Comparison of dual stage ultrafiltration and hybrid ultrafiltration-forward osmosis process for harvesting microalgae (Tetraselmis sp.) biomass

Abstract

In this study, a hybrid ultrafiltration–forward osmosis system was compared with a dual stage ultrafiltration process for the harvesting of marine microalgae. To the best of the author’s knowledge none of the previous studies compared the performance of a dual stage ultrafiltration process with a hybrid UF-FO process for the harvesting of marine microalgae. The application of the hybrid process is expected to reduce the energy consumption for harvesting the microalgae without affecting the concentration factor and final product quality. In forward osmosis, the impact of the feed and draw solutions flowrate and the membrane orientation was investigated. The feed solutions were unfiltered microalgae solution and ultrafiltered concentrated microalgae while the draw solution was brine collected from a thermal desalination plant. A maximum total algal harvesting concentration factor of 37.3 was obtained using the hybrid ultrafiltration-forward osmosis system and the dual stage ultrafiltration process. The flowrate used in the forward osmosis process was 2.5 LPM for the feed solution and 0.8 LPM for the draw solution and the active layer was facing the feed solution (i.e. FO mode). The energy consumption in the hybrid ultrafiltration-forward osmosis system was 24% less than the dual-stage ultrafiltration system.