## 2 A Case Study for the MSW Management of the Procida Island
### Interpretation  
A sensitivity analysis was carried out by modelling two alternative scenarios for the Procida management scheme. The scenario _\"Procida--Biometlane\"_ was defined according to which the organic fraction collected separately is sent to an anaerobic digestion plant aimed at recovering biomethane from biogas, which is sent to an upgrading unit instead of to the CHP. The LCI inventory was quantified based on data reported by [25], assuming the same anaerobic digestion plant utilised for the 2021 scenario but equipped with a three-stages membrane upgrading unit. Good performances in terms of CO\({}_{2}\) removal efficiency (of about 98%) and methane slip (lower than 1%) were obtained. This alternative strategy for bioresistance management could be easily implemented in the near future since several AD plants for biomethane production have been active in Italy since 2020 because of the national legal framework, which provided incentives for plant operators [26].  
The scenario _\"Procida--EE Mix 2030\"_ assumes a future Italian electricity mix with larger percentages of non-fossil and renewable energy sources (from 51% to 43% with respect to 2020), mainly as a result of a higher share of wind energy (from 7% to 14% with respect to 2020) and a lower share of energy from natural gas (from 49% to 43%), as shown in ANNEX C. The future electricity mix (2030) was derived starting from that utilised for the 2021 base case scenario and considering national energy trends predicted by the European Community until 2050 [27].  
These two sensitivity scenarios were implemented considering the waste composition and the share of separate collection defined for the Procida management scheme of 2021. These assumptions appear reasonable since the municipality showed rather stable condi  
Figure 5: Life-cycle impact assessment for Procida’s MSW management in 2011 and 2021, with the contributions of each specific stage. Results refer to the chosen functional unit (“the treatment of 1 tonne of MSW”) and are normalised in “person”year” (the average impact in a specific category caused by a person during one year in Europe). NC = non-carcinogens; RI = respiratory inorganics; LO = land occupation; GW = global warming; NRE = non-renewable energy.  
tions in terms of the quantity and composition of collected waste in recent years [7] due to the achievement of rates of separate collection greater than 70%--already higher than the value of 65% required by European legislation (ANNEX A). This enabled quantification of the sensitivity to change of a single assumption, neglecting other background conditions (such as the waste composition).  
The sensitivity analysis results (Figure 6) showed that the implementation of scenario \"_Procida-Biomethane_\" could lead to further improvements for RI (7%), GW (171%) and NRE (3%), with reference to Procida 2021. These good performances were mainly related to the utilisation of biomethane for transportation use (with a vehicle fleet composed of 50% cars and 50% trucks), which replaces the production and utilisation of diesel for travelling the same distances, leading to avoided burdens greater than direct ones. The same scenario could lead to a worsening for LO (4%) due to the energy necessary for plant operations, which is provided by external sources in this AD configuration.  
Again, with reference to Procida 2021, the scenario \"_Procida--EE Mix 2030_\" showed a worsening for the same categories, with values of up to 68% for GW. This is explained by the higher share of renewable energy sources, which have limited greenhouse emissions and lead to lower avoided impacts for AD and WtE plants. These results make the role of biomethane production from biowaste still more crucial. The scenario represents an efficient way to reduce fossil and non-renewable sources in the future when the energy mix will mainly comprise renewable sources.