The structure of Ciliated Protozoa communities in biological sewage-treatment plants

Samples of mixed-liquor from 39 activated-sludge plants and of biological film from 49 rotating discs were examined microscopically for the presence of Ciliated Protozoa. 45 and 47 species of Ciliates were identified in activated-sludge plants and rotating discs, respectively.Most of the ciliate species, which are frequent inhabitants of activated-sludge, were found also in rotating discs. Statistical analysis based on affinity index and on recurrent groups, made it possible to reconstruct the structure in species of ciliate communities both in activated-sludge plants and in rotating discs.