Simultaneous devulcanization and denitrification: a novel approach for valorization of both ground tire rubber and nitrate-containing wastewater

This study focused on a new approach for valorization of both ground tire rubber (GTR) and nitrate-containing wastewater via simultaneous devulcanization and denitrification. Initially, sulfur-based autotrophic denitrifiers were successfully enriched from three different seed sludge sources, biological nutrient removal (BNR) sludge, anaerobic digester sludge and BNR sludge of a leather organized industrial zone WWTP. Average nitrate removal efficiencies were 96-98%. Biological devulcanization (biodevulcanization) of GTR was later investigated with these enriched cultures. Results revealed that biodevulcanization was only achieved with the culture enriched from BNR sludge of the leather organized industrial zone WWTP, as 3.9% sulfur removal (desulfurization efficiency). Metal sulfate precipitation was speculated to cause an underestimation of the desulfurization ratio. Fourier-transform infrared spectroscopy (FTIR) results demonstrated a decrease in the intensity of the C-S bonds and an increase in intensity of S-O bonds in treated GTR samples. This was attributed to the oxidation of sulfidic crosslinks, i.e. verification of biodevulcanization. This study indicated that simultaneous biodevulcanization and denitrification could be a promising process for valorization of both GTR and nitrate-containing wastewater which in turn would support circular economy and sustainable development.