Preparation and properties of eggshell-sodium alginate composites and their application in rhizobium culture.

In this study, six kinds of eggshell powder and polysaccharide composites with varying raw material ratios were prepared as bacteria carriers using polyvinyl alcohol (PVA), sodium alginate (SA), and eggshell powder as raw materials. Rhizobia were immobilized by cultivating them with the eggshell-SA/PVA composites. The composites before and after immobilization were characterized by scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FTIR), and simultaneous thermal analysis, and their degradation properties were measured. After rhizobia immobilization, the storage properties of the prepared materials were investigated under different pH and temperature conditions. The results showed a large number of rhizobia were fixed on the composite. Infrared and thermogravimetric results indicated good cross-linking of PVA and SA. The biodegradability results suggest that the prepared composite materials can be degraded by microorganisms in the environment. The storage performance test results showed that immobilized rhizobia had the best survival activity after 60 days of storage at pH 6.5, with bacterial content remaining above 8 lg CFU/g. Furthermore, it was observed that lower pH (4.5) and low temperatures (4°C) significantly impacted rhizobia survival activity, and the amount and particle size of eggshell powder in the carrier influenced bacterial survival. However, under extreme conditions, the eggshell-PVA/SA composite prepared in this experiment exhibited good protection for rhizobia.