Comparison of the filtration characteristics between attached and suspended growth microorganisms in submerged membrane bioreactor

An attached growth bioreactor was designed to minimize the effect of suspended microorganisms on membrane fouling in submerged membrane bioreactor. Comparison of mixed liquor from attached and suspended growth systems was made to elucidate major factors giving rise to different filtration characteristics. Unexpectedly, the rate of membrane fouling of the attached growth system was about 7 times higher than that of the suspended growth system despite similar characteristics of soluble fraction from the two reactors. Filtration performance proved to depend on the concentration of mixed liquor suspended solids (MLSS). Better filtration performance with suspended growth was explained by the formation of dynamic membranes with suspended solids. A series of analyses such as hydraulic resistance, specific cake resistance, scanning electron microscope, and atomic force microscope were carried out to elucidate the different filtration characteristics of the two systems.