## 2 Materials and Methods
### DATA4: The M-GRT Computer Support Tool
#### 2.1.1 M-GRT Environmental Control Procedure  
The environmental control procedure considered by the M-GRT model is shown in Figure 1. This procedure considers a set of criteria in order to compare and determine the feasibility of the two scenarios for the selected municipalities: the projection of recyclers based on the recyclable waste census, the reduction in methane emissions and the reduction in the carbon footprint.  
The projection of both official and formalized recyclers between 2021 and 2030 was carried out by analyzing the relationship between the amount of usable solid waste and per capita production, as shown in Equations (1) and (2).  
\[\begin{split} PPC=\frac{\text{Per capita waste production }\left(\frac{\text{kg}}{\text{day}}\right)}{\text{Number of inhabitants}}\end{split} \tag{1}\]  
\[\begin{split} P_{R}=\frac{\text{Waste production }\left(\frac{\text{kg}}{\text{dia}}\right)}{\text{ PPC}_{0}}*\ PPC_{1}\end{split} \tag{2}\]  
where \(\ PPC\) = per capita waste production (kg/(day-person)), \(P_{R}\) = recycler's projection, \(\ PPC_{0}\) = per capita waste production in the current year (kg/(day-person)) and \(\ PPC_{1}\) = per capita waste production in the following year (kg/(day-person)).  
To determine the reduction in methane emissions, the LandGEM model was used [42]. This model calculates the methane emissions of the municipalities and their equivalent factor in CO\({}_{2}\) emissions (21 kg CO\({}_{2}\) eq/t), according to the criteria established by the Intergovernmental Panel on Climate Change--IPCC [43]. Equations (3) and (4) were used to calculate methane emissions in the municipalities:  
\[\begin{split} CF_{CH4}=E*F_{e}\end{split} \tag{3}\]  
\[\begin{split} E=E_{CH4}*R\end{split} \tag{4}\]  
where \(CF_{CH4}\) = reduction in methane emissions (kg CO\({}_{2}\) eq), \(E\) = methane emissions produced by the municipality (kg CO\({}_{2}\) eq), \(F_{e}\) = equivalent factor, \(E_{CH4}\) = methane emissions on every final disposal site and \(R\) = recyclable waste/ total waste ratio.  
To analyze the carbon footprint, the emissions generated by solid waste transportation were taken into account based on the difference between the calculated distance between the collection center and the final disposal site.  
First, the collection frequency and the capacity of the collection vehicles (13 t) were considered. Once the distances were computed, their value was multiplied by the greenhouse gas emission factor established by the Intergovernmental Panel on Climate Change --IPCC (0.68653 kg CO\({}_{2}\) eq/km). Equation (5) shows the methodology of calculation of the transportation carbon footprint reduction:  
\[CF_{Tt}=(D_{0}-D_{A})*F_{r}*F \tag{5}\]  
Figure 1: Definition of criteria for the environmental control procedure in the M-GRCT model.  
where \(CF_{Tt}\) = transportation carbon footprint reduction (kg CO\({}_{2}\) eq/km), \(D_{0}\) = distance between the collection center and the final disposal site (km), \(D_{A}\) = distance between the municipality and the collection center (km), \(F_{R}\) = collection frequency and \(F\) = emission factor (kg CO\({}_{2}\) eq/km).  
To compute the carbon footprint reduction generated by leachates, the weight of processed recyclable waste and the greenhouse gas emission factor established by the Intergovernmental Panel on Climate Change--IPCC ( 0.022 kg CO\({}_{2}\) eq/t) were used. Equation (6) shows the methodology of calculation of the leachate carbon footprint reduction:  
\[CF_{L}=(Recyclable\ waste\ weight)*F_{L} \tag{6}\]  
where \(CF_{L}\) = leachate carbon footprint reduction (kg CO\({}_{2}\) e) and \(F_{L}\) = greenhouse gas emission factor (kg CO\({}_{2}\) e/t).  
Accounting for all this information, the total greenhouse gas footprint reduction can be obtained by adding the three previous terms, as shown in Equation (7).  
\[CF_{T}=CF_{CH4}+CF_{Tt}+CF_{L} \tag{7}\]