COMPARATIVE-ANALYSIS OF THE ACTIVATED-SLUDGE MICROFAUNA IN SEVERAL SEWAGE-TREATMENT WORKS

A quantitative survey of the protozoan microfauna at 17 activated sludge plants, has been carried out during a period of 1 year. The occurrence and abundance of the most important protozoans were compared with the operational parameters of the plant using multivariate statistical procedures. Principal component analysis (PCA) with Varimax rotation, performed on 19 species of protozoa and 7 physico-chemical parameters, revealed a clear relationship between the presence and abundance of some species and the prevailing environmental factors and plant operating conditions. In particular the shelled amoebae Arcella and Euglypha, and the sessile ciliate Vaginicola crystallina were directly associated to nitrifying conditions. Conversely, the sessile ciliates Vorticella microstoma and Opercularia spp showed an inverse relationship with the aforenamed operational condition and were directly associated with other plant conditions such as sludge loading, low dissolved oxygen in the aeration tank, and high BOD values in the final effluent.