Guidance for Investigating Calcite Precipitation by Urea Hydrolysis for Geomaterials

Abstract

Microbially Induced Calcite Precipitation (MICP) is a sustainable method of stabilizing (i.e., 2 cementing) loose sandy deposits and/or to create an impervious barrier within the soil mass. 3 MICP can occur through various biochemical pathways, among which 'Urea Hydrolysis (UH)' is considered to be the most efficient method of biochemically inducing calcite 5 precipitation. To date, the geotechnical engineering community investigating MICP has 6 tended to focus on the hydro-mechanical behaviour of the end product, i.e. MICP cemented 7 sands; however, many biochemical factors that affect reaction-rate kinetics and MICP 8 outcome have been understudied or neglected. This study investigated the kinetics of UH and 9 compared different sources of urease enzyme: those microbially cultivated in the laboratory 10 (i.e., Sporosarcina pasteurii) and those extracted from plants (i.e., Jack bean meal), to 11 investigate the influence of urea concentration, buffer capacity, and cell harvesting method on 12 UH. Through this study, an attempt has been made to arrive at an optimal concentration of 13 urea, under the influence of the above mentioned parameters along with the buffering action 14 of the soil, on urea hydrolysis. These results have implications towards optimising MICP and, 15 in particular, for upscaling these methods to in-situ applications.

Bio‐mediated soil improvement: An introspection into processes, materials, characterization and applications

“…As a key part of the urease enzyme structure, the nickel ion has been shown to be an essential trace element for maintaining sufficiently high ureolytic activity of urease‐producing bacteria (Svane et al, 2020). In addition, Shashank et al (2018) investigated the effect of buffer solution added with the bacterial suspension on regulating the ureolysis procedure. Adding a buffer solution was found to prevent the instantaneous increase of pH which might lead to a rapid clogging near the injection port during the MICP process.…”

Investigations on biosorption and biogenic calcite precipitation in sands

“…The harvested cells were washed with phosphate-buffered solution (PBS) to remove any leftover spent media. Subsequently, the pelleted cells were resuspended in sterile distilled water and the optical density at 600 nm (OD 600 ) of the bacterial suspension was adjusted to 1.0 (Shashank et al, 2018). This bacterial suspension, with an OD 600 of 1, was used for further experimental studies.…”

Applications of Microbial Processes in Geotechnical Engineering

“…However, due to the Michaelis-Menten kinetics of urea hydrolysis (e.g. Shashank et al, 2018), reaction rates decrease and urea starts to become a limiting factor before it is fully exhausted, hence an unfeasibly long time is required to fully encase the bacteria. To overcome this, some researchers (Bernardi et al, 2014;Harkes et al, 2010) inject subsequent volumes of fresh cementing solution, which may not be fully utilised, but may prove more cost effective as the bacteria is are more expensive to grow, process and transport to site than the cementing solution.…”