Guidance for Investigating Calcite Precipitation by Urea Hydrolysis for Geomaterials

Abstract

Abstract Microbially induced calcite precipitation (MICP) is a sustainable method of stabilizing (i.e., cementing) loose sandy deposits or creating an impervious barrier within the soil mass or both. MICP can occur through various biochemical pathways, and ‘Urea Hydrolysis’ (UH) is considered to be the most efficient of the MICP methods for biochemically inducing calcite precipitation. To date, the geotechnical engineering community that has investigated MICP has tended to focus on the hydromechanical behavior of the end product, i.e., MICP cemented sands; however, many biochemical factors that affect reaction-rate kinetics and MICP outcomes have been understudied or neglected. This study investigates the kinetics of UH and compares different sources of the urease enzyme—those microbially cultivated in the laboratory (i.e., Sporosarcina pasteurii) and those extracted from plants (i.e., Jack bean meal)—to investigate the influence of urea concentration, buffer capacity, and the cell harvesting method on UH. Through this study, an attempt has been made to arrive at an optimal concentration of urea, under the influence of the previously mentioned parameters and the buffering action of the soil, on urea hydrolysis. These results have implications for optimizing MICP and, in particular, for upscaling these methods to in situ applications.