Devulcanization of Ground Tires by Different Strains of Bacteria: Optimization of Culture Condition by Taguchi Method

Biological devulcanization of ground tires (GTs) was evaluated by eleven different bacteria belonging to the genera Thiobacillus, Gordonia, Nocardia, Amycolaptopsis and Pseudomonas. The GTs were treated by each bacterium in a mineral medium and devulcanization was measured by increasing the sulfate of the medium and decreasing the sulfur of the GTs. The effects of incubation time (10 and 20 days) and the percent of ground tire in the medium (0.5 and 5 w/v %) on desulfurization were investigated. No significant changes were observed after 10 days of incubation. The total sulfur contents of all bio-treated GTs were decreased by 6–21% in 0.5% GTs after 20 days of incubation. While in 5% GTs, the total sulfur contents were mainly decreased using Thiobacillus ferroxidans DSMZ 583 and PTCC 1647 up to 27 and 15%, respectively. SEM photograph further indicated a good coherency interface between the bacteria and the GTs. Subsequently, Taguchi method was applied for the optimization of the culture condition of DSMZ 583. An L12 orthogonal array was performed by which the effects of eleven factors in two levels were evaluated. It was found that the amount and mesh size of GTs are the most important factors in biological devulcanization of ground tires.