Biotechnological possibilities for waste tyre-rubber treatment

Every year large amounts of spent rubber material, mainly from rubber tyres , are discarded. Of the annual total global production of rubber material, which amounts to 16-17 million tonnes, approximately 65% is used for the pr oduction of tyres. About 250 millions spent car tyres are generated yearly in USA only. This huge amount of waste rubber material is an environmental problem of great concern. Various ways to remediate the problem have been p roposed. Among these are road fillings and combustion in kilns. Spent tyres, however, comprise valuable material that could be recycled if a proper technique can be developed. One way of recycling old tyres is to b lend ground spent rubber with virgin material followed by vulcanization. Th e main obstacle to this recycling is bad adhesion between the crumb and mat rix of virgin rubber material due to little formation of interfacial sulphu r crosslinks. Micro-organisms able to break sulphur-sulphur and sulphur-car bon bonds can be used to devulcanize waste rubber in order to make polymer chains on the surface more flexible and facilitate increased binding upon v ulcanization. Several species belonging to both Bacteria and Archaea have t his ability. Mainly sulphur oxidizing species, such as different species of the genus Thiobacillus and thermoacidophiles of the order of Sulfolobales, have been studied in this context. The present paper will give a background to the problem and an overview of the biotechnological possibilities for solutions of waste rubber as an envi ronmental problem, focusing on microbial desulphurization.