A CRITICAL-REVIEW OF BIODESULFURIZATION SYSTEMS FOR REMOVAL OF ORGANIC SULFUR FROM COAL

This study evaluates approaches for the biological removal of organic sulphur from coal. In this area, Atlantic Research Corporation's (ARCTECH's) biodesulphurization system is the only one that has been demonstrated on coal with mixed success on a continuous bench-scale unit of 4.54 kg day-1 capacity. Other biocatalytic systems developed by the Institute of Gas Technology (IGT) or Southern Illinois University (SIU) are still in the laboratory-scale microbial selection and screening stage. The successful use by the IGT of a sulphur-limited, continuous chemostat for the selection of bacterial strains with appropriate desulphurization activities has provided a convenient and powerful strain selection technique. The IGT work has also established the possibility of changing the metabolic pathway by proper modification of the bacterial growth medium and introduced the sulphur bioassay technique to help compare the effectiveness of different micro-organisms grown with different substrates under different conditions on a comparable basis. The SIU was successful in mapping the desulphurization genes in a mutant E. coli. There is still a need for faster growing, stable, and more active biodesulphurization micro-organisms than those which have been developed so far. This calls for a programme of strain selection and improvements through molecular genetics, a thorough understanding of coal biodesulphurization metabolism and its associated metabolic pathways, investigation of extracellular enzymatic removal of organic sulphur from coal, and identification of new acidophilic heterotrophs that have broad organic sulphur removal capabilities and that can coexist with other bacterial strains currently used for inorganic sulphur removal.