Membrane bioreactor (MBR) is a combination of membrane processes like microfiltration or ultrafiltration with a biological wastewater treatment process, the activated sludge process. It is now widely used for municipal and industrial wastewater treatment.
A membrane is a material that allows the selective flow of certain substances. In the case of water purification or regeneration, the aim is for the water to flow through the membrane, retaining undesirable particles on the other side.
When used with domestic wastewater, MBR processes can produce effluent of high enough quality for discharge into the sea, oceans, surfaces, brackish bodies, or waterways for usage in urban irrigation. Other advantages of MBR's over conventional processes include a small footprint, easy retrofit, and upgradation of old wastewater treatment plants.