Modelling and simulation of a nitrification biofilter for drinking water purification

For the purification of pure and microbiologically safe drinking water, different treatment steps are necessary. One of those steps is the removal of ammonium, which can, e.g. be accomplished through nitrification in a biofilter. In this study, a model for such a nitrifying biofilter was developed and the model was consequentially used for scenario analysis. A protocol developed for characterisation of wastewater was used to characterise the biofilter influent. A comparison between measured and simulated effluent ammonium, nitrate and oxygen concentrations revealed that the predicting qualities of the constructed model are excellent. As such, the model could be used for further scenario analysis based on model simulations. By simulating the behaviour of the biofilter, it was shown that its capacity to treat unexpected ammonium peaks in the summer time is very limited. Further simulations with the model showed that extensive aeration is not essential for nitrification as sufficiently dissolved oxygen is present in the influent. Therefore the aeration can be reduced to such a level that mixing is ensured. A final set of simulations showed that prolonged ammonium loads can be dealt with by reducing the influent flow rate. The amount of reduction depends of the operating temperature and influent ammonium concentration. The presented simulations can be used by the operators to reduce operating costs and as a decision tool in the case of high ammonium influent concentrations. Water SA Vol. 32(2) 2006: pp.257-26