This thesis was written as a part of the project "Nano-DESTINARA" leading by Umweltbundesamt Wien GmbH in cooperation with Vienna University of Technology. The project involves tests on four nanoparticles - TiO2, Ag, CeO2 and fullerenes - to check their toxicity on the biocenosis of activated sludge by means of tests on acute and chronic effects. There is big number of articles and different projects of nanoparticles' toxic effects, however, none of them is about their potential influence on the environment via wastewaters. In the frame of this project the role of WWTP in emission this contaminants will be investigated. The quantification of the material flow of nanomaterial in municipal wastewater treatment is essential for the calculation of PEC-values (predicted environmental concentration) in risk-assessment for the aquatic environment. In the frame of this thesis a literature research was done to collect the knowledge about previous studies on nanoparticles, especially about concentrations causing the toxic effect. The practical part of thesis was preliminary tests conducted on silver nitrate in different conditions, to adjust the proper methodology for further nanoparticle tests. The results were discussed upon the calculated parameters as oxygen uptake rate, MLSS, different forms of nitrogen and phosphorus concentrations. Tests were conducted mostly without the addition of nanoparticles, only in last week the addition of silver nanoparticles were investigated to confirm the proper matching of the created methodology. The results had presenting that the highest inhibition was observed for the samples with silver nitrate in modified activated sludge at concentrations 50 and 100 mg/L. There was no inhibition in samples with Ag NPs, which might be caused by the dispersant used for sample preparations.