Microbially induced carbonate precipitation (MICP) is a promising technology for solidifying sandy soil, ground improvement, repairing concrete cracks, and remediation of polluted land. By solidifying sand into soil capable of growing shrubs, MICP can facilitate peak and neutralization of CO₂ emissions because each square meter of shrub can absorb 253.1 grams of CO₂ per year. In this paper, based on the critical review of the microbial sources of solidified sandy soil, models used to predict the process of sand solidification and factors controlling the MICP process, current problems in microbial sand solidification are analyzed and future research directions, ideas and suggestions for the further study and application of MICP are provided. The following topics are considered worthy of study: (1) MICP methods for evenly distributing CaCO₃ deposit; (2) minimizing NH₄⁺ production during MICP; (3) mixed fermentation and interaction of internal and exogenous urea-producing bacteria; (4) MICP technology for field application under harsh conditions; (5) a hybrid solidification method by combining MICP with traditional sand barrier and chemical sand consolidation; and (6) numerical model to simulate the erosion resistance of sand treated by MICP.

Microbial-induced CaCO₃ precipitation (MICP) is an innovative and rapidly developing technology for sand solidification. The idea for this research project was built based on the concept of sustainable development and environmental protection. The specific material used for solidification was soluble calcium ions generated by the reaction of limestone waste, a kind of calcium-rich industrial waste from a quarry, and acetic acid. Using Ca(CH₃COO)₂ (prepared from limestone waste) as a calcium source resulted in a 31.87% lower MICP cost compared to using CaCl₂. An unconfined compressive strength (UCS) test was conducted to characterize the macroscopic mechanical properties of bio-cured sand columns. The mineral composition and the microstructure of sand columns were examined by using X-ray diffraction (XRD) and environmental scanning electron microscopy (ESEM). After response surface optimization, the optimal conditions for the reaction of limestone and CH₃COOH were determined, and the calcium acetate yield was up to 96.81%. The UCS of sand samples treated with limestone/acetic acid was 10.61% higher than that of samples treated with calcium chloride. This research confirmed the feasibility of cheap limestone waste and soluble calcium ions generated by acetic acid as a calcium source, instead of calcium chloride, for solidifying sand columns in the MICP process.

Recognizing the limitations of Microbially Induced Calcite Precipitation (MICP) for sand consolidation, particularly the insufficient mechanical strength and the uneven distribution of precipitated calcite, our research takes an innovative approach. For the first time, we compare the potential of various polypeptide additives, including polylysine, polyaspartic acid, and polyglutamic acid, to enhance the MICP process. The optimal polypeptide was determined as polylysine, which could increase sand samples’ unconfined compressive strength (UCS) by 35.03% after MICP treatment. The optimal polylysine concentration is 100 mg/L, and the cementing liquid cost increased by only 3%. When the polylysine concentration exceeded 100 mg/L, the UCS of sand-solidified samples decreased. Environmental scanning electron microscope (ESEM) images showed that calcium carbonate and sand were bonded more tightly with polylysine added, and the distribution of calcium carbonate was uniform in the sand samples treated by MICP. X-ray diffractometer (XRD) showed calcium carbonate’s crystal form is calcite. This research signifies a crucial step forward in optimizing MICP for sand consolidation, potentially transforming applications in construction, geotechnical engineering, and environmental remediation.