Crystal precipitation in bio-slurry: effects of urea and calcium chloride using non-growing <i>Sporosarcina pasteurii</i>

Calcite precipitation by non-growing cells occurs more rapidly in the laboratory than with proliferative cells. Sporosarcina pasteurii was grown in urea-containing nutrient broth, and then harvested, washed, and resuspended in a solution. This bacterial suspension was mixed with an equal volume of a reactant solution containing calcium chloride and urea at different concentrations. The precipitate formed was collected, dried, and analyzed using X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy, field emission scanning electron microscopy, and particle size analysis (PSA). This study investigated the effects of urea and calcium chloride concentrations on the type and size of the crystals formed. The most effective concentrations of urea and calcium chloride were both 0.3 M. Semi-quantitative XRD analysis revealed that 97% of the precipitate was calcite, with only 3% being vaterite at these concentrations. PSA results indicated that, in a 0.3 M solution of urea and calcium chloride, most particles ranged in size from 0 to 60 nm. The results show that higher reactant concentrations lead to more precipitate in the slurry, but with a lower percentage of calcite; additionally, the size of the calcite crystals also increases. This study not only reaffirms the ability of non-growing cells to precipitate calcite but also investigates the precise relationship between reactant concentrations, crystal type, and particle size. These insights provide a deeper understanding of bio-slurry and its potential applications in fields like concrete and soil enhancement.