Six tests were carried out delaying the air intake in order to determine the influence of a pre-storage stage (between 0 and 48 h) in organic matter removal and ammonification processes. The kinetic model proposed by Quiroga & Sales predicted successfully the total and soluble COD profiles. The maximum consumption rates were reached in tests with 0 and 30 It without initial aeration. There was no advantage in pre-storage times higher than 30 h, as the non-biodegradable organic matter increased. Concerning ammonium consumption in nitrification, the adjustment to Quiroga & Sales model demonstrated kinetics with an order varying between zero and one. This change in the reaction order was associated to an inhibition due to free ammonia. The experimental data adapted themselves fairly well to the proposed kinetic model. (C) 2003 Elsevier Ltd. All rights reserved.