ABSTRACT
31A simple and reliable method to measure the activity of ammonia and nitrite oxidisers in mixed bacterial cultures was developed. This method considers nitrification as a two-step process and can also be applied to measure the effects of specific inhibitors on the activity of nitrifiers. It allows measuring of the short-term effect of an inhibitor on both the ammonia and nitrite oxidisers in one test under controlled environmental conditions (pH, temperature).
The developed method differentiates between the ammonia and nitrite oxidisers by consecutive injection of NO2 − and NH4 +. The main advantage of this method is avoiding the use of metabolic inhibitors for ammonia or nitrite oxidisers, as used by other methods.
The method was applied in two different procedures, both using an enriched culture of nitrifiers. In the first procedure a small reactor of 10 mL in which the oxygen consumption rate (OUR) was used to determine the ammonia and nitrite oxidisers activities. This procedure only takes a few minutes per sample and therefore is suitable for screening of a large number of inhibitors in a short time period. In the second procedure a reactor of 500 ml was used in which the ammonia and nitrite consumption rate was determined. This procedure takes several hours. The advantage compared to the other procedure is, however, that the obtained substrate consumption rate can be used to determine the kinetic parameters of the ammonia and nitrite oxidisers.
Both procedures were used to determine the inhibitory effects of salt (NaCl up to 15 g Cl−/L) on an enriched culture of nitrifying bacteria at lab-scale. The results obtained with the small reactor of 10 mL and the 500 mL reactor in the case of NaCl are very similar and in agreement with the results obtained for pure cultures of ammonia and nitrite oxidisers. The results of the method demonstrate its potential to accurately determine the individual activities of nitrite and ammonia oxidisers.
