Modelling Biological Leachate Treatment in a Sequencing Batch Reactor

Old landfill leachates are characterised by a low content of biodegradable COD when compared to TKN. Therefore, biological nitrogen removal can only be achieved if external COD is added for denitrification. In this study leachate treatment in a lab-scale sequencing batch reactor was modelled using the activated sludge model N. 1 with minor modifications. The model was calibrated using experimental data of one cycle (about six hours) and validated over one entire week of operation. The model was capable of simulating reasonably well the leachate treatment processes. In particular, nitrite-built-up observed in the lab-scale reactor during nitrification was as well simulated by the model. If compared with the experimental periods in which complete nitrification was achieved, the nitrite accumulation diminished the external COD that was necessary for denitrification. The nitrite built-up was monitored using dissolved oxygen concentration behaviour in the reactor and, therefore, this signal could be used to develop a control system for nitrogen removal optimisation.