Effect of powdered activated carbon on the performance of an aerobic membrane bioreactor: Comparison between cross-flow and submerged membrane systems

The effects of powdered activated carbon (PAC) on the performance of an aerobic membrane bioreactor were investigated under two different filtration modes: cross-flow and submerged filtration. Under a cross-flow microfiltration mode, floe breakage resulting from sludge recirculation caused a rapid decrease in the microbial floe size and the release of colloidal and soluble components including extracellular polymeric substances (EPS). The released components caused rapid loss of membrane permeability by the formation of a dense cake layer on the surface of the membrane. Biological activated carbon (BAC) sludge formed by the addition of PAC released lower amounts of fine colloids and EPS. Although the pattern of floe breakage of the BAC sludge by pumping shear was similar to that of conventional activated sludge, PAC in the BAC microbial floe adsorbed or entrapped some microfloc components into the floe and reduced permeability loss by approximately 35% compared with conventional activated sludge. Under a submerged microfiltration mode, the effect of PAC addition was more pronounced. For the BAC sludge, the increase in transmembrane pressure was more sluggish and, thus, the operating interval could be extended up to 3 times that for the submerged membrane bioreactor with normal activated sludge.