Date of Award

Spring 1983

Project Type


Program or Major


Degree Name

Doctor of Philosophy


The microbial ecology of rotating biological contactors (RBC) is a combination of complex interrelationships among bacteria, protozoa, and metazoa and their perceived environment. Since very little information is available on the microorganisms inhabiting the biofilms, the major objective of this research was to increase the understanding of the biological interactions occurring in RBC biofilms as a function of organic loading. Biofilms, in pilot-scale RBCs receiving 2.0, 4.0, and 6.0 g TOC/m('2)(.)d of settled domestic sewage, were examined using light and electron microscopy. The microbial community, composed of filamentous and unicellular bacteria, zooflagellates, amoebae, ciliates, nematodes, and rotifers is complex and depends on the organic loading rate. Filaments found in initial biofilm studies were identical as Sphaerotilus in both morphological and ultrastructural characteristics. At high loading rates Gram-positive and Gram-negative bacteria appear to store sulfur and poly-(beta)-hydroxybutyrate. As loading rates decrease Gram-negative bacteria, with fewer inclusion bodies, predominate. At very low loading rates the biofilm constituents are almost exclusively prosthecate-like and nitrifying-like bacteria. A theoretical biogeochemical profile of RBC biofilms exposed to different loading rates has been developed based upon the availability of organic carbon and oxygen. Protozoan and metazoan succession progresses from zooflagellates and small amoebae to free-swimming bacteriovorous ciliates, and then to peritrichs, rotifers, and carnivorous ciliates and giant amoebae (> 40 (mu)m). This succession is primarily a function of the feeding efficiencies of the organisms and predator-prey relations. The pilot-scale studies indicated that protozoa and metazoa might be suitable indicators of effluent quality. To verify the pilot-scale results the biofilms of five full-scale RBCs were examined. A simple and rapidly executed strategy has been developed, based on the on-line RBC data, which predicts effluent BOD(,5) as a function of the numbers of Uronema, Epistylis, giant amoebae and rotifers observed.