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Publications archive - Waste and recycling

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Key departmental publications, e.g. annual reports, budget papers and program guidelines are available in our online archive.

Much of the material listed on these archived web pages has been superseded, or served a particular purpose at a particular time. It may contain references to activities or policies that have no current application. Many archived documents may link to web pages that have moved or no longer exist, or may refer to other documents that are no longer available.

A National Approach to Waste Tyres

Commonwealth Department of Environment, 2001

6.1.3 Resource depletion

One of the major drivers in attempts to reduce the volume of tyres or other rubber products disposed to landfill or burned for energy appears to be to reduce the loss of the resources contained in the waste rubber products. In addition to the material resources in the products, disposal takes up landfill space, which is also a resource and is limited in many areas.

The major resources consumed in the manufacture of a tyre are:

When reviewing the resource issues it is instructive to consider the relative proportion of resources used in tyres against those used in other parts of a car. For example:

From this it can be seen that tyres contribute only a small component of the material and energy flows associated with transport, and even complete recovery of the resources in tyres would have little impact on the overall resource flows associated with transport. Conversely, any change in the transport system such as reduction in the distance travelled would reduce factors such as fuel consumption as well as result in a proportional reduction in waste tyre generation.

Because of the intermixing of materials in the construction of a tyre and because of the chemical changes (vulcanisation), in practice none of the component materials can be utilised or recovered in its raw form.

Steel from tyres is not generally recycled because it is difficult to handle and is contaminated by rubber and other coating agents, and this reduces its value. As far as could be determined, little if any steel is recovered from the tyres that are currently recycled, though the steel in waste tyres burned in cement kilns contributes to the requirements for iron in cement.

In order for rubber to be recycled to displace new rubber it must be devulcanised, which is difficult to achieve at a competitive price and has potentially high environmental impacts. The rubber in tyres is a mix of natural and various synthetic rubbers, which cannot be practically separated even if they are devulcanised. This decreases the value of the rubber for subsequent uses.

Rubber in ‘crumb’ form is inert and difficult to bond to other materials generally resulting in a deterioration of the properties of any product into which it is incorporated.

From this it can be seen that the recovery of rubber and associated materials in tyres has technical limitations and involves processes that may result in greater environmental impacts than those associated with disposal to landfill.

In respect of energy, the content of the 18 million EPU of waste tyres generated in Australia each year is equivalent to the fuel consumed in about 2 weeks of a typical large coal fired power station. Overall, the energy in waste tyres is less than 0.5% of the total energy consumed to generate electricity or the energy used in transport in Australia.

In respect of landfill volume, the mass of waste tyres generated each year is less than 1% of the total solid waste generated. In considering landfill capacity, it is volume rather than mass that is the critical factor. On a worst case ‘whole tyre’ basis, the volume of waste tyres is estimated to be approximately 8% of the volume of solid waste12. In practice a large proportion of tyres are processed to reduce their volume before being landfilled, so the actual proportion of landfill capacity taken up by waste tyres is several times smaller than 8%.

6.2 Manufacture

As a sector, the rubber industry is a relatively small component of the overall economy and the total contribution to environmental impacts is proportionally small. Over 50% of passenger and truck and bus tyres are imported as well as all larger and specialty tyres. A significant proportion of other rubber products is also imported. Consequently the local manufacturing impacts are lower in proportion to population than in countries that export a significant quantity such as the US.

In Australia there are limited aggregated data on the environmental impacts from the manufacture of rubber products or from retreading and recycling. Available energy and greenhouse statistics indicate that greenhouse gas emissions from the rubber industry are likely to be less than 0.1% of the national total. When compared to the nearly 30% contribution attributable to road transport it can be seen that the impact from the manufacture of rubber products is small at a national scale.

The potential impacts occur at each stage of the rubber manufacturing process. The main potential impacts from manufacture are noise and air pollution. Air pollutants include odours from heating rubber and volatile organic compounds (VOC) from solvent use in rubber manufacture. Liquid wastes, primarily contaminated water, are also a potential source of impact. There is also a range of solid wastes but the overall quantities are small and have low potential impact. Advice from State environmental regulators is that the tyre plants in Australia are not a significant source of complaints.

The overall conclusion, based on available evidence, is that the environmental impacts of the tyre manufacturing industry are only a small proportion of national totals and are far exceeded by the energy consumption due to tyres in use, predominantly in road transport.

6.3 Use

Environmental impacts of rubber products are likely to be dominated by tyres due to the significant proportion of rubber used in tyres, as well as the direct bearing of tyres in use on the energy consumption of transportation due to rolling resistance.

The environmental impacts of tyres in use are summarised in Table 6.3.

Table 6.3 Impact of tyres in use

Impact Discussion
Noise Tyres produce noise via a range of mechanisms. Tyre noise makes up a large percentage of the noise from cars and other vehicles and traffic noise in general has a significant impact on communities. Noise barriers/mitigation is a significant factor in road design.Tyre noise can be reduced by design of the tyre and road surface.
Dust The contact surface of a tyre wears off in use and is emitted as dust.Approximately 0.03g of tyre dust is generated per km.In Australia it is estimated that over 20,000 t of tyre dust is emitted per year which may be associated with air and water pollution as discussed in Section I.6.3.2.
Fuel consumption Energy is needed to turn a tyre and this is called rolling resistance. Rolling resistance accounts for about 15% of the energy that is used in moving a car. Rolling resistance is increased by higher vehicle loads and by under-inflation of tyres. It is estimated that for every 20 kPa reduction in pressure rolling resistance increases by 2%. In Australia it is estimated that approximately 1% of the total greenhouse emissions from transport result from incorrect inflation of passenger vehicle tyres.

6.3.1 Noise from tyres

Noise generated by tyres makes up a significant proportion of the noise generated by traffic. Tyre noise is generated by a range of mechanisms and is affected by both road condition and the design and compounding of the tyres. Some tread patterns are reported to reduce noise generation and pitch while others, such as the lugs on off-road tyres, are relatively noisy.

Traffic noise exposure in capital cities in Australia is shown in Figure 6.2. According to the Motor Vehicle Environmental Committee:

"In 1989-90, an Australian Environment Council (now ANZECC) study of the exposure of the Australian population to road traffic noise indicated that, on the basis of OECD criteria, over 9 per cent of the Australian population is exposed to ‘excessively high’ levels of noise (68 dB(A) Leq 24hr or above) and 39 per cent to ‘undesirable’ levels (58 dB(A) Leq 24hr or above). For Sydney, these figures increased to 10 per cent and 42 per cent respectively."

(ANZECC (1992) Motor Vehicle Environmental Committee Strategic Plan Part 2)

Percent of dwellings exposed to traffic noise in capital cities in Australia

Figure 6.2 Percent of dwellings exposed to traffic noise in capital cities in Australia

6.3.2 Dust

Rubber is worn off tyres during use particularly during high stress operation such as cornering, braking and acceleration. During its life a tyre loses a significant proportion of its tread accounting for about 10% of the mass of a tyre and 30 to 50% of the rubber. A new 10 kg passenger tyre can be expected to lose about 1.5 kg of rubber as ‘dust’ during use or approximately 0.03 g per km. Aggregate losses of dust from tyres for all road traffic across Australia are of the order of 20,000 tonnes per annum.

The impact that this dust has on the environment is not known but studies in the UK have suggested that a significant source of polycyclic aromatic hydrocarbons (PAH) in waterways is due to tyre dust. Studies in Germany also attribute zinc and other metals in the runoff from roadways to tyre dust.

A recent study reported in New Scientist13 suggests that levels of PAH and fine particulates (referred to as PM10 when below 10 Ám in size) attributable to tyre wear exceed the emissions from vehicle exhaust and is responsible for significant health impacts across Europe.

6.3.3 Fuel Consumption

Tyres contribute to the fuel consumption of vehicles by virtue of the energy needed to flex the tyre as it deforms during rolling. This ‘rolling resistance’ accounts for about 15% of the energy used to drive a car on level ground at 100 km per hour. During the life of each tyre, approximately 200 litres of fuel is estimated to be consumed in overcoming rolling resistance, and this represents about 3% of the fuel used by a car. Rolling resistance is dependent on the properties of the tyre, the load and inflation pressure14, but is not greatly affected by speed (unlike, for example, wind resistance).

It is estimated that a 20% under-inflated tyre will increase fuel consumption by around 5%15. A limited study by the NRMA16 noted that tyre maintenance and attention to correct tyre pressure was very poor in Australia. The survey found that 25% of cars in the sample had tyres under inflated by more than 10%. If this statistic is extrapolated across the country it is estimated that the fuel consumption and emissions due to passenger vehicles is approximately 1% higher due to tyre under inflation. A 1% increase in fuel consumption in passenger cars is equivalent to about 4 Mt of CO2. Obviously, these estimates should be considered as order of magnitude accuracy only but they indicate the scale of potential impact. It should also be noted that under inflation also decreases the life of a tyre as discussed in Section I. 8.3.

6.4 Recycling and reuse

6.4.1 Impacts of retreading tyres

There are in the order of 100 retreaders in Australia. Many retreading operations are small scale and do not require an environmental protection licence to be held indicating the lower level of controls that are required and/or necessary.

The impacts from retreading are in some ways similar to those from tyre manufacture as they involve many of the same basic materials and processes. Retreading is, however, a more simple process and involves only the tread and outer surface of the tyre, and not the casing which includes the steel and fabrics. New treads or rubber compound used to form a tread are sourced and processed in the same way as in the manufacture of new tyres.

Sources of environmental impact from retreading are given in Table 6.4.

Table 6.4 Environmental impacts from retreading

Energy and material use As retreading extends the life of a tyre and utilises much of the original materials and structure, the net result is a decrease in materials and energy used in comparison with new tyres.
Air emissions The primary areas of concern appear to be VOCs (volatile organic compounds) from solvents, bonding agents and rubber compounds. Odour may also be an issue in some areas.
Solid wastes Some waste is produced from retreading facilities due to reject tyres, rubber, retreads and compounding material. The rubber removed from used tyres before retreading is generally sold as rubber crumb, so does not constitute a waste.

The impacts from retreading should be contrasted with the benefits of retreads against providing new tyres. Retreading a tyre consumes considerably less material and energy than that required for a new tyre, with a proportional decrease in other impacts. This point is discussed further in Section I.6.7.2.

6.4.2 Impacts of tyres used in marine environments

Tyres have been widely used in breakwaters, artificial reefs and riverbank erosion control. The assessment of the impacts of tyres in marine environments is divided.

On one hand, tyres are stable and resist degradation and leaching of the components.

On the other hand, tyres do leach both organic and inorganic substances. Abernethy17 reports that tyres in water are lethal to rainbow trout in certain circumstances. There are lingering concerns on the impacts artificial reefs have on local ecosystems. Though artificial reefs made from tyres are reported to be rapidly colonised by some marine organisms they are not equally colonised by fish. The stability of tyre artificial reefs has also been questioned with reports of reefs breaking up in bad weather. This is, however, more a matter of defective construction rather than related directly to environmental impacts of tyres.

Tests conducted in accordance with the standard US EPA Toxicity Characterisation Leaching Procedure (TCLP) found that contaminants from tyres were below the TCLP thresholds. However, it has been observed that the TCLP may not be sensitive to the chemicals found in tyres.

6.4.3 Impacts of tyres in energy recovery

The four main options for energy recovery are:

Waste tyres have a higher energy content than coal and a lower overall greenhouse coefficient due to the natural rubber content as shown in Table 6.5. This makes tyres an excellent energy source.

Table 6.5 Comparison of energy generated and greenhouse gas emissions between tyres and other fuels

Fuel EnergyGJ/t Greenhouse gas emissions
kgCO2/t kgCO2/GJ
Tyres shredded with majority of steel removed19 32 2,391 7520
Whole tyres 27 2,080 7721
Thermal coal 27 2,430 90
Brown coal 10 922 95
Oil 46 3,220 70
Natural Gas 39 1,989 51

The non-combustible components of tyres contain a range of potentially toxic materials that can be released to the atmosphere if tyres are burned in an uncontrolled fashion (as is the case for fires in illegal dumps). Emissions can include dioxins and furans, which are carcinogenic, as well as oxides of nitrogen and sulphur.

Studies on the use of tyres in cement kilns have generally concluded that the impacts are either positive or neutral compared to the combustion of other fuels. However this needs to be considered on a case by case basis as it is dependent on good operating practice as well as the particular characteristics of the tyres used and the kiln. The combustion characteristics of tyres are such that only processes that have relatively high temperatures and long residence times can be used.

6.5 Disposal

6.5.1 Impacts of tyres in landfill and mines

As with their behaviour in marine environments, the impacts of disposal of tyres on land are determined by the possibility of the escape of the toxic components from a stable matrix. The authors are not aware of any reports of major environmental impacts as a result of appropriate disposal of tyres to controlled landfill or in mines notwithstanding the fact that millions of tyres have been disposed of in this way. However, it must be acknowledged that there is limited experience with long-term impacts (50 years or more).

The objections to landfilling tyres appear to be driven mainly by materials handling and operational issues, the exhaustion of landfill space and resource issues as discussed below, rather than environmental impacts themselves.

Tyres in landfills are also associated with fire risks. For example, the WA Used Tyre Regulations provide that tyres are buried in batches of volume not exceeding 40 m3 or less than 1,000 whole tyres, separated by at least 100 mm of soil.

Operational problems
Whole tyres are reported to float if buried. Corbett has challenged the validity of this and the mechanisms which cause it to occur.

Whole tyres are not easy to manage with equipment generally available in a landfill.

These are not issues in the case of shredded tyres which are routinely disposed to landfill.

Landfill space
Whole tyres have large ‘voids’ which consume available space (approximately 75% of the volume of a whole tyre is void).

Waste tyres are generated at greater rates in areas where population is highest and these are the areas where landfill space is limited.

Resource issues
This issue is discussed in Section 6.1.
Future use
Tyres reportedly destabilise a landfill and may impact on the useability of the landfill area for future use.

6.5.2 Impacts of tyres on land – uncontrolled

Impacts due to the uncontrolled disposal of tyres to land are similar to those for stockpiles as discussed in Section 6.5.3. In addition, waste tyres can have a visual impact and form breeding locations for pests and vermin. Gullies and watercourses, which are favoured disposal sites for tyres, can become increasingly eroded due to the changed water flow patterns.

6.5.3 Impacts and risks of waste tyre stockpiles

When the tyre waste issue is discussed the impacts of stockpiles of tyres above ground are generally the dominant factor. The issues with tyre stockpiles are listed in Table 6.6.

Table 6.6 Environmental impacts of tyre stockpiles

Fire Tyre stockpile fires pose a major environmental threat. The fires produce thick toxic smoke.
Runoff during and after tyre stockpile fires is likely to be contaminated.
Fires produce oil, which can flow from the fire and cause contamination or spread the fire.
Due to the large size of stockpiles and the intensity of tyre fires they pose a significant hazard to persons, equipment and adjacent buildings.
Fire fighting costs for a ‘typical’ fire in a tyre dump can be of the order of $100,000.
Mosquitoes Tyres trap water, and this in turn provides a breeding site for mosquitoes. In tropical areas, particularly, this can pose a significant threat to human health due to diseases carried by mosquitoes. May also be economic, environmental and human impacts from pesticides used to control mosquito populations in improperly disposed tyres.
Weeds Outdoor tyre stockpiles can provide a habitat for weeds. Where land is disturbed or noxious weeds are already present, the problem can be exacerbated.
Vermin Tyre stockpiles are reported to be a breeding ground and habitat for vermin such as rats. The authors have not found evidence of actual impacts but assume that the presence of these vermin is associated with the presence of sources of food in or near stockpiles.
Visual impact Tyre stockpiles have been known to exceed many millions of tyres and present a large ugly reminder of the failure to manage the waste tyre issue.

6.6 Transportation

Each stage in the life cycle of a tyre involves transportation. The materials that are used to make tyres and other rubber products are made and distributed around the world. Rubber products are also transported locally and internationally. At the end of its life a tyre is transported once more, and during recycling further transport of recycled rubber occurs. This section analyses the significance of the impact of transport in the life cycle of a tyre.

Australia manufactures its own tyres as well as importing a significant proportion. Australia also manufactures some proportion of the raw materials used to make tyres as well as importing raw or semi-processed materials. The distance travelled and the modes of transport involved in the life cycle of a tyre are varied and a full analysis is complicated. However, by making reasonable simplifications and assumptions, it is possible to arrive at useable estimates of the relative impacts of the transport requirements at different points through the life cycle. Further comment on the life cycle of a tyre is made in Section 6.7.

Ignoring the in-use contribution, transport accounts for approximately 4% of the total energy and greenhouse emissions associated with a tyre, suggesting that transport impacts are not a major contributor to tyre energy usage. This ‘whole system’ perspective does not, however, take into consideration other transport emissions and impacts, or the locations where they occur. For example, relatively small emissions of nitrogen oxides from trucks in major cities may be far more significant than, say, emissions associated with sea transport between countries.

The overall estimate of 4% given above is based on assumptions about the mode of transport and average distances travelled. Table 6.7 contains estimates of energy use and greenhouse emissions for different modes of transport. It can be seen that emissions from light commercial vehicles are several times greater than those for articulated trucks or rail. It is noted that waste tyres are often transported with smaller vehicles (particularly from the initial collection point) and this increases the emissions significantly.

The values in the table are subject to considerable uncertainty because of variations in the load carrying capacity and fuel consumption of vehicles that fall into each of the general classifications. A review of several published sources and calculations based on published load and fuel consumption data suggest that the values used for rigid trucks in particular may be too high by 2 or 3 MJ/tonne km. However, for the purpose of this report, the figures in the table are sufficiently robust to provide a valid comparison of the efficiency of transporting tyres by different modes of transport. For more accuracy actual tyre transport data would be required. In particular, the effect of the mass versus volume constraints of bulk transportation of tyres and part loading during collection and distribution would also need to be taken into consideration.

Table 6.7 Energy used in transport task22

Transport mode MJ/tonne km kg CO2/tonne km
Light Commercial 5 0.35
Rigid truck 3.5 0.24
Articulated truck 1.4 0.095
Rail 0.5 0.035
Sea 0.3 0.022

Figure 6.3 illustrates the relationship between greenhouse gas emissions and the magnitude of the transport task for different modes of transport.

Relationship of greenhouse gas emissions to transport

Figure 6.3 Relationship of greenhouse gas emissions to transport task for different modes of transport23

Figure 6.4 provides an estimate of the aggregate greenhouse emissions of transporting the entire 18 million EPU generated annually (approximately 170,000 tonnes) by different transport modes. The diagram can be used to provide a quick estimate of the order of magnitude of greenhouse gas emissions for transporting tyres (whether new or waste tyres). For example, on a national basis the annual greenhouse gas emissions if waste tyres are transported on average 100 km by light trucks are equivalent to approximately 6,000 tonnes of CO2. The corresponding figure for articulated trucks would be approximately 4,000 tonnes CO2 less.

Estimated aggregate greenhouse emissions

Figure 6.4 Estimated aggregate greenhouse emissions for transporting the entire 18 million EPU of waste tyres by various modes of transport

Another parameter that can be considered in relation to transport is the distance that a waste tyre can be carried before the impacts from transport exceed the benefits derived from recycling or other application for which the tyre is transported. The simplest way to make this comparison is on the basis of energy consumed. It must be emphasised that the use of energy as a basis of comparison ignores other issues associated with both transport and energy recovery or recycling operations.

The energy content of a tyre is approximately 27 GJ/t for whole tyres and 32 GJ/t for shredded tyres with most of the steel removed. Estimates for the distance that a tyre could be transported before more energy is consumed in transport than is recovered from the tyre are given in Table 6.8. It can be seen from the entries in the table that there is a positive energy recovery even when using light commercial vehicles over distances of several thousand km. The values in Table 6.8 are only approximate, being based on a simple analysis with an uncertainty of at least ▒20%. The comments made above in relation to the uncertainty in the energy intensity of different modes of transport remain valid.

Table 6.8 Transport distance before the energy from transport exceeds the energy recoverable from the tyre

Mode Distance
Light commercial vehicle 5,400km
Rigid truck 7,714 km
Articulated truck 19,286 km
Rail 54,000 km
Sea 90,000 km

6.7 Preliminary life cycle assessment of tyres and selected waste tyre management options

The following section includes a preliminary life cycle assessment of some aspects of tyre production, use and recycling. The values quoted are preliminary only and have not been fully validated. They are based on data from a variety of sources of varying reliability. In some instances we have been forced to make our own best estimate for energy and greenhouse emissions.

6.7.1 Manufacture

The breakdown of energy and greenhouse emissions for the production of the raw materials used to manufacture rubber products is shown in Table 6.9. The total energy and greenhouse emissions computed from the raw material estimates to manufacture a range of tyres are shown in Table 6.10.

Table 6.9 Energy and greenhouse emissions associated with the raw materials used in tyres and other rubber products

Material Energy
(MJ/kg)
Greenhouse
(kgCO2/kg)
Natural rubber 8 0.4
Synthetic rubber 110 5.0
Carbon black 125 5.7
All other additives 100 8.2
Fabric 45 2.1
Steel tyre cord 36 3.2
Manufacture (per kg tyre) 11.7 1.86

  Table 6.10 Energy and greenhouse emissions to produce tyres


Passenger
(9.5kg)
Truck and bus
(45kg)
Earthmoving24
(3,500kg)

MJ kgCO2 MJ kgCO2 MJ kgCO2
Natural rubber 11 0.5 51 2 3,969 182
Synthetic rubber 361 16.5 1,637 75 127,339 5,826
Carbon black 268 12.3 1,299 59 101,063 4,624
All other additives 95 7.8 425 35 33,075 2,724
Fabric 25 1.1 43 2 3,308 151
Steel tyre cord 59 5.3 391 35 30,429 2,729
Manufacture 117 18.5 553 88 42,998 6,832
Transport of materials 38 2.8 191 14 14,884 1,077
Total 974 65 4,591 310 357,063 24,143
Total per kg 103 6.8 102 6.9 102 6.9

 


10Assume a car has 1 tonne of steel and tyres contain 15% steel or approximately 7.5kg for five tyres.

11Assume that over its life a car uses 3 sets of tyres each consuming 32 L of oil equivalent for a car that travels 150,000km at 10L/100km.

12Based on the tyre shipping volume (worst case) average of 0.1m3/EPU and an average compacted municipal solid waste density of 0.8 t/m3 and a waste generation rate of 2.5 kg/person/day.

13 New Scientist 10 April 1999.

14 To a certain extent an increase in load is equivalent to a decrease in pressure.

15UK Environment Agency (undated), Tyres in the environment.

16NRMA (1993), Are your tyres letting you down?, November.

17Abernethy S (1994), The Acute Lethality to Rainbow Trout of Water Contaminated by an Automobile Tire.

18Pyrolysis can also be classified as material recovery of components such as oil, carbon black and metals.

19The rubber in a tyre is approximately 30% natural rubber, which is assumed to have no net greenhouse impact due to the sequestering of carbon dioxide by rubber trees. It is noted that these values are approximations for comparison only and do not take into account the full life cycle impacts of the fuels.

20Estimate only, based on carbon content of the constituents of tyres.

21ibid

22Lenzen (1999). The values taken from the source are for direct energy consumption only.

23The transport task is a function of both weight (in most cases) and distance, and is conventionally measured in units such as tonne kilometres (tonne km). Energy efficiency for transport is the quantity of energy needed to accomplish one unit of the transport task and this is the basis used for comparison across modes.

24As may be deduced from the table entries, the values for large earthmoving tyres have been extrapolated from those for truck tyres and the proportion of steel and other materials in earthmoving tyres may be different from that indicated.