Continuous flocculation-sedimentation for harvesting Nannochloropsis salina biomass

Abstract

A continuous flow process is developed for recovery of the biomass of the marine microalga Nannochloropsis salina. Flocculation–sedimentation is used to recover the biomass from an algal suspension with an initial dry biomass concentration of 0.5gL−1, as would be typical of a raceway-based biomass production system. More than 85% of the biomass initially in suspension could be settled by gravity in a flocculation–sedimentation device with a total residence time of ∼148min. Aluminum sulfate was used as an inexpensive, readily available and safe flocculant. The optimal flocculant dosage (as Al2(SO4)3) was 229mgL−1. Relative to a highly effective 62-min batch flocculation–sedimentation process for the same alga and flocculant, the continuous flow operation took longer and required nearly double the flocculant dose. The design of the flocculation–sedimentation system is explained.