The aim of this thesis, carried out within the course of the EU-funded research Project POWERSTEP, is to investigate the applicability of duckweed in wastewater treatment in removing nitrogen based on the principle of the APS duckweed plant system. The motivation for this investigation is the intended combination of the Hydrotech drum filter with the APS duckweed plant system at case study one of the POWERSTEP project. The goal is to demonstrate and market a new wastewater treatment concept heading towards energy positive wastewater treatment plants. The investigations within the scope of the thesis were carried out on a laboratory scale to identify suitable duckweed species, the optimal duckweed mat density, relative growth rate (RGR), doubling time and the ammonium removal under the given conditions at the case study. From the four tested duckweed species Lemna Minor, Lemna Minuta, Landoltia Punctata and Spirodela Polyrhiza, the species Lemna Minor and Landoltia Punctata adapted best to the given wastewater composition. In a mix population of Lemna Minor and Landoltia Punctata a mat density of 0.075 g·cm-2 was determined to be best in suppressing competitive submerged algae growth and enabling duckweed relative growth rates of 0.072 d-1 and doubling times of 9.93 days. Based on the APS duckweed plant system, mean daily ammonium removal of 0.56 g N·m-2·d-1 and a daily ammonium degradation efficiency of 72.75% to a mean ammonium effluent of 12.26 mg·l-1 was shown at a lab-scale for a retention time of 24 hours. Based on the results of this research, it can be concluded that the principle of the APS duckweed plant system under the use of Lemna Minor and Landoltia Punctata can be applied to remove ammonium from wastewater achieving high reduction rates.