Dewatering Algae Using An Aquaporin-Based Polyethersulfone Forward Osmosis Membrane

Low energy requirement in algae harvesting is necessary for sustainable biofuel production. Forward osmosis (FO) can provide a potential alternative for low energy consumption by using osmotic pressure between the draw solution (DS) and feed solution (FS). In this study, an aquaporin-based polyethersulfone (PES) membrane was evaluated for algal dewatering using FO. Three different types of DS (NaCl, KCl and NH4Cl), different cross flow velocities (CFVs), and configuration variations were compared to determine the FO performance to dewater Chlorella vulgaris. For short-term operation (500 min), the average water fluxes were 5.6, 4.8, and 4.3 L m−2 h−1 for NaCl, KCl, and NH4Cl, respectively and all DSs showed increased fluxes with increased CFVs. In particular, this study found that NH4Cl is the best candidate among the three tested DSs for improved water flux and low reverse salt flux for the aquaporin-based PES FO membrane. Natural seawater was also tested and revealed well-defined DS performance compatible with NaCl. For a longer duration experiment, 81% of algae dewatering was achieved with a 29% flux drop which may be attributed to the increasing FS concentration, concentration polarization and the loosely attached algal biofilm on the membrane surface. Overall, this study demonstrates a new iteration of the aquaporin-based PES membrane for algal dewatering in FO application