Effect of Abrupt Increase in Ammonium Load on Activity of the Anammox Bacterial Community in a Sequencing Batch Reactor

— The transition process caused by an abruptly increased ammonium load (2.5-fold) on the microbial community of a sequential batch reactor carrying out nitrogen removal from the water via nitritation-anammox was studied. The community developed in the bioreactor at incoming ammonium concentration of 200 mg N/L removed 76.5% of the inflowing nitrogen and was satisfactorily described by the BioWin mathematical simulator with corrected coefficients. Abrupt increase of nitrogen load from 200 to 500 mg N/L resulted in ammonium concentration at the reactor outlet increasing from 27 to 280–290 mg N/L, with nitrogen removal efficiency dropping to 40%. The calculation using the BioWin simulator showed that the efficiency of the nitritation-anammox process should increase in the course of a month and stabilize at the level close to the original one (76.5%). However, experimental data did not support this calculation: no increase in efficiency was observed during this period. Changes in the structural and functional characteristics of the biofilms and aggregates, which were not accounted for in the model, were probably responsible for discrepancies between the experimental and calculated data.