Biofilm communities and operational monitoring of a rotating biological contactor system

A full scale rotating biological contactor (RBC) system has been studied fo r a year. The main objective was to determine the distribution of protozoan and metazoan communities inhabiting the RBC biofilms, and to relate them t o the BOD5 content along RBC train. RBC system operated efficiently as show ed the removal of TBOD5 and TSS along the plant. A weak nitrification proce ss took place at last stages of the system. Orthophosphates and pH average values were maintained quite similar throughout the RBC stages. Microscopic al counting indicated that communities were mainly made up of ciliated prot ozoa, although the abundance and diversity of species varied widely along t he different RBC stages. A careful characterisation of ciliate species was carried out, with Vorticella convallaria, Epistylis entzii and Carchesium p olypinum being the most abundant species in the whole system. Metazoa only reached a noticeable proportion in the last stages of the system. Spatial d istribution of biofilm communities reflected the environmental changes obse rved as waste purification progresses. Associations between microorganisms and BOD5 concentrations were studied by correlation analysis. Results chief ly revealed the importance of ciliated protozoa in this biological system. They showed a high abundance on the biofilms and some groups - cyrtophorids , hypotrichs, scuticociliates and pleurostomatids ciliates - were closely r elated to a decrease of BOD5 content.