STRUCTURE OF A PROTOZOAN COMMUNITY IN A PERCOLATING FILTER

Structural factors of the microbial community of a percolating filter have been investigated. The presence of some ciliate species has been related to physico-chemical and plant operational Variables by means o f ordination procedures. In an 87-d study period, large variations in density of some species were observed. A limited number of environment al parameters strongly affect ciliate community composition. Major str uctural factors are sloughed biofilm wasting and nitrogen loading: bot h induce disturbance and make the community revert to 2 less mature ph ase. Moderate disturbance episodes reduce the effectiveness of competi tive mechanisms.