MEMBRANE FOULING IN SUBMERGED MEMBRANE BIOREACTORS DURING PEAK WET WEATHER FLOW. MODELING FOR DESIGN AND OPERATION

A mathematical model that describes the dynamic behavior of submerged membrane fouling was incorporated into a hydraulic model of an MBR. It incorporates internal fouling of the membrane due to pore blocking and reduction, and fouling due to cake formation. The model allows the evaluation of operational strategies of the membrane as a result of a given input hydrograph to the plant. It produces the evolution of transmembrane pressure TMP as a function of time as the hydrograph transits through the plant. Changes in concentration of MLSS in each of the reactors as a result of the operation are presented. Three operational strategies are evaluated. The effect of having a VFD in the return flow of the membrane tank, and the tradeoff between more membrane filtration capacity or having an EQ tank at the head of the plant are discussed. The presence of the VFD is beneficial because it limits the concentration of MLSS in the membrane tank and reduces cake associated TMP. It is observed that the duration of the peak flux required from the membrane is critical in the overall behavior of the system. A lower peak flux of greater duration can be a more challenging condition to the membrane system than a higher peak flux of short duration. When selecting a design storm for membrane sizing is important to specify not only the return frequency but also the duration. No attempt was done to incorporate changes in filterability of the sludge due to changes of the chemistry of the water matrix during the storm. These effects can be added in the future; however, it is expected that their effect further emphasize the conclusions reached here.