This is how the MBR looks like about three quarters filled up with activated sludge. The bubbles are produced by air that is blown into the reactor at the bottom of the container. The aeration has two functions: 1) support the microorganisms in the sludge with oxygen; 2) assure the constant removal of solids accumulating on the membrane surface by a blower directly underneath the membrane device. Picture: Katharina Löw, July 2011