Sunday, April 29, 2007

Influence of operational conditions for dibenzothiophene desulfurization by Gordonia sp. F.5.25.8

Mônica Yumi Menezes Sassaki1, Claudia M. S. Ribeiro2, Juliana Vaz Bevilaqua2, and Denise M. G. Freire1. (1) Instituto de Química, Universidade Federal do Rio de Janeiro, Av. Athos da Silveira Ramos 149, Rio de Janeiro, Brazil, (2) CENPES, PETROBRAS, Av. Jequitiba 950 radial 5 sala 552, Rio de Janeiro, Brazil

Sulfur content restrictions in fuels have stimulated the development of desulfurization technologies as such as the research for alternative processes, among them, the biodesulfurization. Biodesulfurization is based on the selective removal of sulfur from the molecule and the maintenance of the carbonic skeleton intact, keeping mostly its calorific value. Usually, dibenzothiophene (DBT) is used as a model compound to study the microbial desulfurization, as it is worth as representing petroleum sulfured contaminants.
The aerobic bacterial strain Gordonia sp. F.5.25.8, isolated by PETROBRAS researches from contaminated soil, is able to use DBT as the sole sulfur source. This strain removes sulfur from DBT through selective oxidation, presenting 2-hydroxybiphenyl (2-HBP) as final metabolic. In this study, the influence of operational conditions was studied on batch growth of Gordonia sp. F.5.25.8. In order to reduce experimental effort and evaluate the main effect of pH (6-8), temperature (30-38°C) and agitation (150-200 strokes per min) on operational condition, it was performed a fractionated factorial experimental design with three variables at two levels and central point. The biomass growth was monitored through absorbance measures at 600nm, and also pH, glucose concentration, and desulfurization activity were assayed during cell cultivation. Substrate (with initial DBT concentration of 46ppm) and final product quantifications were performed by HPLC. A new methodology was developed to evaluate the desulfurization by Gordonia sp. F.5.25.8, using 3gDCW.L-1 of cells in growth conditions (glucose as carbon source and NH4Cl as nitrogen source) for 45 hours which led to a DBT desulfurization rate up to 0.11mgDBT.g-1.h-1.