Effect on the oxidation characteristic at lignite of two types of endogenous microorganisms from coal

In recent years, coal biotechnology has gained considerable popularity due to its economic, eco-friendly, and sustainable advantages, which offer a novel perspective and pathway for the development of green technologies aimed at preventing and controlling coal spontaneous combustion (CSC). Two endogenous microorganisms from lignite were succeeded in extracting in this work, namely Aspergillus and Bacillus velezensis. Subsequently, the effect of these microorganisms on the microscopic structure and macroscopic oxidation characteristics of coal was investigated by X-ray diffraction, Fourier-transform infrared spectroscopy, and thermogravimetric analysis. The results revealed that both Aspergillus and Bacillus velezensis treatments altered the microcrystalline structure of the coal, disrupting the aliphatic hydrocarbon structure and oxygen-containing functional groups of the coal molecules. Particularly, the OH - O hydrogen bond of two kinds of microbial treatment coal samples content respectively decreased significantly by 17.29 % and 11.06 % compared to the raw coal sample. However, the effects of different microorganisms on coal varied. Thermodynamic behavior demonstrated that the critical temperature of the two treated coal samples was delayed by 29.44 degrees C and 26.62 degrees C, and the ignition temperature was delayed by 11.31 degrees C and 5.18 degrees C. Overall, all characteristic temperature points of the Aspergillus group were delayed, but the maximum weight loss rate temperature and the burn-out temperature of the Bacillus velezensis group exhibited slight advancement. The thermal mass loss characteristics also changed during the oxidation combustion stage. In addition, the average activation energies of oxidized combustion stage calculated by the Kissinger-Akahira-Sunose method were 74.26 kJ/mol and 78.61 kJ/mol, respectively, and 82.41 kJ/mol and 86.15 kJ/mol for the Friedman method, which were both increased compared to the raw coal. The results indicate that both Aspergillus and Bacillus velezensis have effects with varying degrees on the coal oxidation characteristics. It can be observed that the effect of treatment with Aspergillus is better than Bacillus velezensis from the overall changes in characteristic temperature points. This work lays the foundation for investigating the effect of microbial action on the oxidative properties of CSC.