Abstract

Ammonium oxidation to nitrite nitratation and nitrite oxidation to nitrate (nitratation) were studied in a suspended biomass system (SBS) and an immobilised biomass system (IBS). Nitritation and nitratation rates at several substrate concentrations were obtained through respirometry. Process kinetics were evaluated by comparing different substrate inhibition models. The applied statistical criteria prove that the Aiba equation is the best model to describe nitritation inhibition by ammonium in the SBS and the IBS whereas the Haldane equation is the best model to describe nitratation inhibition by nitrite in both systems. The ratios between the kinetic coefficients in both systems suggest that the IBS coefficients are influenced by internal mass transfer in the biofilm. Moreover, the small difference in these coefficient ratios in the nitritation and the nitratation processes suggests that the distribution of the ammonium-oxidising and the nitrite-oxidising biomasses in the biofilm is homogeneous. © 2003 Elsevier Ltd. All rights reserved.