BIODESULFURIZATION OF ALKYLATED DIBENZOTHIOPHENES USING WHOLE CELLS OF Pseudomonas Putida CECT5279: COMPARISON OF SUBSTRATE CONSUMPTION RATES
Integration of life sciences & engineering
Integration of Life Sciences & Engineering - Poster (T5-P)
Keywords: BIODESULFURIZATION, ALKYLATED, DIBENZOTHIOPHENES, Pseudomonas Putida
Nowadays, the massive consumption of fossil fuels in our society has become an important environmental problem. Therefore, more and more restrictive legal limitations have been imposed in order to control sulphur emissions in combustion processes. Many technologies have been proposed [1], among all of them, deep hydrodesulphurization (HDS) has been the most extensively employed (improved catalysts, advanced reactor designs, combination with distillation, etc.). However, the European Union has fixed for 2009 a maximum sulphur content of 10 ppm in diesel fuel [2], this fact demands severe operation conditions if HDS is used, which could affect fuel properties. Since 90’s, biodesulphurization (BDS) has been proposed as an alternative technology, which joined with a previous HDS process, can solve these problems. This technique employs micro-organisms, both wild and genetically modified (GMO) as catalysts, allows to degrade sulphur aromatic molecules using mild conditions of temperature and pressure, avoiding C-C bond breakdown, and conserving fuel characteristics. Most of BDS studies have used dibenzothiophene (DBT) as model compound. Nevertheless, many of the recalcitrant compounds to HDS are alkyl-DBTs.
In this work, a GMO, Pseudomonas putida CECT 5279, has been used as biocatalyst in a BDS process. As well as DBT, the substrates employed have been alkyl-DBT compounds (4-methyl and 4, 6-dimethyldibenzothiophene). It is assumed that these alkyl-DBTs are metabolized by means of a similar metabolic pathway to that usually admitted for DBT, called 4S route [3]. The aim of this work is the study of the alkyl-DBTs consumption rates compared, under the same conditions, with the DBT one.
The cells employed as biodesulphurizing catalyst were obtained in a 2L stirred tank bioreactor using a BSM medium [4], at 30ºC, 1 L/L/min of air flow rate and 200 rpm of stirrer speed. Cells for carrying out BDS resting cells assays were collected at different growth times: 5, 19 and 41 hours. BDS resting experiments were conducted in an orbital shaker at 30ºC and 210 rpm, using 250 mL Erlenmeyer flasks containing 40 mL HEPES medium. Different sulphur substrates (DBT and Me-DBTs) were used alone and combined as binary mixtures. In this last case, the biomass concentration used was doubled because of the double substrate concentration. Biomass was monitored by absorbance measurements at 600 nm. HPLC-UV-diode Array (with a C-8 Supercosil, 3m, 150 x 4.6 mm column) was employed to analyze the evolution of all intermediates compounds of the 4S route.
Experimental results show that the more alkylated the substrate is, the more difficult the degradation results. There is a clear influence of cell age in the substrate consumption rates. Cells with a bigger growth time achieve quicker alkyl-dibenzothiophenes degradation. It was also observed that two isomers forms of Me-HBP (final product of BDS route) are generated through the 4S route.
REFERENCES
[1] Babich, I. V.; Moulijn, J. A., Fuel 82, 607-631 (2003).
[2] European Directive (2003/17/CE).
[3] Olfield, C.; Pogrebinsky, O.; Simmonds, J.; Olson, E. S.; Kulpa, C.F., Microbiol. 143, 2961 (1997)
[4] Martin, A. B.; Alcon, A.; Santos, V. E.; Garcia-Ochoa, F., Energy & Fuels 18, 851-857 (2004) and 19, 775-782 (2005).
Presented Wednesday 19, 13:30 to 15:00, in session Integration of Life Sciences & Engineering - Poster (T5-P).
