Development of nitrification inhibition assays using pure cultures of Nitrosomonas and Nitrobacter

Restricted requirements for nitrogen reduction at wastewater treatment plan ts have increased the need for assays determining the inhibition of nitrifi cation. In this paper, two new essays studying ammonia oxidation and nitrit e oxidation, respectively, are presented. As test organisms, pure cultures of Nitrosomonas and Nitrobacter isolated from activated sludge are used. Th e assays are performed in test tubes where the bacteria are incubated with the compound or wastewater to be tested. The nitrification rate is measured during 4h and compared with reference samples. The test organisms were cha racterised with respect to temperature, pH and cell activity. Optimum tempe rature was 35 degreesC for Nitrosomonas and 38 degreesC for Nitrobacter; op timum pH was 8.1 for Nitrosomonas and 7.9 for Nitrobacter. There was a line ar relationship between the nitrification rate and the cell concentration i n the studied interval. The cell activity decreased slightly with storage t ime. A significant level of inhibition was calculated to 11% for the Nitros omonas assay, and to 9% for the Nitrobacter assay. The assays are applicabl e to determination of nitrification inhibition in samples of industrial was te waters or influents of treatment plants, or chemical substances likely t o be found in wastewater. (C) 2000 Elsevier Science Ltd. All rights reserve d.