Control of Membrane Fouling Occurring in Membrane Bioreactors (MBRs)

Abstract

Membrane bioreactor (MBR) is a promising technology for future wastewater management. However, occurrence of membrane fouling in the process hinders widespread application of this technology. There are two types of membrane fouling: physically reversible fouling and physically irreversible fouling. The former is the fouling that can be cancelled by physical cleaning such as hydraulic backwashing, whereas the latter is the fouling that needs chemical cleaning to be cancelled. In the operation of MBRs, physically reversible fouling is usually dominant. Therefore, control of physically reversible fouling with a low energy consumption is important. In most of commercialized MBRs, control of physically reversible fouling is attempted by intensive aeration through aerators placed beneath the membrane modules. Various design factors including bubble size, air flow rate and arrangement of aerators and membranes would affect the efficiency of cleaning by aeration. Currently, however, it is totally unclear what is occurring in MBR tanks: multiphase flow in MBRs composed of biomass suspension with high viscosities, bubbles and membranes is too complex to monitor. As a result, no rational method for design of aeration for MBRs is available, which leads to considerable underestimation of the performance of MBRs. Application of advanced research methods of multiphase flow could change this situation: rational design of MBRs is enabled by the aid of cutting-edge knowledge on multiphase flow.