Effect of mechanical scouring by granular activated carbon (GAC) on membrane fouling mitigation

The mitigation of membrane fouling due to the mechanical scouring behavior of granular activated carbon (GAC) particles of diameters ranging from 0.9 to 4.6 mm was studied using a GAC tangential shear-membrane filtration cell, wherein GAC was directed to scour the membrane surface by a magnetic stirrer placed 10 mm above the membrane. Two membrane pore sizes (namely, 0.1 and 0.45 μm), two permeate fluxes (namely, an above- and below-threshold flux) and two operation modes (namely, continuous and intermittent filtration) were investigated. Results indicated that: (1) GAC marginally improved threshold flux values, with the benefits more significant for the larger-pore membrane; (2) For continuous filtration, the presence of GAC reduced the cake layer resistance, but increased the irreversible resistance; (3) For intermittent filtration, GAC was surprisingly less effective in reducing cake layer resistance compared to continuous filtration for the smaller-pore membrane, but did not increase the irreversible fouling resistance; (4) Both threshold flux and fouling layer resistance were independent of GAC particle diameter, which contradicts the inertial lift model and thereby affirms the dominance of the mechanical scouring behavior studied here; (5) A model developed, based on momentum transfer between the GAC particle and foulant, provided a mechanistic understanding.