**4. Conclusions**

AHP method was applied for sustainability assessment of waste treatment scenarios with energy and resources recovery for Mexico City. This research extends the knowledge basis of comparison of waste managemen<sup>t</sup> in emerging countries with low municipal waste managemen<sup>t</sup> performance. The study does not only present information on economic instruments but also ranks them.

The study was conducted to compare the new waste managemen<sup>t</sup> plan for the city (WTE) with alternatives: "business-as-usual" scenario, AD of organic fraction, and MBT. The goal of the study was a scenario ranking using a model based on multicriteria analysis for sustainability assessment of the waste managemen<sup>t</sup> scenarios. The pairwise comparison was done by a group of experts from Mexico City. The results of this show that the most sustainable scenario, environmentally, socially, and economically, is Scenario 4-WTE, with a ranking priority of 30.78%. These results confirm that the

decision made by the governmen<sup>t</sup> of Mexico City to introduce waste incineration is sustainable from environmental, economic, and social aspects. The analysis suggests the next steps should focus on the introduction of the new regulation, improving the infrastructure, including roads, and increasing human resources. These results can help decision makers in other megacities in developing countries in introducing a successful and sustainable waste managemen<sup>t</sup> system. However, this is challenging for emerging economies that cannot easily afford waste-to-energy plants due to their high costs. Since the willingness to pay for waste managemen<sup>t</sup> is not higher than 0.4% of GDP, WTE is out of the reach of countries with a per capita GDP below 3000 US\$ [59].

The following constraints of this model should, however, be considered. According to the indicator ranking, environmental criteria have the highest priority, therefore, the WTE scenario was ranked first. But it should be noted that, due to the lack of data, European standards were used for the life-cycle inventory, and the efficiency rate of the source separation was assumed to be perfect. Another restriction of the present AHP analysis is that pairwise comparison was made by only 5 experts, because the process is time-consuming and the authors received only 5 filled-out questionnaires out of 14. The results of sensitivity analysis showed that the outcome of the study is not stable and, therefore, less reliable. Further research should involve a larger number of experts making the indicators ranking, to give higher validation to the results. Determination and precise evaluation of the indicators for assessing the sustainability of waste managemen<sup>t</sup> should be focused on as well. Moreover, further study needs to be undertaken on the feasibility of WTE technology in the Mexican context, which has the typical constrains in developing countries: data acquisition, inadequate collection systems, and reduced ability to collect charges [60].

**Supplementary Materials:** The following are available online at http://www.mdpi.com/2313-4321/3/3/45/s1. Figure S1: Mass flow diagram of Baseline Scenario; Figure S2: Mass flow diagram of AD Scenario; Figure S3: Mass flow diagram of MBT Scenario; Figure S4: Mass flow diagram of Incineration Scenario; Table S1: Details of the flows of the MFD of Baseline Scenario; Table S2: Details of the flows of the MFD of AD Scenario; Table S3: Details of the flows of the MFD of MBT Scenario; Table S4: Details of the flows of the MFD of incineration Scenario.

**Author Contributions:** N.T. realized the interviews and wrote the paper. A.V.M. conceived and supervised the study. A.A.C.S. contributed in the data analysis.

**Funding:** The first author received financial support for the conduct of this study from DAAD (German Academic Exchange Service) within the program IPID4ALL and Heinz Neumüller Foundation.

**Conflicts of Interest:** The authors declare no conflict of interest.
