Microbial solubilization of coal.

Several different strains of fungi have been shown to solubilize some types of low-ranked coal, apparently by an extracellular process. Oxidative pretreatment enhances the microbial action, allowing the use of a variety of coal feedstocks. The resulting product, which is primarily a mixture of polar organic compounds with moderate to high molecular weights and a high degree of aromaticity, is water-soluble. Possible processing concepts include the use of continuous bioreactors configured as either fixed or fluidized beds.