Investigating the Effect of Biological and Chemical Factors on the Reaction Kinetics and Mineralogy of Ureolytic Bio-Cementation

Abstract

Microbially Induced Calcite Precipitation (MICP) is a bio-mediated soil improvement method that has received significant recent attention for its ability to transform soil engineering properties through precipitation of calcium carbonate minerals on soil particle surfaces and contacts. Despite significant advances in treatment application techniques and characterization of post-treatment engineering properties, relationships between biogeochemical conditions during precipitation and post-treatment material properties have remained poorly understood. Bacterial augmentation, stimulation, and cementation treatments can vary dramatically in their chemical constituents, concentrations, and ratios between researchers, with specific formulas perpetuating despite limited understanding of their implications on reaction kinetics and end-state mineral products. In this study, small-scale batch experiments were used to systemically investigate how biogeochemical conditions during bio-cementation may influence ureolysis and calcium carbonate precipitation kinetics and precipitate mineralogy using direct aqueous measurements, X-ray diffraction (XRD) analyses, and scanning electron microscope (SEM) imaging. The results of these experiments revealed that reactant concentrations, process by-products, and common soil cations such as magnesium can have significant effects on the kinetics of microbial ureolysis during bio-cementation. Additionally, experiments suggested that the presence of various biological factors including growth factors, non-ureolytic spectator cells, and extracellular polymeric substances may have important consequences with respect to the mineralogy, morphology, and distribution of produced bio-cementation. Through the identification of critical chemical and biological factors affecting bio-cementation material properties, the long-term chemical and mechanical resilience of bio-cementation can be better understood and improved.