PROSPECTS FOR BIODESULFURIZATION OF COAL - MECHANISMS AND RELATED PROCESS DESIGNS

Recent developments in microbiological desulfurization of coal are reviewed. Microbiological removal of organic sulfur from coal remains to be proven conclusively, but is under active study for petroleum biodesulfurization. Microbiological removal of pyritic sulfur from coal is well established in the laboratory and recent efforts have been aimed at scale-up designs and process considerations. Microbiological depyritization may be as inexpensive as other forms of advanced coal desulfurization but it has not been tested on a large scale. Processes based on 'indirect' bioleaching of pyrite from coal may also have applications. Other forms of sulfur in coal, such as elemental sulfur, are usually quantitatively insignificant, but nonetheless can be removed microbiologically. Thermophilic bacteria remove pyritic sulfur from coal at faster rates than mesophilic bacteria, in part due to faster abiotic rates of pyrite oxidation at elevated temperatures. Future work in biological desulfurization of coal should include studies on treatment of waste coal or refuse material.