Design of a Strategy to Provide the Collection Service of Urban Solid Waste in Communities Without IT: A Case Study of Mexico

Abstract

This work aimed to design a strategy for providing a collection service of urban solid waste in communities without it, using a case study in Sombrerete, Zacatecas, Mexico. The service is provided to the municipal seat and 17 of the 173 communities, resulting in a collection coverage of 10%. Information provided by the Cleaning Department of Sombrerete was collected and analyzed on the number of collection vehicles, communities served, and final waste disposal sites. Communities without urban solid waste collection and disposal services were identified. The strategy was designed to increase the collection coverage using geographic information systems, vehicle routing problem tools, and territory sectorization. Waste collection routes were developed for 11 sectors without service, and final waste disposal sites were evaluated based on environmental protection criteria of the Mexican Official Standard. The technical and economic feasibility of the strategy were analyzed. The results obtained were the design of the collection routes strategy to increase the coverage to 100% in Sombrerete. The designed strategy was feasible since it did not require the purchase of waste collection vehicles and hiring more staff. Approximately MXN 1000 (≈USD 54, EUR 47) in economic benefits were achieved weekly.

1. Introduction

Investigations on urban solid waste have garnered increasing attention due to urbanization, industrialization, and population growth [1]. A worldwide generation of 2.1 billion tons of waste was estimated in 2023, with an increase to 3.8 billion tons predicted by 2050. At least 33% of the waste is mismanaged globally today through open dumping or uncontrolled burning [2,3]. According to the Waste Global Database 2024, Mexico ranks seventh among countries with the highest waste generation (53.1 million tons of generated waste annually) and second in Latin America and the Caribbean, after Brazil (79.1 million tons of generated waste annually) [4]. Therefore, like other countries, Mexico faces significant challenges and opportunities in its waste management system.

Urban solid waste comprehensive management includes the stages of generation, storage, collection, transportation, transfer, and treatment or disposal [5]. The global direct cost of waste management was estimated at USD 252 billion in 2020. This cost rises to USD 361 billion when the costs of contamination, poor health, and climate change from deficient waste disposal practices are considered. An increment of USD 640.3 billion is projected by 2050 without urgent action on waste management [2]. Collection and transportation are two fundamental stages that can significantly increase or decrease the costs of the whole management system [6].

Waste collection and transportation represent between 80% and 95% of the total cost of waste management [7]. Therefore, this data emphasizes the need to optimize these processes. The waste collection service is performed with highly specialized equipment (stationary or vacuum containers) in developed countries, incorporating separation procedures for materials valorization, such as plastic, metal, glass, and others. However, simple collection systems with manual waste loading, traditional storage methods, and non-specialized vehicles are commonly used in developing countries [6].

In addition, while most waste is collected, reused, and recycled in industrialized countries, collection and adequate disposal are not yet a reality for most developing countries. Latin America, Africa, and Asia are the continents with the highest concentration of developing countries which face challenges associated with ineffective technology, weak infrastructure, inadequate funding, a lack of environmental education, and limited waste collection coverage [1].

Consequently, waste collection coverage and frequency are common issues in developing countries of Latin America, Africa, and Asia, since they tend to be low or null in the communities of their cities due to the degree of urbanization or the distance from the municipal seat [1,6,8]. As a result of these issues, government authorities must evaluate the cost-effectiveness of their waste management systems, especially waste collection services [8].

The waste collection service based on an optimal route design improves collection efficiency by saving costs associated with fuel consumption, reducing distances traveled, and minimizing greenhouse gas emissions [6,8]. Optimal route design can be solved using geographic information systems (GISs) and the vehicle routing problem tool. This tool searches for the best routes to visit a location set (collection points) by multiple vehicles. It considers vehicle capacity, time windows, and driver skill factors [9]. Several studies have demonstrated the success of applying spatial analysis to design a solid waste collection system using GISs and vehicle routing problem tools [6,8,9].

In Mexico, municipal authorities are responsible for managing urban solid waste. The waste management system includes cleaning, collecting, transporting, treating, and disposing of waste at an appropriate site. These responsibilities are established in Article 115, Fraction III, of the Political Constitution of the United Mexican States (supreme law of Mexico) [10] and Article 10 of the General Law for the Prevention and Comprehensive Management of Waste [11]. More than 102,895.00 tons of urban solid waste are generated daily in Mexico. However, 83.93% and 78.54% of the waste are collected and confined at a final waste disposal site, respectively [12].

Mexico shows a high waste collection coverage [13]. Mexican municipal authorities reported that 2311 of the 2478 municipalities (93.3%) provided waste collection and disposal services in 2020 [14]. However, this data does not show that 93.3% of the population benefited from this service. Various communities within a territory constitute a municipality in Mexico. One of them is the municipal seat. Collection service is primarily provided within the municipal seat and nearby communities, discriminating against most of them. Sometimes, communities have informal waste collectors who realize unsustainable practices, such as uncontrolled burning and disposal of waste in clandestine dumps [15].

Mexico is politically divided into 32 federated entities, as shown in Figure 1 [16]. One of them is Zacatecas, which has a territorial extension of 75,275.3 km² (3.8% of the national surface area) and is divided into 58 municipalities with a population of approximately 1.6 million in 2020 (1.3% of the country’s population) [17]. Zacatecas is one of the five federated entities that contribute less to the gross domestic product (GDP) annually (<1.0%) [18], reflecting the recession of its economy. Sombrerete is one of the 58 municipalities of Zacatecas, Mexico, as shown in Figure 1 [19]. This municipality was taken as a case study by an investigation in 2018. The most common practices carried out by the population of three communities included uncontrolled burning and using organic waste as livestock feed in unsanitary conditions. The main reason for these actions was the lack of waste collection and final disposal services [20].

This work aimed to design a strategy for providing a collection service of urban solid waste in communities without it, using a case study in Sombrerete, Zacatecas, Mexico. Nowadays, the population served by the municipal authorities is unknown, or at least there are no official records. This paper presents a scientific research approach applied to a practical case, presenting results using rigorous techniques to propose or solve the global problem of waste management. While the research is approached from a local and specific perspective, it is an example of what is happening in Mexico and other parts of the world. The lack of rigorous scientific techniques in designing strategies, optimizing resources, and managing waste adequately leads to various environmental problems described in the manuscript. Therefore, the article focuses on showing the results obtained from employing a strategy based on robust techniques in a real case.

Additionally, this study provides an alternative to extend the waste collection service to all communities of Sombrerete using GISs and the vehicle routing problem tool, ensuring that the designed system does not cause technical or economic conflicts for the municipal authorities and can be implemented in the short term. Therefore, the information provided by this study demonstrates that it is possible to expand waste collection coverage to all communities using GIS tools by optimizing collection routes with the technical and economic support of the municipality itself for planning and promoting comprehensive waste management. Hence, the hypothesis to be tested consisted of designing a strategy for providing collection services of urban solid waste to the entire population of Sombrerete, Zacatecas, Mexico, with a collection coverage of 100% and the technical and economic support of the municipality itself, without requiring an investment in more vehicles, fuel, or staff. By applying the strategy designed in this work to other case studies of Mexico and worldwide, a more sustainable and efficient waste management with environmental, social, and economic benefits could be achieved.

2. Materials and Methods

The methodology of this study consisted of five steps, as shown in Figure 2 and described below.

2.1. Step 1: Data Collection on the Current Situation of Waste Collection Service

In this first step, the waste manager of the Cleaning Department of Sombrerete was interviewed to collect information on the number of transport units, the number of trips made per unit, the number of staff participating, the work day (h), the percentage of collection coverage in the municipality (%), the per capita waste generation (kg/inhab./d), and the communities or populations served in waste collection.

2.2. Step 2: Identification of Communities with and Without Waste Collection Service

In this second step, all Sombrerete communities were identified and classified into those with and without collection service. These criteria were represented in a thematic map made in a GIS. The number of communities was obtained from the official Demographic and Social Information portal provided by the National Institute of Statistics and Geography of Mexico [21] and confirmed by the Cleaning Department of Sombrerete.

The ‘Population and Housing Census 2020’ section was consulted in the portal. Then, the metadata was downloaded in the ‘Open Data’ tab, selecting Zacatecas. The metadata corresponded to an Excel spreadsheet, where the name, population size, and location of the communities of Sombrerete were the data collected, omitting the rest of the information provided in the spreadsheet.

The information was confirmed with the waste managers to identify the communities served with the waste collection service provided by the Cleaning Department of Sombrerete.

2.3. Step 3: Sectorization of the Sombrerete Territory and Design of Waste Collection Routes

The Sombrerete territory was divided into 18 sectors based on waste collection coverage in this third step. Waste collection routes were designed for communities without services.

The sectors were established based on the population size per community reported by the Demographic and Social Information portal [21] and data provided by the Cleaning Department of Sombrerete, referring to per capita waste generation in the municipality and the load capacity of collection vehicles in tons. This information was essential to define the waste collection coverage in each sector (amount of population served), the type of collection vehicle to use, and the collection frequency.

The collection route’s design was carried out using the ArcGIS Pro trial version 3.4 software (Environmental Systems Research Institute Inc., Redlands, California, USA). First, the blocks, roads, block fronts, area services, and community polygons were taken from the digital library of the National Institute of Statistics and Geography of Mexico [22]. Likewise, the Mexican Elevation Continuum section of the continental relief was obtained from the digital library [23]. The elevation information was used to design the collection routes from the upper to the lower part, as suggested by the Technical Manual on Generation, Collection, and Transfer of Urban Solid Waste in Mexico [24]. Subsequently, the information on the transportation networks (community streets) was processed into a dataset, modifying the attributes of the roads by community, such as distances, vehicle velocity, and work times. In this case, layers of stop points were made for waste collection based on the fixed stop or corner collection method [25].

Finally, the collection routes were designed using the vehicle routing problem tool. This instrument establishes a set of optimal routes (over shorter distances and times) for a fleet of vehicles to serve a group of users using an algorithm called ‘Dijkstra’ [26]. The algorithm identifies the shortest paths from the origin to all other nodes and terminates once the destination or final point is reached. Therefore, this algorithm has several advantages over other shortest path algorithms, since it guarantees the shortest path in a weighted graph, offering efficiency in optimal path problems and scalability for large graphs, which is crucial for efficient waste collection route planning [26,27].

The design of collection routes also considered the basic rules established in the Technical Manual on Generation, Collection, and Transfer of Urban Solid Waste of Mexico [24], which are (1) the beginning of route begins at the place of shelter of the collection vehicles, and ends at the final waste disposal site; (2) the routes must not be fragmented or overlapped; (3) the routes start from the upper to the lower, especially on streets with steep slopes or high differences in level; (4) increase the productive distance (distance used to collect waste and not just move around); (5) the waste collection must perform on both sides of the street when it is possible; (6) avoid U-turns or left turns; and (7) do not collect in very narrow streets or alleys, in this case, use the fixed stop or corner collection method. The simulations in SIGs with the vehicle routing problem tool were performed twice to validate the results.

The collection time was between one and three minutes at sub-stops within the route. This time was estimated based on observed data by the staff of the Cleaning Department of Sombrerete.

The percentage of collection coverage was calculated by Equation (1):

$$Collectioncoverage(\%)={\displaystyle \frac{Numberofinhabitantsserved}{Totalnumberofinhabitants}}\times 100$$

(1)

2.4. Step 4: Identification of Final Waste Disposal Sites

In this fourth step, final waste disposal sites were identified and analyzed to provide waste disposal service by sector. The current sites were evaluated under the location restrictions stipulated in the Mexican Official Standard NOM-083-SEMARNAT-2003 [28].

The current number and location of final waste disposal sites and communities that dispose of their waste in these sites were provided by the Cleaning Department of Sombrerete. Then, a multi-criteria analysis using GISs was performed to determine suitable and unsuitable areas for the location of final waste disposal sites based on the location restrictions stipulated by the Mexican Official Standard [28]. The location restrictions were the criteria to evaluate with values of ‘0’ and ‘1’ as weights: ‘0’ when the location restriction is not accomplished, and ‘1’ when it is.

Table 1. Location restrictions in the multi-criteria analysis for final waste disposal sites.

Location Restriction	Criteria 1	Reference
-Airfields and airports	Distances higher than 13 km	[29]
-Communities with more than 2500 inhabitants	Distances higher than 500 m	[29]
-Surface water bodies	Distances higher than 500 m	[30]
-Public supply wells	Distances higher than 500 m	[31]
-Natural Protected Areas	Outside	[32]
-Wet ecosystems, plains, and aquifer recharges	Outside	[30]
-Geological faults and fractures	Outside	[33]
-Flood zones	Outside	[34]

¹ Criteria established in the Mexican Official Standard NOM-083-SEMARNAT-2003 [28].

shows the location restrictions (evaluated criteria) considered in the multi-criteria analysis for the location of final waste disposal sites.

Then, the map algebra tool calculation was applied to obtain a result, identifying the appropriate areas for the location of final waste disposal sites. The information generated was compared with the current location of the final waste disposal sites to determine if they are located appropriately. If not, recommendations were made based on the location restriction not being implemented.

2.5. Step 5: Technical and Economic Evaluation of the Designed Strategy of Waste Collection Routes

In this last step, the technical and economic feasibility of the designed waste collection routes were evaluated for short-term execution by the waste managers in Sombrerete.

The technical feasibility was assessed by determining whether the number of waste collection vehicles and staff is sufficient to provide waste collection services in all the communities of Sombrerete based on the designed strategy. If more vehicles and staff are required, the municipal authorities were asked if it would be feasible to acquire vehicles and hire more staff in the short term, based on the economic resources to which they have access.

The economic feasibility was evaluated by determining the number of waste collection vehicles, waste load capacity, fuel consumption, and the staff required to provide waste collection services in all the communities of Sombrerete, based on the designed strategy. Then, the expense of the proposed collection service and the current expenditure provided by the Cleaning Department were compared using Equations (2) and (3):

$${Benefit}_{currentwastecollection}={Costs}_{current}-Investment$$

(2)

$${Benefit}_{proposedwastecollection}={Costs}_{proposed}-Investment$$

(3)

where Benefit_{current waste collection} is total benefit of current waste collection in MXN; Benefit_{proposed waste collection} is total benefit of proposed waste collection based on the designed strategy in MXN; Costs_current is total cost of the current waste collection service in MXN; Costs_proposed is total cost of the proposed waste collection service based on the designed strategy in MXN; and Investment is budget available to the Cleaning Department of Sombrerete to invest in fuel during the waste collection service in MXN.

3. Results

3.1. Current Situation of Waste Collection Service in Sombrerete

The municipality of Sombrerete has 173 communities, including the municipal seat. The collection service is provided for the municipal seat and 17 communities, as shown in Figure 3. Therefore, the percentage of collection coverage is approximately 10% and 64% in terms of the community and population served, respectively. In total, 14 transport units registered for the waste collection service; however, only 12 units operate. Details of the transport units are shown in Tables S1 and S2. A total of 24 staff provide the collection service (a driver and one or two helpers) with a working day that starts at 5:00 h and an undefined departure time since it depends on the duration of the collection route. Every week, MXN 2000 (≈USD 108, EUR 93) could be invested in fuel per unit for the collection, for a total investment of MXN 24,000 (≈USD 1285, EUR 1107). However, the actual expenditure on fuel consumption ranges between MXN 13,500 (≈USD 723, EUR 623) and MXN 14,000 (≈USD 750, EUR 646). The collected waste is approximately 30 t/d, increasing to 35 t/d on holidays. Hence, the municipality generates approximately 0.5 kg/inhab./d of waste per capita.

3.2. Communities with and Without Waste Collection Service

The population distribution in the 173 communities of Sombrerete is shown in Table S3. The collection service is provided for the municipal seat and 17 communities. The communities with waste collection services are shown in Figure 3. The collection coverage is 10% in terms of served communities. A population of 40,602 inhabitants is provided with the collection service (Table S4). Therefore, the collection coverage is 64% of the served population.

Figure 4 shows communities without waste collection services. The services are not offered to 22,909 inhabitants of 156 communities. The communities were represented by an ID number, which can be consulted in Table S3. This lack causes the population to resort to unsustainable practices in waste management that affect the environment and human health, such as the uncontrolled burning of waste (the most performed practice), the use of organic waste as livestock feed in non-sanitary conditions, and mixing urban solid waste with hazardous waste, as was reported by Aguilera-Flores et al. [20].

3.3. Designed Waste Collection Routes

Figure 5 shows the proposed sectorization of the Sombrerete territory to extend the waste collection service, resulting in 18 sectors for the 173 communities. The number of communities for each sector varied because it was calculated based on three factors: per capita waste generation, the waste load capacity of the vehicle used by the Cleaning Department, and the number of inhabitants per community.

Table 2. Sectorization of the Sombrerete territory to extend the waste collection service.

Sector Number	Number of Communities Served	Number of Inhabitants Served
1	19	2986
2	23	1237
3	18	2632
4	17	3197
5	3	1464
6	5	3105
7	8	2484
8	20	1336
9	13	858
10	7	1538
11	2	1507
12	1	2455
13	3	4038
14	1	25,068
15	4	3297
16	9	873
17	14	3063
18	6	2373
Total	173	63,511

shows information on the distribution of communities and population per sector. Table S5 shows information in detail.

Communities in sectors 1 to 11 lack waste collection services, so the collection routes were designed for these eleven sectors. Although sectors 12 to 18 already have collection services, nearby communities with fewer than 200 inhabitants were included to increase service coverage.

Sector 12 considers the Col. Hidalgo community, which already has waste collection services. Therefore, the waste collection route for Col. Hidalgo remained unchanged.

Comales and Tres Marias communities, with four and two inhabitants, were included in the waste collection route for the Col. Gonzalez Ortega community in sector 13. It was proposed that Comales and Tres Marias residents leave their waste on a specific day of the week at a corner of the road. The waste collection vehicle would only make one fixed stop in each community. This action does not interfere with the collection service provided to the community of Col. Gonzalez Ortega, nor does it generate technical or economic problems (fuel consumption).

Sector 14 includes the municipal seat. Its waste collection routes remained unchanged.

San Pedro Chupaderos (Chupaderos) and General Francisco R. Murguia, with 91 and 89 inhabitants, could be included in the current waste collection routes for Charco Blanco and Ignacio Allende communities in sector 15. It was proposed that residents leave their waste on a specific day of the week at a corner of the road, as in sector 13. The collection service in Charco Blanco and Ignacio Allende is provided only once a week (Table S2). However, the Collection Department confirmed that waste collection in San Pedro Chupaderos (Chupaderos) and General Francisco R. Murguia could be carried out only with fixed stops on a corner at the side of the road without interfering with the collection services or generating technical or economic problems (fuel consumption).

Santa Cruz, El Solar, Santa Cruz de las Playas (El Tutano), Santa Martha, La Piramide [Rancho], and La Casita (Angel Ulloa Rodarte) communities, with six, six, five, four, four, and one inhabitants were included in the current waste collection routes for San Jose de Mesillas (Mesillas), San Juan de la Tapia (La Tapia), and Col. El Orion communities in sector 16. The proposal was again based on community residents leaving their waste on a specific day of the week at a corner of the road for waste collection. This action does not generate technical or economic problems (fuel consumption) with the current waste collection service.

San Francisco de las Flores (El Ranchito), Tapia Blanca, Noria San Pantaleon (La Noria), Carretas, San Juan de los Laureles (San Juan del Alamo), Quinta Santa Monica (Jose Olvera), and San Francisco de Organos [Restaurante] communities, with 63, 32, 31, 6, 6, 4 and 2 inhabitants, were included in the current waste collection routes for San Martin, San Jose de Felix, San Francisco de Organos, Providencia, El Alamo, San Agustin (San Agustin de la Victoria), and San Antonio de Belen (San Antonio) communities in sector 17. The proposal was again based on the conditions described for the other sectors.

Santa Rita, Ojito de Huatitapa, and El Ranchero Chido [Restaurante] communities, with 197, 10, and 2 inhabitants, were included in the current waste collection routes for Villa Insurgentes (El Calabazal), Ojo de Agua, and Salas Perez communities in sector 18. The proposal was based on the same conditions as other sectors for the cases of the Ojito de Huatitapa and El Ranchero Chido [Restaurante] communities. However, Santa Rita could be included in the third trip when waste collection is performed in the Salas Perez community since both have similar population sizes, and the collection vehicle would not be saturated with waste. Although this inclusion could cause technical and economic problems, the cleaning department considered that this community could be included in the current collection route. It does not generate inconveniences regarding workers’ work schedules, fuel consumption, and waste loading capacity, among others. Therefore, the collection route was not designed for this sector either.

Table 3. Summary information on the designed waste collection routes for 11 sectors in Sombrerete, Zacatecas, Mexico.

Sector	Day of the Collection	Number of Trips	Schedule (h)		Collection Time (min) 1	Distance (km) 2	Number of Stops	Number of Sub-stops	Communities Served	Population Served	Collected Waste (kg)	Final Waste Disposal Site 3
			Start	End
1	Monday	3	07:30	15:00	222	173.30	8	66	19	2986	823.5	1
	Tuesday	2		14:29	80	336.86	7	29			313.5
	Wednesday	2		13:09	95	289.34	4	57			356.0
2	Monday	3	07:30	14:17	120	200.75	18	31	23	1237	512.5	1, 4
	Tuesday	1		09:50	37	112.78	5	10			106.0
3	Tuesday	2	10:20	15:59	89	168.97	5	40	18	2632	521.0	1, 4
	Wednesday	3	07:30	15:38	177	351.04	13	44			795.0
4	Thursday	3	07:30	14:04	109	168.16	13	30	17	3197	453.0	1, 4
	Friday	4	07:30	17:07	250	154.76	5	77			1100.5
5	Monday	4	07:30	14:56	205	77.87	5	64	3	1464	732	4
6	Monday	2	07:30	14:34	205	124.74	4	62	5	3105	947.50	4
	Tuesday	2	07:30	12:36	126	67.83	2	40			605.00
7	Tuesday	1	13:06	16:46	102	78.28	2	31	8	2484	439.5	3, 7
	Wednesday	2	07:30	13:44	200	93.47	6	61			802.5
8	Thursday	3	07:30	16:24	194	175.52	19	54	19	1336	668.00	1
9	Tuesday	2	07:30	14:39	126	173.59	13	28	13	858	429.00	1
10	Wednesday	4	07:30	19:46	184	295.43	8	56	7	1538	769.00	1
11	Monday	3	07:30	13:54	163	94.87	3	50	2	1507	753.5	2

¹ The value considered only productive time, that is, the time of the working day in which waste is collected. ² The value considered only productive distance. It did not include the distance from the garage to the start of the collection route of trip 1, between trips, from the end of the route of the last trip to the final waste disposal site, and from the final waste disposal site to the garage. ³ ID number is based on Figure 6.

summarizes the design of waste collection routes for the remaining 11 sectors. The ID number corresponds to the final waste disposal sites (Figure 6) where people currently dispose of their waste or are supposed to do so. Tables S6–S16 show details of the designed waste collection routes. Figures S1–S40 show the generated maps of the designed waste collection routes.

3.4. Final Waste Disposal Sites in Sombrerete

Six open-air dumps, one landfill, and one closed final waste disposal site were identified as final waste disposal sites in Sombrerete, Zacatecas, Mexico. Figure 6 shows the distribution of these sites in the municipality.

Table 4. Communities with disposal services per final waste disposal site in Sombrerete, Zacatecas, Mexico.

Final Waste Disposal Site Location	Final Waste Disposal Site Type	Served Communities	Served Population	ID Number in Figure 6
Municipal seat	Landfill	Municipal seat, San Martin, Col. El Orion, San Juan de la Tapia (La Tapia), San Jose de Mesillas (Mesillas), San Antonio de Belen (San Antonio), Providencia, El Alamo, San Jose de Felix, and San Agustin (San Agustin de la Victoria)	28,573	1
Charco Blanco	Open-air dump	Charco Blanco and Ignacio Allende	3117	2
Villa Insurgentes (El Calabazal)	Open-air dump	Villa Insurgentes (El Calabazal), Salas Perez, and Ojo de Agua	2164	3
Col. Gonzalez Ortega	Open-air dump	Col. Gonzalez Ortega, Jose Santos Bañuelos (Bañuelos Nuevo), and Jose Santos Bañuelos (Bañuelos Viejo)	5495	4
Region of the municipality of Miguel Auza 1	Open-air dump	Col. Hidalgo	2455	5
Ejido Zaragoza	Open-air dump	Ejido Zaragoza (Francisco R. Murguia)	1093	6
Plan de Guadalupe	Open-air dump	Plan de Guadalupe	466	7
Municipal seat	Open-air dump	Not applicable 2	Not applicable 2	8

¹ Miguel Auza is another municipality of Zacatecas, which borders Sombrerete to the south. ² The final waste disposal site is currently closed.

shows the communities with waste disposal services per final waste disposal site in Sombrerete, Zacatecas, Mexico.

Table 4 shows that the municipal seat and 20 communities have waste disposal services, representing a disposal coverage of 12% and 68% regarding served communities and population, respectively. There are 152 communities and 20,140 inhabitants who lack a final waste disposal site. This situation promotes the creation of clandestine dumps, which impact human health and the environment, causing air and water pollution, soil degradation, and climate change (emission of greenhouse gases by uncontrolled open burning) [35].

On the other hand, Sombrerete has a landfill in a suitable zone that complies with the location restrictions stipulated by the Mexican Official Standard [28]. The final waste disposal sites of Col. Gonzalez Ortega and Plan de Guadalupe are also in suitable zones which accomplish the location restrictions of the Mexican Official Standard [28]. The open-air dumps of Charco Blanco, Villa Insurgentes (El Calabazal), and Ejido Zaragoza are located at less than 500 m from surface water bodies and human settlements.

People living close to open-air dumps suffer from diseases associated with the spread of water and air, such as cholera, dengue, diarrhea, tetanus, and others. Likewise, the population could be exposed to chemicals, toxic fumes, contaminated water, and dust, which damage their health [36,37].

Surface water bodies near open-air dumps are susceptible to pollution with leachate. The leachate contains halogens, heavy metals, hydrocarbons, pesticides, and xenobiotics, which are highly injurious to human health and the environment [38,39]. Therefore, both conditions represent a significant environmental risk. It is recommended that the authorities take action to enclose the areas, avoid waste dispersion, and construct and operate liner systems to collect leachate and prevent waste from reaching the population or streams.

3.5. Benefits of the Designed Strategy of Waste Collection Routes

The technical proposal based on the transport units and staff to provide waste collection services to all inhabitants of Sombrerete is shown in

Table 5. Transport units for the waste collection service in Sombrerete, Zacatecas, Mexico.

Brand and Model (ID)	Fuel Tank Capacity (L)	Efficiency (km/L)	Sector	Collection Days	Number of Trips	Total Distance of the Route (km) 1	Fuel Consumption (L)	Investment (MXN) 2
Chevrolet ‘Silverado’ 2005 (49)	90	9.61	1	Monday	3	202.50	21.07	544.70
				Tuesday	2	366.06	38.09	984.66
				Wednesday	2	318.54	33.15	856.84
Nissan ‘NP300’ 2020 (Ne1)	80	11.68	2	Monday	3	229.95	19.69	470.53
				Tuesday	1	149.72	12.81	306.36
			3	Tuesday	2	198.21	16.97	405.58
				Wednesday	3	557.24	47.71	1140.24
			4	Thursday	3	197.36	16.90	403.84
				Friday	4	209.43	17.93	428.54
Ford ‘Ranger’ 2018 (84)	80	11.50	5	Monday	4	132.54	11.53	275.45
			9	Tuesday	2	202.79	17.63	421.45
			10	Wednesday	4	324.63	28.23	674.67
			11	Thursday	3	127.42	11.08	264.81
Chevrolet ‘Silverado’ 2005 (68)	90	9.61	6	Monday	2	179.41	18.67	446.19
				Tuesday	2	122.50	12.74	304.66
			7	Tuesday	1	105.58	10.98	262.57
				Wednesday	2	144.93	15.08	360.43
			8	Thursday	3	204.72	21.30	509.13

¹ The value considered the productive distance (waste collection route shown in Table 3) and the distance from the garage to the start of the collection route of trip 1, between trips, from the end of the route of the last trip to the final waste disposal site, and from the final waste disposal site to the garage. ² An average price of gasoline and diesel of MXN 23.90 (≈USD 1.28, EUR 1.10) and MXN 25.85 (≈USD 1.38, EUR 1.19) per liter was considered.

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Based on Table 5, the total cost of the proposed waste collection service is MXN 9060.65 (≈USD 485, EUR 418). Currently, the Cleaning Department has a budget of MXN 24,000 (≈USD 1285, EUR 1107) per week for investing in fuel. The cost of current waste collection services averages MXN 14,000 (≈USD 750, EUR 646). The total benefit of the current waste collection, estimated by Equation (2), is MXN 10,000 (≈USD 536, EUR 462). Therefore, the total benefit of the proposed waste collection would be MXN 939.35 (≈USD 51, EUR 44) using Equation (3). While the municipality earned a profit of approximately MXN 10,000 (≈USD 536, EUR 462) for providing collection services only to some communities, its budget is MXN 24,000 (≈USD 1285, EUR 1107), and approximately MXN 23,000 (≈USD 1232, EUR 1061) could be used to serve all communities in Sombrerete. However, the Cleaning Department must consider whether reducing its weekly profit from 10,000 (≈USD 536, EUR 462) to MXN 1000 (≈USD 54, EUR 47) would affect other expenses of the collection service, such as employee pay, vehicle maintenance, or container purchase.

Additionally, this strategy does not generate technical conflicts. The Cleaning Department of Sombrerete has 12 waste collection vehicles and 24 staff. The design only considers using four transport units. Hence, these units could be exchanged weekly with the other units. Therefore, the results obtained in this work support the implementation of the designed strategy in the short term. The strategy is technically and economically accessible to the government authorities of Sombrerete, Zacatecas, Mexico. Likewise, this study could be extended to other municipalities in Zacatecas, states of Mexico, or even cities in other countries where waste collection services need to be improved and expanded.

4. Discussion

This study designed a strategy to extend the collection coverage of urban solid waste to 100% in Sombrerete, Zacatecas, Mexico, without occasioning technical and economic problems. The current service is provided for the municipal seat and 17 communities, with collection coverage percentages of 10% and 64% for the served community and population, respectively. The current investment in this service is MXN 24,000 (≈USD 1285, EUR 1107) per week, and MXN 2000 (≈USD 108, EUR 93) is invested in fuel per unit for collection. The service has 24 staff (a driver and one or two helpers) and 12 transport units. An economic benefit of approximately MXN 1000 (≈USD 54, EUR 47) could be obtained from the designed strategy. The cost of proposed waste collection services averages MXN 23,060.65 (≈USD 1235, EUR 1064) each week. This work proposed to optimize collection routes in a study area. However, the designed strategy could be replicated in nearby municipalities, other states of Mexico, and countries of Latin America with similar socioeconomic characteristics and waste collection infrastructure conditions [6,15,40]. However, it is essential to consider some limitations of this investigation.

The first limitation was the collection time, which ranged from one to three minutes per sub-stop. However, this time depends on multiple factors, such as the number of containers, amount of waste, vehicle collection capacity, traffic, number of staff, patterns of urban settlements, and narrow or unpaved streets, among others [6,41]. These factors, in turn, could affect the efficiency, quality, and costs of the estimated collection service. For this reason, one suggestion is to implement the designed collection system where collection time, fuel consumption, and cost must be frequently monitored to evaluate feasibility and propose opportunities for improvement in case of any failure.

Another limitation is that the localities of the municipality do not have enough containers and lack designated collection points. This study identified potential collection points that could be used for this purpose, as the design was based on collecting waste through a fixed-stop or sub-stop system. Therefore, the operational feasibility of the system will depend on the availability of containers and the pertinency of the proposed collection points in communities with low population density. In this sense, the Cleaning Department of Sombrerete should allocate resources to acquire containers, evaluate operational feasibility, and promote environmental education to the general population and workers on the waste management system.

The inhabitants play a significant role in the system, educating and engaging them in waste reduction practices, such as composting, valorization, and recycling, which furthers a sense of responsibility and commitment, contributing to long-term environmental sustainability [6,42]. Local and regional public policy implementation improve the waste management system. An example is the initiative carried out in a low-income community near Bangkok, Thailand, based on the theory of change. This theory involved diverse participation approaches to meet the needs of various community members, promote equality, foster horizontal relationships, and distribute incentives [43].

In addition, inter-municipal cooperation has the potential to generate economies of scale and reduce financial costs on waste management. A case study in 22 municipalities of Ecuador showed that those that invested in more complex cooperation types achieved better integrated waste management performance, particularly on final disposal, citizen participation, inclusion of recyclers, and environmental sustainability [44].

On the other hand, optimizing waste collection routes achieves cost savings (up to 44%) and reduces greenhouse gas emissions (between 17% and 70%) [8]. Therefore, the optimized collection route models with GIS also contribute to mitigating the environmental impact caused by an inadequate waste management system.

Finally, when an optimal waste collection design without supportive policies and infrastructure is developed, it will result in an unsuccessful collection system with low service coverage, time loss, equipment deterioration, high costs, and the creation of open dumps [25,42]. Therefore, governments of developing countries must address public policies, promote inter-municipal cooperation, and generate diverse financing mechanisms to achieve effective waste management systems and reach environmental sustainability goals in sustainable urban planning.

5. Conclusions

This work designed a strategy to achieve 100% collection coverage of urban solid waste in Sombrerete, Zacatecas, Mexico. The Sombrerete territory was sectorized into 18 sectors. Therefore, waste collection routes for 11 sectors without service were designed using the vehicle routing problem tool and geographic information systems. Likewise, final waste disposal sites were evaluated under the environmental protection criteria stipulated in the Mexican Official Standard. The designed strategy was technically and economically feasible. The purchase of waste collection vehicles and hiring of staff are not required, and economic benefits of MXN 1000 (≈USD 54, EUR 47) per week were achieved. Therefore, the implementation of this strategy will bring socioeconomic and environmental benefits by reducing the negative impacts on the environment and the health of the population, which are affected by the uncontrolled burning of waste, the generation of clandestine dumps, and the proliferation of harmful fauna, promoting sustainable urban planning in the comprehensive waste management of the municipality. The hypothesis raised in this study was accepted since it was possible to design a strategy for providing a collection service for urban solid waste to the entire population of Sombrerete, Zacatecas, Mexico, with the technical and economic support of the municipality itself, without requiring an investment in more vehicles, fuel, or staff.