ABSTRACT
The biological treatment systems discussed to this point-ponds, trickling filters, and rotating biological contactors (RBCs)—have been around for years. The trickling filter, for example, has been around and successfully used since the late 1800s. The problem with ponds, trickling filters, and RBCs is that they are temperature sensitive, remove less BOD, and cost more to build (particularly trickling filters) than the activated sludge systems that were later developed.
