Coal biotransformations under aerobic conditions: screening and characterization of potential biocatalysts

Coal is one of the important energy sources; however, the direct combustion of raw coals is discouraged due to their low calorific value and the production of harmful gases. Microbial transformation of coal is an eco-friendly method to convert raw coal into clean and cost-effective valuable products like humic, fulvic acids, and other complex organic compounds. In present study, out of 51 bacterial isolates, 05 isolates, designated as ANK-4, AN-25, ANK-30, BD4, and Mn-250 were selected based on their degradation/solubilization activity for lignite as well as bituminous coal samples. All the isolates showed ligninolytic activity as determined by Azure-B decolorization and Manganese oxidation assays as well as by Guaiacol and α-Naphthol tests. For the bio-treated lignite and bituminous coals, the Z-average size was 434.2 to 187.5 and 587.6 to 280.2 nm and zeta potential was −35.2 to −29.3 and −32.6 to −23.8 mV, respectively. Morphological and molecular studies showed that the isolated bacteria belong to genus Bacillus and Kocuria. The coal solubilization/degradation and ligninolytic activities as well as size and zeta potential studies indicated that the isolated bacteria could be potential candidates for development of green technologies for conversion of coal into valuable products for fuel and non-fuel applications.