## 1 Introduction  
Considering the severe consequences that improper waste management systems can pose for the environment and society, valorization of municipal solid waste (MSW) represents a relevant matter for policymakers [1]. Waste management is a major source of greenhouse gas emissions and provides an opportunity to reduce carbon emissions that have yet to be fully exploited [2]. Indeed, the long-standing exploitation of fossil fuel has resulted in global warming due to significant greenhouse gas emissions with its attendant environmental and health problems [3]. Recycling of MSW plays a crucial role in a sustainable society, where waste management strategies should promote an efficient development of MSW recycling markets [4]. The European Union recently issued, in January 2017, a broad and complex set of regulations, for the action plan for the circular economy which included promoting waste recycling across the member states with the aim of achieving the target for recycling 70% of MSW by 2030 [1]. The recycling of waste, in a model based on the circular economy, plays a significant role by reducing the environmental impact associated with waste management, allowing increased availability of resources for industry, and promoting investment and job creation in the recycling sector [4]. The refore, MSW should always deal with the using wastes as substitutes for primary materials and as an energy source, thus, reducing environmental pollution [5]. The introduction of various support schemes that promote the use of renewable resources and the energy and climate policies of the European Union have encouraged the development of anaerobic digestion plants for energy production [6]. There are mainly two technologies for the conversion of the organic fraction of municipal solid waste (OFMSW) into secondary materials, i.e., composting (aerobic digestion) and anaerobic digestion [7]. Composting is a strategic technology for the sustainability of agricultural activities that can fix critical issues such as the disposal of crop residues and livestock wastes [8]. The main output of the composting process is compost that can be used as a fertilizer in the agricultural sector. Anaerobic digestion combines energy recovery with material recovery, obtaining the following two types of outputs: biogas, principally comprising CH4 and CO2 and a semi-solid residue, also known as digestate [9; 10]. The refore, anaerobic digestion is included as a waste-to-energy technology, because a variety of waste can be converted into energy resources in order to create valuable opportunities both in terms of energy recovery and environmental impact, such as reducing greenhouse gas emissions [11]. Biogas is a mature renewable energy technology, and it is produced starting from anaerobic digestion from several feedstocks, such as agricultural residues, energy crops, OFMSW, and organic waste produced by industry [12]. Anaerobic digestion is widely used to transform biomass residues into a biogas [13]. Indeed, it is largely used worldwide to generate energy from biogas, with the aim of bringing significant environmental and economic benefits [6]. Although anaerobic digestion is one of the most widely investigated methods used in the production of energy from different kinds of organic waste [14], the biogas needs to be purified or upgraded to natural gas (biomethane) grade before its final consumption as a fuel [3]. The biogas produced during anaerobic digestion can be converted to renewable electricity and heat through cogeneration to be used on site or exported to an electricity network or can be upgraded to biomethane for injection into natural gas networks for user consumption or possibly compressed and dispensed as vehicle fuel [13]. The solutions for MSW management should be environmentally sustainable, as well as cost-efficient and socially acceptable [15].