A sequencing batch reactor (SBR) was operated to selectively grow a nitrite oxidising microbial community and was called the nitrite oxidising SBR (NOSBR). The nitrite oxidising characteristics of the reactor biomass were studied as well as the microbial composition. Molecular biological methods of clone libraries were used to evaluate the microorganisms in both the seed sludge and in the NOSBR sludge. We have found that the nitrite oxidation in the NOSBR was due the presence of bacteria from the Nitrospira phylum and not because of the presence of Nitrobacter which were in very low numbers in the NOSBR and not detected in the seed sludge. We hypothesize that the unknown nitrite oxidising bacteria in wastewater treatment plants are a range of species related to Nitrospira moscoviensis. A suite of primers were developed from the clone sequence data and used in a diagnostic polymerase chain reaction to prove the presence of these novel nitrite oxidisers in a range of full scale and laboratory scale activated sludge plants.

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