The influence of granular materials on the operation and membrane fouling characteristics of submerged MBRs

Aeration to mitigate membrane fouling accounts for the largest fraction of energy consumed in membrane bioreactors (MBRs). To reduce the energy consumed during MBR operation, alternative methods must be developed to control membrane fouling. Granules should be introduced into submerged MBRs to mitigate membrane fouling due to their mechanical cleaning effect on the membrane surface. This study assessed the possible reduction in aeration for submerged MBRs through introducing granules and investigated membrane fouling characteristics from using granules. Two bench-scale MBRs operated in parallel with synthetic wastewater, and granules were introduced into one MBR. The MBR with granules operated stably even after aeration was reduced by 50%. Reversible fouling was almost entirely controlled through the introduction of granules. However, the granules promoted irreversible fouling due to cake elimination, which acted as a dynamic filter. The overall benefit from granules was apparent; although, reversible fouling dominated in the absence of granules. The foulant characteristics differed with granule use. These characteristic changes were also explained by the absence of the dynamic filtration effect.