Influence of Nitrate on the Bacterial Flora of Activated Sludge under Anoxic Condition

A two-year survey of bacterial populations in activated sludge was carried out in a municipal sewage treatment plant receiving industrial wastewater having a high nitrate content. Phosphorus removal was not improved with a modified operation with a dissolved oxygen (DO)-deficient selector. In these circumstances, the anoxic selector in the aeration tanks acted as a site for denitrification not as a site for phosphate incorporation. The ecological interactions between the different bacterial species are thought to occur in the anoxic zone. Possible competition between the Pseudomonas/Alcaligenes group and the Acinetobacter/Moraxella group was suggested under laboratory conditions. Commensalism between the Enterobacter/Aeromonas group and the Acinetobacter/Moraxella group was observed by using a Nuclepore membrane-dialysis culture technique.