A stable achievement of nitritation with strong nitrogenous wastewaters is considered as a difficult task in practice, probably due to the fate of interaction between dominating heterotrophs and nitrifier species. An experimental study was carried out to examine the organic effects in lab-scale biofilm nitritation reactors. The control unit without organic addition showed a stable nitritation performance for more than 220 days of operating period. The nitritation activity gradually failed at the reactors with an organic addition, but the nitritation activity eventually recovered with a prolonged aeration. It was not possible to explain the nitritation recovery with neither free ammonia inhibition concept nor DO competition hypothesis in these cases. The results suggest that the nitritation with organic requires a long start-up period for acclimation. In addition, the results of quinone profile analysis were in agreement with nitritation activity in reactors. The diversity of microbial community in the nitritation reactors could be described by the quinone profiles.

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