One-year (2004) comprehensive investigations in a semi-industrial pilot plant (5 m3) were carried out with the aim of assessing the influence of operational parameters on the partial nitritation/Anammox system performance. In the system designed as a moving-bed biofilm reactor, the influent nitrogen load to the Anammox reactor was progressively increased and a stable Anammox bacterial culture was obtained. Interaction between subsequent aerobic and anaerobic conditions in the partial nitritation and Anammox reactors, respectively, granted conditions to remove nitrogen through the nitrite route. It implies that the oxygen supply can be limited to a high extent. A control strategy for the partial nitritation step relied on concomitant adjustment of the air supply with a variable influent nitrogen load, which can be monitored by both pH and conductivity measurements. In the Anammox reactor, an influent nitrite-to-ammonium ratio plays a vital role in obtaining efficient nitrogen removal. During the 1-year experimental period, the Anammox reactor was operated steadily and average nitrogen removal efficiency was 84% with 97% as the maximum value.

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