The document summarizes microbial-induced calcite precipitation (MICP) for soil stabilization. MICP uses bacteria to cement soil particles together through the precipitation of calcite. The document discusses (1) how bacteria induce calcite precipitation through their urease enzyme activity, (2) how MICP improves soil properties like strength and permeability through calcite bridging of soil particles, and (3) laboratory experiments demonstrating the effect of MICP on stabilizing sandy soils.

1. SOIL STABILIZATION
USING BACTERIA
Microbial-induced
calcite precipitation
Advisor: Dae-Wook Park
Presenter: Tri Ho Minh Le
Student ID: 1720095

2. Content
1. Introduction
2. MICP mechanism
3. Effect of MICP to soil properties
4. Application of MICP
5. Conclusion
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Microbial-induced calcite precipitation

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Mechanical compaction is recommended for sandy soils and is effective or economical to a
depth less than 10m.
Chemical stabilization is typically recommended for expansive soils.
• Environmentally safe techniques such as pre-wetting and moisture barriers are only
possible for small confined spaces and are not suitable for larger construction projects such
as highways and railways which spread for miles.
• As mentioned above, artificial cementation techniques are not always feasible and
environmentally friendly.
Introduction
However, reduction in the use of artificial cementation techniques can be practiced by
substituting with environmental friendly techniques or materials. One such method of soil
stabilization technique is, Microbial Induced Calcite Precipitation (MICP).
This technique employs microbes as a primary factor for stabilization. Successful
implementation of MICP will have its application in a wide variety of civil engineering
fields

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Introduction

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Introduction

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Introduction
The prime role of microbes in the precipitation of minerals is their ability to create an alkaline
environment through various physiological activities (Douglas & Beveridge, 1998). Calcium
carbonate (calcite) precipitation is observed to be a general mineral precipitation process in the
microbial world under ambient environment
Urease producing bacteria have been used in the oil industry to reduce the permeability of the
surface and subsurface media thus reducing the flow of the fluid and enhancing the recovery of oil
from reservoirs and limiting the spread of the contaminants from a spill site. This process is called
mineral plugging. The increase in pH due to the formation of ammonia as a byproduct during the
breakdown of urea in the presence of4 urease enzyme as a catalyst, this increase in pH provides a
favorable condition for the precipitation of calcite in the presence of calcium ions.

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 When a soil is treated using MICP technique, microbial induced calcite bridges adjacent soil particles,
cementing soil particles together
 The precipitation of calcite between particle-particle also helps in reducing the permeability,
compressibility and increasing soil strength MICP can be achieved in two ways:
 Bio-stimulation- This method involves the modification of the environmental condition by
stimulating the indigenous bacteria present in the soil. This is done by introducing various
nutrients into the soil.
 Bio-augmentation- This method involves the introduction of the required microbes along with
nutrients required to stimulate the microbes into the soil.
 Bio-stimulation is normally favored over bio-augmentation, as stimulating native microbes that are
accustomed to the environment is likely to be more stable than artificially introducing bacteria into
new environment (Burbank et al., 2013). However, the main challenge exists in the uniform treatment
of microbes within the site and the time associated with stimulation and growth. To overcome these
challenges, researchers often prefer bioaugmentation
Introduction

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Introduction
Figure below shows a picture of S. pasteurii plated on LB
plate that was used in this research. The growth media
used to grow the microorganisms was primarily Luria
Broth (LB).

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MICP Mechanism
There are 106-1012 bacterial cells in a gram of
soil. S. pasteurii (previously known as Bacillus
pasteurii) species of Bacillus group, a common
alkalophilic soil bacterium have high urease
enzyme activity. S. pasteurii use urea as an
energy source which hydrolyzes CO(NH2)2
(urea) into NH3 and H2CO3.

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MICP Mechanism

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A. Temperature
Microbes can survive in extreme conditions from -60°c in
Antartica to temperature greater than 150°c in hydrothermal
vent. Temperature plays a vital role in the microbial activity.
There is a specific relation between growth rate and metabolic
rate with the temperature. As the temperature increases to
optimal temperature the growth rate and metabolic also
increases but with increase or decrease of temperature above
and below optimal temperature. Most bacteria found in soils
are mesophilic in nature with optimal temperature of 25°C to
35°C.
MICP Mechanism
Limiting Factor for bacteria growth

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MICP Mechanism
Limiting Factor for bacteria growth
B. Water potential
has the logarithmic relationship with microbial metabolism
similar to temperature and microbial metabolism. Some microbes
exist without water by going in to resting stage called spores but
none can survive without water. Water potential is the measure of
force required to move water. This force is the combination of
osmotic pressure, gravity, surface tension and pressure.
C. PH
Microbial growth, metabolic activity and cell-
surface charge are effected by change in pH of
the surroundings
D. Light
Light is the main source of energy for phototrophic
microbes. Energy is produced by synthesizing
organic carbon by fixing carbon dioxide. Light can
damage DNA and if let unrepaired this may cause
mutations of the microbe. Many aerobic microbes are
rich in enzymes which can prevent from the damage
of the light

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Central to the issue of treatment uniformity is the
geometric compatibility between the microbes
(either native or augmented species) and the soil in
which they are injected. The relatively small size of
microbes, typically between 0.5 and 3µm (Madigan
and Martinko, 2003), is advantageous.
Soil particles cover a broad range in size, with a
primary differentiation being made between
“coarse” and “fine” grained soils at 75µm particle
size (Fig. 2). As a result, microbes are capable of
travelling through many soil types.
Application of MICP

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Application of MICP
Generalize treatment procedure
With improvement of soil properties being the primary objective, methods are needed to
determine how the byproducts of a given bio-mediated chemical process are altering the soil
properties. The three primary methods of geophysical measurements that can be utilized are
the shear wave velocity, compression wave velocity, and resistivity (the inverse of
conductivity). Since these methods induce very small or no strain (the case for resistivity), the
soil and treatment process is undisturbed by the measurements
Generalize tracking procedure

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Application of MICP
Laboratory application
Bio-augmentation Followed by Stimulation
Bio-augmentation alone resulted in unsatisfactory results. This may be
due to the dormancy of microbes with no moisture and oxygen within the
microbial environment. When microbes become dormant, all the
metabolic activities slow down. During this period, microbes become
unable to produce any urease enzymes to hydrolyze urea in the system
and as a result no calcite can be precipitated. In this bio-augmentation
followed by stimulation method soil samples were prepared as in the
case of bio-augmentation method. The samples instead of being cured at
constant temperature and humidity, were placed in a nutrient delivery
system.
Nutrient Delivery System
In order to stimulate the bacteria mixed into the soil, substrate solution
consisting of urea and CaCl2 solution need to be passed through the soil
sample. As the permeability of these soils is very low (< 10-6 cm/sec)
gravity feeding was not feasible in the available time frame. Hence, for
this purpose a nutrient solution delivery system was developed as shown
in Figure 10. The substrate in the pressurized container was pushed into
the chamber under pressure which percolated through the sample.

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Effect of MICP to soil properties

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Effect of MICP on soil properties
Laboratory application

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Laboratory application
Effect of MICP on soil properties

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***10 U/mL (1 U = 1 µmol urea hydrolyzed per minute)
This suggests that the
CaCO3 formed slowly, which
is due to the slower
hydrolysis of urea caused by
the lower urease activity, are
more effective to form
“bridges” that bond the sand
grains together in a more
effective way.
Fig. 1. Effect of the different urease activity on (a) UCS and (b) permeability of the bio- cemented
samples
Fig. 2. SEM images of bio-cemented samples treated with different urease activities (a-c: 50 U/mL,
UCS = 713 kPa, and CaCO3 content = 0.061 g/g sand; d-f: 5 U/mL, UCS=709 kPa, and CaCO3
Effect of MICP on soil properties

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Effect of MICP on soil properties
Laboratory application

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Effect of MICP on soil properties
Laboratory application

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Effect of MICP on soil properties
Laboratory application

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Effect of MICP on soil properties
Laboratory application

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Effect of MICP on soil properties
Laboratory application

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Effect of MICP on soil properties

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Effect of MICP on soil properties

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Effect of MICP on soil properties

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Conclusion
MICP has emerged as an effective and ecofriendly method for
environmental remediation. MICP is used in various fields to
remediate heavy metals and radionuclides from contaminated
environments and for sequestration of atmospheric CO2. In
addition, the same technology can be used to improve soil and
sand quality, as well as cement sealing of concrete. MICP
applications are not limited and are useful to other applications
to produce safe and environmentally stable products. Even
though the MICP process has many merits, further study is
needed to overcome the limitations to use of this technology
prior to its commercialization.

30. Thank You.
Tri Ho Minh Le
lehominhtri92@gmail.com
010 4981 1032

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Environment Condition
for Bacteria
Each sample contained 95.87kg of soil
mixed with 20ml of medium with
bacteria. The bacteria were fed daily, by
introducing 20ml of liquid with nutrient
in the top of the mould (see Figure 1) and
purging 20ml of liquid from the bottom.
The same volume of soil was used for the
soil and soil-cement specimens, but in
this case there was no inclusion of the
drainage system.