Membrane Fouling in Membrane Bioreactor

The performance loss caused by membrane fouling is the fundamental drawback of membrane filtration. In the membrane bioreactor (MBR), all wastewater coming into the process must pass the absolute barrier of the membrane because inability to do so can directly lead to the necessity of bypassing a portion of untreated wastewater to river, lake, or ocean during the peak flow. It has been observed that small particles and macromolecules classified as either soluble microbial products (SMP) or extracellular polymeric substances (EPS) play a major role in membrane fouling rather than the microbial floc particles that consist of the majority of mixed liquor suspended solids (MLSS). This observation is well supported theoretically because the SMPs and the EPSs have higher tendencies to deposit on the membrane surface because of the low back-transport velocity, as discussed in Section 1.2.5. SMP and EPS are also subject to strong interaction with the membrane surface through charge and van der Waals interactions.