## 2 Materials and Methods
### Scenario Design  
On the basis above, five MSW disposal strategies were designed, as shown in Table 3. Besides, the Figures 2-6 showed the GHG emission boundary under the five scenarios. The descriptions of the five scenarios are as follows:  
_Scenario 1_: mixed waste + landfill + incineration. As the baseline scenario, according to the current landfill and incineration ratio in Beijing, part of the waste was landfilled (10341t/d), and part of the waste was incinerated (10341t/d). The heat generated by incineration was used for electricity generation, which is in line with the current disposal mode in Beijing. The incineration residue was landfilled  
_Scenario 2_: classified waste + landfill + incineration + composoting. According to 50% separation rate, MSW was divided into kitchen waste and residual waste for source-separated collection. The separated kitchen waste was composted, and residual waste was landfilled and incinerated in proportion as Scenario 1. The heat generated by incineration was used for electricity generation. The incineration and composoting residues were transported to landfill.  
_Scenario 3_: classified waste + incineration + composoting. This scenario had the same classification as that of Scenario 2, with the difference that all residual waste was incinated instead of being landfilled, and the incineration residue was landfilled.  
_Scenario 4_: classified waste + landfill + incineration + composoting + recycling. According to 50% separation rate, MSW was divided into kitchen waste, recyclable resources, and residual waste. The separated kitchen waste was composted, the recyclable resources were sent to the recycling center as renewable resources, the residual waste was landfilled and incinerated in proportion as Scenario 1, and the incineration and composoting residues were landfilled.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Scenario** & **Landfill (t/d)** & **Incineration (t/d)** & **Composing (t/d)** & **Recycling (t/d)** \\ \hline Scenario 1 & 10341 & 9200 & — & — \\ Scenario 2 & 7867 & 6999 & 4675 & — \\ Scenario 3 & — & 14,866 & 4675 & — \\ Scenario 4 & 5523 & 4913 & 4675 & 4430 \\ Scenario 5 & — & 10,436 & 4675 & 4430 \\ \hline \hline \end{tabular} Note that for comparison purposes, the MSW quantity in all scenarios is consistent with the baseline scenario (Scenario 1), which is the sum of the landfill and incineration treatment volumes in Beijing per day in 2017.  
\end{table}
Table 3: MSW disposal quantity by different treatment way in five scenarios.  
Figure 2: GHG emissions evaluation boundary in Scenario 1.  
It should be specified that the proportion of residual mixed waste components varied when kitchen waste or recyclable resources were separated. As shown in Table 4, Scenarios 2 and 3 had the same the composition but were different from Scenario 1 as the result of separating kitchen waste.  
Figure 5: GHG emissions evaluation boundary in Scenario 4.  
Figure 6: GHG emissions evaluation boundary in Scenario 5.  
The waste composition in Scenario 4, 5 varied from Scenario 2, 3 because of the separation of both kitchen waste and recyclable resources. Besides, heat value of residual mixed waste also varied with the change of waste composition.