## 3 Results and Discussions
### Economic Analysis: Cost and Benefit
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & **Items** & \begin{tabular}{c} **Scenario 1** \\ **(\(\boldsymbol{\xi}\)/(tonne*Y))** \\ **min-MAX** \\ \end{tabular} & \begin{tabular}{c} **Scenario 2** \\ **(\(\boldsymbol{\xi}\)/(tonne*Y))** \\ **min-MAX** \\ \end{tabular} & \
\begin{tabular}{c} **Scenario 3** \\ **(\(\boldsymbol{\xi}\)/(tonne*Y))** \\ **min-MAX** \\ \end{tabular} &
\begin{tabular}{c} **Reference** \\ **min-MAX** \\ \end{tabular} \\ \hline \multirow{3}{*}{Cost} & Initial costs & 18.49–78.15 & 50.62–243.51 & 39.9–131.58 & [7, 8, 12, 25, 26, 27, 28] \\ \cline{2-6}  & Operation and & 13.33–25.93 & 9.23–14.43 & 7.56–35.53 & [7, 8, 12, 24, 27, 28, 13, 29, 30, 31] \\ \hline \multirow{3}{*}{Benefit} & Revenue from compost & 5.60–29.91 & X & X & [7, 8, 32] \\ \cline{2-6}  & Revenue from electricity energy sales & X & 3.87–27.63 & X & [13, 29] \\ \cline{2-6}  & Revenue from biomethane sales & X & X & 13.57–47.16 & [27, 28, 30, 31, 32] \\ \cline{2-6}  & CO\({}_{2}\) emissions avoided & 0 & 0.44–4.39 & 1.47–4.39 & [7, 31, 32, 33, 34] \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Cost and benefit item assessment per scenario tested. The same approach was carried out to investigate the costs and benefits in anaerobic digestion process conditions, for renewable energy electricity production. The initial costs for Scenario 2 (Table 1) were quite different relative to those investigated for Scenario 1. In fact, according to different literature reviews, [PERSON] et al. [25] and [PERSON] [26], where the latter implemented an economic assessment of upgrading and selling biogas starting from a typical farm-based anaerobic digestion plant in Northern Ireland assumed as reference, reported that the initial costs for anaerobic digestion in a biogas plant could range from 50.62 to 243.51 \(\upxi\)/tonne of waste. An assessment from other diverse literature reviews was done in order to evaluate the accuracy of this range. In a report by [PERSON] et al., in Pakistan's context, the initial costs for a novel anaerobic bioenergy plant were about 64.62 \(\upxi\)/tonne of waste as input in a digester [29]. However, as claimed by [PERSON] et al. [13], the total initial costs for a commercial thermophilic biogas plant located in Spain, where a combined heat and power system produced electricity and then sold it to the network, were 54.91 \(\upxi\)/tonne of waste. In relation to the operation and maintenance costs, according to [PERSON] et al. [29] and [PERSON] et al. [13], these ranged from 9.23 to 14.43 \(\upxi\)/tonne of waste (Table 1). The renewable electricity produced sales in the benefits of this scenario. As Table 1 shows, the benefits are located in a range from 3.87 to 27.63 \(\upxi\)/tonne of waste per year, according to [PERSON] et al. [13]. In the assessment carried out by [PERSON], the income was 15.63 \(\upxi\)/tonne of waste per year resulting from electricity sold [26]. Differently from Scenario 1, in this scenario one should also consider the benefits arising from the CO\({}_{2}\) emissions avoided, that can be quantified through SendeCO2 [18], which will affect the social NPV computation. The se ranged from 0.44 to 4.39 \(\upxi\)/tonne of waste per year (Table 1), as reported by [PERSON] et al. [26] and [PERSON] and [PERSON] [7]. Other different literature assessments, by [PERSON] et al. [32] and [PERSON] and [PERSON] [33], showed values, respectively, of 3.49 and 3.00 \(\upxi\)/tonne per year. Finally, an assessment for Scenario 3, i.e., anaerobic digestion for biomethane injection into natural gas networks for user consumption, can be set out. The initial costs for Scenario 3 ranged between 39.90 and 131.58 \(\upxi\)/tonne of waste (Table 1) according to the experience of [PERSON] et al. [12], who evaluated the profitability of small-scale biomethane plants concerning two typologies of substrates, and [PERSON] et al. [27], who investigated the economic feasibility of a biomethane plant for a Mexican city, identified initial investment costs for upgrading biogas to biomethane.