## 1 Introduction  
Waste treatment plants, which are part of municipal infrastructure, are very significant from the point of view of urban development. Waste management objects, including mechanical-biological treatment plants (MBT), are an indispensable part of the municipal infrastructure [1, 2]. Municipal solid waste has the potential for recovery of materials and energy and can be a renewable source [3, 4, 5, 6]. Due to the improvement in the amount of newly built mechanical-biological treatment plants in Europe, the qualitative characteristics of odour emissions from these investments is becoming a requisite for the attention of appropriate planning of future installations, and also protection of health of both their operating employees and people living in areas close to the plants [7, 8]. These reasons contributed to the publication of scientific papers presenting measurements and chemical characteristics of emissions from waste treatment plants [8, 9, 10]. Some of the above-mentioned works focus on the investigation of parameters that bring to the development of unpleasant smells into focus [8, 9]. Odour emissions pose trouble due to their influence over public health through the nuisance of people [11]. The odorants, which are the chemical compounds causing a characteristic unpleasant smell,are naturally associated with potential danger, arduousness and can result in damaging psychosomatic effects. Therefore, the emission of gases polluted by malicious substances into the atmosphere is a meaningful environmental problem [12; 13; 14]. So far, the research into the field of odours has mainly focused on sewage treatment plants [15], swim housing [16], landfills [17] and farms with animal husbandry and biogas facilities [18]. [PERSON] et al. [11] identified the need to find relationships between biological waste treatment processes and environmental impacts, including odour emissions; but so far, research on odour emission factors for fermentation processes and composting of municipal waste is rare [19; 20]. Municipal waste biogas plants make up a part of MBT installations. Either the mechanical or biological parts constitute sources of odour emissions [21]. Chemical compounds with a nuisance can be emitted during the various unit operations, storage and transport of collected waste, mechanical processing for preparation to the next processes, biological processing in anaerobic conditions, dewatering of digestate and also aerobic stabilisation [2]. According to [PERSON] and [PERSON] [22], who analysed biogas plants located on the territory of Czech Republic, one of the primary kinds of impact of investments on the environment is the emission of various pollutants; for instance, odours. These researchers came to the conclusion that one of the most important causes of odour emission is the incorrect organisation and also lack of encapsulation of technological processes. Odour emission in the waste treatment depends on various factors, for instance: the type of the raw material (waste subject to the processes), processing methods, applied design solutions and the operating method of the installation, including the technological regime. A previous paper [23] presents the results of the analysis of the impact of technologies used at two biogas plants located in Poland, as well as the observance of the technological regime. Municipal mixed waste produced in households is characterised by a high content of biodegradable fractions. Process gases, which are released during the above operations contain organic (volatile organic compounds, which include ketones, alkanes, alkenes, alcohols, acids, terpenes and also organic sulphur compounds) and inorganic compounds (H\({}_{2}\)S, NH\({}_{3}\)). These chemical compounds may constitute a significant source of odour nuisance either in cities or in villages and pose a threat to public health and safety of the natural environment [24; 25; 26; 27]. Ammonia is particularly dangerous for the eyes and respiratory system [28; 29].