Desulfurization of vulcanized rubber by a synergism of chemical and biological treatment, with the strains Gordonia desulfuricans and Rhodococcus erythropolis

Abstract

Developing and improving methods for the management of rubber waste accumulation and its recycling are crucial in addressing environmental problems, and desulfurization is a critical preliminary step before the rubber degradation. This study evaluates the desulfurization of pre- and post-treated vulcanized rubber using a green chemistry method that combines microwave (MW) with hydrogen peroxide and sulfur-oxidizing bacterial strains, Gordonia desulfuricans and Rhodococcus erythropolis. The results indicate that the rubber particles subjected to a synergism of a both treatments were able to continue being desulfurized despite the preliminary treatment. This can be verified in a greater mass loss (14.1 ± 0.8 % using G. desulfuricans, and 11 ± 0.4 % using R. erythropolis, with MW pretreatment) and sulfate release when combining both treatments (14.4 ± 0.7 mg/g using G. desulfuricans, and 22.4 ± 1 mg/g using R. erythropolis, with MW pretreatment). Also, significant changes in C-S and S-O bands, and greater surface fragmentation. A decrease in cross-link density was also observed in cultures with unpretreated rubber and in particles biologically pretreated with subsequent chemical treatment (5.18 × 10⁻⁴±3.2 × 10⁻⁵ using G. desulfuricans and 5.4 × 10⁻⁴±4.5 × 10⁻⁵ using R. erythropolis, with MW post-treatment). In addition, the analyses of metals copper, lead, chromium, barium and antimony showed that they were detected in concentrations lower than the maximum limits allowed for effluent discharges to sewage networks, which allows to consider that it consists of an environmentally safe method, reaching values of 1341, 3.6, 3.2, 42, and <1 μg/L, respectively with MW method. Finally, when evaluating desulfurization with biological pretreatment, and subsequent chemical treatment, better results were obtained.