maximize separation efficiency while minimizing any contamination both up- and downstream in the biomass production process. Microalgae flocs in the coagulation step needs to be designed appropriate based on the separation technology of choice: settling versus flotation. The aim of this study was to evaluate and optimize dissolved air flotation using ferric chloride versus alkaline coagulation for Nannochloropsis occulata. Separation efficiency has been compared as a function of the required coagulant dose of optimal separation and the resultant solid:liquid ratio both in the case of sedimentation and flotation. Ferric chloride as coagulant resulted both in a better separation and concentration of the biomass as function of coagulant dose compared to alkaline coagulation. However this coagulant will lead to accumulation of iron in the biomass prior to further processing. Floc size distributions as a function of various stirring speeds have been measured to understand the mechanism of floc formation and breakage. This will lead to a better understanding of the interaction of formed flocs with dissolved air bubbles in a marine system, resulting in optimized separation by flotation. These results will be discussed as a case study illustrating the general challenges of the integration of flocculation based harvesting processes in the production of marine microalgae biomass