Abstract
Gravity-driven membranes (GDM) generally achieve high retention performance in filtration of organic matter with a smaller size than the membrane pore, yet the in-depth mechanism remains unclear. Thorough analysis of the retention mechanism is crucial for optimizing GDM properties and improving GDM filtration performance. The performance and interaction mechanism of gravity-driven ceramic membrane (GDCM) filtrating smaller organic matter (SOM) were systematically studied. Rejection rate grew noticeably for like-charged foulant, whereas it only grew slightly for opposite-charged foulant as operation height decreased. Flux declined more seriously at lower operation height, probably due to heavier cake fouling caused by the rejected foulant. Interactions of ceramic membrane-SOM were analyzed through extended Derjaguin-Landau-Verwey-Overbeek theory (XDLVO) and hydrodynamic permeation drag (PD). Among van der Waals (LW), acid-base (AB), and electrostatic (EL) forces in XDLVO, EL played a significant role on GDCM filtrating SOM, and altering membrane electrostatic property could greatly influence SOM filtration. Furthermore, the rising PD force largely weakened the EL dominant zone with operation height increasing, while barely influencing the LW and AB dominant zones. Therefore, the weakened EL-dominant repulsive zone caused less rejection of like-charged foulant with operation height increasing. Fe2O3- and MnO2-modified membranes further validated the comprehensive influence of LW, AB, EL, and PD interactions on GDCM filtration. The possible "trade-off" of pore blocking-cake fouling with operation height decreasing demonstrated potential enhancement for both rejection and antifouling performance by electrically modified membrane under ultralow pressure. This study provides insight on membrane selection/preparation/modification and performance control of ultralow pressure-driven filtration.
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