Study On Microbial Desulfurization Of Waste Rubber

Recently, with the rapid development of world economy and science, the use of rubber products increases gradually around the world and the amount of waste rubber also increases sharply. However, the waste rubber products are hard to degrade naturally because of their stable three-dimensional network structure, which results in a series of environmental and resource wasting problems. Compared with traditional physical and chemical regeneration methods, microbial desulfurization has many irreplaceable advantages:mild reaction conditions, simple equipment, low energy consumption, no pollution, etc. It has gradually become the focus of attention and study in recent years. Based on previous studies, I mainly did the following work in this paper:Firstly, it has been proved that Tween 20 is the optimal surfactant in the bio-desulfurization experiment with Sphingomonas sp. Based on that premise, this paper further studied the influence of Tween 20 dosage on Sphingomonas sp. growth and bio-desulfurization effect. By examining the water contact angle, swelling values, crosslink density, element content of rubber samples and the mechanical properties of SBR composite filled with rubber powder, we choose the best dosage of Tween 20 and determined the co-culture conditions of desulfurization. The results showed that surfactant Tween 20 can significantly improve the affinity between rubber and microorganisms and effectively improve the desulfurization effect. In the study of the Tween 20 dosage range, it had no inhibitory effect on the metabolism of Sphingomonas sp. The surfactant has different effect on different rubber. For GTR, SBR, NR, the best dosage of Tween 20 was 0.5 g/L,1 g/L,2 g/L respectively.Secondly, basic processing conditions of mixed bacteria were determined by comparing Sphingomonas sp. and Gordonia sp. and suitable medium was selected through the exchange of culture medium. Then we studied the influence of different inoculation methods on Sphingomonas sp./Gordonia sp. growth and bio-desulfurization effect. The results showed that these two bacteria could both grow well in Sphingomonas sp. medium. So the medium was chosen to be the optimal medium for mixed bacteria. By analyzing and comparing the desulfurization effect, the most suitable inoculation method was selected for rubber (GTR, SBR, NR). Research showed that in Sphingomonas sp./Gordonia sp. co-culture process, different inoculation methods lead to different total biomass, which resulted in the alteration of the desulfurization effect. And the best inoculation method for different rubber was varying. For GTR and NR, when Gordonia sp. was inoculated 24 hours ahead and these two bacteria in the same proportion (5:5), desulfurization effect was the strongest. For SBR, when Sphingomonas sp. and Gordonia sp. was inoculated at the same time and in the same proportion (5:5), desulfurization effect was the best.Thirdly, Sphingomonas sp., Gordonia sp. and their mixed bacteria were used to desulfurize three kinds of rubber (GTR, SBR, NR) respectively. The microorganisms'growth characteristic was studied and desulfurization effect on GTR was evaluated systematically by measuring the water contact angle, swelling values, crosslink density, element content of rubber samples and desulfurization depth on GTR. Besides, the mechanical properties of SBR composite filled with GTR or DGTR were studied. The results showed that during co-culture desulfurization process, the biomass of the mixed bacteria was higher than any single bacteria, which indicated that these two kinds of bacteria can promote each other and grow together. Compared with single strain, the mixed bacteria had better desulfurization effect on rubber (GTR, SBR, NR) and caused deeper desulfurization depth on GTR surface. It showed that esulfurization with mixed bacteria had certain advantages.Finally, the desulfurization mechanism of mixed bacteria was explored by analyzing the distribution of bacteria on SBR/NR rubber surface and the damaged morphology of film. The results showed that Gordonia sp. mainly degrades rubber while Sphingomonas sp. mainly desulfurizes the rubber. They can coordinate with each other and play the role of desulfurization together.