1. Overview

Unrecycled tire waste is an enormous global problem because of their non-biodegradability, their flammability (see tire fires) and their chemical composition that leads to leaching of toxic substances into the ground on dumping and hazardous fumes on incineration. Since they are hefty, thick, and made of multiple materials, scrap tires present distinct challenges in recycling and disposal. In 2007,around 300 million ELTs had been produced in the United States.^[1] In 2008 around one billion ELTs were being produced globally each year with an estimated further four billion already in stockpiles and landfills. Global production in 2008 was about 1.5 billion new tires. The U.S. as the largest producer of ELTs alone produced generated 291.8 million tyres in 2009 as estimated by the U.S. Rubber Manufacturers Association.^[2][3] In 2013, 3,824 thousand tonnes (3,764,000 long tons; 4,215,000 short tons) of tires were generated in the U.S.^[4] Newer figures (2015) talk about 450 million scrap tires generated annually in the U.S.^[5]

According to the RMA, as reported elsewhere,

52% of scrap tires are burned for fuel

12% are used in crumb rubber products

16% is used for civil engineering applications

at least 14% is ground and dumped in landfills^[5]

Used tires

Waste or Scrap tires are made out of a material which can have no economic end use. This means that tires which are no longer suitable for use on vehicles due to wear or damage, can be recycled to serve a new economic purpose (rubber asphalt and concrete, fuel alternatives, carbon sources, etc.).^[6] The United States disposes of 279 million waste tires each year, representing over 4 million tons of scrap waste.^[7] The Economic problem with tires is that the polymeric materials that they are made of, do not decompose easily. Even after heavy use and wear, only a few grams are abraded from each tire before they are deemed not serviceable. This means that nearly the entire amount of rubber is discarded, and a valuable resource is left to become an environmental pollutant, if left to be disposed of.^[8]

2. The Disposal of Waste Tires

Waste tires are generally discarded after only a small amount of rubber is worn away. Even so, these tires are unfit for further use in the vehicles they were made for. At the same time they are also unwelcome in landfills and have been proven to be an environmental threat. Whole tires can be used for a number of applications, including artificial reefs, breakwaters, erosion control, playground equipment, and highway crash barriers.^[9] Due to the sheer volume of disposable tires, they take up a great deal of valuable space in landfills. In addition, they have been known to bubble to the surface of land fills as they tend to trap methane gas. This bubbling can contaminate local water systems, as it can damage the landfill liners that are meant to control contaminants. The different stabilizers and flame retardants added to tires have also been known to kill advantageous bacteria in the soil, creating yet another economic problem. Originally, this was the primary form of disposal for scrap rubber (70% in 1977), but due to the decreasing availability of space, this process is no longer considered feasible.^[8]

Since the inability for landfills to provide adequate space for tire disposal, other forms of disposal and reclamation have been put into place, using waste tires as both commodities (new tires) as well as a form of energy (fuel alternative).

 

Used tyres (2) - geograph.org.uk - 917186. By Paul McIlroy, CC BY-SA 2.0, https://commons.wikimedia.org/w/index.php?curid=13610427

Waste tires create problems such as landfilling, health, and environmental challenges. Accumulation of waste tires, which are non-biodegradable polymers due to the presence of fillers, steel cord, organic, and inorganic components, is a major environments concern. Different agencies in the world are now recycling waste tires and other rubber goods into useful products instead of polluting the environment.^[10] In 2010 the Newfoundland and Labrador Government proposed that all waste tires in the province be shipped to Corner Brook to be burned and used as fuel. This was quickly delayed and further denied. A stock pile of waste tires that reached 1.9 million tires in 2010 was a major environmental headache for the government. Environment Minister Ross Wiseman said the Multi-Materials Stewardship Board (MMSB), a provincial agency that promotes recycling, reached agreements with Holcim (Canada) Inc. and Lafarge Canada Inc. They agreed to ship tires to Quebec where they will be burned for energy.^[11]

2.1. Environmental Issues

The disposal of tires in landfills have proven to have negative effects on the environment. Not only do they take up a great deal of space within a landfill, but their process of decomposing has created a wide variety of issues that have made their disposal in landfills unfeasible and in many regions, banned. The process of bubbling of trapped methane gas has been linked to increased mosquito and other insect breeding (increase risk of disease spreading), contamination of both underground and above ground water systems, as well as chemically destroying many beneficial bacteria that grow in the soil within and surrounding a landfill.^[8] Tires have been stock piled for years both legally (landfills) and illegally. In the United States alone there are about two billion around the country, with an estimated 279 million to be added to this number in the next few years. The legal stockpiling of tires increases the risk of fires which can burn for months on end, creating further pollution in the air and ground, while the illegal disposal of tires in forests, water ways and empty lots have caused pollution which cannot be regulated.^[12] The most obvious hazard associated with the uncontrolled disposal and accumulation of large amounts of tires outdoors is the potential for large fires which are extremely detrimental to the environment. Once a large pile catches fire, it is very hard, if not impossible, to extinguish.^[13]

3. Recycling of Waste Tires

The inability of landfills to properly deal with the disposal of tires has spurred the research into ways to successfully recycle tires into commodities and resources, such as concrete, asphalt and other tires. To convert the waste tire into a valuable product, it must first be reduced in size and then recycled. The recycling process begins first by shredding tires into small manageable chips, which are then cooled to cryogenic temperatures, causing the pieces to become brittle. These brittle pieces are then pulverized into a material that must be screened to remove large chunks of rubber or polymer. Finally, the remaining fibre and magnetic material are separated from the pulverized material using a magnetic separator and a vibrational separator. This form of recycling is environmentally friendly, and allows a valuable resource to be used again and again.^[14] There is a potential for using waste tire rubber to make activated-carbon adsorbents for air-quality control applications. Such an approach provides a recycling path for waste tires and the production of new adsorbents from a low-cost waste material.^[15] Also, recycled rubber from tires is used as a component of various products commonly known as "tire derived products". Such products include asphalt paving mixtures and as extenders in a variety of rubber products such as roofing materials, walk pads, carpet and flooring underlay and other products. More such products are being developed.^[16]

4. Waste Tire Fees

In most states in the United States of America, a fee is included in every new tire that is sold. Waste Tire fees can be collected by states, importers, and sellers, the latter being the most common case. These fees are collected to help support tire-recycling programs throughout the states of the United States of America. State tire-recycling programs are created to reduce the amount of scrap tires in stockpiles. The table below shows the tire fees in each state in the United States of America:

5. Waste Tire Uses

There are many different uses for waste tires that are beneficial in helping reduce the amount of waste tires in stockpiles. Recycled Waste Tires are used in creating Synthetic Turf in sports arenas. Synthetic Turf is made up of Crumb rubber which is recycled rubber from automotive or truck scrap tires. Waste Tires are also used to make Rubber Mulch which is used in gardens and playgrounds. Waste Tires have also been known to be used in making track and field pavements, roads, and shooting targets. Recycled Waste Tires have several recreational uses. Recycled Waste Tires are used for tire swings, flower pots, compost bins, retaining walls, and sandals in developing companies. Recycled Waste Tires can also be used as fuel energy. Waste Tires used as fuel are either shredded or whole, depending on the combustion device being used. The type of fuel produced from Waste Tires is known as Tire-derived fuel (TDF).

6. Waste Tire U.S.-Mexico Border Issues

The region in the Mexico-United States border has failed to manage the stockpiles of waste tires. Some neglectful regions between the U.S. and Mexico border have given up on managing the stockpiles. The lack of waste tire management on the border will lead to health, fire, and environmental hazards in the area. In 2003, A program was set up and signed and included objectives to help reduce the stockpiles of waste tires in the region in-between the U.S. and Mexico border. The program was the US-Mexico Border 2012 Program. This program had a goal to clean the three biggest waste tire stockpiles that were located in the region. In 2004, the US-Mexico Bi-national Commission expressed its strategies for dealing with the waste tire problem in the region. They expressed its strategy through a letter that was signed in November of 2004. The Bi-national program's target objective was "to develop and cooperate on an environmentally sustainable, comprehensive scrap tire management strategy." The US-Mexico Border 2012 Program is the third initiated bi-national agreement that aimed to protect the public health and environment that was in the shared region in-between the U.S. and Mexico border. This program was initiated by the United States Environmental Protection Agency (EPA) and Mexico's Secretaria de Medio Ambiente y Recursos Naturales (SEMARNAT). In the updated US-Mexico Border 2020 Program, it addresses that one of the challenges it faces is the waste-tire management problem that has occurred over the past.

The content is sourced from: https://handwiki.org/wiki/Engineering:Waste_tires