The Department for Transport’s Vehicle licensing statistics for 2012 [1] gives a figure of 34.6 million for the number of vehicles licensed for use on British roads.  Therefore, taking into account approximately 1.5 million of these vehicles are motorcycles, it means approximately 135 million tyres are currently in use on our roads.  This figure is in fact likely to be higher with the inclusion of heavy goods vehicles with more than four wheels.  On top of this, it is estimated a further 200 million end of life tyres exist, with a further 55 millions waste tyres being produced each year in the UK according to the Environment Agency [2]. Whilst these figures are only approximations, they give a sense of the scale of the issue of waste tyre disposal. These figures become of particular concern when the potential environmental impact of waste tyres is taken into account.

Typical tyre compositions found in the EU [3]

Environmental Risks

Heavy metals and pollutants that form only small percentages of the total composition of tyres such as lead and zinc, have the potential to leach into groundwater, the longer a tyre is left to breakdown the greater the chance of toxins being released into the environment. Many tyres at the end of their life are shredded, whilst this may aid various end of life processes such as recycling and transportation, if left exposed the shredded material will more readily leach toxins into the environment due to an increased surface area.

Discarded tyres also have a tendency to collect water which in turn can act as breeding grounds for mosquitoes should the water become stagnant.  The mosquitoes can then act as a transmitter of various vector-borne diseases such as malaria and dengue fever.

Tyres also pose a fire risk, with the composition meaning tyres will readily combust, the emissions of which pose a distinct threat to human health.  Emissions given off from burning tyres are known to contain toxins and particulate matter that will have a detrimental effect on the human respiratory system [4].

An incident that occurred near Knighton in Powys, Wales in 1989 highlighted the environmental impact tyres can have if managed incorrectly. The landfill site was holding somewhere in the region of 10 million tyres, which at the time was legal. The tyres caught alight and astonishingly continued burning until 2001, lasting a total of 13 years. [5] During this time leachate discharged from the landfill site entered the River Teme, affecting local water supply and freshwater habitats.  The site itself remains heavily contaminated however impermeable barriers and settlement tanks are now in place to contain the leachate and restrict any from entering local watercourses.

Whilst at the time the of the Knighton incident, sending waste tyres to landfill was legal, the practice was outlawed by the European Union in The European Landfill Directive [6] in 2003 who later went on to ban shredded tyres from being and landfilled in 2006. The only exception being ‘bicycle tyres and tyres with an outside diameter above 1400mm’.

Options Available

With EU law now banning the landfilling of tyres, ways of reusing and recycling end of life tyres have been developed over the years.

Before recycling a tyre, some tyres have the option to be retreaded. Retreading tyres will naturally extend the life of a tyre therefore reducing the pressures involved with environmentally reusing and recycling of end of life tyres.  Retreading is already widely used on plane and heavy good vehicle (HGV) tyres, and if the tyre frame stays intact, larger tyres such as those used for plans and HGVs can be retreaded up to four times. However, a car tyre can only be retreaded once.

One of the main techniques used for end of life tyres is shredding or crumbing which reduces the tyre into small enough pieces to fit various applications.  For example, the rubber crumb is used on many sports surfaces to form a synthetic turf, it can be also be used for brake linings, livestock mats, carpet underlay and as an additive to asphalt for road surfacing.  Applications for shredded tyres can also be found in the construction and civil engineering industries.  Tyre derived aggregate as they are known are largely used as a backfill material. End of life tyres have also found applications in the marine environment.  Tyres have been used to create artificial reefs and used for coastal defences. In both cases the tyres are usually compressed together to from a large bonded blocks of tyre material.

Tyres can also be used to fuel kilns in industries such as steel production, and used in cement kilns in the concrete industry.  Using tyres as a carbon source for burning does have its advantages, for example the kilns are capable of consuming whole tyres making them an easy way to reuse end of life tyres, and the tyre material has a calorific value 20% more than coal.  Despite the advantages, there are concerns about the emissions given off when using tyre material as a fuel in such a process.

An alternative method to incineration of waste tyres uses a contained oxygen free environment to heat the material. This process is called pyrolysis and noticeably reduces emissions. The heat breaks down the various compounds in the tyre material in a similar way to the fractional distillation process used when producing petroleum.  The products of tyre pyrolysis include fuel oil, carbon black, steel wire and small amount of non condensable gas. The fuel oil accounts for between 40 and 45% of the final product and can go on to be used in other industrial or commercial processes. Around 35% of output is carbon black which can be reused in numerous applications in rubber product manufacturing. The steel wire totals around 10 to 15% of the product, this can be sent to scrap dealers and recycled elsewhere, whilst the gas accounts for between 10 and 12% and can also be burned to produce energy [7].

It should be noted that a tyre’s main environmental impact comes during its main life where it impacts the vehicles fuel consumption.  Taking into account a tyres fill life cycle, it is estimated the in use fuel consumption accounts for 75.2% of its environmental impact [8].

All major tyre manufacturers are now producing ‘greener’ tyres, with Pirelli claiming their latest eco tyre has a reduced rolling resistance of 20%, reducing overall fuel usage by up to 4%.  The materials used in construction claim to reduce the environmental impact during production, use and end of life, and the overall life of the tyre is meant to average 30% longer.  The industry is clearly making steps forward taking into account the whole life cycle of the tyre. However with growing numbers of vehicles on the road, the tyre recycling industry will have to take further steps forward to keep up.

Find out more ways you can help reduce your environmental impact.

[1]https://www.gov.uk/government/publications/vehicle-licensing-statistics-q2-2012

[2]http://www.environment-agency.gov.uk/homeandleisure/waste/138215.aspx

[3]http://www.etra-eu.org/index.php?option=com_content&view=article&id=77&Itemid=66

[4]http://greenliving.nationalgeographic.com/environmental-impacts-throwing-away-tires-20116.html

[5]http://www.wao.gov.uk/assets/englishdocuments/Environment_Agency_Wales_Waste_Management_agw_2004.pdf

[6]http://www.central2013.eu/fileadmin/user_upload/Downloads/Document_Centre/OP_Resources/Landfill_Directive_1999_31_EC.pdf

[7]http://www.pyrolysisoil.net/PRODUCTS_SOLUTIONS/Tire_Pyrolysis_Plant/Continuous-Scrap-Tire-Pyrolysis-Plant.html#.UYitr0rcA7Z

[8] http://www.nokiantyres.com/environmental-effects-while-using-a-tyre