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Tyres

INTRODUCTION

Tyres have been making transportation more efficient and travel more comfortable since they were first invented for horse-drawn carriage wheels in 1845. Early tyres were made from latex which is a natural extract of the rubber tree. These days tyres are made in several stages using many different materials as summarized below:

The constructed tyre is placed in a mould and inflated. Heating under pressure in the mould shapes the tread and vulcanizes the rubber.

Tyres are designed to accommodate a variety of vehicles, surfaces and weather conditions. For example, truck tyres tend to have a higher percentage of steel to reinforce the structure. Tyres still have the same basic design and, despite variation, there is enormous potential for reuse or recovery due to the vast quantities of waste tyres generated each year.

ENVIRONMENTAL IMPACT OF WASTE TYRES
Tyres are designed to last and are therefore difficult to break down and separate into their constituent parts.

Adding to this problem, disposal releases potentially harmful compounds into the environment, e.g. polyaromatic hydrocarbons (PAHs), benzene and phenol which have suspected carcinogenic properties. Studies in Sweden estimate that 14 tonnes of PAHs are deposited onto Swedish roads each year through tyre wear (ENDS 1999). Landfill disposal and incineration also release these harmful substances.

Most countries have relied on landfilling to dispose of tyres but the limited space and the potential for reuse has led to many countries imposing a ban on this practice. Landfills are not leak-proof which means that hazardous substances generated during the decomposition of material can filter down through the site and into the surrounding area. In this way it has the potential to pollute water courses and affect living organisms. Tyres tend to rise to the surface of landfill sites and restrict the future use of the land (Pavlou 1997).

Burning tyres can have a serious environmental impact. Whilst tyre fires are uncommon, they produce vast quantities of harmful emissions that will pollute the atmosphere and water courses through run-off. The high energy content of tyres means they can burn for long periods. For example in Wales, a tyre fire started in 1989 in a covered tip containing 10 million tyres was still burning nine years later.

FACTS AND FIGURES

The main manufacturers of the 1,000 million tyres produced each year are Korea, Japan and Canada. The UK produces 37 million tyres a year and this figure is expected to rise by 60% over the next 20 years (Waste Manager 1998).

In 1996, 121 million tyres were in use in Britain and their total distance travelled equated to 700 billion km (Warmer Bulletin 1999a). With current trends in traffic growth, it has been estimated that this figure will reach 200 million tyres by 2021 (Environment Agency 1998).

The average tyre life is 48,000 km, after which it must be replaced (Residua 1999). Most vehicle owners will have this done at a garage which will then dispose of the old tyre.

Even though tyre usage is increasing, the markets for reusable car tyres from re-treading appear to be declining. Tyre design for single-use is a contributing factor. Another reason for the lack of growth in recycling is that planned inv.htmlent has failed, been cancelled or delayed.

Fly-tipping of tyres is a major problem for many local authorities as well as abandonment of end-of-life vehicles (see Types of Waste A-Z Listing: End of Life Vehicles). With limited resources in local authorities to deal with them, the problem of abandonment of scrap tyres by fly tippers will increase.

In 1998, the Used Tyre Working Group reported on the current trends with an overall recovery of 70% of the 40 million tyres scrapped (465,000 tonnes):

Even with the growth in many sectors it is estimated that 120,000 tonnes of tyres were sent to landfill.


LEGISLATION

Scrap tyres are bulky, a potential fire hazard and contain environmentally toxic substances. Their disposal is therefore controlled by several regulations outlined below:

In 1995, the Scrap Tyre Working Group (STWG) was established as a producer responsibility initiative and industry response to the EU targets for scrap tyres, as set by the European Commission Priority Waste Stream Group (PWSG). For the scrap tyre waste stream, the group proposed two targets of 25% for re-treading and 65% for recovery/recycling, leaving a maximum of 10% for disposal.

However, from 2003, when the Landfill Directive is implemented in the UK, there will be no capacity for landfilling. The STWG have predicted that the UK will fall behind this requirement with an anticipated 10% of tyres destined for disposal.

WASTE MANAGEMENT OPTIONS

Figure 1 shows the current disposal methods in the UK.

Figure 1 Disposal Routes for Tyres

Disposal Routes for Tyres
SOURCE: USED TYRE WORKING GROUP 2001


REDUCE
With increasing numbers of vehicles on the road, reducing the use of tyres is an almost impossible task. However, reducing the amount of tyre waste generated is possible.

Prolonging the life of tyres can be achieved with new tyre technology and with better care of tyres during use. Some simple care guidelines are as follows:

A more rigorous enforcement of tyre safety law would improve the general condition of the majority of tyres in use and save drivers money.

In addition to stemming tyre disposal, reducing the quantities of potentially harmful substances used in their manufacture is another way of reducing the environmental impact of tyre waste. In Sweden PAHs have been eliminated from many car tyres. This has yet to be taken up by the rest of the European tyre industry due to the lack of customer demand or regulatory pressure (ENDS 1999).

REUSE
Discarded tyres can be reused in various ways. Examples of direct reuse include:

Research into whether old tyres can be used as an artificial reef to prevent erosion in coastal regions is currently underway. Investigation has concentrated on the potential effects of harmful leachates on marine life. The results are not likely to be known until the end of 2001, but if positive could significantly impact upon the use of scrap tyres (Waste Manager 1998). Artificial reefs have been constructed in other countries and experiments relating to toxicity of submerged tyres have been carried out. In Canada, initial laboratory results suggested there is production of leachate that is toxic to aquatic life. As a result of these results, tyres were removed from an artificial reef in Alberta. However, tyres that had been submerged for a number of years did not show any toxicity (Environment Agency 1998).

Re-treaded tyres must conform to strict standards. In the UK this standard is BS AU144e. With more encouragement from the government (for example, lowering VAT on these tyres) this valuable resource could be further exploited.

In the UK, over 50% of all truck tyres and 100% of aeroplane tyres are re-treaded. In this way, commercial vehicle tyres can be used up to three or four times. However, as yet, very few car tyres are re-treaded (www.environment-agency.gov.uk). The lack of market development for car re-treads is attributed to relatively inexpensive imported tyres and public scepticism regarding the quality of the reused tyres (Warmer Bulletin 1999b). With reduced demand from merchants for good quality scrap tyres (casings), the price is falling, further depressing opportunities for recovery. Re-treading in the UK is declining rapidly with a number of large companies closing down and export markets collapsing.

RECOVERY
Tyres can not be re-treaded or reused indefinitely. Instead of disposing of them they can be recycled. Recovery and recycling can convert the waste into either a useful material or energy. Yet the STWG reported that tyre recycling and recovery actually fell in 1998 (Materials Recycling Week 1999a). The rising number of waste tyres has prompted much concern. The following options are likely to become increasingly important when disposal is no longer permitted.

Material Recovery
Tyres contain a number of materials that can be recovered. Using a technique called pyrolysis, activated carbon and steel can be recovered for further use. However, pyrolysis involves relatively small quantities of tyre waste and a market for the recovered products needs to be ensured.

Granulation
Scrap tyres can be ground into a crumb and used in a variety of applications. These include:

Research is also underway into the use of crumb rubber in road surfaces to reduce noise pollution. The Highways Agency and the Road Traffic Research Laboratory have laid crumb rubber from 6,000 tyres on a 2.5km stretch of dual carriageway and are monitoring the results (Warmer Bulletin 1999b). If successful, widespread use is extremely likely which would strengthen the presently fragile crumbing industry.

Energy Recovery
The 48% rubber content of tyres makes them a high energy source and therefore a potential fuel. One application for this valuable energy source is to power high-temperature kilns used by the cement industry. In 1997 24,000 tyres were disposed of this way and the STWG predict that cement kilns could be used to dispose of a further 145,000 per year (Warmer Bulletin 1999b). The STWG is now being criticised for placing too much emphasis on this process and disregarding other potential solutions (Materials Recycling Week 1999b).

Energy requirements comprise 70% of the cost of the kiln, so a more cost-effective source of energy in the form of waste tyres is an attractive option. This form of incineration involves the complete combustion of the tyre leaving no residue that has to be disposed of afterwards. However, burning the tyres produces emissions that have to be carefully controlled to ensure they do not enter the environment. Gases are therefore filtered and cleaned (a process known as scrubbing) so that the final emissions are within limits set by the Environment Agency (EA).

For a waste recovery system to be widely adopted it must be economically viable to use waste rather than virgin energy sources. At present, use of tyre waste in cement kilns is economical but if emission limits are tightened, the cost of installing purification equipment may outweigh the cost saving of using tyre waste as a fuel (Warmer Bulletin 1999b).

Pyrolysis
There is one commercially operated pyrolysis plant in the UK. The operation is small enough to be transportable so it can be taken to where there is a large stockpile, as opposed to tyres being bulk transported to one site. It is able to process up to 90,000 tyres per year. Unlike incineration, the energy is recovered in a form that can be stored and used when needed. Table 1 lists the by-products that are produced.

Table 1 By-products from the pyrolysis of one tonne of tyres

PRODUCT % PERCENTAGE KILOGRAMS
Carbon 41 410
Oil 23 240
Gas 22 230
Steel 14 145

SOURCE: ADAPTED FROM ENVIRONMENT AGENCY 1998


The carbon produced can be used by the rubber and plastics industry. It is likely that pyrolysis has a growing part to play in meeting the Landfill Directive targets. New stakeholders are becoming involved such as Coalite (manufacturers of smokeless coal). The increased use of natural gas and other fuels for heating has led to spare capacity at the Coalite plant in Bolsover, Derbyshire. The plant was built in 1936 and used for production of smokeless coal. Coalite engineers have utilised this existing technology to provide a tyre pyrolysis chamber. It is forecast that the plant will process 15,000 tonnes of tyres annually.

DISPOSAL
Landfill is the only disposal option for scrap tyres in the UK. In 1999, the Used Tyre Working Group reported that 120,000 tonnes were sent to landfill either directly or as part of the end of life vehicle disposal chain.

However, by 2003 the EU Landfill Directive will have made landfilling of whole tyres illegal, so all tyres will have to be shredded. By 2006, the landfilling of shredded tyres will be prohibited, so disposal will no longer be an option for tyre waste. With this in mind, the focus will be on reuse, recovery and recycling.

CASE STUDIES

V.PROMPT
v.Prompt (Voluntary Partnership for Responsible Management of Post-consumer Tyres) is a voluntary alliance set up by Waste Tyre Solutions in response to the future recycling and reuse targets. This alliance aims to demonstrate to the Government and the EU that post-consumer tyres are being managed in a responsible way. Independent auditing will assess environmental performance of the organisation.

Tyre recyclers and retailers can register with v.Prompt and receive a certificate to demonstrate that all the tyres they receive are dealt with in the proper manner. In return v.Prompt ensure complete accountability for the tyres they handle from collection through to final 'green' disposal. Currently Waste Tyre Solutions achieve nearly 90% recovery of the 250,000 tyres they handle each week and are aiming at 100% in the long term.

SOURCE: WASTE TYRE SOLUTIONS 2000

THE NETHERLANDS

In Holland tyre disposal to landfill is illegal. Targets for reuse, recycling and energy recovery have been set at 60%, 20% and 20%, respectively. To date, 60% of the 65,000 tonnes of scrap tyres generated per year are reused, 8% are recovered for materials and 32% are used for energy recovery.

Tyre manufacturers are also legally obliged to take back old tyres, ensuring that they are dealt with in the proper manner, with minimal effect on the environment.

SOURCE: WARMER BULLETIN 1999C

FUTURE TRENDS

Whilst tyre usage is increasing, the markets for reusable car tyres from re-treading appear to be declining. There are a number of options for dealing with waste tyres but these do not appear to be sufficiently cost effective to drive the market for recovery. Tyre design for single-use is a contributing factor. Another reason for the lack of growth in recycling is that planned inv.htmlent has failed, been cancelled or delayed.

Legislation to control waste disposal is tightening with the requirement to divert waste from landfill. Tyres, in particular, represent a very difficult disposal problem if landfill is not an option when the Landfill Directive is implemented. Without adequate alternatives current trends in the fly-tipping of tyres will worsen, increasing the problems faced by local authorities. Limited resources already present serious difficulties when dealing with scrap tyres.

The Scrap Tyre Working Group (STWG) identified that there were a number of mechanisms for dealing with the landfill ban including statutory producer responsibility and a levy on new tyres. They have rejected these in favour of a market-based approach. STWG forecast a growth in recovery rates over the next four years particularly with reference to the use of tyres to fuel cement kilns. The cement sector has the opportunity to expand the capacity for tyre recovery, but the industry has recently been slow in developing additional sites with these facilities. It is forecast that there will be an increase in recovery to 2003 to an anticipated 90%. This leaves a gap of 10% that would still have to be landfilled, after being shredded. Stakeholders would then have a further 3 years to comply with the complete banning of tyres by increasing recovery to reach 100% by 2006.

Without inv.htmlent to increase capacity, the STWG predictions for recovery rates will not be met. Market solutions alone will not meet the requirement of the landfill ban and without statutory instruments the UK is unlikely to meet the 100% tyre recovery target. It would appear that, despite the STWG recommendation for a market-based approach, statutory measures will be needed to effect tyre recovery before the landfill ban comes into force.