Starting from the industrial revolution, the exponential human population growth, combined with technological development, has resulted in a continuously increasing waste flow. The recent Circular Economy action plan, published by the European Commission, reports a prevision of the annual waste generation increase around 70% by 2050 [
1]. The waste problem is due to both the amount and the modification of the waste type which affect the management system [
2]. This topic represents a priority for the modern society, since the management choices have multiple effects: social, environmental, technical and economic [
3‐
5]. The well-known waste hierarchy identifies prevention as the most important strategy. Nevertheless, the necessity to integrate all the available options by decision-making tools, able to involve all the stakeholders, is evident [
3,
6‐
9]. Municipal waste (MW) covers an essential role for the whole waste management system. Many definitions of MW are used in each country, often affected by different aspects, mainly waste origin, materials and collectors [
10,
11]. The Directive 99/31/EC defined MW as waste from households and other waste with similar composition and nature [
12]. Furthermore, EUROSTAT includes similar wastes generated by small businesses and public institutions, excluding those from agriculture and industry [
13]
. The management of MW is currently one of the most serious and controversial issues, at local and regional scales, even more in developed countries [
2]. The disposal in landfilling sites represents the most common strategy of MW management (also in developed countries), despite the evolving regulations [
14‐
16]. This practice produces significant environmental impacts, if the disposed waste flow has high putrescible content and it is managed with low technical and management precautions [
14]. Indeed, this fraction acts on the production of two flows: the leachate (mainly critical for aquifer) and greenhouse gases (GHG, which cause global warming). Leachate production is promoted by rainwater infiltrations, combined with chemical and physical phenomena, resulting in inorganic and organic contaminants, with potential effects for human and environmental health [
17,
18]. Furthermore, the modern facilities include containment systems to prevent the release of pollutants [
18]. GHG include a mixture of mainly carbon dioxide and methane (in comparable concentrations) with traces of H
2S, H
2, N
2O and NH
3 [
19,
20]
. The reduction of GHG emissions represents one of the most important priorities worldwide, currently [
21,
22]. The possibility of a mechanical biological treatment (MBT), before the final disposal, could be implemented to stabilize the biologically degradable components, with the main advantages of recovery of recyclable materials, reduction of the volume of waste to dispose, and reduction of the organic matter content [
20,
23]. More in detail, MBT is a simple practice able to combine mechanical separation with the biological stabilization of organic matter by aerobic/anaerobic stabilization and bio-drying [
14,
20,
24‐
30]. The number of MBT facilities has increased in Europe (about 570 active facilities, in 2017), mainly in the last two decades to satisfy the legal obligation to both limit biodegradable waste in landfilling sites and increase recycling and energy recovery from waste [
24,
27,
28,
31,
32]. The Italian scenario identified 131 MBT in 2018, since this country adopted the European Union sanitary landfill regulation by Legislative Decrees 36/2003 (implementation of Directive 1999/31/EC) and 205/2010 (transposition of European Directive 2008/98/EC), which specifies that the disposal of solid waste is possible after a ‘‘pre-treatment” (not better specified) when the limits of composition defined by the regulation are not respected [
6,
12,
33‐
36]. Several papers summarize the benefit of an MBT implementation (as pre-treatment before landfilling) [
27,
37‐
40]; nevertheless, some authors highlight the impact (both environmental and economic) due to MBT operations. They suggest critically assessing when the treatment is really advantageous [
2,
14,
41,
42]. In this regard, some studies perform analysis (e.g., with life cycle assessment, LCA approach) to prove that the improvement of recycling systems can produce higher positive effect than MBT [
28,
43]. The reason is the decrease of organic fraction in the input flow to MBT facility and the low value of the resulting product, often considered a waste to dispose of [
42]. In agreement with these conclusions, Trulli et al. (2018) recommended the pre-treatment for developing regions, with low separate collection levels.
Starting from the current state of the art, the present paper considered a landfilling site for MW, located in Central Italy, where satisfying recycling levels are achieved. The facility, operating from 1999, includes an MBT from 2018, able to stabilize MW before the final disposal. The site peculiarities allowed a deepened study of the landfill behavior before and after the MBT introduction, by monitoring biogas emissions, leachate production, odors, and site settlement. The possibility of a long-time on-site detection represents a strength of the present paper.