Application of experimental research methodology to the study of nitrification in mixed culture

Nitrification is an aerobic process formed by two consecutive reactions: nitritation and nitratation. Using an experimental research methodology, we have studied the specific effects and the possible interactions between initial ammonia concentration, pH and temperature on these two reactions as well as on the experimental conditions leading to a nitrite build-up. In the experimental field studied (35 < [N-NH4+]o mg.l−1 < 90, 15 < T°C < 25 and 7 < pH < 8.5), the statistic interpretation of the results shows that only temperature and pH have a significant positive effect on ammonia removal. Moreover, the effect of these two parameters is linear. As for nitrite accumulation, the temperature effect is negligible and a strong interaction between [N-NH4]o and pH is revealed. When the values of these two variables are high, nitratation is inhibited and 50% of the nitrogen introduced at the beginning accumulates temporarily in the form of nitrites. The results clearly show that a high NH3 concentration inhibits Nitrobacter , starting from between 6.6 and 8.9 mg N-NH3.l−1. This research enables a better understanding of the nitrite build-up phenomena which can be thus minimized or maximized in the case of new process of nitrogen treatment.