The effects of nanoparticles on performance and stability of anaerobic digestion of sewage sludge were investigated in four reactors. One reactor was fed with only sewage sludge(control reactor) while the remaining ones were fed with sewage sludge with the addition of the following additives:1) silver nanoparticles(NPs reactor); 2) ionic silver(AgNO3 reactor); 3) diluent used for nanoparticles(DIS reactor). The results indicated that: 1) the form of silver had significantly affected the methane yield as well as the share of hydrogen sulphide in the biogas, however this was not the case for VS removal; 2) the tested additives did not significantly affect methane content; 3) the addition of nanoparticles had a positive effect on the kinetic parameters of anaerobic digestion; for the aforementioned sample, the maximum rate of methane production was significantly higher in comparison to other trials executed in this experiment. Additionally, a shorter lag time phase was observed for the feed with the additive in the form of silver NPs; 4) control and Ag reactors harboured similar microbial diversities, in the reactors submitted to Ag-NPs or DIS microbial communities were very different from the other ones; in Ag-NPs reactor, with a 5-fold increase in the number of Methanosarcina genus compared to the control reactor. ? 2021 Elsevier Ltd. All rights reserved.