Taguchi optimization of dibenzothiophene biodesulfurization by Rhodococcus erythropolis R1 immobilized cells in a biphasic system

• Optimization of factors affecting biodesulfurization in a biphasic system was performed by Taguchi methodology.
• Biodesulfurization of Ca-alginate immobilized cells coated by nano-Al2O3 particles and surfactants were studied.
• Viability of immobilized cells after each step of the successive runs has been investigated by flow cytometry.
• Addition of nicotinamide and riboflavin increased the stability of immobilized cells and their biodesulfurization efficiency.

Organic sulfur components of the petroleum are too resistant to be removed by the conventional desulfurization processes. This study aimed to investigate the removal of dibenzothiophene (DBT) as an organic sulfur compound, from the oily phase by a bioprocess employing the immobilized cells. Rhodococcus erythropolis R1 cells were encapsulated in calcium alginate beads by considering factors such as the alginate concentration, size of the beads, the concentration of surfactants and Ɣ-Al2O3 nano particles for optimizing biodesulfurization (BDS) via Taguchi approach. The impact of two cofactor precursors (nicotinamide and riboflavin) on the long term BDS efficiency was also examined. The results indicated that the optimum factor levels for the bigger is better criterion could be achieved at 20% (w/w) of Ɣ-Al2O3 nano particles, alginate beads size equal to 1.5 mm, 1% (w/v) of the alginate and 0.5% (v/v) of span 80. The related statistical analysis showed that the concentration of Ɣ-Al2O3 nano particles was the most significant factor in the BDS process. Moreover, the addition of nicotinamide and riboflavin significantly decreased the biocatalytic inactivation of the immobilized cells system after successive operational steps enhancing the BDS efficiency by more than 30% after four steps. It can be concluded that a combination of the nano Ɣ-Al2O3 particles with alginate immobilized cells could be very effective in biodesulfurization process.