Fouling of low-pressure membranes treating natural waters can be substantially mitigated by pre-depositing a thin layer of micron-size adsorbent particles on the membrane – referred to as microgranular adsorptive filtration (μGAF).
Researchers at the University of Washington in Seattle have investigated the role of adsorbent particle size, adsorbent surface loading, and membrane pore size in fouling of μGAF systems by natural surface water.
Testing of μGAF using heated aluminium oxide particles (HAOPs) and powdered activated carbon (PAC) reveals that fouling in such systems occurs both on the membrane and in the cake layer.
Fouling on the membrane is primarily caused by soluble natural organic matter (NOM), and is exacerbated by the use of larger adsorbent particles and smaller-pore membranes.
Such fouling is mitigated by removal of foulants in the pre-deposited layers, so the extent of mitigation is proportional to the adsorbent surface loading, i.e. the thickness of the cake layer.
By contrast, fouling in the cake layer is caused by larger foulants, such as colloids and particulate matter. Such fouling is insensitive to the layer thickness.
The use of smaller adsorbent particles improves the capture of colloids and particles, but also exacerbates such fouling. In these cases, increasing the membrane pore size decreases the rate of fouling on the membrane, but does not affect the cake layer fouling.
Journal of Membrane Science, Volume 433, 15 April 2013, Pages 32–38.
