Sulphur-Utilizing Microorganisms in Biotechnological Applications - Rubber Recycling and Vanadium Reduction

Sammanfattning: Biotechnological processes offer environmentally friendly and sometimes cost-effective alternatives to traditional chemical and mechanical methods. It is important to take advantages of the opportunities these processes provide to fulfil the demands and expectations of a future environmentally sustainable society. This work exploits the possibilities of applying biotechnological methods to allow recycling of two different materials of environmental concern: rubber and vanadium. Worldwide deposition of waste rubber materials, for example vehicle tyres, constitutes environmental threats and a source of unutilized raw material. The problem with rubber recycling resides in the sulphur cross-links created between the rubber polymers during vulcanization. These cross-links give the material its excellent and characteristic properties, but also make it impossible to melt and reshape, as one can do with, for example, glass and plastics. In this work, the sulphur-oxidizing bacteria Acidithiobacillus and the sulphur-reducing archaeon Pyrococcus furiosus have been used to break the sulphur cross-links in vulcanized rubber materials, which improved the physical properties of the recycled rubber. The effect of different grinding methods on the biotechnological treatment and the mechanical properties, the toxicity of rubber additives to the desulphurizing microorganisms and the possibilities of biotechnological detoxification of rubber with fungi have also been investigated. Vanadium and its compounds are used in several important industrial processes. It is also present in heavy oil and is hence accumulated in the waste resulting from heavy oil combustion. Vanadium-containing waste materials are traditionally deposited in landfills or recovered by leaching with acids. This work has shown that Acidithiobacillus are capable of biological reduction of vanadium, which reduces the toxicity of the metal and increases its solubility, thereby enhancing the possibility of biotechnological recovery from industrial waste.