Pilot-scale crossflow ultrafiltration of four different cell-sized marine microalgae to assess the ultrafiltration performance and energy requirements

Four marine microalgae (e.g., Tetraselmis, Picochlorum, Dunaliella, and Synechococcus) with different cell sizes were harvested using pilot-scale ultrafiltration. Average permeate fluxes were 16.75, 19, 25.35, and 33.75 L/m2h at 60 min for Synechococcus, Dunaliella, Picochlorum, and Tetraselmis, respectively. The concentrating factors for Synechococcus, Picochlorum, Dunaliella, and Tetraselmis were 46.6, 42, 39.2, and 39.5, respectively. The highest and lowest microalgal biomass retention was 47.1 and 41.7% for Tetraselmis and Synechococcus, respectively. Due to higher microalgal biomass retention, initial crossflow velocities of 0.16 to 0.18 m/s were reduced to 0.02 to 0.05 m/s for Tetraselmis and Dunaliella sp. The total harvesting energy requirement by membrane and centrifuge was 16.44 - 28.48 GJ/tonne biomass; the smaller the cell size, the lower the energy requirement. The optimum biomass concentrating factor by the membrane filtration process also depended on size; for optimum total energy requirement, tangential flow filtration (TFF) could concentrate a smaller strain more than a larger strain.