Fixed-®lm treatment systems are probably the oldest used
wastewater treatment processes. The main objective of all
these processes for aerobic treatment is the elimination
of organic matter in wastewater. One type of ®xed-®lm
treatment is the rotating biological contactor (RBC) system,
where the support surface moves through the
wastewater. In this way organics diffuse through the bio-
®lms and are metabolized by microorganisms present in
the bio®lms formed over the support. The bio®lms generally
consist of a mixed population of bacteria, protozoa,
and fungi. In the bacteria, ®laments often are an integral
part of the bio®lms, and their function may, beyond their
organic removal ability, serve as a structural stabilizing
bio®lms component. However, there are few works about
these microorganisms [1±6, 8±10].
This paper deals with the identi®cation of ®lamentous
microorganisms present in the bio®lms formed over the
RBC surface.