Loading effect and surface loading mechanism of gangue-based carrier materials on bacterial strain

Microbial technology has been extensively applied in the ecological restoration of arid mining areas in northwestern China. Effective microbial carrier materials can significantly enhance the adaptability and functionality of microorganisms in complex soil environments. To develop suitable carrier materials for rhizosphere-promoting bacteria, coal gangue and straw waste were utilized to prepare gangue-based biochar composites. The loading capacity of these materials for Azotobacter chroococcum was assessed through degradation experiments. The surface loading mechanisms were systematically investigated using scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), zeta potential analysis, atomic force microscopy (AFM), surface viscoelasticity measurements, and macroscopic adsorption tests. The results indicated: Compared with pure biochar, gangue-based biochar exhibited a higher loading capacity for the , tested strains. The optimal loading conditions were determined to be a solid-liquid ratio of 1 g∶50 mL, a loading time of 36 hours, a pH of 8, and a temperature of 30 ℃, under which the macroscopic adsorption rate reached 68.74%. The optimal preparation parameters for the solid waste-based curing ball were found to be 4% sodium alginate, 1% chitosan, and a crosslinking time of 12 hours. These balls significantly enhanced the biomass and metabolic activity of the strains, with the metabolic entropy of the loaded microorganisms being 32.53% lower than that of the single curing ball. Moreover, the phosphorus removal efficiency achieved by the curing ball was 63.99% higher than that obtained using pure bacterial liquid treatment. In comparison with pure biochar, the adsorption process of gangue-based biochar followed the Elovich model, while its adsorption behavior conformed to the Langmuir isotherm model. The adsorption process is endothermic in nature. Compared to pure biochar, gangue-based biochar demonstrates enhanced adsorption capacity and a thicker adsorption layer for Azotobacter chroococcum. Furthermore, the biofilm formed on its surface exhibits improved structural stability and increased viscoelastic properties. Microstructural analysis of the solid waste-based curing ball reveals a denser and more extensive pore network within a 2 μm field of view. The presence of Si–O functional groups on the material surface provides additional zeolitic adsorption sites, while –COOH functional groups are capable of forming multiple hydrogen bonds with amino groups present on the microbial surface, thereby significantly enhancing the microbial loading capacity of the material. The gangue-based carrier materials also maintains favorable charge stability under conditions of high salt ion concentration (mineralization degree of 10 g/L). The average adhesion force of solid waste-based curing balls reaches 2.87 nN, which is significantly higher than that observed for other materials. As a result, these spheres exhibit excellent microbial loading capacity and environmental adaptability, contributing to enhanced microbial biomass and metabolic activity. This improvement leads to increased degradation efficiency of microorganisms toward coal gangue and provides a promising carrier material for promoting the functional performance of microbial strains in soil environments.