An Investigation of Bacterial Calcium Carbonate Precipitation in Organic Soil for Geotechnical Applications (original) (raw)
Related papers
Annals of Microbiology
Purpose Stabilization of weak soil can be achieved through different methods, some of which include jet column, cement stabilization and fly ash stabilization. Unfortunately, the use of the aforementioned methods of soil improvement affects the environment negatively thereby leading to environmental degradation. With the aforesaid impediment in mind, the need for devising methods of weak soil improvement becomes pertinent. Methods Bacillus sp. — a non-pathogenic organism found abundantly in soil — was investigated in this study as a potential agent of soil improvement. The usability of Bacillus sp. in soil improvement was investigated with direct shear tests and permeability tests under optimum conditions in this study. Result Time-dependent study on the effect of the ureolytic bacteria Bacillus sp.-induced calcium carbonate precipitation shows reduction in permeability and increase in the strength of the soil under study. On exhaustion of the available nutrients in the soil, howeve...
Buildings, 2021
Microbial-induced carbonate precipitation (MICP) is a bio-inspired solution where bacteria metabolize urea to precipitate. This carbonate acts as a bio-cement that bonds soil particles. The existing framework has focused mainly on applying MICP through infiltration of liquid bacterial solutions in existing soil deposits. However, this technique is inefficient in soils with high fines content and low hydraulic conductivity, and thus few studies have focused on the use of MICP in fine soils. The main objective of this study was to evaluate the effect of MICP applied to compaction water in soils containing expansive clays and sandy silts. This approach searches for a better distribution of bacteria, nutrients, and calcium sources and is easy to apply if associated with a compaction process. In soils with expansive minerals, the effect of MICP in swelling potential was explored at laboratory and field scales. In sandy silts, the evolution of the stiffness and strength were studied at th...
Calcium carbonate induced precipitation for soil improvement by urea hydrolysing bacteria
Existing methods for improving the engineering properties of soils are diverse with respect to their final outcome. Grouting by chemical additives is currently one of the most commonly used soil stabilization techniques; however, it may have some environmental, reproducibility and health concerns. These drawbacks and the increasing population in regions of limited land drive the need to develop new technologies for ground improvement. The aim of this work is to introduce and examine a newly emerging microbiological process, known as microbial induced calcite precipitation (MICP), for soil stabilization. MICP is a promising technique that utilizes the metabolic pathway of bacteria to form calcite precipitation throughout the soil matrix, leading to an increase in soil strength and stiffness. The study investigates the geotechnical properties of bio-cemented silica sand under different degrees of saturation at which bio-cementation occurs. A series of laboratory experiments are conducted including the sieve analysis, permeability, unconfined compression strength and consolidated undrained tri-axial tests. The results confirm the potential of MICP as a viable alternative technique that can be used successfully for soil improvement in many geotechnical engineering applications, including liquefaction of sand deposits, slope stability and subgrade improvement. The results also indicate that higher soil strength can be obtained at lower degrees of saturation, negating the belief that biocemented soils need to be treated under full saturation conditions.
Soils and Foundations, 2015
In the past few years, the use of bacterial calcium carbonate precipitation has become popular as a ground-improvement technique for sandy soil. However, this technique has not been applied to organic soil. This study focused on bacterial calcium carbonate precipitation and its effect on the compressibility and strength of organic soil. A special injection system was prepared for inducing a bacterial solution into several samples. The bacterial solution was supplied to the samples by gravity for 4 days in specific molds designed for this work. Calcite precipitation was observed by monitoring the changes in the pH value and by measuring the amount of calcium carbonate in the organic soil. The changes in compressibility and strength were measured before and after the bacterial treatment. The test results showed that the pH values in the treatment medium reached the ideal values that are appropriate for calcite precipitation. It was found that the amount of precipitated calcium carbonate in organic soil increased by about 20% in the treated samples compared to that in the untreated samples. Moreover, the test results indicated that the bacterial treatment influenced the compressibility and shear strength of the organic soil. The results were supported by an energy-dispersive x-ray (EDX) analysis.
About calcium carbonate precipitation on sand biocementation
Engineering Geology, 2020
The contribution of indigenous bacteria and of some possible precipitation due to chemical reactions occurring during the treatment of sandy soils through microbially induced calcite precipitation (MICP) is investigated in this paper considering two different grading size distributions. This is a novelty, because the presence of the feeding solution alone in the soil (usually used as control test, and named here as CICP) is usually not quantified as it is assumed that the total amount of calcium carbonate is formed only due to ureolytic activity of the bacteria added to soils. However precipitation can occur because bacteria naturally exist in soils and also, even if less likely, due to CO 2 sequestration in a process called chilled ammonia process. The justification is because the ions necessary for forming calcium carbonate, both by the indigenous bacteria or by CO 2 sequestration are supplied in the feeding solution (solution with urea, ammonium and a calcium source). Experimental tests were performed on a set of sand samples subjected to biological treatment using bacteria and another set exposed to chemical treatment using only the feeding solution, after checking that natural bacteria present in the soil would not interfere with the process. The samples were prepared with similar dry density. They were analysed through mercury intrusion porosimetry tests, chemical analysis and unconfined compression strength tests performed after partially drying the samples. Although the hydrolysis of urea made by the added bacteria speeds up the precipitation of calcium carbonate, the results showed that CICP appears to be independent from sand grading size distribution and introduces significant strength increment. For this reason, the treatment will have effect even if the bacteria added die. Nevertheless, it is important to promote adequate conditions for these bacteria to survive because higher strength values were measured in the samples where MICP treatment was done, and therefore the effectiveness of the technique increases in significant manner.
Soil bacteria that precipitate calcium carbonate: mechanism and applications of the process
Acta Agronómica
Las bacterias con actividad ureásica son microorganismos que se encuentran en el suelo, y que en presencia de urea y calcio, pueden producir carbonato de calcio, proceso conocido como precipitación de calcio inducida microbiológicamente (PCIM). Este artículo trata este proceso y su mecanismo, además de las ureasas de origen bacteriano, los cristales de carbonato de calcio formado, los factores que afectan la eficiencia la PCIM, como el tipo de bacteria, las concentraciones de células bacterianas, el pH, la temperatura y las concentraciones de calcio y urea. Además, se incluye las aplicaciones como la remoción de metales pesados en aguas, la bioconsolidación, biocemento y secuestro de CO2.
Influences of Calcium Sources and Type of Sand on Microbial Induced Carbonate Precipitation
2017
Microbial Induced Calcite Precipitation (MICP) is commonly carried out by injecting chemical solutions (e.g., urea and calcium source) and bacteria (e.g., Sporosarcina pasteurii, B. megaterium) to the soil where treatment is required. This research aims to explore a new source of calcium chloride. The new source was the egg shells. It has been exploring the feasibility of using a new source of calcium in improving the engineering properties of two different types of fine sand (river and silica sands). Also, explore the impact of the sand type on the results of MICP. Set of laboratory tests were conducted, including calcium carbonate content, unconfined compressive strength, soil permeability and microscopy Investigation (SEM). The results indicate that use calcium chloride produced of egg shells has the same effectiveness of that of pure calcium chloride (analytical grade) in the cementation solution. This was demonstrated clearly by measure the Precipitated Calcium Carbonate content, where the same amount of Calcium Carbonate of both calcium sources was precipitated. But it was slightly higher in the river sand. In both cases (river and silica sands samples) the use of cementation solution contained calcium chloride made of egg shells has a significant effect on the permeability, but the effect was greater in the silica sand samples. Also, the effect of using cementation solution contained calcium chloride made of egg shells was exactly the same effect of using cementation solution contained analytical grade of calcium chloride. Finally, from SEM images, the calcium carbonate type in all cases was the calcite and the crystals sizes were relatively same. But the crystals type of calcite was changed according to the type of sand.
Microbial Carbonate Precipitation as a Soil Improvement Technique
Geomicrobiology Journal, 2007
In order to evaluate MCP as a soil strengthening process, a five meter sand column was treated with bacteria and reagents under conditions that were realistic for field applications. The injection and reaction parameters were monitored during the process and both bacteria and process reagents could be injected over the full column length at low pressures (hydraulic gradient < 1; a flow rate of approximately 7 m/day) without resulting in clogging of the material. After treatment, the column was subjected to mechanical testing, which indicated a significant improvement of strength and stiffness over several meters. Calcium carbonate was precipitated over the entire five meter treatment length. Improvement of the load bearing capacity of the soil without making the soil impermeable to fluids was shown with microbial carbonate precipitation, and this is a unique property compared to alternative soil treatment methods that are currently available for use in the subsurface.
MICP technology is relatively one of the new technology emerge in the field of improving the soil. Therefore, this technique needs more intensive research before it becomes usable in widespread. This research aims to study the effect of calcium source type, concentration of the cementation solution, the soil type, the use of cementation solution consists of a combination of calcium sources, on the calcium carbonate content, the crystal formation, the porosity, and the strength. Set of laboratory tests were conducted, including porosity, calcium carbonate content, unconfined compressive strength and microscopy investigation (SEM). The results presented in this study revealed that using the cementation solution composed of calcium acetate and calcium chloride, which is made of egg shells and urea with MICP technique can improve the mechanical properties of the fine sand. Also, the use of a cementation solution containing variety mixtures of calcium sources did not show any noticeable difference in improving the properties of treated sand compared with sand treated with a cementation solution containing one type of calcium. The use of low concentrations of cementation solution provides a greater improvement in the engineering properties of the treated soil.