Waste management is an important element of sustainable urban development. One of the directions of waste management is mechanical-biological treatment (MBT) of waste with biogas installation. In addition to the benefits of purifying waste from separate collection and sorting of raw material waste from the mixed waste stream (subsequently diverted to recovery or recycling), this direction is also characterised by energy benefits (energy production from biogas). Mechanical and biological treatment of municipal waste inevitably entails also negative impacts, such as odour emission. In Poland, there are no legal regulations concerning odour nuisances. Reference could be made, inter alia, to BAT conclusions on waste treatment or standards in other countries. There are many methods of testing for odour emissions, but none of them, taken individually, characterises it sufficiently. The paper presents the results of research carried out in one of the biogas plants in Poland. The results present the sources of the highest odour emission in the examined plant, to which they belong: digestate during the second-stage oxygen stabilisation in the open air and pump station of technological sludge.