(702b) Study of MF Membranes for Microalgae Dewatering and Surface Modification for Fouling Mitigation
AIChE Annual Meeting
2022
2022 Annual Meeting
Separations Division
Antifouling Membranes for Water Purification
Friday, November 18, 2022 - 8:21am to 8:42am
Microalgal cultivation is an efficient approach for CO2 capture and utilization. Microfiltration (MF) membranes have been investigated for concentrating dilute algae (<0.5 g/L) because of their high efficiency. However, the membranes suffer from fouling by organic matters in the algae solutions, and there lacks an understanding of membrane fouling with real algae solutions. In this study, we evaluate the dewatering performance of commercial polyethersulfone (PES) MF membranes in dead-end and cross-flow systems. The membrane surface is also modified with hydrophilic zwitterions using bio-inspired dopamine to improve antifouling properties. The effects of membrane molecular weight cut-off (MWCO), surface hydrophilicity, algae concentration, and hydrodynamics properties on the dewatering performance were thoroughly investigated. The pristine membranes exhibit water permeance of 225 and 80 LMH/bar in the dead-end test against 1 and 10 g/L algae, while the zwitterion modification almost doubles water permeance to 386 and 166 LMH/bar, respectively. Moreover, the zwitterion-modified membrane exhibits 20% higher permeance than the pristine membrane in the long-term cross-flow test, confirming the enhanced antifouling properties. The fouling behaviors in both membranes can be satisfactorily described using the Hermia fouling model. The membranes show permeance lower in the cross-flow tests with a Reynolds (Re) number of ~1,000 than in the dead-end tests with a Re number of 65,000. This result is also consistent with the thickness of the cake layer formed on the membrane surface, i.e., 20 microns after the cross-flow test and 2 microns after the dead-end test. For sustainable operation, the membranes are also cleaned using deionized water or NaOH solutions, and both cleaning methods can recover more than 75% water permeance. Understanding the fouling mechanisms of the membranes with real algae solutions can be critical to designing membranes for this important application.