Biofilm Communities and Operational Monitoring of a Rotating Biological Contactor System

A full scale rotating biologicalcontactor (RBC) system has been studied for a year.The main objective was to determine the distributionof protozoan and metazoan communities inhabiting theRBC biofilms, and to relate them to the BOD₅content along RBC train. RBC system operatedefficiently as showed the removal of TBOD₅ and TSSalong the plant. A weak nitrification process tookplace at last stages of the system. Orthophosphatesand pH average values were maintained quite similarthroughout the RBC stages. Microscopical countingindicated that communities were mainly made up ofciliated protozoa, although the abundance anddiversity of species varied widely along the differentRBC stages. A careful characterisation of ciliatespecies was carried out, with Vorticellaconvallaria, Epistylis entzii and Carchesiumpolypinum being the most abundant species in the wholesystem. Metazoa only reached a noticeable proportionin the last stages of the system. Spatial distributionof biofilm communities reflected the environmentalchanges observed as waste purification progresses.Associations between microorganisms and BOD₅concentrations were studied by correlation analysis.Results chiefly revealed the importance of ciliatedprotozoa in this biological system. They showed a highabundance on the biofilms and some groups– cyrtophorids, hypotrichs, scuticociliates andpleurostomatids ciliates – were closely related to adecrease of BOD₅ content.