Applications of Membrane Processes in Treatment of Municipal Wastewater

A membrane bioreactor (MBR) is the combination of a membrane module and a bioreactor, which can retain high concentrations of mixed liquor suspended solids (MLSS)in the aeration tank. This results in a number of benefits, such as, lower sludge wastage rate, smaller aeration tank volume and higher ability to withstand shock loading.In a crossflow MBR, the membrane module is placed outside the bioreactor and the mixed liquor is driven into the membrane module. With the crossflow filtration, it is intended to eliminate or minimize the filter cake from being built up, by creating a shear force. Shear lysis of microbial flocks due to high shear forces induced by the crossflow velocity and high-energy costs resulted in adopting immersed membrane bioreactor. In an immersed MBR, the membrane module is immersed inside the aeration tank and the mixed liquor is generally sucked from the effluent side. Build-up of the cake layer is often removed by the uplifting airflow from aerators.Recent advancements in membrane technology has given an impetus to the development of membrane bioreactor for the treatment of municipal wastewater. In this paper, the trends in the municipal wastewater treatment with the application of both crossflow MBR and immersed MBR will be reviewed. The paper will also highlight advantages, disadvantages, suitability, and efficiencies of the membrane processes to treat municipal wastewater.