Freeze-thaw durability and shear responses of cemented slope soil treated by microbial induced carbonate precipitation

Application of microbially induced calcium carbonate precipitation with urea hydrolysis to improve the mechanical properties of soil

Ureolysis-driven microbially induced carbonate precipitation (MICP) is a naturally occurring process facilitated through microbial activities and biogeochemical reactions to produce calcium carbonate (CaCO3) mineral. MICP serves as an alternative ground improvement binder method to conventional technologies which is sustainable, requires low energy for its treatment process, results in a minimal carbon footprint and could offer economic benefits. In the last two decades, MICP has drawn great interest from the scientific community because of its practicality to stabilize granular soils, repair concrete cracks and remediate heavy metals. To obtain successful MICP application, it is vital to understand the conditions that favor its process. This paper, therefore, provides an overview of literature on CaCO3 precipitation mediated by ureolysis-driven MICP and its mechanism. The review includes a discussion on sources of urease enzyme from microorganisms used to induce CaCO3 crystal formation required for implementation of MCIP for ground improvement. Moreover, the key factors that influence the outcome of MICP and bio-engineering testing methods typically used to evaluate MICP performance are also highlighted. Finally, this review also provides insight on the current drawbacks (i.e. ammonium production, scale-up bioprocess and treatment cost) affecting MICP technology and recommendations for future consideration.

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Bioprecipitation of calcium carbonate mediated by ureolysis: A review

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

Production of urease enzyme from ureolytic bacteria (e.g. Sporosarcina pasteurii) is essential for precipitation of CaCO3. This bioprocess is notably utilized for soil improvement, biocementation and bioremediation of heavy metals. Despite the viability for field-scale implementation as a suitable alternative to conventional treatment methods, most reports in the literature are constrained to laboratory-scale. Thus, this study demonstrates an economic strategy to scale-up the production and cultivation of ureolytic bacteria using a custom-built stainless steel stirred tank reactor (3 m3). Scalability of the bacterial cells was carried out from 214 L to 2400 L seed cultures for 90 h. Technical-grade ingredients (food-grade yeast extract media and chemicals) were used for scale-up production of the bacterial cells. The growth profile, pH and urease activity were subsequently monitored throughout the in-situ production period. Biocementation on sand mould specimens was also performed using bacterial cultures obtained from the reactor and low-grade cementation reagents. The sand columns were grouped into different treatment cycles to determine the effect of ureolysis. CaCO3 content, effluent pH and microstructural analyses (scanning electron microscopy with energy dispersive X-ray spectroscopy) of the treated soil samples were also evaluated. The results show that scale-up production of ureolytic bacteria cells under non-sterile conditions using a custom-built reactor for industrial MICP application is feasible.

A feasible scale-up production of Sporosarcina pasteurii using custom-built stirred tank reactor for in-situ soil biocementation

Microbial induced carbonate precipitation (MICP) is relatively an innovative soil improvement technique, learnt from the bio-mediated geochemical reactions that naturally occur in the earth surface. During the MICP, CaCO3 is metabolically precipitated in soil pores, cement the particle contacts and improves the strength and stiffness of soil. Environment temperature is one of the most key factors that determines the efficiency MICP. The purpose of this study is to investigate the feasibility of stabilizing the slope soil of cold subarctic region (Hokkaido, Japan). The implication of MICP in cold subarctic zones remains as a major challenge, as the enzymatic performance of the bacteria typically declines during lower temperatures hence insufficient formation of CaCO3 in soil matrix. Therefore, as a potential approach, this study attempted to investigate the feasibility of using the bacteria which have been adapted to native cold climatic conditions. The objectives of this paper are evaluating (1) the effect of temperature in bacterial response, and (2) the effect of grain size distribution in cementation mechanism. The observations suggest that the enzyme activity of the bacteria is negligible at and above 30 °C, whereas it is significant at relatively lower temperatures. The comparison of treated soils suggests that the fine content in slope soil increased number of particle contacts, facilitated effective packing, and promoted the effectiveness of MICP compared to that of uniformly graded sands. Finally, the technical feasibility in slope soil stabilization was well demonstrated using model solidification test. The limitations in stabilizing the slope are also discussed in detail.

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Feasibility study for slope soil stabilization by microbial induced carbonate precipitation (MICP) using indigenous bacteria isolated from cold subarctic region

Microbial Induced Carbonate Precipitation (MICP) has recently become a new technology for stabilizing the slope surface. The applicability of MICP, however, is limited in fine-grained soils due to the restrictions regarding the transportation of bacteria cells. The purpose of this study was to assess the feasibility of an alternative called Bacterial-Enzyme Induced Carbonate Precipitation (B-EICP) for stabilizing the fine-grained slope soils. Unlike the MICP strategy (involving whole-cells of bacteria), the proposed B-EICP utilizes bacterial urease to induce the bio-cement formation within soil. The whole-cell culture of Lysinibacillus xylanilyticus was subjected to cyclic sonication to extract the free urease suspension. The B-EICP treatment was performed to the columns prepared using two different soils obtained from representative expressway slopes. The cementation responses of the proposed B-EICP were compared with that of typical MICP method, especially from the following viewpoints, (i) adaptability to soil with high fine-grained content, (ii) conditions under which B-EICP can be effectively applied and (iii) cementation under low temperature. The results revealed that the extract solution had higher urease activity compared to original bacteria culture, and the activity remained more stable at low temperature conditions (15°C). The results further confirmed that B-EICP method is more suitable for stabilizing soils with large amount of fine particles. Comparing with MICP, the B-EICP resulted higher unconfined compressive strength (over 1200 kPa) and deeper cementation in the silty sand. Microscale analysis suggested that the B-EICP could induce smaller calcium carbonate crystals than that by MICP, but the number of crystals in B-EICP were significantly more, thus contributed to increased particle-particle cementation.

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Takashi Iki

Papers

Feasibility study for slope soil stabilization by microbial induced carbonate precipitation (MICP) using indigenous bacteria isolated from cold subarctic region

Feasibility of bacterial-enzyme induced carbonate precipitation technology for stabilizing fine-grained slope soils