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Biotechnology Letters 24: 401–405, 2002.© 2002 Kluwer Academic Publishers. Printed in the Netherlands.401Microbial desulfurization of solubilized coalKitae Baek1, Chung-Sik Kim2, Hyun-Ho Lee2, Hyun-Jae Shin3& Ji-Won Yang1,∗1Biological and Environmental Engineering Laboratory, Department of Chemical Engineering, Korea AdvancedInstitute of Science and Technology (KAIST), 373-1, Kusong-dong, Yusong-gu, Taejon 305-701, Republic of Korea2LG Institute of Environment, Safety & Health, Yonsei Engineering Research Centre, 134 Shinchon-dong,Seodaemoon-gu,Seoul 120-794, Republic of Korea3EnzBank, Inc., 309 BVC, Korea Research Institute of Bioscience and Biotechnology (KRIBB), Yusong, Taejon305-333, Republic of Korea∗Author for correspondence (Fax: +82-42-869-3910;E-mail: jwyang@kaist.ac.kr)Received 7 November 2001; Revisions requested 22 November 2001; Revisions received 7 January 2002; Accepted 9 January 2002Key words: biodesulfurization, rhodochrous IGTS8, Rhodococcus, solubilization, solubilized coalAbstractMicrobial desulfurization of low rank coal by Rhodococcus rhodochrous IGTS8 was investigated using threedifferent pretreated coal samples. Solubilized coal was desulfurized more efficiently than hard coal and moresulfur was extracted from biologically solubilized coal than from chemically solubilized coal. Microbial desulfur-ization combined with biological solubilization removed75% of the total sufur while the microbial desulfurizationcombined with chemical solubilization removed 63%.IntroductionCoal is an abundant and economical source of en-ergy and has the potential to become increasinglyimportant. A major disadvantage associated with useof coal as a fuel is emission of SO2 into the envi-ronment during direct combustion. With increasingawareness of threats to the global environments fromgreenhouse effect and acid rain, various technologieshave been established and used for the desulfuriza-tion of coal. To develop a more economical system,microbial desulfurization has been studied by severalresearch groups (ElSawy & Gray 1991, Klein et al.1994, Matsui et al. 2001, Rubiera et al. 1999, Shen-nan 1996). However, microorganisms cannot contactsulfur bonded with coal structures due to hydropho-bicity of the coal surface and diffusion limitationsresulting from the size of coal particles (Erincin et al.1998, Kilbane & Jackowski 1992). The latter problemhas been approached by chemical solubilization of thecoal (Kilbane & Jackowski 1992, Stoner et al. 1990)and by microbial solubilization using bacteria andfungi (Shin et al. 1995). Solubilization removes mostof the inorganic sulfur from the coal but there havebeen no reports on the efficiency of microbial desul-furization of biologically solubilized coal. This studycompares the efficiency of microbial desulfurizationof coals solubilized chemically and biologically.ExperimentalOrganism and growthRhodococcus rhodochrous IGTS8 (ATCC 53968) hasgrownon modifiedbasal salt mediums (BSM) consist-ing of2.44g KH4PO4, 14.05g Na2HPO4·12H2O, 2 gNH4Cl, 0.2 g MgCl2·6H2O, 0.001 g CaCl, 0.0006 gFeCl, and 20 ml glycerolin 1 l of sterile distilled water(Kilbane& Jackowski1992).For seedculture, 0.024gNa2SO4was used as sulfur source in 1 l of sterile dis-tilled water. The pH of BSM was 7. Incubations wereperformed at 30?C and 200 rpm.