Optimization of pH and temperature for degradation of tyre rubber by Bacillus sp. strain S10 isolated from sewage sludge

• Rubber tyre degrading Bacillus sp. strain S10 was isolated from sewage sludge.
• Strain S10 can utilize rubber tyre pieces as carbon and energy source at pH 7 and temperature 35 °C.
• Scanning electron micrographs showed roughness of surface with cracks and pits after culturing with strain S10 in MSM.
• Strain S10 could mineralize the rubber tyre pieces into CO2 as indicated by the release of CO2 in Sturm test experiment.

Rubber products, especially tyres, are highly recalcitrant that accumulate in environment after disposal. One possible way of getting rid of spent rubber and tyre waste is to degrade it by using microorganisms. The present study was conducted to optimize some of the physical parameters for degradation of tyre rubber by Bacillus sp. S10, in liquid mineral salt medium (MSM). This strain was previously isolated from the sewage sludge, collected from the sewage treatment plant, Rawalpindi. Effect of temperature (25–40 °C) and pH (5–10) on the growth of Bacillus sp. S10 in liquid MSM, containing tyre rubber as a sole source of carbon, was studied. The optimum degradation of tyre rubber was observed at pH 7 and 35 °C. Slide test with Schiff's reagent showed purple coloration, indicating the formation of aldehydes as a result of degradation by Bacillus sp. S10. Visible surface changes were observed through Scanning Electron Microscopy (SEM) analysis of treated tyre pieces incubated in MSM along with Bacillus sp. S10 with respect to untreated pieces as control. The degradation of tyre pieces was determined gravimetrically, by measuring the CO2 evolved through Sturm test. The amount of CO2 produced in case of test was found higher than the control samples. It is concluded from the results, that Bacillus sp. S10 has potential to degrade rubber tyres, hence it can be applied on spent rubber pieces under controlled environmental conditions.