Effect of intensive membrane aeration and membrane flux on membrane fouling in submerged membrane bioreactors: Reducing specific air demand per permeate (SADp)

The effects of membrane module configuration and membrane flux on specific air demand per permeate (SADp) required for stable operation of a submerged membrane bioreactor (MBR) for treating municipal wastewater were investigated. An intensively aerated membrane module was developed to reduce the membrane fouling in submerged membrane bioreactors. In this module, coarse bubbles can be introduced at higher density in the vicinity of the membrane fibers, made of polytetrafluoroethylene (PTFE), which has a very high tensile strength (90-110 N/fiber) even though it has high porosity (about 80%). By applying the intensively aerated membrane module developed in this study to pilot-scale MBRs, very low membrane fouling rate was achieved during the continuous MBR operation. The observation of fiber movements using high speed camera revealed that the membrane-fiber vibration in the intensively aerated module were apparently intensified compared with those in a conventional membrane module. Reducing membrane flux was also beneficial for reducing SADp. When the MBR equipped with the intensively aerated module, stable continuous MBR operation without any membrane cleaning for two months under low SADp (8.8 m3-air/m3-permeate) was achieved by lowering membrane flux to 16 L/m2 h (or 0.4 m3/m2/day), even in the short membrane height of 0.5 m. These results strongly suggest that there is still great room for improving the efficiency of membrane aeration by optimizing hydrodynamics around membrane modules.