## 2 Potential of Municipal Waste to Energy Production--Review  
The introduction indicates the need for the construction of a waste management system for any local government unit. The main task of such a system is to use waste as a source of raw materials including raw materials for energy production. The volume of energy generated from waste depends, first and foremost, on the methods of processing, allowing for the recovery of energy in variable forms, generally in the form of heat generated in the combustion process [40; 41]. Waste can be, as a source of energy, a significant element of the local energetic balance [42]. A good example here is the municipality of Copenhagen, which adopted in 2011 a strategy for development until 2025, which will eliminate the use of coal as the energetic raw material [43]. The share of energy generated from municipal waste in Copenhagen's energetic mix will finally be approximately 40%. In 2018, 12.5 million t of mixed municipal waste was stored in Poland. Most of the waste, i.e., 9971.2 thousand t, was generated in households, which made up 83% of total generated waste. The remaining part of the waste, i.e., 1997.5 thousand t of household and commercial types, collected from the servicing of municipal infrastructure and entrepreneurs, amounted to 17%. Analysis of the morphological composition of waste delivered to plants using methane-biological processing technology (MBT), based on results of research work performed in 20 plants located in Poland, shows a great potential for broadly understood recovery [44]. Classification of particular waste components in terms of their use leads to distinguishing the following groups: Group No I--recyclable materials (glass, metals, synthetic materials qualified for recycling), Group No II--waste having high energetic value (paper, cardboard, textiles, composites and synthetic materials not qualified for recycling, as well as wood), Group No III--biodegradable waste (BIO1, BIO2, BIO3) and Group No IV--waste classified as useless or dangerous. Percentage shares of particular waste components in mixed waste as well as in fractions separated with an 80-90 mm mesh screen, as average values obtained from research work performed in various plants in Poland, are shown in Table 1.  
Waste possessing values of recyclable materials (Group No I) recovered for mixed waste during the manual separation process can be obtained, as a rule, exclusively from the oversize fraction separated in, e.g., rotary drum sifters featuring mesh not less than 8 cm; the total content is 37.2%. A method of using Group No II, defined as RDF, considering its high calorific value of 18-24 MJ/kg, is combustion [44]. The application of screening and mechanical separation of mixed waste resulting in energetic raw material in RDF form allows, in the extreme case, for an increase in the calorific value from 8.4 to 25.0 MJ/kg [45]. A calorific value exceeding 11 MJ/kg guarantees, in principle, energetic efficiency of combustion or gasification exceeding 65%, which allows for classification of the process as energy recovery [46]. According to the International Energy Agency, the calorific value of waste to be used in combustion processes should not be, for process profitability, below 7942 kJ/kg [47]. In Germany, one of the biggest EU economies, the volume of RDF separated in MTP installations increased from 31% in 2006 [48] to 34.2% in 2017 [49]. A significant criterion for the application of the available techniques of thermal transformation of mixed municipal waste is relatively high humidity, which reduces their calorific value. The use of more advanced techniques such as, for example, pyrolysis or gasification, requires higher calorific value of waste; this is associated with a necessity to apply proper methods of batch preparation [50; 51]. Unfortunately, pyrolytic installations of an industrial scale used for waste processing are unreliable, which has been proved by plants closing shortly after being put into operation.