Ciliatological characterization of a biological reactor that eliminates nitrogen with intermitent aeration.

Ciliates present in an activated sludge biological reactor used for removal of nitrogen compounds with intermitent aeration were determined. The reactor had a working volume of 30 liters, a hydraulic residence time of 20 hours, and a cell retention time of 15 days. Operating temperature was 15 degrees C, and it was fed with domestic sewage. Aeration was given in pulses, one hour aeration and one hour without aeration, feeding sodium acetate to favour denitrification processes. Elimination efficiency was 95% of the dissolved organic matter. During the pseudostable operating phase, 16 species of ciliates (Phylum Ciliophora) were found. They were distributed as follows: 13 Genera; 12 Families; 7 Orders; 6 Subclasses; 5 Classes, and 3 Subphyla. From them, 9 are free swimmers and 7 are pedunculates. The Subphylum with higher diversity of species was the Ciliophora. The Oligohymenophorea Class was the best represented, corresponding to the Peritricha Subclass the highest number of species. Almost all the ciliates found have been reported as common inhabitants of activated sludge wastewater treatment plants with high removal efficiencies. They are catalogued as saprobe ciliates, within a and b masosaprobe levels. The presence of this ciliate community agrees with the carbon and nitrogen compounds removal efficiencies. Consequently, there exists the possibility of evaluating the operational efficiency of an aerobic/anoxic reactor using direct ciliates observations.