Nitrification monitoring in activated sludge by oxygen uptake rate (OUR) measurements

A simple measuring system was developed that yields information about the presence of NH+4 and NO−2 nitrogen in mixed liquor samples. In addition, it allows monitoring of the rate of both NH+4 and NO−2 oxidation simultaneously with the carbon substrate oxidation using OUR measurements. The method is based on the subsequent addition of NaClO3 and allylthiourea, selective inhibitors of Nitrobacter and Nitrosomonas respectively, to the mixed liquor sample in a closed batch respirometer. The presented method is valuable for detailed monitoring of the nitrification process in a reactor: it is simple, inexpensive, robust and generally applicable for nitrifying reactor systems. The measurement of NH+4 and NO−2 oxidation rates enables the operator to detect the presence of NH+4 and NO−2 species. This allows action to be taken to improve the performance of the system. The method is validated on a SBR. It is indicated that optimal SBR phase scheduling can be based on such OUR measurements.