BACTERIA AND PROTOZOA POPULATION-DYNAMICS IN BIOLOGICAL PHOSPHATE REMOVAL SYSTEMS

Population dynamics of polyphosphate-accumulating bacteria (PP bacteri a) was studied in a laboratory sequencing batch reactor simulating ana erobic-oxic sludge system. The competition between PP bacteria and ano ther microorganism (''G bacteria'') for anaerobic-oxic utilization of acetate as the sole source of organic carbon was observed. The competi tion was found to be seriously influenced by protozoan and metazoan gr azing: Predation-resistant ''G bacteria'' forming large compact flocs outcompeted PP bacteria. Several breakdowns of enhanced biological pho sphorus removal were observed. The first one was related to the develo pment of an euglenid flagellate Entosiphon sulcatus and attached cilia tes Vorticella microstoma and V. campanula. The second system collapse was connected with a rapid proliferation of rotifers. An alternative- prey predation was thought to be a mechanism of PP bacteria eliminatio n.