Optimized biosynthesis and performance enhancement of γ-PGA from Bacillus licheniformis: a study on wettability, microstructure, and environmental performance

Extensive research has been conducted to mitigate the hazards of coal mine dust. Dust suppressants are crucial for enhancing the dust and fall efficiency of water media. Currently, environmentally-friendly, functional, polymeric, and microbial dust suppressant, which represent new types of suppressants, are primarily in the experimental and exploratory stages. Commercial models are not yet mature, and further validation through field tests and over time is required to assess the continuous effectiveness, environmental friendliness, safety, economic feasibility, and simplicity of the process of new dust suppressant. Consequently, this study utilized response surface methodology to optimize the conditions for microbial fermentation to synthesize the biobased dust suppressant γ-PGA. The fermentation extracts of Bacillus licheniformis were analyzed by thermogravimetric analysis. Infrared spectroscopy was employed to explore the functional group structure of the synthesized products; the wettability of γ-PGA was tested using an optical method for measuring contact angle/surface tension and transmission electron microscopy. The results indicated that screening, optimizing, and culturing Bacillus licheniformis could produce γ-PGA fermentation fluid with a maximum yield of 23.76 g/L. Infrared spectroscopy analysis showed that the purified product contained typical functional groups of γ-PGA. Changes in the contact angle of γ-PGA solution with coal dust over time demonstrated that brown coal was wetted extremely quickly, with the largest change in contact angle; within 5 min of dropping the fermentation liquid, the contact angle sharply decreased from 69° to 0°, completely wetting the brown coal. Transmission electron microscopy revealed that the coal pores became looser when wetted by water, and when the γ-PGA wetted the surface of the coal dust, the solution penetrated into the pores, forming a liquid film that enveloped the medium within the coal pores and suppressed the native dust. Due to the abundance of free carboxyl groups (a-COOH), amino groups (NH-), and carbonyl groups (CO) on the molecular chains of γ-PGA, along with numerous hydrogen bonds between the γ-PGA chains, γ-PGA has a strong ability to absorb and retain water, making its capacity to wet solids significantly stronger than that of plain water. This research is expected to lay the experimental foundation for the development of green and efficient dust suppression materials for mining applications. In mining applications, γ-PGA solutions demonstrate versatile dust suppression capabilities. For operational face dust control, γ-PGA can be applied through high-pressure spray systems directly onto coal mining surfaces. Its rapid wetting properties enable immediate capture of airborne particulates. In material transportation systems, γ-PGA combined with foaming agents generates dust-suppressive foam that adheres to conveyor belts or coal loads in mining vehicles. Pre-wetting treatments using γ-PGA solutions prior to coal crushing operations leverage the polymer's exceptional water absorption and retention capacities. This pretreatment reduces coal brittleness, thereby minimizing the generation of new particulates during mechanical fragmentation processes. The technology exhibits potential for cross-industry adaptation. In construction demolition scenarios, γ-PGA formulations could integrate with dust suppression cannons to mitigate transient particulate emissions. Road dust management represents another promising application, where γ-PGA solutions may enhance the longevity of surface moisture retention when deployed via standard road sprinkler systems, thereby reducing maintenance frequency.