Sunday, April 29, 2007

Evaluation of recycled paper sludge hydrolyzate as a potential nutrient source for dibenzothiophene desulfurization by Gordonia alkanivorans strain 1b

L. Alves1, S. Marques1, J. Matos1, R. Tenreiro2, and F.M. Gírio1. (1) Biotechnology Department, INETI, Estrada do Paço do Lumiar, 22, 1649-038 Lisboa, Portugal, (2) Centro de Genética e Biologia Molecular and Instituto de Ciência Aplicada e Tecnologia, Universidade de Lisboa, Faculdade de Ciências, Edifício ICAT, Campus da FCUL, Campo Grande, 1749-016 Lisboa, Portugal

Biological desulfurization of fossil fuels may offer an alternative process to reduce sulfur dioxide emissions responsible for environmental pollution. One of the limiting factors to use this process is the cost associated to the production of biocatalysts, mainly due to the costs associated to culture media formulation. The utilization of carbon sources derived from industrial wastes may thereby represent an interesting alternative for low-cost fermentation processes. The purpose of this work is to evaluate the performance of recycled paper sludge (RPS) as feedstock for a biodesulfurization process using Gordonia alkanivorans strain 1B.
Polysaccharides of RPS were hydrolyzed with a formulation of Celluclast®1.5L with Novozym®188, which was also previously dialyzed to remove possible sulfur contaminants. The hydrolyzates were used for carbon source supplementation of culture medium. Whereas strain 1B grew faster on non-dialyzed hydrolyzate, only dialyzed hydrolyzate allowed dibenzothiophene (DBT) desulfurization. With dialyzed hydrolyzate on a 10 g/L glucose concentration, 250 μM DBT was consumed after 4 days, with a maximum specific productivity of 2-hydroxybiphenyl of 1.09 μmol/g(biomass)/h, corresponding to a desulfurization rate similar to the one obtained with pure-grade glucose. The supplementation of RPS hydrolyzate only with phosphate and ammonia was enough to support strain 1B growth. It was also demonstrated that strain 1B is able to desulfurize a model oil containing DBT, 4-methylDBT and 4,6-dimethylDBT, with a 2.7-fold reduction on total sulfur (from 6 to 2.23 mM) after 5 days of cultivation.

In conclusion, DBT biodesulfurization using RPS seems potentially feasible, providing guidance for further development of a highly efficient process.