A Two-stage Immobilized Cell Bioreactor With Bacillus subtilis and Rhodococcus erythropolis for the Simultaneous Production of Biosurfactant and Biodesulfurization of Model Oil

Two vertical rotating immobilized cell reactors (VRICRs), one with the bacteria Bacillus sp. BDCC-TUSA-3 and the other with R. erythropolis, were constructed, with polyurethane foams as an attachment support. They were optimized for surfactin production and biodesulfurization (BDS) of dibenzothiophene (DBT), respectively. Then, the two bioreactors were combined to form a two-stage VRICR where an appropriate fraction of Bacillus sp. reactor effluent, containing surfactin, was mixed with the influent fed into R. erythropolis bioreactor, containing DBT in hexadecane. The BDS rate and volumetric reactor productivity were greatly increased to 210.5 mM 2HBP.kg(-1).h(-1) and 16.6 mM 2HBP.L-1.h(-1), respectively. Sulfur concentration decreased from 398 down to <5 ppm. Additionally, surfactin was produced at high concentration (4.8 g.L-1) with a volumetric reactor productivity of 720 mg(surfactin)L(-1).h(-1), which represents an extra added-value product that could markedly decrease operating costs. This study presents a feasible technology for efficient removal of sulfur from sulfur-containing fossil fuels and the production of biosurfactant as well.