Bio-Trapping of Ureolytic Microorganisms on Sand Surfaces to Enhance Microbially Induced Calcium Carbonate Precipitation

Microbially induced calcium carbonate precipitation (MICP) has been widely studied for its potential to improve sustainability in the construction industry and geotechnical applications. The presence of urease-producing bacteria is essential for catalyzing the conversion of urea into ammonium and carbonate ions to promote CaCO₃precipitation. The effectiveness of the MICP process highly depends on the spatial uniformity of the bacterial concentration and CaCO₃precipitation. In this study, we functionalized sand surfaces with amine groups to trap urease-producing bacteria from the planktonic phase to enhance MICP. The purpose of this study was to investigate the impact of 3-Aminopropylmethyldiethoxysilane (AMDES) treatment on microbial viability, attachment, and urea hydrolysis. Bioactive sand surfaces were prepared using 1% AMDES to create positively charged surfaces to promote the adhesion of urease-producing bacteria <i>Sporosarcina pasteurii via </i>electrostatic interaction. This approach enables the concentration of urease-producing bacteria on the sand surface, which can then precipitate a full monolayer of CaCO₃ acting as an initial binder to adjacent sand particles. X-Ray Photo Electron Spectroscopy (XPS) was used to confirm the amine groups on the functionalized surface. Zeta Potential measurement was used to understand the changes in surface charges, which proved the negatively charged sand surface becomes positively charged after AMDES treatment. Microbial growth and viability after on AMDES-treated sand were measured using Optical Density(OD₆₀₀), and Confocal laser scanning microscopy (CLSM) of live dead stained cells, respectively, and compared to untreated sand. The results demonstrated that the bio-trapping of microorganisms on AMDES-treated sand surfaces reduced the growth rate of microorganisms and potentially compromised microbial viability. CLSM images of live dead stained cells at 0h showed more bacteria with compromised cell walls attached to AMDES-treated sand. Untreated sand particles did not show any bacterial attachment at 0h. After 24 hours of growth, CLSM images showed no bacterial growth on AMDES-treated sand and untreated sand particles showed densely packed live bacteria. Ureolytic activity was measured using a colorimetric Jung assay. Although the growth of the microorganisms was slowed with the AMDES treatment, ureolytic activity was maintained, and urea was completely hydrolyzed although at a slower rate. The resulting biocemented structures show excellent density and edge definition, which exceed those of conventional MICP. Our results show that bio-trapping of urease-producing bacteria on sand particles may promote uniform and effective biocementation of sand.