The control of wastewater treatment plants requires an extensive monitoring programme based
on physicochemical costly routine analysis. Microbial populations are well known indicators of
operational conditions in biological reactors. This research was carried out by the CENTA and the
University of Minho in the scope of the Erasmus programme. The aim of the work was the
development of a simplified approach, based on biological indicators, for monitoring small biofilm
wastewater treatment processes. In that regard, protozoa and metazoan were monitored at
CENTA experimental plants - namely a trickling filter and a rotating biological contactor -, and
correlated with influent wastewater and effluent composition. The relationship between
wastewater performance and the microbiological composition of the biofilm was identified and
assessed. Results indicate that a methodology based on the bioindicators provides useful data
for process monitoring and control of small wastewater treatment plants, thus diminishing the
associated costs of routine analysis and providing information when such analysis aren’t easily
available
