Flocculation of Pseudomonas delafieldii R-8 by γ-Polyglutamic Acid Combined with Celite for Biodesulfurization of Model Oil

γ-polyglutamic acid (PGA) was firstly used for recovery and immobilization of Pseudomonas delafieldii R-8 cells in biodesulfurization process. The PGA mediated flocculation was combined with celite adsorption to immobilize R-8 cells and the as-prepared immobilized cells showed a high initial specific desulfurization rate at 0.243 mmol l-1 h-1 and a good desulfurization stability with 95% desulfurization activity remained after 6 batches of desulfurization processes.

Desulfurization of Model Oil Containing Dibenzothiophene or 4,6-Dimethyl Dibenzothiophene by Alginate Immobilized Cells

Gram-negative bacterium, Pseudomonas delafieldii R-8 (CGMCC 0570) is capable of desulfurizing dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (4,6-DMDBT) to produce corresponding monohydroxydimethylbiphenyl. The immobilization of the resting cells of this strain in Ca-alginate gel effectively improved the stability of the cells and the desulfurization ability per amount of cells. 1 mmol/L of DBT and 4,6-DMDBT could be completely degraded in about 1 d. About 39 percent of the activity for 4,6-DMDBT was recovered after immobilization. The desulfurization activity was increased with the decrease of the diameter of the beads. The Ca-alginate immobilized cells could be used repeatedly for over 190 h with the addition of calcium ions to strengthen them. A thin layer of hydrophobic polyurea was coated on the surface of Ca-alginate gel using a simple method. The desulfurization activity was enhanced after the coating.

Biodesulfurization of Dibenzothiophene by Microbial Cells Coated with Magnetite Nanoparticles

ABSTRACT Microbial cells of Pseudomonas delafieldii were coated with magnetic Fe3O4 nanoparticles and then immobilized by external application of a magnetic field. Magnetic Fe3O4 nanoparticles were synthesized by a coprecipitation method followed by modification with ammonium oleate. The surface-modified Fe3O4 nanoparticles were monodispersed in an aqueous solution and did not precipitate in over 18 months. Using transmission electron microscopy (TEM), the average size of the magnetic particles was found to be in the range from 10 to 15 nm. TEM cross section analysis of the cells showed further that the Fe3O4 nanoparticles were for the most part strongly absorbed by the surfaces of the cells and coated the cells. The coated cells had distinct superparamagnetic properties. The magnetization (δs) was 8.39 emu · g−1. The coated cells not only had the same desulfurizing activity as free cells but could also be reused more than five times. Compared to cells immobilized on Celite, the cells coated with Fe3O4 nanoparticles had greater desulfurizing activity and operational stability.