Chitosan enhances calcium carbonate precipitation and solidification mediated by bacteria.

Formation of the biominerals in living organisms is mainly associated with organic macromolecules. These organic materials play an important role in the nucleation, growth, and morphology controls of the biominerals. Current study mimics this concept of organic matrix- mediated biomineralization by using microbial induced carbonate precipitation (MICP) method in combination with the cationic polysaccharide chitosan. CaCO3 precipitation was performed by the hydrolysis of urea by the ureolytic bacteria Pararhodobacter sp. SO1 in the presence of CaCl2, with and without chitosan. The crystal polymorphism and morphology of oven-dried samples were analyzed by X-ray diffraction and scanning electron microscopy. The amount of precipitate obtained was higher in the presence of chitosan. The precipitate included both of the CaCO3 and the chitosan hydrogel. Rhombohedral crystals were dominant in the precipitate without chitosan and distorted crystal agglomerations were found with chitosan. Sand solidification experiments were conducted in the presence of chitosan under different experimental conditions. By adding chitosan, more strongly cemented sand specimens could be obtained than those from conventional method. All of these results confirm the positive effect of chitosan for the CaCO3 precipitation and sand solidification.