Evaluation of municipal solid waste management system of Quito-Ecuador through life cycle assessment approach

In Latin America and the Caribbean, the suitable processing of waste through the use of landfills is around 55%, while the local governments with municipal solid waste (MSW) management plans are around 20%. In Quito, for instance, approximately 2000 ton/day of solid waste are collected, and disposed in El Inga Landfill. The objective of this study is evaluating the MSW management of Quito through Life Cycle Assessment (LCA) approach. For achieving this goal, the ISO 14040 methodology was followed and SimaPro 8.4 was used as analysis software. The functional unit used is 1 ton of MSW, while, the material of study was the waste generated in households, commercial sector, schools and markets; whose values were obtained by the public companies EMASEO-EP, EMGIRS-EP, as well as from the open-access data of the city. The results show that using of biogas from the landfill allows the maximum saving of greenhouse gases (GHG) emissions. Therefore, the biogas plant is the process with less environmental impact. The compaction and transportation of MSW displayed a slightly higher impact comparing with the previous process, presenting the second-best environmental performance. On the other hand, the leachate treatment shows the greatest environmental impact according to the model, despite of the effluents does not exceed the permissible limits of the environmental Ecuadorian legislation. The researchers consider suitable the analysis of composting and anaerobic digestion techniques as complementary options to reduce this environmental impact, due to the high organic fraction in the analyzed waste.


INTRODUCTION
Waste represent a significant challenge for human health and environment, especially in Latin America and the Caribbean (LA&C), where the implementation of modern technologies of MSW management and applicative approaches like the Circular Economy are delayed or nulled (Center for Clean Air Policy 2018; Goicochea, Fabregat 2015). Open dumps are still high in the region, thus most countries are trying to eradicate them, and adopting landfills. Nowadays, the options system of Quito - tons/year, of which 61.4% are organic, 9.4% paper or cardboard, 11% plastic, 2.6% glass and 2.2% scrap. Nevertheless, there is the possibility of recovering organic nutrients using biological waste treatment (Damgaard, Christensen 2010). The increase in the generation of MSW has slow down its management by need of high economic investment, representing a social, economic, and primarily environmental concern. Although, the Municipal Decentralized Autonomous  is identical for all environmental flows. While the endpoint factors correspond to areas of protection: human health, ecosystem quality, and resource scarcity. Therefore, Endpoints provide better information, but it has more uncertainty than middle points (Huijbregts et al. 2017).
Two perspectives can be evaluated for residues: modeling of waste disposal of a product or comparison of various waste disposal alternatives. It might allow finding the most suitable waste disposal and generates co-products as energy with the smallest loads on the environment (Klöpffer, Grahl 2014). Under this context, the present study evaluates the MSW management system of Quito -Ecuador through life cycle assessment approach, focusing on the management of domestic and commercial waste, because they are generated massively and continuously, representing an important environmental load.

MATERIALS AND METHODS
The evaluation was realized using the Environmental management -life cycle assessment - This research uses the average values of a year of activities, considering the following components: the consumption of fuels, electrical energy, chemical reagents, energy production, liquid discharges, gas emissions as well as their chemical composition, solid waste percentage.
The key data for the replicability of the model has been displayed in the section of functional unit and system boundary. However, it is not possible to share all the input and output data due to confidential rules of the responsible institutions for MSW management.  Figure 1 shows the limits and boundaries established for the present study.

Life cycle inventory and main assumptions
The characterization of the MSW used in this study, is presented in Table 1   The impact caused by the trucks that connect the Transfer Stations and El Inga landfill were evaluated. However, the following vehicles were not considered mechanical sweepers, pressure washers, skid steer loaders, side load collectors, front loading and rear loading, washing containers, dump trucks, truck tractors, trucks for collection in rural parishes and roll of-on truck.
Neither the maintenance of the vehicles was not considered in this study and for collection.

Life cycle impacts assessment method (LCIA)
There are several methods and databases used worldwide such as: US Life Cycle Inventory

RESULTS AND DISCUSSION
The MSW management in Quito was analyzed in four stages: biogas generation, compaction, leachate treatment, and transportation. Figure 3 shows

Transportation
The

Compaction
The compaction is developed using 20 heavy machineries, among them: excavators, loaders, motor graders, rollers, compactors, among others. During, the 2017 the compaction carried out around 33618 trips approx., to decrease the waste volume. This process exhibits the second-best environmental performance, yet the difference with the previous stage is negligible. According to the endpoints displayed in Figure 4, the use of resources had more influence than the ecosystem and Human health.

Leachate treatment
The compaction process creates an anaerobic environment for methane production.

Biogas Recovery Facility
The   A life cycle assessment was conducted using the ReCiPe 2016 method, finding that the biogas capture system is the process with less environmental impact, showing even some negative values. The second process with less impact is the compaction, with loads in almost all the parameters very close to transportation, the third one. The process with the greatest impact according to the proposed model is the leachate plant, nonetheless, the effluents of its process did not exceed the limits based in the Ecuadorian legislation in any parameter.
For future studies, it is suggested to consider social and economic factors to have an integral assessment of this service, as well as, evaluating some scenarios considering the high percentage of organic matter. In the same way, recycling process could be an interesting case of study in the future, not just for the environmental load saving, but also for the generation of incomes to the people that work near to the area.