(135d) Study of MF Membranes for Microalgae Dewatering and Surface Modification for Fouling Mitigation

Microalgal cultivation is an efficient approach for CO₂ capture and utilization. As the algae solutions are dilute (<0.5 g/L), dewatering is an extremely energy-intensive step for algae harvesting and conversion to biofuels and valuable chemicals. MF membranes have been investigated for dewatering due to their high energy-efficiency and well-controlled pore sizes to reject microalgae (1-5 microns). However, the membranes suffer from fouling by organic matters in the algae solutions, and most studies use a single foulant instead of real algae solutions. There lacks an understanding of membrane fouling with real algae solutions. In this study, we evaluate the dewatering performance of commercial polyether sulfone (PES) MF membrane in dead-end and cross-flow systems. The membrane surface was also modified with hydrophilic materials such as zwitterions and graphene oxide (GO) to improve antifouling properties. The membranes were characterized using a goniometer, SEM, etc. The effects of membrane molecular weight cut-off (MWCO), algal concentration, transmembrane pressure, and membrane cleaning on the dewatering performance were thoroughly investigated. The fouling behavior in the membranes can be described using the Hermia fouling model. The modified membranes exhibit higher water permeance than the pristine membranes when challenged with different concentrations of algae, indicating that the surface modification improves antifouling properties. For example, the GO-modified and zwitterions-modified membranes show 30% and 50% higher water permeance than the unmodified membranes under different feed pressures, respectively. Membranes show much higher water permeance in the dead-end cells than the cross-flow system due to the higher Re numbers in the dead-end cells. After the fouling, the membranes were cleaned using deionized water or NaOH solutions, and both cleaning methods can recover more than 75% water permeance.