Chris, you win...
That is a RBC (Rotating Biological Contactor). The rotation is created by a diffuser placed underneath the RBC off a little in the front or back of the apparatus. The idea is to place only 1/3 of it in the water and the other two thirds is out of the water.
The idea is that the corrigated material gives a greater surface area for biological growth that will help to consume nutrients.
As it rotates, it allows the bacteria to absorb the nutrients and as it is out of the water it is absorbing oxygen. By rotating, one can ensure that there is even flow of water and air to maximize the bacterial community.
It is also known as "Bacteria Inn Express"
