Desulfurization of diesel oils by a newly isolated dibenzothiophene-degrading Nocardia sp. strain CYKS2

A dibenzothiophene (DBT)-degrading bacterial strain was isolated from dyein g industry wastewater and identified as Nocardia sp. CYKS2. The newly isola ted bacterial strain Nocardia sp. CYKS2 was able to convert DBT to 2-hydrox ybiphenyl (2-HBP) as the dead-end metabolite through a sulfur-specific path way. Other organic sulfur compounds, such as thiophene derivatives, thiazol e derivatives, sulfides, and disulfides were also desulfurized by Nocardia sp. CYKS2. In batch culture, 0.2 mM DBT was completely desulfurized in 60 h . After DBT was depleted, neither cell growth nor 2-HBP production was obse rved. When a model oil which DBT was dissolved in hexadecane was treated wi th growing cells, DBT was desulfurized from 10 mM to about 2 mM in 80 h. In this case, desulfulization rate was 0.279 mg-sulfur/(L-dispersion . h), wh ich was about 2.5 times higher than that in the previous case of batch cult ure. When diesel oil was treated, the sulfur content decreased from 0.3 to 0.24 wt % in 48 h. A volumetric phase ratio of oil to water was 1/10 in thi s case. The sulfur decreased from 0.3 to 0.2 wt % in 48 h, when the volumet ric phase ratio was 1/20. The desulfurization rates were 0.909 and 0.992 mg -sulfur/(L-dispersion . h), respectively.