Investigation on the improvement of operating conditions by using the venturi injector in membrane bioreactors

There are many advantages of using a membrane bioreactor (MBR) in wastewater treatment. These advantages can be summarized as better effluent quality, less footprint, being modular and less waste sludge production. Due to these advantages, application fields and the installation capacity of MBR technology have been constantly increasing and numerous studies have been done to improve this technology. However, in addition to its advantages, MBR technology has important disadvantages. One of the most important disadvantages is the blocking of membrane pores and surface as it is being used, in other words, membrane fouling. As membranes become fouled, the energy utilization efficiency of the system drops; therefore, treatment cost of the system increases. When a specific fouling point is reached, the system should be shut down and the membranes are subjected to an intensive cleaning process. This case increases the operation cost of MBRs substantially. To mitigate the most important disadvantage of the MBRs, which is membrane fouling, a lot of research has been done in terms of production of less fouling membranes, development of new membrane modules and optimization of operating conditions. In this study, the effectiveness of a novel aeration method on membrane fouling reduction and on the improvement of oxygen transfer efficiency was investigated. In this scope, the required air was ensured to enter the system spontaneously by integrating a venturi injector to a submerged MBR. It is aimed to clean the membrane surface more efficiently by directing the jet flow through the venturi injector to the membrane surface. In studies performed with the synthetic and real wastewater, by supplying the same amount of air, it is observed that the oxygen concentration in MBR was very high compared to that supplied by the blower. Membrane fouling studies indicate that the with the same flux and aeration rate, transmembrane pressure (TMP) development is much lower in the venturi injector system at the same flow and aeration rate, and the difference between the blower and venturi aeration systems is observed to increase more as the system flow increases. In parallel to that under the same conditions, it was observed that the venturi system reached to the maximum TMP value later than the blower system. In parallel, comparing to the blower system, the venturi system, set under the same conditions, reached much later to the TMP value determined within the scope of this study. Keywords: Venturi, membrane bioreactor, fouling, aeration