Uso da respirometria na avaliação da influência do pH na capacidade ativa das bactérias nitrificantes.

Abstract

Several studies related to nutrient removal have been developed with the objective to know the best environment for the development of the Nitrosomona and Nitrobacter bacteria, which are responsible for the nitrification process. This way, seeking to contribute for the evolution of the aerated systems, where the nitrification occurs, the present work has the objective of developing a respirometry based methodology for the assessment of the nitrifying bacteria reaction rate by varying of the bulk pH. Besides, it is intended to know the ideal pH range for growth of these bacteria. The studied pH range was 5,0 to 8,5. The applied methodology had the following steps: (1) a volume of 2 litres of mixed liquor was collected from a existing pilot-scale Bardenpho treatment plant, and the oxygen utilising rate (OUR) was measured until it reached the endogenous value; (2) the pH was adjusted by the addition of HC1 or NaOH; (3) addition of NH4C1 (lOmgN/L) as substratum; (4) OUR was measured, until it reached the same endogenous value of the beginning of the test. The same process was repeated, starting from (2), for the Nitrobacter bacteria, but NaN02 (lOmgN/L) was added as substratum. Others analyses were accomplished such as: pH, alkalinity, ammonia, nitrite and nitrate, in six moments of each experiment run for confirming the credibility of the respirometry test. This work showed the effectiveness of the applied methodology in the oxidative rate monitoring of the nitrifying bacteria, since it can supply real-time data for the correction of an eventual introduction of undesirable pH in the treatment system. Besides, the obtained results showed that the reaction rate of the Nitrobacter was, on average, 25% larger than the reaction of the Nitrosomonas. In acid pH values, the nitrifying bacteria has its oxidative capacity inhibited, with growth rate of 0,12 d-1 for Nitrosomonas, and 0,18 d-1 for Nitrobacter. In neutral pH's values, the maximum growth rate of those bacteria was 0,6 d-1 and 0,8 d-1 for Nitrosomonas and Nitrobacter respectively. In alkaline pH's value, Nitrobacter presented larger sensibility, and Nitrosomonas had hardly any variation in its oxidative capacity. Therefore, with the obtained results, it was shown that variations on the pH influence the activity of the nitrifying bacteria, what was demonstrated by the variation on the oxidative capacity and on the growth rate of these bacteria. Besides, it was observed that in none of the studied pH's values the activity of the nitrifying bacteria was completely inhibited, which showed that, in the this pH range, these bacteria are capable to oxidise, although in a limited way, the existent nitrogen.