Degradation of scrap tyre by Bacillus sp. – Kinetic aspects of major environmental parameters and identification of potential growth substrates

This study aimed to elucidate some kinetic aspects involved during the degradation of waste scrap tyre by a Bacillus sp. previously isolated. After a 5-day cultivation, 2.03 ± 0.22% and 0.005 ± 0.001% of weight loss were observed for tyre sample and control group, respectively. The potential organic compounds leached out from tyre, identified by GC-MS, mainly consisted of n-alkanes and some alkylated phenols. A mixture of tetradecane, nonadecane, and 2,4-di-tert-butylphenol (60 mg l−1 total concentration) supported the isolate growth during the 5-day cultivation. The n-alkanes were removed more effectively (tetradecane, 64.93% and nonadecane, 47.92%) than the alkylated phenol (3.03%), contributing to the tyre degradation by Bacillus sp. observed. The optimal conditions were determined as 6.70 mg l−1 dissolved oxygen concentration, pH 7, 10% (v/v) inoculum size, 30 °C, and 120 mm2 tyre surface area. The highest maximum specific growth rate (μmax) (0.06 OD unit d−1 for S and SI) and the shortest lag phases (0.28 d for S and 0.17 d for SI) were obtained under the optimized conditions for the Bacillus sp. incubation. The electron micrographs showed the isolate ability to colonize the waste tyre surface. [Display omitted] •Tyre-degrading Bacillus sp. isolated from scrap tyre.•Highest μmax and shortest λ at pH 7, 30 °C, 6.7 mg l−1 DO concentration, 120 mm2 tyre surface area, and 20% inoculum size.•Growth of isolate on a mixture of major organic compounds leached out from tyre.•n-alkanes removed more effectively (64.93% tetradecane and 47.92% nonadecane).•Colonization and degradation of tyre by isolate confirmed by SEM.