Impact of forward flushing and backwashing on the flux performance of gravity-driven membrane (GDM) filtration

Abstract

Gravity-driven membrane (GDM) filtration has received increasing attention as a sustainable drinking water technology due to its low energy consumption with little maintenance, and capability of clean water production. However, the low flux in GDM filtration is considered as an obstacle to limit the widespread GDM application. To enhance the flux performance, this study investigated membrane cleaning strategies through laboratory-scale GDM experiments. In GDM experiments using a filter holder-type reactor, backwashing and forward flushing methods were inter-compared, in which both methods showed similar cleaning performance. As forward flushing is typically easy to implement, further studies were conducted for the forward flushing. A range of forward flushing conditions were tested, in which the following optimal flushing conditions were determined; flushing rate of 50mL/min, duration of 30 s, and interval of 12 h. The net water production could be increased with the increasing flushing rate and decreasing flushing interval while it was less affected by the flushing duration. The GDM with forward flushing were also tested in a submerged-type reactor, showing similar impact of the optimized forward flushing conditions on the flux performance while the pressure-normalized fluxes were generally larger in the submerged-type than the external-type reactor. Further studies are needed to confirm the cleaning performance of forward flushing in more realistic GDM operation scenario.