Microbially induced carbonate precipitation (MICP) technology holds great potential in enhancing soil properties. MICP can be employed to enhance the stability and strength of diverse sandy soil, but it has the shortcoming of low curing efficiency. In response to the identified problem, this study aims to investigate an optimized treatment protocol that involves formulating a cementing solution in a hydrochloric acid (HCl) solution to enhance the solidification rate in the MICP reaction and evaluate its effectiveness. The results indicate that when preparing a 1 M cementing solution in a 0.2 M HCl solution, it promotes the rapid bonding of calcareous sand particles, resulting in an unconfined compressive strength (UCS) of 1312.6 kPa in the sand column after five treatments. Compared to the conventional test group, the experimental group containing HCl exhibited an approximately 1357% increase in UCS. The analysis unveiled the pivotal role of metal ions dissolved from calcareous sand by HCl in enhancing the UCS of MICP-treated calcareous sand. The proposed experimental methodology serves as a valuable tool for designing treatment strategies for MICP-cemented calcareous sand in practical engineering applications.

Microbially induced carbonate precipitation (MICP) is a promising biogeotechnical technology, but its large-scale application is constrained by the high cost and energy consumption of bacterial cultivation and harvesting. This paper presents a metal ion-induced flocculation strategy for the preparation and storage of high-density Sporosarcina pasteurii seed cultures. The flocculation performance and biological effects of Ca²⁺ and Fe³⁺ were systematically compared. Ca²⁺ achieved efficient flocculation through electrical double-layer compression while maintaining near-neutral pH, thereby preserving urease activity and bacterial viability. Even at an inoculation ratio of 1:10,000, the recovered bacteria exhibited rapid regrowth and high urease activity. In contrast, although Fe³⁺ induced rapid flocculation at low concentrations, the acidic conditions severely impaired bacterial viability and regrowth. Cryopreservation with glycerol at −20 °C maintained bacterial activity for at least 90 days and markedly outperformed storage at 4 °C. The recovered flocculated bacteria exhibited CaCO₃ precipitation performance comparable to that of freshly cultured suspensions. This study provides a simple, economical, and scalable strategy for the preparation and long-term storage of MICP seed cultures, facilitating the practical implementation of large-scale biogeotechnical applications.