Trickling filters and rotating biological contactors (RBCs) are in common use in the US and protocols for their debottlenecking, rerating and optimization should be developed . A WERF survey showed that about one-third of large utilities employ some form of biofilm system. Ironically, such systems receive virtually no research funds and are often inadequately understood. The purpose of this paper is to briefly review those technologies available for debottlenecking, rerating and optimization of biofilm systems so that research needs can be identified that, if satisfied, will allow protocols to be developed by WERF.