Our paper analyzes nitrogen and phosphorus removal from sewage in a biofilter. The analysis was based on the multi-variant simulations of the combined system: fixed-film – activated sludge performance. An activated sludge ASIM 2d model related with the model of pollutions’ transformations in fixed film was used for the calculations. The results of exploitation analyses performed on the objective treatment plant – average daily rate of wastewater, pH, COD values, total suspended solids, total Kjeldahl nitrogen, nitrate nitrogen, total phosphorus, and alkalinity – were used as input parameters for the calculations. The results indicated that there is a possibility of including fixed-film in the activated sludge technology in order to improve nitrogen and phosphorus removal from the sewage. The nitrification process will be performed in fixed-film, whereas nitrogen and phosphorus removal from the sewage will be performed in anoxic chambers, which operate in the activated sludge technology. Denitrifying the dephosphatation process guarantees the high level of total phosphorus reduction (81%) and the 42% total nitrogen reduction, but only if the whole easily decomposable substrate will be consumed by microorganisms in the anoxic chamber and if enough nitrates will be present in the environment.