Optimization and Mechanism of Ca²⁺ Biosorption by Virgibacillus pantothenticus Isolated from Gelatine Wastewater

Gelatine-processing wastewater contains much residual sludge due to its high calcium ion concentration and chemical oxygen demand. In this study, N3-4, a microbial strain with excellent calcium tolerance capacity, was screened and identified as Virgibacillus pantothenticus using morphological observation, physiological and biochemical testing, and 16S rRNA sequence analysis. Its growth characteristics were investigated, and the maximum adsorption of calcium reached 572.43 μg/g under the optimal conditions (contact time, 72.68 min; biomass dosage, 1.3 g/l; initial calcium concentration, 142.01 mg/l). Conditions were optimized using response surface methodology and structural characterization. The structure of the bacterial pellets was altered from flat to rough, accompanied by bulges and sediments after Ca²⁺ treatment, according to structural characterization. Energy-dispersive X-ray spectroscopy of the bacterial precipitates under calcium(II) treatment revealed the immobilization of Ca²⁺ species on the bacterial cell surface. The results indicate that –OH, –NH₂, C≡C, C=O, –CH₂, –C–O–, and –C–N groups play a significant role in calcium dispersion on the surface of V. pantothenticus.