# Sustainable Italian Cities: The Added Value of Biomethane from Organic Waste
## 3 Materials and Methods
### Input Assumptions  
The robustness of an economic analysis is determined by the choice of input variables. For this reason, this work opted to use the values reported in the literature (Table 4), and, regarding subsidies, followed the inputs reported in the decree. The opportunity cost of the capital measured the return of a project with the same risk level, and was assumed to be equal to 5%. The lifetime of the project was hypothesized to equal the period of the subsidies provided in the previous version of the decree, which was 20 years. Year 0 was fixed in 2018, and 6 months was defined as the construction time of the plant. A pressure swing adsorption (PSA) technique was considered in the upgrading phase. Regarding the unitary value of the subsidy (\(\mathrm{i}_{\mathrm{c}ic}^{\mathrm{u}}\)), the following value was used:  
\[\mathrm{i}_{\mathrm{c}ic}^{\mathrm{u}}=375/1231=0.305\ /\mathrm{m}^{3}\quad\text{single counting} \tag{48}\]  
\[\mathrm{i}_{\mathrm{c}ic}^{\mathrm{u}}\ast\mathrm{c}_{\mathrm{c}}=0.305\ast 2 =0.610\ /\mathrm{m}^{3}\quad\text{double counting} \tag{49}\] \begin{table}
\begin{tabular}{l c c} \hline \hline
**Variable** & **Value** & **Reference** \\ \hline c\({}_{\rm C}\) & 2 & [44] \\ C\({}_{\rm CH}\) & 1231 m\({}^{3}\) & [65] \\ c\({}_{\rm CH}^{\rm Li}\) & 0.13 kWh/m\({}^{3}\) & [77] \\ c\({}_{\rm C}^{\rm u,2^{\prime}s}\) & 0.29 kWh/m\({}^{3}\) & [72] \\ C\({}_{\rm inv}^{\rm Com}\) & 53,000 \(\rm\upxi\) & [78] \\ C\({}_{\rm inv}^{\rm dig}\) & 680,000–2,250,000 & [79] \\ C\({}_{\rm inv}^{\rm dig}\) & \(\rm\upxi\) & [80] \\ C\({}_{\rm inv}^{\rm Li,s}\) & 237,500 \(\rm\upxi\) & [27] \\ C\({}_{\rm inv}^{\rm Li,2^{\prime}s}\) & 2250–6300 & [27] \\ C\({}_{\rm inv}^{\rm Li,a}\) & 25,000 \(\rm\upxi\)/y & [63] \\ C\({}_{\rm O}^{\rm com}\) & 47,000 \(\rm\upxi\)/y & [78] \\ C\({}_{\rm o}^{\rm dig}\) & 45,000–440,000 & [79] \\ C\({}_{\rm o}^{\rm dis}\) & \(\rm\upxi\)/y & [80] \\ C\({}_{\rm o}^{\rm dis}\) & 20,000 \(\rm\upxi\)/y & [80] \\ C\({}_{\rm o}^{\rm dis}\) & 0 \(\rm\upxi\) & [81] \\ C\({}_{\rm OFMSW}^{\rm}\) & 49 \(\rm\upxi\)/ton & [27] \\ C\({}_{\rm ts}^{\rm h}\) & 2–3 \(\rm\upxi\)/ton & [81] \\ c\({}_{\rm CO2}\) & 1.84 kg/m\({}^{3}\) & [82] \\ cfgas & 0.0105 MWh/m\({}^{3}\) & [63] \\ CIC & 375 \(\rm\upxi\) & [44] \\ i\({}_{\rm ic}^{\rm u}\) & 0.305 \(\rm\upxi\)/m\({}^{3}\) & [44] \\ Inf & 2\% & [27] \\ l\({}_{\rm bs}\) & 6\% & [80] \\ l\({}_{\rm us}\) & 1.5\% & [80] \\ N & 20 y & [27] \\ n\({}_{\rm debt}\) & 15 y & [83] \\ n\({}_{\rm oh}\) & 8000 h & [83] \\ n\({}_{\rm op}\) & 6 & [81] \\ n\({}_{\rm s}\) & 10 y & [44] \\ p\({}_{\rm b}^{\rm u}\) & see Section 3.2 & [25] \\ Pbionethane & see Section 3.5 & [44] \\ p\({}_{\rm cic}^{\rm u}\) & see Section 3.4 & [27] \\ p\({}_{\rm CO2}^{\rm u}\) & 10 \(\rm\upxi\)/ton & [79] \\ P\({}_{\rm compost}\) & 50 \(\rm\upxi\)/ton & [84] \\ P\({}_{\rm df}\) & 10\% & [82] \\ P\({}_{\rm e}\) & 0.13 \(\rm\upxi\)/kWh & [79] \\ P\({}_{\rm l}\) & 1\% & [84] \\ P\({}_{\rm apo}^{\rm 1*}\) & 20\% & [85] \\ P\({}_{\rm apo}^{\rm 2*}\) & 10\% & [84] \\ P\({}_{\rm mno}^{\rm 2}\) & see Section 3.5 & [72] \\ P\({}_{\rm TV}\) & 40\% & [63] \\ p\({}_{\rm ra}^{\rm u}\) & 800 \(\rm\upxi\)/ton & [81] \\ Q\({}_{\rm Compost}\) & 2000–15,000 tons & [82] \\ QOFMSW & see Section 3.2 & \\ Q\({}_{\rm z}\) & 50 ton/y & [81] \\ r & 5\% & [27] \\ r\({}_{\rm bm}\) & 97\% & [42] \\ r\({}_{\rm CO2}\) & 97\% & [81] \\ r\({}_{\rm d}\) & 3\% & [83] \\ R\({}_{\rm gross,4}^{\rm GW}\) & 70 \(\rm\upxi\)/ton & [27] \\ S\({}_{\rm biogas}\) & 150–1500 kW & \\ S\({}_{\rm Siomethane}\) & 50–500 m\({}^{3}\)/h & \\ \%CH\({}_{\rm d}\) & 60\% & [86] \\ \%CO\({}_{\rm 2}\) & 47\% & [87] \\ \%PPTV & 5\% & [44] \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Input assumptions. Concerning the selling price of biomethane (\(\rm p_{\rm biomethane}\)), some data were available (\(\rm p_{\rm PTV}\)), namely: from 19.44 \(\rm\upxi\)/MWh (February 2019) to 27.78 \(\rm\upxi\)/MWh (July 2018) [43]. The conversion factor (\(\rm cf_{\rm gas}\)) was 1 \(\rm\ m^{3}=0.0105\) MWh.