Muhammad Ghauri

Abstract:

Coal is one of the most abundant non-renewable fossil fuels in Pakistan and remained a viable source for the generation of electricity in the country. However, in general, the quality of local coal is too low to offset the practical, economic, and regulatory barriers to its utilization. Sulphur accounts for one of the major impurities in the coal and mainly occurs in inorganic and organic forms. Combustion of high sulphur coal releases environmental pollutants like sulphur dioxide, sulphuric acid, hydrogen and nitrogen sulphides. To enhance the quality of the coal and consequently reduce its environment damaging impact, sulphur in coal needs to be removed before its combustion. Some of the conventional chemical and physical methods have responded effectively towards the removal of sulphur, but, the use of hazardous chemicals and elevated operating temperatures make such processes unattractive and less eco-friendly. The environmental regulatory authorities all over the world are stressing for the development of eco-friendly processes when it comes to coal usage. Microbes act as a store house of several biomolecules/enzymes; they can be used for bioprocessing of coal on an industrial scale for technical exploitation with environmental responsibilities. In NIBGE, Industrial Biotechnology Division has been carrying out research pertaining to various aspects of bioremoval of inorganic and organic sulphur from coal. We have explored the area of biodepyritization (inorganic sulphur removal) of coal at laboratory and industrial scale successfully. The possibilities of using fermentors and drum reactors for depyritization have been demonstrated with substantial removal of pyritic sulphur from coal. For upscaling, we developed a 300 tonne heap bioleaching process by using mixed consortium of mesophilic and moderately thermophilic iron and sulphur oxidizing bacteria i.e., Acidithiobacillus ferrooxidans, Acidithiobacillus thiooxidans and Sulfobacillus thermosulfidooxidans, where about 70% of the total sulphur was removed in 36 days. In case of organic sulphur removal studies, we isolated more than two hundred bacterial isolates and tested them for their ability to remove organic sulphur from model compound like dibenzothiophene (DBT), a major thiophenic compound present in fossil fuels. Out of 214 isolates, eleven exhibited organic sulphur metabolizing activity. Most of the isolates belonged to different species of genus Gordonia. Other isolates had close similarities with Amycolatopsis flava, Microbacterium nematophilum, Mycobacterium senegalense and Rhodococcus spp (Eu-32). The sulphur removal potential of Rhodococcus spp. (Eu-32) was investigated using coal from Dukki, Baluchistan, which resulted in 60% reduction of organic sulphur content in 15 days. We have reported an extended DBT desulphurization pathway in Rhodococcus spp. (Eu-32) using chromatographic techniques like HPLC and GC-MS.