Logistics is defined as the element of the supply chain process that plans, implements and controls the efficient and effective flow and storage of goods, services and related information from the point of origin to the point of consumption to meet the needs of the client [1
]. In recent years, Logistics has grown in complexity by opening its doors to a greater number of factors such as society, economics, social responsibility, sustainability and the environment. In this regard, concerns about environmental care have become an important factor, not only for the business sector, but also for society, government and social organizations.
This has paved the way for the concept of Green Logistics and Reverse Logistics:
Reverse Logistics (RL) encompasses all the logistic activities from used products which are no longer required by the users to products again usable in a market. Within the environmental context, RL has been successfully applied for recovery, recycling and reuse of end-of-life electrical and electronic equipment [3
]. Figure 1
presents the basic activities or processes in an RL system [6
Green Logistics (GL) is focused on restricting damage to environment during the process of Logistics. It is based on the global environment maintenance and sustainable development [7
At present, the term GL is often used interchangeably with RL. However, in contrast to RL, GL resumes logistic activities that are primarily motivated by environmental considerations [11
]. The most significant difference is that RL focuses on saving money and increasing value by reusing or reselling materials to recover lost profits and reduce operating costs; in turn, GL focuses on the transportation [8
]. GL looks for alternatives so that the transport factor is favorable and the related costs are reduced, in addition to providing a green image for the company [12
]. The activities considered are designed to measure environmental impacts on transportation, reduce energy consumption and reduce the use of materials. As presented in Figure 2
, recycling, remanufacturing, and reusable packaging are the common processes that contribute to GL and RL. As discussed in [13
], these processes have the most significant negative impacts on sustainability.
Hence, efforts to achieve sustainability within the supply chain should be focused on these processes. Particularly, tire waste management involves RL processes than can be improved to achieve sustainability.
The massive manufacture of tires and the difficulties to proper handling, once they have been used, constitute one of the most serious environmental problems of recent years at a worldwide level. This is because a tire needs large amounts of energy to be manufactured, and, in order to prevent it from being part of clandestine dumps, it requires a specialized recycling process after the end of its useful life [14
Hence, management of tire waste is an important aspect of sustainable development due to the following environmental aspects [15
as transport is one of the main logistic activities, there is an increasing demand for new tires and generation of scrap tires (end-of-life tires). Globally, an estimated one billion tires reach the end of their useful lives every year;
scrap tires are usually shredded and disposed of in landfills, or stockpiled whole. Stockpiling leads to two significant hazards: it creates an ideal breeding ground for disease-carrier fauna, and fires;
the void space of tires in landfills capture explosive methane gas which can represent a fire hazard, contaminate local water systems, and damage the landfill liners;
chemical components such as stabilizers and flame retardants added to tires can kill advantageous bacteria in the soil.
Commonly, car owners take their worn tires to the tire shop, where they are replaced by new ones. Then, after the store has accumulated a certain number of tires, they are taken out of the store. Depending on the economic conditions, worn tires can be restored, transformed into energy, transformed into a new product, or buried [17
]. Figure 3
presents the various stages of the life of a tire, from the acquisition of the raw material to its manufacture, use, and disposal [18
However, RL processes in all industries are not widely performed. This is due to not enough knowledge about methodologies and tools to perform integrated Green-Reverse Logistics. In order to be sustainable, GL must consider environmental factors such as pollution, noise and climate change, which must keep a balance with economic and social factors. This can be achieved through RL as it influences the reduction of environmental impacts and the recovery of economic value. Particularly, within the manufacturing and transportation industries, RL and GL have become very important to reduce contaminants (chemical waste, emissions, etc.).
In the specialized literature, different processes and strategies have been proposed to improve on sustainable practices to increase recycling rates of tire waste and reduce landfilling. Table 1
presents a review of some of the most significant proposals.
In general, most of the research has been performed on technical aspects of recycling processes and not on the management of RL processes. In this regard, recycling is one of the elements within a waste management system and an effective waste management system is crucial to address the problems caused by used tires.
As reported in [32
], there are five key factors highlighted by the United Nations that must be present for the establishment of waste management systems:
policies and regulations;
proper financial mechanisms;
stake holder participation; and
As reviewed in Table 1
, there have been works on the analysis and development of strategies for tire waste management considering these factors in specific countries [19
]. Thus, regional legislation plays an important role in the successful implementation of these strategies.
In this context, the present work is focused on developing a conceptual RL model for the tire waste management systems of Mexico and Russia due to an absence of works and consensus regarding RL strategies in these countries. While finding a better strategy cannot be assured due to different regional conditions of financial mechanisms, regulations, involving entities and technologies in each country, the contribution of the proposed RL model consists of the following:
review of the factors (i.e., policies and regulations, supporting institutions, financial mechanisms) regarding the current tire waste management strategies in the EU, Japan, Mexico and Russia;
analysis regarding the most important RL processes in these strategies associated with economic and sustainable benefits;
development of a conceptual integrated RL model with these processes. The proposed RL model is focused on re-manufacturing or retreading and diversification to make it economically accessible and sustainable.
The advances of the present work are structured as follows: in Section 2
, a review of the organization aspects of RL is presented. Then, in Section 3
, the background of the RL processes and regulations in Russia, Mexico, the European Union (EU) and Japan are reviewed and discussed. The proposed conceptual RL model, which is focused on re-manufacturing and diversification, is presented in Section 4
. State-of-the-art diversification techniques which can also be considered by general RL schemes are also presented. Finally, in Section 5
and Section 6
, the outcomes of the proposed model and conclusions are discussed.
4. Proposed RL Strategy for Tire Waste
As previously discussed, tires at the end of their useful life are one of the biggest concerns with regard to the environment due to the pollution it causes. In addition, they have a practically unlimited degradation time due to the reticulated structure of rubbers and the presence of stabilizers [57
Through the tire recycling process, the main materials that make up the tire can be used, such as: 70.0% rubber powder, 25.0% steel, and 5.0% textile fibers. According to the importance of this waste in terms of its composition material and its role in society, its recycling becomes vital for the care of the environment. In order to do this, and due to the impact that it generates all over the world, to a lesser or greater degree, mainly in countries like Russia and Mexico, it is indispensable to visualize it not only as a matter of recovery of recyclable material but as a total economic system.
The implementation of RL involves environmental and economic benefits in the different areas of implementation. In particular, the economic benefits are dependent on the degree of implementation in the process of transformation and distribution of companies. As for the recycling of products that have some degree of contamination such as tires, the economic benefits are obtained as follows:
If efficient processes of re-use or re-manufacturing of goods (whether fast and inexpensive) are established, the cost of raw material and production of new goods can be reduced (instead of re-making a tire, re-conditioning of a used tire can be cheaper).
The collection of used tires that are candidates for re-conditioning must be efficient (e.g., it must be of minimum time). Therefore, the optimization of collection routes can provide faster and cheaper re-utilization processes that can substitute a percentage of the purchase cost of raw material or manufacturing (from scratch) of a new product.
Improvement in the environmental aspect is a consequence of these measures, and better government support (investment funds) can be accessed if these practices are encouraged.
If a fixed area of re-conditioning of tires is established, it will be possible to have an area that receives raw material (in this case, used tires) that can give sustenance to inventory in case of breakdown. This also involves savings and service level improvement.
On the other hand, tires that have reached the end of their useful life (it is not possible to re-condition them) support other industries (generate income).
For this reason, two strategies focused on re-manufacturing (or re-treading) and diversification are considered.
4.1. Re-Manufacturing or Retreading Strategy
The tire is mostly discarded due to wear of the tread, which has between 10.0% and 20.0% of all the material and the energy contained in it [58
]. The process of retreading involves placing a layer of non-vulcanized rubber on a worn tire that will cover the tire’s tread and shoulders. The process is then completed by placing the tire inside a mold so that, by means of pressure and temperature, the new drawing is inserted therein.
The re-manufacturing of this waste is a strategy that takes care of the environment, as it recovers the value of the components of the tire waste, which would otherwise end up in landfills. There is no doubt that the tire retreading process leads to significant savings in energy demand by 66.0% in production capacity and materials in the manufacturing process due to the minimization of raw material requirements [59
The costs of retreaded tires are 30.0–50.0% less than the cost of a new tire. This makes it attractive to consumers, such as truck fleet operators who travel long distances and demand higher tire replacement rates. This sector represents the biggest retreading industry due to the following aspects:
Maintenance and replacement of tires is the third highest cost for fleet operators, after labor and fuel.
The renewal rate for tire replacement is much higher for heavy truck fleets.
Tire retreading is desirable from the point of view of economic and material saving.
According to the Michelin Factbook (2001), retreaded tires account for 44.0% of the total tire replacement market for heavy truck tires. Retreading has an environmental impact in terms of processing of raw materials, manufacture and use. Among these impacts, the following can be mentioned:
Reduction of energy savings in the field of transient technological changes in tires;
Reconditioning of energy-saving tires in the field of inefficiency of degradation of retreaded tires compared to new equivalent tires;
Energy saving of retreading of tires in the scope of the variations of the product.
According to the Tire Retread and Repair Information Bureau (TRIB), retreaded tires can last 75.0% to 100.0% of the life of a new tire, based on the quality of the retreading process. Retreading has its advantages and disadvantages, which are shown in Table 12
This strategy can use the criterion of creating a network for the re-manufacturing and tire re-use network. The first network is aimed for the recovery of the tires and their latter re-manufacture. In this type of network, the original tire manufacturers usually play a very important role, being sometimes solely responsible for the design and management of RL systems, whose design responds to multilevel, decentralized characteristics, for which synergies are sought with the direct channel. The second network is aimed for re-introducing the recovered tires into the SC (vulcanization) once the necessary cleaning and maintenance activities are carried out. In these networks, there are decentralized structures whereby original and re-used products are simultaneously circulated and in which the cost of transport appears as the most significant [6
4.2. Diversification Strategy
To produce recycled products of equivalent quality and price, the industry must invest heavily in new technologies. Doing so would be taking advantage of a cheap resource, which allows them to generate secondary products for sale. This investment creates an opportunity to close the recycling cycle and therefore to close the SC, paying attention not only to production and processing, but also to the collection of the waste generated to be used as raw material for other processes within the company (or to open a channel with new clients).
One of the materials with greater presence in tires is the dust generated from them, as well as the steel and the textile fibers. The market for these materials is very broad and their use can be seen in family parks, sports courts, roads, among other elements, which are presented in Table 13
Diversification has its advantages and disadvantages, which are shown in Table 14
For this strategy, a recycling network could be used. This type of network usually has simple structures, few links and it is centralized. These networks are characterized by requiring, for an efficient management of the same, a high volume of recovered products which generally are of little unit value. The high transformation costs determine the need for high utilization rates of these networks and the search for economies of scale [6
4.3. Integrated RL Scheme
Both strategies show the advantages and disadvantages of its implementation within the framework of RL. However, it is necessary to know what the interests of the company are in order to take the best decision to generate greater benefits, but how does RL can influence the tire manufacturing process? The proposed adaptation of the RL process is described in Figure 10
As presented in Figure 10
, after the customers use the tires and they reach the end of their cycle of use, RL becomes a vital part of the proposed waste management strategy. In addition, it is important to observe that this RL structure has the purpose of minimizing the generation of non-recoverable waste, thus reducing the source of contaminants. This is the reason for the elimination process being absent in Figure 10
In general, the management of the RL structure can be performed by the following entities:
a third-party (public or private) company can perform the whole process of collection, classification, and re-manufacturing of the out-of-use tire;
the manufacturing company itself can extend its participation within the RL process assuming some responsibilities.
While companies (either the manufacturing company, or third party companies) are considered for most of the RL processes, the users or customers are considered as a vital part of the waste collection process. This is proposed to support a culture of sustainable waste management as achieved in Japan and the EU. Nevertheless, it is important to point out that, as in the EU, good law legislation is the key for the success of the RL processes [26
]. In Mexico, tax incentives can improve the collaboration of users and private entities in the collection process. Particularly, the adaptation of the Extended Producer Responsibility
system, which has been successfully implemented in the EU and Colombia, can be of significant benefit in Mexico and Russia. In this aspect, while Russia is not a member of the EU, since 2015, there have been amendments to the Russian 1998 Federal Law on Waste from Production and Consumption
to implement legislation similar to those of the EU for extended take-back obligations (i.e., collection and recycling) on producers and importers of certain products and packaging.
In addition, the proposed stages for waste collection can be extended with different logistic networks for recovery. As an example, Figure 11
presents the logistic chains proposed in [61
] for tire waste management where:
The first logistic chain considers that the product is recovered by the same company that manufactures it (thus, the company only recovers the tires that were manufactured by it).
The second logistic chain considers that the company recovers (1) its own tires, and (2) tires manufactured by its competition (e.g., other companies), leading to reach a greater volume of tires to carry out its processing.
The third logistic chain considers that the entire recovery process is carried out by a third-party company, which may be contracted by the manufacturer whose product is collected for the same purpose. This chain can also be extended for the creation of other products (diversification), either by means of this contracted company or by the manufacturing company itself. The third-party company can also perform the whole process or simply be a part of it.
The fourth logistic chain is related to the previous chain and it represents the case in which the company that is collecting the product does it for a different manufacturing process than the production of tires. This leads to the diversification for new markets.
Regarding the specific stages of re-manufacturing and diversification, the alternatives reviewed and discussed in Section 4.1
and Section 4.2
can be extended with the following novel approaches:
Manufacturing processes focused on decreasing rolling resistance of tires. This can lead to improving fuel efficiency, reducing
emissions, and extending the useful life of the tire [54
Standard use of the “Reduce Index” (Re Index) to objectively measure and assess processes focused on achieving a longer wear life of tire for different vehicles [54
Use of recycled tire crumb (RTC) for the manufacturing of construction materials. The RTC has been identified as a promising approach to create lightweight cellular concrete (LCC) due to its insulation properties regarding sound, water, and temperature [25
]. Countries with regions with extreme weather conditions such as Russia can get benefits from this proposal.
Recycling processes based on state-of-the-art advances in chemical studies on the effects of amount, size and morphology of rubber granulate grains for the creation of modern polymer-rubber composites from used tires [26
Extend on thermo-mechanical devulcanization based on extrusion as a standard for recycling on an industrial scale. As discussed in [23
], it is the most environmentally appropriate approach to tire recycling in comparison to chemical, ultrasound, microwave, and mechanical devulcanization.
5. Discussion on Findings
The current environment requires companies to increase the utilization of resources and optimize their practices through the incorporation of logistic processes. The consideration of a reverse flow in the logistic functions can support these objectives. Specifically, recycling of used or worn tires is the most urgent aspect to achieve sustainability within the tire industry.
According to Russian legislation, the organization of waste collection and recycling is under the responsibility of local authorities. However, classification and recovery are rarely performed by the Russian waste management system by the following situations: shortening of legislative regulation, the absence of strict requirements to separate waste, weak public awareness, and lack of collection stations and markets. Additionally, there is also a low efficiency in garbage trucks, and lack of transfer stations and incineration plants [62
Not having an effective recycling process leads to the generation of waste. In Russia and Mexico, the most common form of waste treatment is landfill disposal. However, most landfills in operation are already overloaded and some constitute environmental and epidemiological hazards. Landfill problems in Russia and Mexico are due to non-compliance with environmental and sanitary standards, and closing of landfills without waste recovering. To reduce the dependence on landfills, the development of effective recycling processes can be established by reinforcing regulations, tax incentives, and improvement of disposal technologies (e.g., by-products or energy from waste). For this, business strategies can improve the economic outcomes of recycling. However, it is important to mention that, even with the latest recycling or re-manufacturing technologies, landfill is the main disposal strategy in the short and medium term.
In this regard, countries within the EU, such as Spain, Sweden and France, have achieved 100.0% recycling rates since 2011 [19
], and the Extended Producer Responsibility (EPR)
system has proved to be a suitable mean to accomplish this objective. This system can be adapted to Mexico and Russia as it was performed in Colombia [21
]; however, it is important to consider the following difficulties:
while incentives are considered within the EPR, and the company can rely on third-party companies for collection, recycling and re-manufacturing (including diversification), some processes may be too expensive and/or complex. This can limit the intended impact or commitment of all entities within the SC;
implementation and compliance of new RL legislation may represent additional administrative and economic burden to local governments;
among the critical factors for recycling are the management and transportation costs which must be performed by the responsible entity. In general, the collection of tire waste is not only carried out by the public (i.e., government) companies, but also by private companies that use this waste as raw material for their production processes (e.g., diversification). While transportation costs have reduced the collection tasks due to inefficient route planning, there is also an inefficient cooperation between public and private companies to accomplish these tasks.
The conceptual RL model presented in Figure 10
can support the decisions regarding the main processes to be considered for a waste management strategy. In addition, it can motivate the participation of companies in transportation and/or diversification through the appropriate visualization of the RL processes.
In this model, retreating or re-manufacturing have the following economic and environmental advantages for sustainability:
savings in the energy used for production by 66.0%;
30.0–50.0% cheaper than the manufacturing cost of a new tire;
a re-manufactured tire can have a useful life of 75.0–100.0% when compared to a new tire;
very appropriate for heavy truck operators where the tire replacement rate is high.
On the other hand, market diversification represents an important investment opportunity that may be an option to close the SC cycle that includes both Direct and Reverse Logistics, as it would not only be paying attention to the process of production, but also to the problem of generated waste. This waste can be used as raw material within the SC’s production process, or be used as raw material for new production lines designed to launch new products. This would help the companies to keep current customers or to obtain new customers by opening their doors to a secondary market. In this case, technologies such as those presented in [23
] can make recycling and diversification more environmentally and economically viable.
However, as previously discussed, governmental and financial support is needed to invest in high-level recycling technology, and, at the same time, to obtain the highest rates. The attractiveness of secondary products and energy from waste also needs to improve economic and legal instruments, and public campaigns and procurement should be used to raise awareness of waste as a valuable resource. In addition, it is important to mention that landfills, even with future technologies and regulations, cannot (and will not) be eliminated completely in the short and medium term, independently of the RL strategy.
The present work defined a conceptual RL model for the tire waste management systems of Mexico and Russia due to an absence of work and consensus regarding RL strategies in these countries. For this purpose, a comprehensive review of tire waste management strategies in the EU and Japan, leading countries in recycling and sustainable practices, was performed. In addition, the current status in Mexico and Russia was reviewed considering the factors highlighted by the United Nations for the establishment of waste management systems.
This review provided the background to identify two specific RL processes: re-manufacturing and diversification, as a means to make a tire waste management system economically accessible and sustainable. These processes were integrated within an RL model considering the most standard processes performed in the EU where the Extended Producer Responsibility (EPR) is a recommended scheme that has provided benefits in countries such as Spain, France, Italy, and Colombia. Finally, a review on recycling technologies for diversification was discussed to support economic benefits.
Although a better strategy over the reviewed strategies cannot be assured due to the different regional conditions of financial mechanisms, regulations, involving entities and technologies established in each country, within the context of Mexico and Russia the proposed RL model can provide the guidelines to incorporate re-manufacturing and diversification in their waste management systems as no previous works concerning these countries have been reported. In addition, the present work can be improved regarding its limitations as no empirical research has been performed in Mexico and Russia regarding quantitative assessment of RL processes. This assessment represents also an approach to improve other strategies as those performed in the EU, Japan, Colombia, Italy and Romania.
Thus, as future work, the following aspects are considered:
design of a Green-Reverse logistic model (e.g., by means of mixed integer linear programming) to improve the distribution network required for the collection, recycling, and diversification tasks;
incorporation of economic variables within the RL structure to establish an efficient business model between all entities involved in the recycling process;
incorporation of inventory supply strategies as a mean to optimize tire waste processing.