A review on material and energy recovery from waste tyres

The tyre industry in Botswana produces and sells thousands of tyres annually generating volumes of waste tyres which contribute towards the country's waste management challenges. At the end of their useful life, most tyres end up at waste dumping sites while a small fraction is recycled or reused, posing a health, safety and environmental hazard. The same desirable that make tyres, such as immunity to biodegradation, chemical reagents and photochemical decomposition tend to make their disposal a challenge. On the other hand, the number of vehicles on Botswana roads is continuously escalating due to more affordable imports from Japan, thus increasing the demand for tyres. The scope of this study is to review methods employed to recover materials and energy from waste tyres. Shredded waste tyres have found applications in civil engineering such as making culverts, retaining walls, ravine crossings and highway embankments. Other miscellaneous uses include playground swings, doormats, shoe soles, etc. The use of pyrolysis technology as an energy and material recovery mode from waste tyres has been of great interest in past studies. On average a single passenger vehicle tyre has between 30000kJ/kg and 35000kJ/kg potential energy, this is much higher than that of coal and biomass of the same mass, with lower ash content. The process yields potentially three revenue streams being; oil, carbon black and synthesis gas. The economic feasibility of waste tyre pyrolysis is determined primarily by product price, production capacity and production cost. Further processing of the pyrolytic oil and char and having a sustainable market for the derived products can greatly improve the economics of the process.