Comparison of inhibition assays using nitrogen removing bacteria: Application to industrial wastewater

Three pure culture assays for measurements of inhibition of the nitrogen removal process were tested and compared. The methods were performed using pure cultures of bacteria responsible for three reactions; ammonia oxidation, nitrite oxidation and nitrite reduction. The inhibition caused by 48 samples of industrial wastewater was determined and the results for the three inhibition assays were compared. The correlation coefficients were calculated to be between 0.63 and 0.73. The inhibition of the pure culture methods was also compared with results from another investigation, where the inhibition by the same wastewaters was determined by a screening method based on activated sludge. The best correlation was found with the ammonia oxidation assay. The heavy metal content was statistically analysed for relationships with inhibition using a linear model with stepwise linear regression. Although zinc was a significant inhibitor for all three methods, these responded differently in the second step, which indicate that the bacteria are not inhibited according to the same pattern. The relevance of the three pure culture assays as an inhibition test is discussed and the conclusion can be drawn that they are all needed to give a complete inhibition picture of wastewaters.