Fouling behavior and system performance in membrane bioreactor introduced by granular media as a mechanical cleaning effect on membranes

Abstract

The use of granular polyethylene terephthalate (PET) media provides an effective way to control membrane fouling in aerobic membrane bioreactor (MBR) system under relatively low aeration rate in treatment of synthetic wastewater and real sewage. Without PET media, increasing set point permeate flux caused disproportionate increase in fouling rate. The fouling rate observed at higher flux could not be reduced by lowering the flux due to the formation of irreversible membrane fouling. At fixed aeration rate and permeate set point flux, the fouling rate was much lower with the flat sheet membrane than the hollow fiber membrane as it is combined with the PET media under 5% of packing ratio. The benefit of the granular PET media as suspended carriers to reduce membrane fouling was more pronounced with the flat sheet membrane than the hollow fiber membrane possibly due to better accessibilities and movements of the PET media within flow channels between membranes. However, the use of longer fiber improved beneficial effect of the PET media on fouling reductions than shorter one. It was thought that longer fiber enhanced fiber movement and this should provide synergistic effect on the use of PET media as mechanical cleaning way to control membrane fouling. During the operational period of MBR system, the addition of the rigid spherical PET media in the reactor did not deteriorate treatment efficiency, yielding more than about 97 and 75% in soluble Chemical oxygen demand (COD) and total nitrogen removal efficiencies, respectively.