The desulfurization ability of Sphingomonas subarctica
T7b was evaluated using resting and immobilized cells
with dibenzothiophene (DBT), alkyl DBTs, and commercial
light gas oil (LGO) as the substrates. The resting cells of
S. subarctica T7b degraded 239.2 mg of the initial 250 mg
of DBT/l (1.36 mM) within 24 h at 27oC, while 127.5 mg of
2-hydroxybiphenyl (2-HBP)/l (0.75 mM) was formed,
representing a 55% conversion of the DBT. The DBT
desulfurization activity was significantly affected by the
aqueous-to-oil phase ratio. In addition, the resting cells of
S. subarctica T7b were able to desulfurize alkyl DBTs with
long alkyl chains, although the desulfurization rate
decreased with an increase in the total carbon number of
the alkylated DBTs. LGO with a total sulfur content of
280 mg/l was desulfurized to 152 mg/l after 24 h of reaction.
Cells immobilized by entrapment with polyvinyl alcohol
(PVA) exhibited a high DBT desulfurization activity,
including repeated use for more than 8 batch cycles
without loss of biodesulfurization activity. The stability of
the immobilized cells was better than that of the resting
cells at different initial pHs, higher temperatures, and for
DBT biodesulfurization in successive degradation cycles.
The immobilized cells were also easily separated from the
oil and water phases, giving this method great potential
for oil biodesulfurization.

Keywords: Biodesulfurization, dibenzothiophene, resting cells, immobilized cells, Sphingomonas subarctica