Roles of bacteria and extracellular polymeric substance in calcium carbonate formation: insights from the effects of calcium source and deposition rate on nucleation

Abstract

Microbially induced calcium carbonate has attracted a lot of attention due to its wide range of applications. As a class of microorganisms that can produce carbonic anhydrase, Bacillus mucilaginous has been used in dust control, anti-efflorescence and self-healing concrete. However, due to the differences in the morphology and formation process of calcium carbonate in practical applications, it is difficult to distinguish the role of microbial induction. Therefore, this paper focuses on microbial nucleation under different calcium source conditions, in particular by examining the cells and extracellular polymeric substances (EPS) separately. The results indicate that both cell and extracellular polymers can be used as nucleation sites, and the negative electrical properties of the cell wall and extracellular polymers will have an electrostatic attraction for calcium ions. Cells are deeply involved in crystal formation and induce the development of spherical crystals, especially when the calcium ion concentration in the environment remains consistently low. While the rate of crystal deposition is too fast, the cells are massively adsorbed to the surface instead of providing nucleation. In contrast, EPS has no drastic effect on morphology and crystal form, and organic acids competed with microbial induction. This study may provide useful evidence for the further recognition and identification of biogenic carbonate precipitation.