BACKGROUND: In recent years, new technologies have been developed to deal with streams with high nitrogen loads, most of them based on the anammox process. As a first step in this process, ammonium has to be partially oxidized to nitrite. This partial nitritation is usually carried out through the SHARON process. However, it can also be achieved using other configurations (sequencing batch reactor or biofilm airlift, among others). The aim of this paper is to compare two different feeding strategies (fed-batch and step-feed) for the operation of a partial nitritation-sequencing batch reactor (PN-SBR) treating raw urban landfill leachate. RESULTS: A PN-SBR treating urban landfill leachate was started up and operated using two different feeding strategies: fed-batch and step-feed. When the experimental results were compared, it could be seen that during the step-feed strategy the system was more stable and presented a better performance. In addition, a cycle profile evolution of the reactor in each strategy was carried out to study the dynamics of the main chemical compounds, as well as different physical parameters. The profiles were similar for the nitrogen compounds, but with a difference in behaviour of pH, inorganic carbon and oxygen uptake ratio, which could explain the better performance and stability of the step-feed strategy. CONCLUSIONS: This study has demonstrated that the step-feed strategy is more suitable than the fed-batch because it performs better overall, there is less fluctuation in its operation and it has higher effluent quality stabilization. (C) 2008 Society of Chemical Industry.