## 3 Results and Discussion
### Discussion on Evaluation Results  
It could be seen that CO\({}_{2}\) emissions were superior in the descending order of Case 4, Case 2, Case 3, Case 1, using Figure 5. This reduction was due to the heat supply to the Keiyo Coastal Industrial Zone being as large as 58745 t-CO\({}_{2}\)/Y in Case 2 and 57376 t-CO\({}_{2}\)/Y in Case 4. In Cases 3 and 4, the reduction due to biogas power generation was 6391 t-CO\({}_{2}\)/Y, and this value resulted in a negative CO\({}_{2}\) emission in Case 4. It could be seen that the economic efficiency was superior in the order: Case 4 > Case 2 > Case 3 > Case 1, in Figure 6. This was because the reduction due to heat sales was as large as 1.72 billion yen/Y in Case 2 and 1.63 billion yen/Y in Case 4, as in the case of CO\({}_{2}\) emissions. In addition, the reduction in biogas power generation due to electricity sales was contributed by the fact that Case 3 was larger than Case 1 and Case 4 was larger than Case 2. In Cases 3 and 4, the depreciation expenses were higher than in Cases 1 and 2 because the depreciation costs for utilization as heat are included. However, this result was obtained because the reduction due to heat sales was larger than the rate of increase. It could be said that the case was superior as the plot goes to the lower left from Figure 7, so it could be said that it was superior in the descending order of Case 4, Case 2, Case 3, Case 1. Comparing Cases 1 and 2 in Figure 5, the reduction in Case 1 was 37,118 t-CO\({}_{2}\)/Y, including incinerator power generation and heat supply, whereas Case 2 can reduce 59789 t-CO\({}_{2}\)/Y, which was approximately 1.6 times higher. Comparing Case 3 and Case 4, the reduction in Case 3 is 42528 t-CO\({}_{2}\)/Y due to the addition of fermentation power generation, but Case 4 was 63767 t-CO\({}_{2}\)/Y, which is approximately 1.5 times higher. Since the heat use cases are the first and second best, it could be seen that the effect of reducing the social cost of supplying heat to the Keiyo Coastal Industrial Zone was large. Comparing Case 1 and Case 3, the reduction in CO\({}_{2}\) emissions was approximately 1.1 times greater in Case 3, indicating that even in the case of power generation, the introduction of the MBT system results in a bigger CO\({}_{2}\) emission reduction. This was because it not only reduces the amount of food waste incinated and the amount of CO\({}_{2}\) emitted during waste incineration but increases the amount of digestion gas generated by mixed methane fermentation of food waste and sewage sludge and increases CO\({}_{2}\) reduction. This was also the case when comparing Cases 2 and 4. It could be seen that the annual cost reductions in Cases 2 and 4 are large at 1.80 billion yen/Y and 2.11 billion yen/Y, respectively, and the income from heat sales by using the heat was excellent, as established in CO\({}_{2}\) emissions evaluation presented in  
Figure 10: Results of sensitivity analysis of piping distance. Figure 6. Comparing Cases 1 and 3, Case 3 performs mixed biogas power generation of food waste and sewage sludge and has an annual cost reduction of 1.11 billion yen/Y, which was approximately 1.5 times greater than that of Case 1. The annual cost could be reduced when the MBT system was introduced. Summarizing the above results and evaluating the CO\({}_{2}\) emissions and economic efficiency of the introduction of the MBT system in Ichihara City, it was confirmed from Figure 7 that Case 4, Case 2, Case 3, and Case 1 are superior in descending order. In developing countries, MSW was often treated by landfill and incinerators, and a study that evaluated LCA when the MBT system was introduced found that the case of landfilling MSW produced the worst evaluation result, and the energy efficiency was high when the MBT system was introduced; however, it could be said that the same evaluation results were obtained in this study when the MBT system was introduced in Ichihara City [21].