In order to present the results in an order with respect to the different types of waste, the debris results are shown first and then the results for household waste.
3.2. Household Items Waste from Collapsed and Demolished Buildings
Measurements and statistical data of household item volumes and weights are showed in
Table 3. Weights and volumes were estimated by averaging ten articles per item. From this, the estimated weight of earthquake waste considering only the household equipment mentioned in [
22] per dwelling is 424.16 kg, which represents a volume of 10.17 m
3 (
Table 3).
Table 4 shows the comparation of earthquake waste generation from Mexico City Earthquake, 2017 vs. published studies, notably, there is a low number of publications about earthquake waste management (12), only six studies about earthquake waste have been published in journals, four in proceedings and two in national reports (it is important to emphasize that the magnitude of these earthquakes varies from 5.9 to 9), in this sense, it is also possible to note that only three studies mentioned a waste generation estimation but no one corresponds to the three developing countries studies. These quantities are dramatic, since from the 40 earthquakes with a magnitude greater than 8 in the world [
30], there are 21 datasets about earthquakes that occasioned collapsed buildings in developing countries, but none of them has a study published about the earthquake waste management, to the author’s knowledge.
In order to draw a comparison about the weight of the waste generated in Mexico City and the waste generated by other earthquakes in other countries, it is possible to note that only two studies published their estimates of waste quantities: the earthquakes of 1994 Northridge, US [
33] and 1995 Hyogoken-Nambu, Japan [
34]. By calculating a simple proportion of the total weight of the waste between the number of collapsed buildings, in this case, the results are as follows: 17.5 tons of debris/building from 1994 Northridge Earthquake, US; 100 tons of debris/building from 1995 Japan Earthquake; 1840 tons of debris/building from 2017 Mexico City Earthquake [
29]. The quantities differ by 1 and 2 orders of magnitude; Japan has the smallest quantity and Mexico the largest. In this sense, according to AGU reports [
29], the buildings had an average of four to six floors, and the materials accounted for in the weighing include rubble, metals, agglomerate, masonry, plastic, glass and all soil from the excavating of foundation (see
Table 1). Unfortunately, because neither Japan nor the USA describe the materials considered in the accounting and weighing, nor the number of floors of the buildings, is not possible to develop an equivalent comparison.
3.3. Mexican Recyclable Waste Processing Companies
There are 596 recyclable waste processing companies and temporary waste collection centers registered in Mexican Ministry of Environment and Natural Resources (SEMARNAT, acronym in Spanish) SEMARNAT [
39] and SEDEMA [
40] of which 191 correspond solely to waste collection.
Table 5 shows the results of interviews undertaken to estimate the capacity to receive and subsequently recycle the waste generated by the September 2017 earthquake. Waste weights and volumes were taken from AGU [
29] (rubble) and
Table 3 (household items), considering 122 destroyed dwellings [
16]. Regarding animal carcasses, municipal rabies centers are the public centers authorized to manage animals; they are sent to burial in pits or sanitary landfills in accordance with NOM-042-SSA2-2006 [
41].
Table 5 illustrates that recyclable processing companies have a reception capacity above 100% to process the waste generated by Mexico City after the 2017 earthquake. Namely, the 59 metal recyclers who answered the interview (20% from the total) indicated that each one could receive and easily process the total amount (28,286 tons); this represents a reception capacity of 59 times.
AGU reported that all metal from concrete was returned to owner after crushed works [
29], and the rubble was sent to authorized controlled and uncontrolled landfills called “tiros”. The only construction and demolition recycler enterprise in the Mexico Concretos Reciclados plant has a process capacity of 2000 tons of construction and demolition (C&D) waste per day [
42]. According with Environmental Standard NADF-007-RNAT-2013, this waste presents a daily generation in the country of 16,724 tons; in only Mexico City, daily generation is 7000 tons of C&D waste [
43], of which, according with Mexican Chamber of Construction Industry (CMIC, acronym in Spanish), 49% corresponds to rubble, 39% to soil from excavation and 12% other [
44]. Therefore, 3430 tons per day from rubble and concrete are susceptible to be processed in order to valorized them.
According to the CEO of Concretos Reciclados enterprise, they could expand operations if they would have to receive above their capacity; nevertheless, the enterprise receive less than 600 tons daily (8.57% of the total of the city); furthermore, they did not receive any demolition waste from collapsed buildings after last 2017 earthquake, because there is no policy public to encourage an adequate management of this waste (Enrique Granell, personal communication, 5 February 2018).
It is noteworthy that some surveys [
45,
46,
47] studied the mechanical performance of recycled concrete coarse aggregates (RCA) and highlighted the possibility of using recycled aggregates to produce structural concrete; in that respect, it is commonly believed that the RCA has high porosity and high water absorption, compared to the concrete made with natural aggregate (NSA) [
48]; however, according to Shayan and Xu [
49], it can be used to produce high strength (50 MPa) structural concrete. In this context, Hasan et al. [
48] investigated the feasibility of using recycled materials in concrete by focusing on the fracture mechanism of the specimens. They concluded that the compressive, flexural and splitting strengths of concrete made from recycled concrete stone aggregate (RSA) were greater than those of recycled brick aggregate (RBA). Aggregate failure, which is not acceptable for good quality concrete, has been observed in RBA concrete. Therefore, the use of RBA with NSA is not appropriate to produce good quality concrete but replacing natural stone aggregate with up to 30% of RSA can be effectively used.
Despite all of this, the main problem lies in motivating construction companies to use this material in new buildings, rather than sending C&D waste to recycling facilities. In fact, the Concretos Reciclados’ CEO mentions that construction companies do not buy recyclable material; the government is the only eventual customer (9% of the production). In other words, the recycling company accumulates 91% of the recycled material because of conflicts in existing legislation.
Karunasena et al. [
50] developed a waste analysis based on the Sri Lankan response to the 2004 Asian Tsunami 2004. The analysis concluded that disaster waste recovery and reuse is not optimized in Sri Lanka. Most reusable and recyclable materials are disposed of in landfill sites, due to insufficient knowledge about recycling and because of a lack of capacity. Karunasena et al. [
50] note that it is nearly impossible to maintain a disaster-specific waste management industry. Domingo and Luo [
5] studied construction and demolition waste management after the Canterbury earthquake and identified insufficient capacity for waste processing.
On the other hand, the metal content (from refrigerators and white goods) were sent to metal melting companies in China. However, there is not information of materials nor quantities actually sent to a recycling process. Concerning other types of waste, wood and textile furniture (22,216.2 tons) are disposed in landfills [
25]. In accordance with SEDEMA [
51], electronic waste is separated by type of waste, disassembled and sent to 94 companies for recycling [
39]. Two interviews were held with cars recyclers, which indicated that both could receive up to 500 units per month, to dismantle them and deliver metals and plastics to recycle; tires and textiles are sent to landfills, meanwhile liquids are sent to authorized enterprises. Finally, although hazardous waste, biological infectious waste and contaminated waste were not counted officially, they must have authorized processing before they are sent to their final destination (confinement, treatment or incineration) by companies authorized by SEMARNAT [
52].
3.4. Legal and Regulatory Framework for Waste Management in Earthquake Conditions
In Mexico, the General Law of Ecological Equilibrium and Environmental Protection (LGEEPA, acronym in Spanish) establishes the framework of concurrent competencies of the three levels of government [
53]. Each level has the power to develop, conduct and apply environmental policy, as well as to protect the environment and preserve and restore ecological balance within their jurisdiction [
54]. Municipal solid waste and special waste management is the responsibility of municipal officials and the officials of Mexico City, while hazardous waste management is managed at a federal level. In 2003, the General Law for the Prevention and Integral Waste Management (LGPGIR, acronym in Spanish) was issued as part of the Federal Constitution of Mexico to promote sustainable development, by preventing the generation, and promoting the recovery and integral management of waste, as well as preventing soil contamination [
55] (
Figure 2). However, neither this law nor the associated regulations expressly regulate earthquake waste, which includes all waste categories.
Moreover, Mexico has two Official Mexican Standards issued by SEMARNAT. The first standard, NOM-161-SEMARNAT-2011, establishes the criteria for the classification of wastes requiring special handling and determines which wastes are subject to a handling plan. The standard lists the different types of waste, the procedure for the inclusion or exclusion of specific wastes from the list as well as the elements and procedures associated with the formulation of waste handling plans. This standard applies, at the federal level, to management plans for C&D waste generated by buildings exceeding 80 m
3 [
56].
The other standard is NOM-087-SEMARNAT-SSA1-2002, (named: Environmental Protection Environmental Health Hazardous Waste Biological Infectious Classification and Handling Specifications) [
52], where biological infectious waste (BIW) is defined as those materials generated mainly during health care services that contain biological-infectious agents, and that may cause harmful effects to health and the environment.
In the local context, the Environmental Standard NADF-007-RNAT-2013 establishes the classification and management specifications for construction and demolition waste in Mexico City [
43]; but is does not regulate earthquake waste. In addition, it is relevant to consider risks to health and the environment associated with some components of this waste in regular situations; this could be exacerbated post-earthquakes, when waste volumes increase significantly [
8]. Therefore, it is necessary to stablish a public policy to use a percentage of recycled waste in construction industry framed in guidelines for the efficient use of resources, earthquakes resilience and risk reduction.
Nowadays, Mexico City lacks a policy on this matter; however, ten days after the earthquake of September 2017, SEMARNAT issued, in a reactive way, the document “Criterial for the Management of Construction and Demolition Waste” [
57], where it is mentioned that it is prohibited to consider areas with high environmental value and flooding areas to place and operate a landfill. Nevertheless, waste was only retired from disaster places but did not have a recycling route; they were hardly disposed in landfills controlled and uncontrolled far from the city [
29] (
Figure 3).
The Mexican federal government developed the National Program for Prevention and Integral Waste Management 2009–2012 (
Figure 2), which refers to waste management during risk and disaster situations, through the following line of action: “Prepare general procedures, directories and necessary information to deal with extraordinary waste generation in risk or disaster situations with efficiency and effectiveness, training and adequate communication to the population” [
58]. However, this proposal was part of a reactive and emergent policy, because registering procedures or work logs were not developed as
Figure 3 presented.
In fact, in Mexico City, the Civil Protection Ministry takes the lead after an earthquake occurs, contracting agencies for waste removal. Prevention, preparedness and recovery are all they lead by the local government. In addition, because earthquake waste includes all classes of waste defined in Mexican law (i.e., municipal solid waste, special handling waste and hazardous waste), a management program must enable the articulation of both the Federation and Mexico City officials. Nonetheless, as it can be seen in
Figure 2, the LGPGIR lays the groundwork for the regulation of earthquake waste, either through the official Mexican standards, or through specific strategies or programs.
These observations show that is essential to have a sustainable, post-earthquake waste strategy, dependent from government; however, when an earthquake comes and there is not a governmental strategy, a temporary strategy should establish a public policy that promotes the recycling waste process. Likewise, local authorities should locate and operate temporary collection centers with a sorting process efficient [
59], where the disaster waste can be separated to facilitate delivery to recycling companies and offload landfills, as well as the establishment of registered procedures and work logs.
Subsequently, local governments must develop disaster waste management plans aimed at the prompt and their proper disposal, as recommended by Kawamoto and Kim [
60].
According to the United Nations Office for the Coordination of Humanitarian Affairs Environmental Emergencies Section, Disaster Waste Management Guidelines, the removal and safe management of disaster waste, including earthquake waste, is an important part of the response to and recovery from disaster events. Effective risk management approaches to earthquake (and any other disaster) hazards contribute to the preparation, response and resilience of people’s safety, health and life, as well as the protection of ecosystems [
28]. Nevertheless, after the 2017 Mexico City earthquake, there was no response action strategy for earthquake waste management. At the time of this study, neither the federal government nor the government of Mexico City have an articulate strategy for the sustainable management of earthquake waste. As Chávez and Bojórquez [
61] suggest, this situation highlights the need to strengthen institutional capacities in terms of regulations and public policies to integrate an earthquake waste management program.
Different organizations present management options for disaster waste; in particular, the PAHO [
62] guide was developed for Latin America and the Caribbean context. Although guidelines for disaster waste management exist at an international level, developing countries must adapt them to their own context [
27,
28,
29,
30,
31,
32,
33,
34,
35,
36,
37,
38,
39,
40,
41,
42,
43,
44,
45,
46,
47,
48,
49,
50,
51,
52,
53,
54,
55,
56,
57,
58,
59,
60,
61,
62,
63]. Indeed, they fail to address the managerial and institutional components that influence the effectiveness of a disaster waste management system such as legislative considerations [
8]. In addition, Asari et al. [
3] conclude that it is necessary to identify the specific disaster with high risk, the waste management existent options and their priorities. Due to Mexico being prone to seismic activity [
9], this study is focused on earthquake waste.
3.5. Approach of Flow Chart to Earthquake Waste Management in Mexico City
Given the above, based on types of debris, rubble and household items waste, the quantity of them, existing recycling processing companies, legal frameworks and international guidelines analyzed previously, a flowchart for an earthquake waste management proposal is presented in
Figure 4.
The flow diagram has three columns. The first column indicates waste separation at the disaster site. The separation distinguishes non-separable mixed waste, which is sent to a temporary waste processing site, and separable bulky waste, including worklogs.
The second column indicates, within the dashed square, the temporary site where separation of waste should occur as suggested in UNOCHA [
28] including registered procedures. Outside the dashed square are the bulky waste as vehicles, slabs, water tanks, cylinders containing compressed gas, trees, etc. These objects are suggested to be sent to recycling companies directly from the disaster site. The last column indicates the destination of each type of waste in accordance with Mexican Standards, with registered procedures and worklogs, i.e., recycler, incinerator, landfill or external management authorized by SEMARNAT. This column also points out the possibility that people could recover valuable personal items. In accordance with JSMCWM [
27], it is desirable to enable the possibility for people to recover valuable personal properties, e.g., sentimental valuables such as photo albums; this study proposes to include wallets, jewelry, cell phones and laptops, IDs, personal documents, paintings, metal and stone sculptures, glasses and books.