Successive bacterial desulfurization and regeneration of liquid fuel over Ni-doped carbon beads using a single Enterococcus faecium strain isolated from an industrial wastewater

Adsorptive desulfurization of liquid fuels over a wide sulfur (S) concentration range remains as challenging as the regeneration of spent materials. This study describes the efficient desulfurization of the dibenzothiophene (DBT) and thiophene (TH) containing liquid fuels over 300 - 1200 mg L-1 S-concentration range, using a hybrid approach combining adsorptive desulfurization (ADS) and bacterial desulfurization (BDS) sequentially at 30 degrees C and 1 atm-pressure, with the Ni-doped activated carbon beads and Enterococcus faecium bacterium serving as the ADS and BDS agent, respectively. The novelty is in the successful regeneration of spent adsorbents using the identical bacterium that was used in the BDS step. Notably, the bacterium was isolated from the waste effluent of a petroleum industry, and was characterized via the colony morphology, Gram staining, and identification by 16S rRNA sequencing. ADS step was used over 300 - 1200 mg L-1, before switching over to BDS over the 50 - 300 mg L-1 S-concentration range, the sequential steps indicating an approximately 99% removal of the thiol compounds from the liquid. The spent adsorbents, post sequential test, were regenerated using the bacterial dose of 1% (v/v) of the liquid, and successfully reused up to five cycles of the hybrid method, with similar to 97% DBT and 95% TH removal measured in the last cycle. The spent and regenerated materials were physicochemically characterized by FE-SEM, FT-IR and BET analysis. As the regulations decrease the limits of sulfur content in on-road fuels globally, the proposed hybrid approach combining ADS with BDS, in conjunction with bacterial regeneration can be a potentially energy and cost effective solution to the desulfurization of liquid fuels.