Protozoa and metazoa microorganisms and nitrogen removal efficiency have been studied in a bench-scale upgraded IFAS bioreactor. Sampling was done in three months and the identification of protists was accomplished microscopically. Fifteen species from the genus ciliate protozoans, three species from the genus testate amoebae, one genus of naked amoebae, six species from the genus rotifers, and also nematodes were identified. The most abundant species identified was Vorticella convallaria. The results from the third month of biological treatment in the IFAS system showed an increase in nitrogen removal efficiency accompanied by an increased abundance in the protozoan community especially due to the increased surface area with the attached media.

IFAS, protozoa, metazoa, biological nitrogen reduction.