Enhancement of Proteus mirabilis in ultrasonic suspension field and its degradation process to low-rank coal of Inner Mongolia

The self-developed ultrasonic levitator was used to intensify the culture of the bacterial solution of Proteus mirabilis, and then the enhanced bacterial solution was used to degrade the low-rank coal of Inner Mongolia, and the unfortified bacterial solution was used as a control. The results showed that the optimum ultrasonic suspension conditions of Proteus mirabilis were as follows: the logarithmic growth period was selected, the suspension time was 1 min, the suspension power was 325 W, and the suspension liquid volume was 100 μL. The bacterial solution enhanced by ultrasonic suspension secreted more alkaline substances, the contents of O—H、C—N and C—H functional groups of the bacteria increased after ultrasonic suspension enhancement, which showed that ultrasonic suspension increased the contents of hydrophilic functional groups on the surface of the bacteria and improved the binding sites between microorganisms and coals. The cell membrane permeability increased by 38.46%, and the activity of alkaline protease increased by 20.95%, presenting that the metabolic activity of the strain was improved. Compared with the control group, the plate degradation circle of the enhanced bacteria solution to coal samples increased by about 4.85 mm, and the degradation rate of low-rank coal of Inner Mongolia was 35.96%, which was 12.84% higher than that of the control group. FTIR, XRD, low-temperature N₂ adsorption and GC-MS were used to analyze the degraded solid and liquid phase products, and compared with the control group, it was found that the enhanced bacterial solution had a stronger degradation effect on the oxygen-containing functional groups in the molecular structure of the coal samples. Therefore, the aromatic layer stacking height L_c was lower, the number of aromatic layers N was fewer, and the specific surface area was larger in the crystallite structure of the solid phase products. A total of 33 different compounds were detected in the liquid phase products of the enhanced bacterial solution to degrade the coal sample, and a total of 21 different compounds were detected in the liquid phase products of the unfortified bacterial solution to degrade the coal sample, but the types of major degradation products were similar, including alkanes, esters, amino groups, alcohols and carboxylic acids, and the molecular weights of the liquid phase products were 114−478 and 128−436, respectively. This study proved that the enhanced bacterial solution by ultrasonic suspension was used to degrade low-rank coal could improve the degradation rate of coal samples, and promoted the degradation of low-rank coal by microorganisms.