Subcritical fouling behaviour modelling of membrane bioreactors for municipal wastewater treatment: The prediction of the time to reach critical operating condition

After the advent of critical flux concept, studies on constant subcritical flux operation of membrane bioreactors (MBRs) gained interest, presumably, because of preferred least fouling operational strategy; however, such a chosen operational condition has demonstrated the continuous slow and irreversible fouling followed by a sudden rise in transmembrane pressure (TMP). Such peculiar fouling behaviour has been explained to be evolved due to extracellular polymeric substances (EPS) originated through the course of biological processes inherent to MBRs. A subcritical flux fouling model based on the role of two forms of EPS, viz. bound and free, has been presented here. The model, studied for MBR treating municipal wastewater, could successfully predict the time at which a sudden change in the TMP–time profile occurs; the predicted time of 200 h by the model has shown good agreement with the observed time of approximately 190 h. Although the fouling problem is one of the major bottlenecks for the MBR technology to become widely applicable as an efficient municipal wastewater treatment technology, from the operational point of view, prediction of the time after which severe fouling occurs (a sudden jump in the TMP–time profile) during subcritical operation could be an important step. Such a prediction would help in developing an efficient and well regulated cleaning protocol for better management of MBR treatment plant operations.