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Biodelfurization of petroleum has emerged as a potential alternative to the hydrodesulfurization and oxidative desulfurization processes. However, the main obstacle in its commercial application is the efficiency and practicality of using bacterial cells. Pseudomonas sp. strain KWN5 was tested for the ability to use dibenzothiophene (DBT) in n-tetradecane as the sole sulfur source with two phase oil-water system. The biodesulfurization ability of strain KWN5 was evaluated by immobilized cells with dibenzothiophene as substrates. The cells immobilized by entrapping them with sodium alginate (SA) had high DBT biodesulfurization activity and could degrade 100 mg DBT/L in n-tetradecane of 46.76–100%, depended on concentrations of sodium alginate and cells within 24 h at 37oC with shaking at 160 rpm. The combination of SA concentration of 3% (w/v) with bacterial cells OD660 40 (25.52 mg DCW/mL) has an optimal biodesulfurization activity on 100 mg DBT/L in n-tetradecane, which is equal to 71.85% biodesulfurization. The immobilized cells of Pseudomonas sp. strain KWN5 in alginate beads were more efficient for the degradation of DBT and can be reused for five cycles (220 h) without any loss in their activity. The results of this study clearly show the role of the effects of cell immobilization in increasing the process of biodesulfurization.

ABSTRACT

Organic sulfur compound of fossil fuel are too resistant to be removed by the conventional desulfurization processes. This study aimed to investigate the best growth conditions of Agrobacterium tumefaciens strain LSU20 on desulfurized of dibenzothiophene (DBT) compound in the n-tetradecane as model of oil. The experiments were performed with the medium two-phase system, aqueous phase: mineral salt sulfur free (MSSF) medium and the oil phase: n-tetradecane containing 200 ppm of DBT in the ratio of oil/water (1: 5). The culture of LSU20 that has been aged 4 days (OD660 5) of 0.1 ml inoculated in a test tube containing 5 mL of MSSF medium and 1 ml model of petroleum, grown at temperature variations incubation as follows: 33°C, 37°C, 41°C, 45°C, and 49°C; variations in the initial pH of medium: pH 5.0, 5.5, 6.0, 6.5, 7.0, 7.5, and 8.0; and variations of carbon sources such as glucose, sucrose, glycerol and citric acid. The experiments were conducted using a water bath shaker at 150 rpm for 96 hours of incubation. The results showed that the highest rate of degradation of DBT by LSU20 occurs at a temperature of 37°C, media pH of 7 and glucose as the carbon source, ie with the growth rate reached 0.91 (OD660) and DBT compounds degraded until 76.9% (w/v).