BIODESULFURIZATION OF DBT IN MODEL OIL BY RESTING CELL OF Pseudomonas putida CETC5279. PROCESS ENHANCEMENT
Integration of life sciences & engineering
Integration of Life Sciences & Engineering - Poster (T5-P)
Keywords: biodesulfurization, dibenzothiophene, Pseudomonas putida CECT5279, surfactant
Sulfur dioxide emission through fossil fuel combustion is the mayor contributor to the acid rain and air pollution (Monticello, 2000). For environmental protection, the sulfur in diesel oil will have to be lower than 10 ppm by 2010 in European Union and the USA.
By biodesulfurization (BDS) is possible to remove recalcitrant compounds to conventional hydrodesulfurization (HDS), usually heterocyclic organosulfur compounds like dibenzothiophene (DBT) (Rhee et.al., 1998). Several aerobic bacterial strains have been used to selective desulfurization of DBT via the so-called 4S pathway; in witch 2-hydroxybiphenyl (2HBP) is the final product free of sulfur. In this work, biodesulfurization of DBT in a model oil solution were conducted by resting cells of Pseudomonas putida CECT 5279, a GMO.
The efficiency of a biodesulfurization largely depends on the bioavailability of the DBT in the aqueous phase, where the microorganism exists. The solubility of DBT, a highly hydrophobic compound and their capability to be transported into bacterial cells, is probably the rate limiting step of the biodesulfurization process in biphasic liquid medium.
Several assays were conducted to study the effect of the addition of ethanol as co-solvent, and some non ionic surfactant on desulfurization yield. The resting cell reactions were conducted in orbital incubator, at 30 ºC of temperature and 250 rpm of agitation speed. In all cases the liquid medium contains 50 mg/L of DBT dissolved in hexadecane (organic phase) and HEPES buffer at pH 8 (aqueous phase) in 1:1 volume proportion. The biocatalyst was produced by growing in agitated tank bioreactor (Biostat B, Braun) following a standardized protocol (Martin et.al., 2004). Cells was collected by centrifugation in the late logarithmic phase, conserved in saline serum-glycerol 1:1 volume proportion and stored at -80ºC until use. In all desulfurization assays, the biomass concentration was always 15 g/L of dry cell and the reaction time was 24 hours.
Emulsions were separated by centrifugation to determine DBT and resulting products concentration. The organic and aqueous phases were analyzed by HPLC-UV. The results indicate that the addition of ethanol or surfactant mixed o not with the alcohol, increase remarkably the desulfurization yield. Moreover, the polysorbates Tween 20 and Tween 85, can be used without any problems of separation or cell disruption.
Acknowledgements
The work has been supported by the Spanish Ministry of Science and Technology Project number CTQ2004/06553- C02-02
References
Martin, A.B.; Alcon, A. Santos, V.E.; Garcia-Ochoa, F. (2004). Energy Fuels, 18, 851-857.
Monticello, D. J., Curr.Opin. Biotechnol. 11 (2000) 540-546.
Rhee, S.K., Chang, J.H., Chang, Y.K., Chang, H.N. (1998). App. Environm. Microbiol. 64, 2327-2331.
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Presented Wednesday 19, 13:30 to 15:00, in session Integration of Life Sciences & Engineering - Poster (T5-P).
